/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.wicket.markup.html.form;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.fileupload.FileCountLimitExceededException;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.wicket.Component;
import org.apache.wicket.IGenericComponent;
import org.apache.wicket.IRequestListener;
import org.apache.wicket.Page;
import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.ajax.AjaxRequestTarget;
import org.apache.wicket.behavior.Behavior;
import org.apache.wicket.core.util.string.CssUtils;
import org.apache.wicket.event.IEvent;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.MarkupStream;
import org.apache.wicket.markup.head.IHeaderResponse;
import org.apache.wicket.markup.head.OnEventHeaderItem;
import org.apache.wicket.markup.html.WebMarkupContainer;
import org.apache.wicket.markup.html.form.upload.FileUploadField;
import org.apache.wicket.markup.html.form.validation.FormValidatorAdapter;
import org.apache.wicket.markup.html.form.validation.IFormValidator;
import org.apache.wicket.model.IModel;
import org.apache.wicket.model.Model;
import org.apache.wicket.protocol.http.servlet.MultipartServletWebRequest;
import org.apache.wicket.protocol.http.servlet.ServletWebRequest;
import org.apache.wicket.request.IRequestParameters;
import org.apache.wicket.request.Request;
import org.apache.wicket.request.Response;
import org.apache.wicket.request.mapper.parameter.PageParameters;
import org.apache.wicket.request.parameter.EmptyRequestParameters;
import org.apache.wicket.util.encoding.UrlDecoder;
import org.apache.wicket.util.lang.Args;
import org.apache.wicket.util.lang.Bytes;
import org.apache.wicket.util.lang.Generics;
import org.apache.wicket.util.string.AppendingStringBuffer;
import org.apache.wicket.util.string.PrependingStringBuffer;
import org.apache.wicket.util.string.Strings;
import org.apache.wicket.util.string.interpolator.MapVariableInterpolator;
import org.apache.wicket.util.value.LongValue;
import org.apache.wicket.util.visit.ClassVisitFilter;
import org.apache.wicket.util.visit.IVisit;
import org.apache.wicket.util.visit.IVisitor;
import org.apache.wicket.util.visit.Visits;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * Container for {@link FormComponent}s (such as {@link CheckBox}es, {@link ListChoice}s or
 * {@link TextField}s). Subclass this class to receive submit notifications through
 * {@link #onSubmit()} or nest multiple {@link IFormSubmittingComponent}s if you want to vary submit
 * behavior. In the former case it is not necessary to use any of Wicket's classes (such as
 * {@link Button} or {@link SubmitLink}), just putting e.g. <input type="submit" value="go"/>
 * suffices.
 * <p>
 * As a {@link IRequestListener} the form gets notified of listener requests in
 * {@link #onRequest()}. By default, the processing of this submit works like this:
 * <ul>
 * <li>All nested {@link FormComponent}s are notified of new input via
 * {@link FormComponent#inputChanged()}</li>
 * <li>The form submitter is looked up, e.g. a {@link Button} is contained in the component
 * hierarchy of this form and was clicked by the user:
 * <ul>
 * <li>If an {@link IFormSubmitter} was found which
 * {@link IFormSubmitter#getDefaultFormProcessing()} returns {@code false} (default is {@code true}
 * ), it's {@link IFormSubmitter#onSubmit()} method will be called right away, thus all further
 * processing is skipped. This has the same effect as nesting a normal link in the form. <br>
 * If needed the form submitter can continue processing however, by calling {@link #validate()} to
 * execute form validation, {@link #hasError()} to find out whether validate() resulted in
 * validation errors, and {@link #updateFormComponentModels()} to update the models of nested form
 * components.</li>
 * <li>Otherwise this form is further processed via {@link #process(IFormSubmitter)}, resulting in
 * all nested components being validated via {@link FormComponent#validate()}. <br>
 * <ul>
 * <li>If form validation failed, all nested form components will be marked invalid, and
 * {@link #onError()} is called to allow clients to provide custom error handling code.</li>
 * <li>Otherwise the nested components will be asked to update their models via
 * {@link FormComponent#updateModel()}. After that submit notification is delegated to the
 * {@link IFormSubmitter#onSubmit()} (if just found) before calling {@link #onSubmit()} on this
 * form. Subclasses may override {@link #delegateSubmit(IFormSubmitter)} if they want a different
 * behavior.</li>
 * </ul>
 * </li>
 * </ul>
 * </li>
 * </ul>
 *
 * A Form can be configured for handling uploads with multipart requests (e.g. files) by calling
 * {@link #setMultiPart(boolean)} (although Wicket will try to automatically detect this for you).
 * Use this with {@link FileUploadField} components. You can attach multiple {@link FileUploadField}
 * components for multiple file uploads.
 * <p>
 * In case of an upload error two resource keys are available to specify error messages:
 * {@code uploadTooLarge} and {@code uploadFailed}, i.e. for a form with id {@code myform} in
 * {@code MyPage.properties}:
 *
 * <pre>
 * myform.uploadTooLarge=You have uploaded a file that is over the allowed limit of 2Mb
 * </pre>
 *
 * Forms can be nested. You can put a form in another form. Since HTML doesn't allow nested
 * &lt;form&gt; tags, the inner forms will be rendered using the &lt;div&gt; tag. You have to submit
 * the inner forms using explicit components (like {@link Button} or {@link SubmitLink}), you can't
 * rely on implicit submit behavior (by using just &lt;input type="submit"&gt; that is not attached
 * to a component).
 * <p>
 * When a nested form is submitted, the user entered values in outer (parent) forms are preserved
 * and only the fields in the submitted form are validated. </b>
 *
 * @author Jonathan Locke
 * @author Juergen Donnerstag
 * @author Eelco Hillenius
 * @author Cameron Braid
 * @author Johan Compagner
 * @author Igor Vaynberg (ivaynberg)
 * @author David Leangen
 *
 * @param <T>
 *            The model object type
 */
public class Form<T> extends WebMarkupContainer
        implements
                IRequestListener,
                IGenericComponent<T, Form<T>>
{
        public static final String ENCTYPE_MULTIPART_FORM_DATA = "multipart/form-data";

        public static final String HIDDEN_FIELDS_CSS_CLASS_KEY = CssUtils
                .key(Form.class, "hidden-fields");

        /**
         * Visitor used for validation
         *
         * @author Igor Vaynberg (ivaynberg)
         */
        public abstract static class ValidationVisitor implements IVisitor<FormComponent<?>, Void>
        {
                @Override
                public void component(final FormComponent<?> formComponent, final IVisit<Void> visit)
                {

                        Form<?> form = formComponent.getForm();
                        if (!form.isVisibleInHierarchy() || !form.isEnabledInHierarchy())
                        {
                                // do not validate formComponent or any of formComponent's children
                                visit.dontGoDeeper();
                                return;
                        }

                        if (formComponent.isVisibleInHierarchy() && formComponent.isEnabledInHierarchy())
                        {
                                validate(formComponent);
                        }
                        if (formComponent.processChildren() == false)
                        {
                                visit.dontGoDeeper();
                        }
                }

                /**
                 * Callback that should be used to validate form component
                 *
                 * @param formComponent
                 */
                public abstract void validate(FormComponent<?> formComponent);
        }


        /**
         * Visitor used to update component models
         *
         * @author Igor Vaynberg (ivaynberg)
         */
        private static class FormModelUpdateVisitor implements IVisitor<Component, Void>
        {
                private final Form<?> formFilter;

                /**
                 * Constructor
                 *
                 * @param formFilter
                 */
                public FormModelUpdateVisitor(Form<?> formFilter)
                {
                        this.formFilter = formFilter;
                }

                /** {@inheritDoc} */
                @Override
                public void component(final Component component, final IVisit<Void> visit)
                {
                        if (component instanceof IFormModelUpdateListener)
                        {
                                final Form<?> form = Form.findForm(component);
                                if (form != null)
                                {
                                        if (this.formFilter == null || this.formFilter == form)
                                        {
                                                if (form.isEnabledInHierarchy())
                                                {
                                                        if (component.isVisibleInHierarchy() &&
                                                                component.isEnabledInHierarchy())
                                                        {
                                                                ((IFormModelUpdateListener)component).updateModel();
                                                        }
                                                }
                                        }
                                }
                        }
                }
        }

        /**
         * Constant for specifying how a form is submitted, in this case using get.
         */
        public static final String METHOD_GET = "get";

        /**
         * Constant for specifying how a form is submitted, in this case using post.
         */
        public static final String METHOD_POST = "post";

        /** Flag that indicates this form has been submitted during this request */
        private static final short FLAG_SUBMITTED = FLAG_RESERVED1;

        /** Log. */
        private static final Logger log = LoggerFactory.getLogger(Form.class);

        private static final long serialVersionUID = 1L;

        public static final String UPLOAD_FAILED_RESOURCE_KEY = "uploadFailed";

        public static final String UPLOAD_TOO_LARGE_RESOURCE_KEY = "uploadTooLarge";
        public static final String UPLOAD_SINGLE_FILE_TOO_LARGE_RESOURCE_KEY = "uploadSingleFileTooLarge";
        public static final String UPLOAD_TOO_MANY_FILES_RESOURCE_KEY = "uploadTooManyFiles";

        /**
         * Any default IFormSubmittingComponent. If set, a hidden submit component will be rendered
         * right after the form tag, so that when users press enter in a textfield, this submit
         * component's action will be selected. If no default IFormSubmittingComponent is set, nothing
         * additional is rendered.
         * <p>
         * WARNING: note that this is a best effort only. Unfortunately having a 'default'
         * IFormSubmittingComponent in a form is ill defined in the standards, and of course IE has it's
         * own way of doing things.
         * </p>
         */
        private IFormSubmittingComponent defaultSubmittingComponent;

        /**
         * Maximum size of an upload in bytes. If null, the setting
         * {@link org.apache.wicket.settings.ApplicationSettings#getDefaultMaximumUploadSize()} is used.
         */
        private Bytes maxSize = null;

        /**
         * Maximum size of file of upload in bytes (if there are more than one) in request.
         */
        private Bytes fileMaxSize;

        /**
         * Maximum amount of files in request.
         * A value of -1 indicates no maximum.
         */
        private long fileCountMax = -1L;

        /** True if the form has enctype of multipart/form-data */
        private short multiPart = 0;

        /**
         * A user has explicitly called {@link #setMultiPart(boolean)} with value {@code true} forcing
         * it to be true
         */
        private static final short MULTIPART_HARD = 0x01;

        /**
         * The form has discovered a multipart component before rendering and is marking itself as
         * multipart until next render
         */
        private static final short MULTIPART_HINT_YES = 0x02;

        /**
         * The form has discovered no multipart component before rendering and is marking itself as
         * not multipart until next render
         */
        private static final short MULTIPART_HINT_NO = 0x04;

        /**
         * The index of the hidden fields used to pass parameters.
         */
        private static final int HIDDEN_FIELDS_PARAMS_IDX = 0;

        /**
         * The index of the hidden fields used for the default submit button.
         */
        private static final int HIDDEN_FIELDS_SUBMIT_IDX = 1;

        /**
         * Constructs a form with no validation.
         *
         * @param id
         *            See Component
         */
        public Form(final String id)
        {
                this(id, null);
        }

        /**
         * @param id
         *            See Component
         * @param model
         *            See Component
         * @see org.apache.wicket.Component#Component(String, IModel)
         */
        public Form(final String id, final IModel<T> model)
        {
                super(id, model);
                setOutputMarkupId(true);
        }

        /**
         * Adds a form validator to the form.
         *
         * @param validator
         *            validator
         * @throws IllegalArgumentException
         *             if validator is null
         * @see IFormValidator
         */
        public void add(final IFormValidator validator)
        {
                Args.notNull(validator, "validator");

                if (validator instanceof Behavior)
                {
                        add((Behavior)validator);
                }
                else
                {
                        add(new FormValidatorAdapter(validator));
                }
        }

        /**
         * Removes a form validator from the form.
         *
         * @param validator
         *            validator
         * @throws IllegalArgumentException
         *             if validator is null
         * @see IFormValidator
         */
        public void remove(final IFormValidator validator)
        {
                Args.notNull(validator, "validator");

                Behavior match = null;
                for (Behavior behavior : getBehaviors())
                {
                        if (behavior.equals(validator))
                        {
                                match = behavior;
                                break;
                        }
                        else if (behavior instanceof FormValidatorAdapter)
                        {
                                if (((FormValidatorAdapter)behavior).getValidator().equals(validator))
                                {
                                        match = behavior;
                                        break;
                                }
                        }
                }

                if (match != null)
                {
                        remove(match);
                }
                else
                {

                        throw new IllegalStateException(
                                "Tried to remove form validator that was not previously added. "
                                        + "Make sure your validator's equals() implementation is sufficient");
                }
        }

        /**
         * Clears the input from the form's nested children of type {@link FormComponent}. This method
         * is typically called when a form needs to be reset.
         */
        public final void clearInput()
        {
                // Visit all the (visible) form components and clear the input on each.
                visitFormComponentsPostOrder(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                if (formComponent.isVisibleInHierarchy())
                                {
                                        // Clear input from form component
                                        formComponent.clearInput();
                                }
                        }
                });
        }

        /**
         * Registers an error feedback message for this component
         *
         * @param error
         *            error message
         * @param args
         *            argument replacement map for ${key} variables
         */
        public final void error(String error, Map<String, Object> args)
        {
                error(new MapVariableInterpolator(error, args).toString());
        }

        /**
         * THIS METHOD IS NOT PART OF THE WICKET PUBLIC API. DO NOT USE IT!
         * <p>
         * Gets the IFormSubmittingComponent which submitted this form.
         *
         * @return The component which submitted this form, or null if the processing was not triggered
         *         by a registered IFormSubmittingComponent
         */
        public final IFormSubmittingComponent findSubmitter()
        {
                final IRequestParameters parameters = getRequestParameters(this);

                IFormSubmittingComponent submittingComponent = getPage().visitChildren(
                        IFormSubmittingComponent.class, new IVisitor<Component, IFormSubmittingComponent>()
                        {
                                @Override
                                public void component(final Component component,
                                        final IVisit<IFormSubmittingComponent> visit)
                                {
                                        // Get submitting component
                                        final IFormSubmittingComponent submittingComponent = (IFormSubmittingComponent)component;
                                        final Form<?> form = submittingComponent.getForm();

                                        // Check for component-name or component-name.x request string
                                        if ((form != null) && (form.getRootForm() == Form.this))
                                        {
                                                String name = submittingComponent.getInputName();
                                                if ((!parameters.getParameterValue(name).isNull()) ||
                                                        !parameters.getParameterValue(name + ".x").isNull())
                                                {
                                                        visit.stop(submittingComponent);
                                                }
                                        }
                                }
                        });

                return submittingComponent;
        }

        /**
         * Gets the default IFormSubmittingComponent. If set (not null), a hidden submit component will
         * be rendered right after the form tag, so that when users press enter in a textfield, this
         * submit component's action will be selected. If no default component is set (it is null),
         * nothing additional is rendered.
         * <p>
         * WARNING: note that this is a best effort only. Unfortunately having a 'default' button in a
         * form is ill defined in the standards, and of course IE has it's own way of doing things.
         * </p>
         * There can be only one default submit component per form hierarchy. So if you want to get the
         * default component on a nested form, it will actually delegate the call to root form. </b>
         *
         * @return The submit component to set as the default IFormSubmittingComponent, or null when you
         *         want to 'unset' any previously set default IFormSubmittingComponent
         */
        public final IFormSubmittingComponent getDefaultButton()
        {
                if (isRootForm())
                {
                        return defaultSubmittingComponent;
                }
                else
                {
                        return getRootForm().getDefaultButton();
                }
        }

        /**
         * Gets all {@link IFormValidator}s added to this form
         *
         * @return unmodifiable collection of {@link IFormValidator}s
         */
        public final Collection<IFormValidator> getFormValidators()
        {
                List<IFormValidator> validators = new ArrayList<>();

                for (Behavior behavior : getBehaviors())
                {
                        if (behavior instanceof IFormValidator)
                        {
                                validators.add((IFormValidator)behavior);
                        }
                }

                return Collections.unmodifiableCollection(validators);
        }

        /**
         * Generate a piece of JavaScript that submits the form to the given URL of an {@link IRequestListener}.
         *
         * Warning: This code should only be called in the rendering phase for form components inside
         * the form because it uses the css/javascript id of the form which can be stored in the markup.
         *
         * @param url
         *            The listener url to be submitted to
         * @return the javascript code that submits the form.
         */
        public final CharSequence getJsForListenerUrl(CharSequence url)
        {
                Form<?> root = getRootForm();

                AppendingStringBuffer buffer = new AppendingStringBuffer();

                String action = url.toString();
                if (root.encodeUrlInHiddenFields()) {
                        buffer.append(String.format("document.getElementById('%s').innerHTML = '",
                                root.getHiddenFieldsId(HIDDEN_FIELDS_PARAMS_IDX)));

                        // parameter must be sent as hidden field, as it would be ignored in the action URL
                        int i = action.indexOf('?');
                        if (i != -1)
                        {
                                writeParamsAsHiddenFields(Strings.split(action.substring(i + 1), '&'), buffer);

                                action = action.substring(0, i);
                        }

                        buffer.append("';");
                }
                buffer.append(String.format("var f = document.getElementById('%s');", root.getMarkupId()));
                buffer.append(String.format("f.action='%s';", action));
                buffer.append("Wicket.Event.fire(f, 'submit');");
                return buffer;
        }

        /**
         * Generate a piece of JavaScript that submits the form with the given
         * {@link IFormSubmittingComponent}.
         *
         * @param submitter
         *            the submitter
         * @param triggerEvent
         *            When true, the form will be submitted via standard form submission ({@code requestSubmit()})
         *            including client side validation and firing a javascript submit event, when false via
         *            the {@code submit()} method.
         * @return the javascript code that submits the form.
         *
         * @see #findSubmitter()
         */
        public final CharSequence getJsForSubmitter(IFormSubmittingComponent submitter, boolean triggerEvent)
        {
                Form<?> root = getRootForm();

                String param = submitter.getInputName() + "=x";

                AppendingStringBuffer buffer = new AppendingStringBuffer();
                buffer.append(String.format("var f = document.getElementById('%s');", root.getMarkupId()));
                buffer.append(String.format("document.getElementById('%s').innerHTML += '",
                        root.getHiddenFieldsId(HIDDEN_FIELDS_PARAMS_IDX)));
                writeParamsAsHiddenFields(new String[] {param}, buffer);
                buffer.append("';");

                if (triggerEvent)
                {
                        buffer.append("Wicket.Event.requestSubmit(f);");
                }
                else
                {
                        buffer.append("f.submit();");
                }
                return buffer;
        }

        /**
         * Gets the maximum size for uploads. If null, the setting
         * {@link org.apache.wicket.settings.ApplicationSettings#getDefaultMaximumUploadSize()} is used.
         *
         *
         * @return the maximum size
         */
        public final Bytes getMaxSize()
        {
                /*
                 * NOTE: This method should remain final otherwise it will be impossible to set a default
                 * max size smaller then the one specified in applications settings because the inner form
                 * will return the default unless it is specifically set in the traversal. With this method
                 * remaining final we can tell when the value is explicitly set by the user.
                 *
                 * If the value needs to be dynamic it can be set in oncofigure() instead of overriding this
                 * method.
                 */

                final Bytes[] maxSize = { this.maxSize };
                if (maxSize[0] == null)
                {
                        visitChildren(Form.class, new IVisitor<Form<?>, Bytes>()
                        {
                                @Override
                                public void component(Form<?> component, IVisit<Bytes> visit)
                                {
                                        maxSize[0] = LongValue.maxNullSafe(maxSize[0], component.maxSize);
                                }
                        });
                }
                if (maxSize[0] == null)
                {
                        return getApplication().getApplicationSettings().getDefaultMaximumUploadSize();
                }
                return maxSize[0];
        }

        /**
         * Gets maximum size for each file of an upload.
         *
         * @return
         */
        public Bytes getFileMaxSize()
        {
                return fileMaxSize;
        }

        /**
         * Gets maximum count of files in the form
         *
         * @return
         */
        public long getFileCountMax()
        {
                return fileCountMax;
        }

        /**
         * Returns the root form or this, if this is the root form.
         *
         * @return root form or this form
         */
        public Form<?> getRootForm()
        {
                Form<?> form;
                Form<?> parent = this;
                do
                {
                        form = parent;
                        parent = form.findParent(Form.class);
                }
                while (parent != null);

                return form;
        }

        /**
         * Returns the prefix used when building validator keys. This allows a form to use a separate
         * "set" of keys. For example if prefix "short" is returned, validator key short.Required will
         * be tried instead of Required key.
         * <p>
         * This can be useful when different designs are used for a form. In a form where error messages
         * are displayed next to their respective form components as opposed to at the top of the form,
         * the ${label} attribute is of little use and only causes redundant information to appear in
         * the message. Forms like these can return the "short" (or any other string) validator prefix
         * and declare key: short.Required=required to override the longer message which is usually
         * declared like this: Required=${label} is a required field
         * <p>
         * Returned prefix will be used for all form components. The prefix can also be overridden on
         * form component level by overriding {@link FormComponent#getValidatorKeyPrefix()}
         *
         * @return prefix prepended to validator keys
         */
        public String getValidatorKeyPrefix()
        {
                return null;
        }

        /**
         * Gets whether the current form has any error registered.
         *
         * @return True if this form has at least one error.
         */
        public final boolean hasError()
        {
                // if this form itself has an error message
                if (hasErrorMessage())
                {
                        return true;
                }

                // the form doesn't have any errors, now check any nested form
                // components
                return anyFormComponentError();
        }

        /**
         * Returns whether the form is a root form, which means that there's no other form in it's
         * parent hierarchy.
         *
         * @return true if form is a root form, false otherwise
         */
        public boolean isRootForm()
        {
                return findParent(Form.class) == null;
        }

        /**
         * Checks if this form has been submitted during the current request
         *
         * @return true if the form has been submitted during this request, false otherwise
         */
        public final boolean isSubmitted()
        {
                return getFlag(FLAG_SUBMITTED);
        }

        /**
         * THIS METHOD IS NOT PART OF THE WICKET API. DO NOT ATTEMPT TO OVERRIDE OR CALL IT.
         *
         * Handles form submissions.
         *
         * @see #onFormSubmitted(IFormSubmitter)
         */
        @Override
        public final void onRequest()
        {
                onFormSubmitted(null);
        }

        /**
         * Called when a form has been submitted using a method differing from return value of
         * {@link #getMethod()}. For example, someone can copy and paste the action url and invoke the
         * form using a {@code GET} instead of the desired {@code POST}. This method allows the user to
         * react to this situation.
         *
         * @return response that can either abort or continue the processing of the form
         */
        protected MethodMismatchResponse onMethodMismatch()
        {
                return MethodMismatchResponse.CONTINUE;
        }

        /**
         * THIS METHOD IS NOT PART OF THE WICKET API. DO NOT ATTEMPT TO OVERRIDE OR CALL IT.
         *
         * Handles form submissions.
         *
         * @param submitter
         *            listener that will receive form processing events, if {@code null} the form will
         *            attempt to locate one
         *
         * @see Form#validate()
         */
        public final void onFormSubmitted(IFormSubmitter submitter)
        {
                // check methods match
                if (getRequest().getContainerRequest() instanceof HttpServletRequest)
                {
                        String desiredMethod = getMethod();
                        String actualMethod = ((HttpServletRequest)getRequest().getContainerRequest()).getMethod();
                        if (!actualMethod.equalsIgnoreCase(desiredMethod))
                        {
                                MethodMismatchResponse response = onMethodMismatch();
                                switch (response)
                                {
                                        case ABORT :
                                                return;
                                        case CONTINUE :
                                                break;
                                        default :
                                                throw new IllegalStateException("Invalid " +
                                                                MethodMismatchResponse.class.getName() + " value: " + response);
                                }
                        }
                }

                markFormsSubmitted(submitter);

                if (handleMultiPart())
                {
                        // Tells FormComponents that a new user input has come
                        inputChanged();

                        // First, see if the processing was triggered by a IFormSubmittingComponent
                        if (submitter == null)
                        {
                                submitter = findSubmitter();

                                if (submitter instanceof IFormSubmittingComponent)
                                {
                                        IFormSubmittingComponent submittingComponent = (IFormSubmittingComponent)submitter;
                                        Component component = (Component)submitter;

                                        if (!component.isVisibleInHierarchy())
                                        {
                                                throw new WicketRuntimeException("Submit Button " +
                                                        submittingComponent.getInputName() + " (path=" +
                                                        component.getPageRelativePath() + ") is not visible");
                                        }

                                        if (!component.isEnabledInHierarchy())
                                        {
                                                throw new WicketRuntimeException("Submit Button " +
                                                        submittingComponent.getInputName() + " (path=" +
                                                        component.getPageRelativePath() + ") is not enabled");
                                        }
                                }
                        }

                        // When processing was triggered by a Wicket IFormSubmittingComponent and that
                        // component indicates it wants to be called immediately
                        // (without processing), call the IFormSubmittingComponent.onSubmit* methods right
                        // away.
                        if (submitter != null && !submitter.getDefaultFormProcessing())
                        {
                                submitter.onSubmit();
                                submitter.onAfterSubmit();
                        }
                        else
                        {
                                // the submit request might be for one of the nested forms, so let's
                                // find the right one:
                                final Form<?> formToProcess = findFormToProcess(submitter);

                                // process the form for this request
                                formToProcess.process(submitter);
                        }
                }
                // If multi part did fail check if an error is registered and call
                // onError
                else if (hasError())
                {
                        callOnError(submitter);
                }

                // update auto labels if we are inside an ajax request
                getRequestCycle().find(AjaxRequestTarget.class).ifPresent(target -> {
                        visitChildren(FormComponent.class, new IVisitor<FormComponent<?>, Void>()
                        {
                                @Override
                                public void component(FormComponent<?> component, IVisit<Void> visit)
                                {
                                        component.updateAutoLabels(target);
                                }
                        });
                });
        }

        /**
         * This method finds the correct form that should be processed based on the submitting component
         * (if there is one) and correctly handles nested forms by also looking at
         * {@link #wantSubmitOnNestedFormSubmit()} throughout the form hierarchy. The form that needs to
         * be processed is:
         * <ul>
         * <li>if there is no submitting component (i.e. a "default submit"): this form.</li>
         * <li>if only one form exists (this): this form.</li>
         * <li>if nested forms exist:
         * <ul>
         * <li>if the submitting component points at the root form: the root form</li>
         * <li>if the submitting component points at a nested form:
         * <ul>
         * <li>starting at that nested form, the outermost form that returns true for
         * {@link #wantSubmitOnNestedFormSubmit()}</li>
         * <li>if no outer form returns true for that, the nested form is returned.</li>
         * </ul>
         * </li>
         * </ul>
         * </li>
         * </ul>
         *
         * @param submitter
         *            The submitting component, if any. May be null.
         * @return The form that needs to be processed.
         */
        private Form<?> findFormToProcess(IFormSubmitter submitter)
        {
                if (submitter == null)
                {
                        // no submitting component => default form submit => so *this* is the
                        // form to process
                        return this;
                }
                else
                {
                        // some button submitted this request, this is the form it belongs to:
                        final Form<?> targetedForm = submitter.getForm();
                        if (targetedForm == null)
                        {
                                throw new IllegalStateException(
                                        "submitting component must not return 'null' on getForm()");
                        }

                        final Form<?> rootForm = getRootForm();
                        if (targetedForm == rootForm)
                        {
                                // the submitting component points at the root form => so let's just go with
                                // root, everything else will be submitted with it anyway.
                                return rootForm;
                        }
                        else
                        {
                                // a different form was targeted. let's find the outermost form that wants to be
                                // submitted.
                                Form<?> formThatWantsToBeSubmitted = targetedForm;
                                Form<?> current = targetedForm.findParent(Form.class);
                                while (current != null)
                                {
                                        if (current.wantSubmitOnNestedFormSubmit())
                                        {
                                                formThatWantsToBeSubmitted = current;
                                        }
                                        current = current.findParent(Form.class);
                                }
                                return formThatWantsToBeSubmitted;
                        }
                }
        }

        /**
         * Whether this form wants to be submitted too if a nested form is submitted. By default, this
         * is false, so when a nested form is submitted, this form will <em>not</em> be submitted. If
         * this method is overridden to return true, this form <em>will</em> be submitted.
         *
         * @return Whether this form wants to be submitted too if a nested form is submitted.
         */
        // TODO wicket-7 migration guide: changed from public to protected
        protected boolean wantSubmitOnNestedFormSubmit()
        {
                return false;
        }

        /**
         * Whether this *nested* form wants to be submitted when parent form is submitted. By default,
         * this is true, so when a parent form is submitted, the nested form is also submitted. If this
         * method is overridden to return false, it will not be validated, processed nor submitted.
         *
         * @return {@code true} by default
         */
        protected boolean wantSubmitOnParentFormSubmit()
        {
                return true;
        }

        /**
         * Process the form. Though you can override this method to provide your own algorithm, it is
         * not recommended to do so.
         *
         * <p>
         * See the class documentation for further details on the form processing
         * </p>
         *
         * @param submittingComponent
         *            component responsible for submitting the form, or <code>null</code> if none (eg
         *            the form has been submitted via the enter key or javascript calling form.submit())
         *
         * @see #delegateSubmit(IFormSubmitter) for an easy way to process submitting component in the
         *      default manner
         */
        public void process(IFormSubmitter submittingComponent)
        {
                if (!isEnabledInHierarchy() || !isVisibleInHierarchy())
                {
                        // since process() can be called outside of the default form workflow, an additional
                        // check is needed

                        // FIXME throw listener exception
                        return;
                }

                // run validation
                validate();

                // If a validation error occurred
                if (hasError())
                {
                        // mark all children as invalid
                        markFormComponentsInvalid();

                        // let subclass handle error
                        callOnError(submittingComponent);
                }
                else
                {
                        // mark all children as valid
                        markFormComponentsValid();

                        // before updating, call the interception method for clients
                        beforeUpdateFormComponentModels();

                        // Update model using form data
                        updateFormComponentModels();

                        // validate model objects after input values have been bound
                        internalOnValidateModelObjects();
                        if (hasError())
                        {
                                callOnError(submittingComponent);
                                return;
                        }

                        // Form has no error
                        delegateSubmit(submittingComponent);
                }
        }

        /**
         * Calls onError on this {@link Form} and any enabled and visible nested form, if the respective
         * {@link Form} actually has errors.
         *
         * @param submitter
         */
        protected void callOnError(IFormSubmitter submitter)
        {
                final Form<?> processingForm = findFormToProcess(submitter);

                if (submitter != null)
                {
                        submitter.onError();
                }

                // invoke Form#onSubmit(..) going from innermost to outermost
                Visits.visitPostOrder(processingForm, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(Form<?> form, IVisit<Void> visit)
                        {
                                if (!form.isEnabledInHierarchy() || !form.isVisibleInHierarchy())
                                {
                                        visit.dontGoDeeper();
                                        return;
                                }
                                if (form.hasError())
                                {
                                        form.onError();
                                }
                        }
                }, new ClassVisitFilter(Form.class));
        }


        /**
         * Sets FLAG_SUBMITTED to true on this form and every enabled nested form.
         * @param submitter
         */
        private void markFormsSubmitted(IFormSubmitter submitter)
        {
                setFlag(FLAG_SUBMITTED, true);
                Form<?> formToProcess = findFormToProcess(submitter);

                visitChildren(Form.class, new IVisitor<Component, Void>()
                {
                        @Override
                        public void component(final Component component, final IVisit<Void> visit)
                        {
                                Form<?> form = (Form<?>)component;
                                if ((form.wantSubmitOnParentFormSubmit() || form == formToProcess)
                                        && form.isEnabledInHierarchy() && form.isVisibleInHierarchy())
                                {
                                        form.setFlag(FLAG_SUBMITTED, true);
                                        return;
                                }
                                visit.dontGoDeeper();
                        }
                });
        }

        /**
         * Sets the default IFormSubmittingComponent. If set (not null), a hidden submit component will
         * be rendered right after the form tag, so that when users press enter in a textfield, this
         * submit component's action will be selected. If no default component is set (so unset by
         * calling this method with null), nothing additional is rendered.
         * <p>
         * WARNING: note that this is a best effort only. Unfortunately having a 'default' button in a
         * form is ill defined in the standards, and of course IE has it's own way of doing things.
         * </p>
         * There can be only one default button per form hierarchy. So if you set default button on a
         * nested form, it will actually delegate the call to root form. </b>
         *
         * @param submittingComponent
         *            The component to set as the default submitting component, or null when you want to
         *            'unset' any previously set default component
         */
        public final void setDefaultButton(IFormSubmittingComponent submittingComponent)
        {
                if (isRootForm())
                {
                        defaultSubmittingComponent = submittingComponent;
                }
                else
                {
                        getRootForm().setDefaultButton(submittingComponent);
                }
        }

        /**
         * Sets the maximum size for uploads. If null, the setting
         * {@link org.apache.wicket.settings.ApplicationSettings#getDefaultMaximumUploadSize()} is used.
         *
         * @param maxSize
         *            The maximum size
         */
        public void setMaxSize(final Bytes maxSize)
        {
                this.maxSize = maxSize;
        }

        /**
         * Sets maximum size of each file in upload request.
         *
         * @param fileMaxSize
         */
        public void setFileMaxSize(Bytes fileMaxSize)
        {
                this.fileMaxSize = fileMaxSize;
        }

        /**
         * Sets maximum amount of files in upload request.
         *
         * @param fileCountMax
         */
        public void setFileCountMax(long fileCountMax)
        {
                this.fileCountMax = fileCountMax;
        }

        /**
         * Set to true to use enctype='multipart/form-data', and to process file uploads by default
         * multiPart = false
         *
         * @param multiPart
         *            whether this form should behave as a multipart form
         */
        public void setMultiPart(boolean multiPart)
        {
                if (multiPart)
                {
                        this.multiPart |= MULTIPART_HARD;
                }
                else
                {
                        this.multiPart &= ~MULTIPART_HARD;
                }
        }

        /**
         * @see org.apache.wicket.Component#setVersioned(boolean)
         */
        @Override
        public final Component setVersioned(final boolean isVersioned)
        {
                super.setVersioned(isVersioned);

                // Search for FormComponents like TextField etc.
                visitFormComponents(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                formComponent.setVersioned(isVersioned);
                        }
                });
                return this;
        }

        /**
         * Convenient and typesafe way to visit all the form components on a form.
         *
         * @param <R>
         *            return object type
         * @param visitor
         *            The visitor interface to call
         * @return user provided in callback
         */
        public final <R> R visitFormComponents(final IVisitor<FormComponent<?>, R> visitor)
        {
                return visitChildren(FormComponent.class, visitor);
        }

        /**
         * Convenient and typesafe way to visit all the form components on a form postorder (deepest
         * first)
         *
         * @param <R>
         *            Return object type
         * @param visitor
         *            The visitor interface to call
         * @return whatever you provided
         */
        public final <R> R visitFormComponentsPostOrder(
                final IVisitor<? extends FormComponent<?>, R> visitor)
        {
                return FormComponent.visitFormComponentsPostOrder(this, visitor);
        }

        /**
         * Find out whether there is any registered error for a form component.
         *
         * @return whether there is any registered error for a form component
         */
        private boolean anyFormComponentError()
        {
                // Check ALL children for error messages irrespective of FormComponents or not
                Boolean error = visitChildren(Component.class, new IVisitor<Component, Boolean>()
                {
                        @Override
                        public void component(final Component component, final IVisit<Boolean> visit)
                        {
                                if (component.hasErrorMessage() && component.isVisibleInHierarchy() && component.isEnabledInHierarchy())
                                {
                                        visit.stop(true);
                                }
                        }
                });

                return (error != null) && error;
        }

        /**
         * Visits the form's children FormComponents and inform them that a new user input is available
         * in the Request
         */
        private void inputChanged()
        {
                visitFormComponentsPostOrder(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                formComponent.inputChanged();
                        }
                });
        }

        /**
         * If a default IFormSubmittingComponent was set on this form, this method will be called to
         * render an extra field with an invisible style so that pressing enter in one of the textfields
         * will do a form submit using this component. This method is overridable as what we do is best
         * effort only, and may not what you want in specific situations. So if you have specific
         * usability concerns, or want to follow another strategy, you may override this method.
         *
         * @see #addDefaultSubmitButtonHandler(IHeaderResponse)
         */
        protected void appendDefaultButtonField()
        {
                AppendingStringBuffer buffer = new AppendingStringBuffer();

                // hidden div
                buffer.append(String.format("<div hidden=\"\" class=\"%s\">",
                        getString(HIDDEN_FIELDS_CSS_CLASS_KEY)));

                // add an empty textfield (otherwise IE doesn't work)
                buffer.append("<input type=\"text\" tabindex=\"-1\" autocomplete=\"off\"/>");

                // add the submitting component
                buffer
                        .append(String.format("<input id=\"%s\" type=\"submit\" tabindex=\"-1\" name=\"%s\" />",
                                getHiddenFieldsId(HIDDEN_FIELDS_SUBMIT_IDX),
                                defaultSubmittingComponent.getInputName()));

                // close div
                buffer.append("</div>");

                getResponse().write(buffer);
        }

        /**
         * Where {@link #appendDefaultButtonField()} renders the markup for default submit button
         * handling, this method attaches the event handler to its 'click' event. The 'click' event on
         * the hidden submit button will be dispatched to the selected default submit button. As with
         * {@link #appendDefaultButtonField()} this method can be overridden when the generated code
         * needs to be adjusted for a specific usecase.
         *
         * @param headerResponse
         *            The header response.
         */
        protected void addDefaultSubmitButtonHandler(IHeaderResponse headerResponse)
        {
                final Component submittingComponent = (Component) defaultSubmittingComponent;
                AppendingStringBuffer buffer = new AppendingStringBuffer();
                buffer.append("var b=document.getElementById('");
                buffer.append(submittingComponent.getMarkupId());
                buffer.append("'); if (b!=null && b.onclick!=null && typeof(b.onclick) != 'undefined') ");
                buffer.append(
                        "{  var r = Wicket.bind(b.onclick, b)(); if (r != false) b.click(); } else { b.click(); };  return false;");
                headerResponse.render(OnEventHeaderItem
                        .forMarkupId(getHiddenFieldsId(HIDDEN_FIELDS_SUBMIT_IDX), "click", buffer.toString()));
        }

        /**
         * Template method to allow clients to do any processing (like recording the current model so
         * that, in case onSubmit does further validation, the model can be rolled back) before the
         * actual updating of form component models is done.
         */
        protected void beforeUpdateFormComponentModels()
        {
        }

        /**
         * Called (by the default implementation of 'process') when all fields validated, the form was
         * updated and it's data was allowed to be persisted. It is meant for delegating further
         * processing to clients.
         * <p>
         * This implementation first finds out whether the form processing was triggered by a nested
         * IFormSubmittingComponent of this form. If that is the case, that component's
         * onSubmitBefore/AfterForm methods are called appropriately..
         * </p>
         * <p>
         * Regardless of whether a submitting component was found, the form's onSubmit method is called
         * next.
         * </p>
         *
         * @param submittingComponent
         *            the component that triggered this form processing, or null if the processing was
         *            triggered by something else (like a non-Wicket submit button or a javascript
         *            execution)
         */
        protected void delegateSubmit(IFormSubmitter submittingComponent)
        {
                final Form<?> processingForm = findFormToProcess(submittingComponent);

                // collect all forms innermost to outermost before any hierarchy is changed
                final List<Form<?>> forms = Generics.newArrayList(3);
                Visits.visitPostOrder(processingForm, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(Form<?> form, IVisit<Void> visit)
                        {
                                if (form.isSubmitted())
                                {
                                        forms.add(form);
                                }
                        }
                }, new ClassVisitFilter(Form.class));

                // process submitting component (if specified)
                if (submittingComponent != null)
                {
                        // invoke submit on component
                        submittingComponent.onSubmit();
                }

                // invoke Form#onSubmit(..)
                for (Form<?> form : forms)
                {
                        form.onSubmit();
                }

                if (submittingComponent != null)
                {
                        submittingComponent.onAfterSubmit();
                }
        }

        /**
         * Returns the id which will be used for the hidden div containing all parameter fields.
         *
         * @param idx
         *            The index of the div to keep different divs apart.
         * @return the id of the hidden div
         */
        private final String getHiddenFieldsId(int idx)
        {
                return getInputNamePrefix() + getMarkupId() + "_hf_" + idx;
        }

        /**
         * Gets the HTTP submit method that will appear in form markup. If no method is specified in the
         * template, "post" is the default. Note that the markup-declared HTTP method may not correspond
         * to the one actually used to submit the form; in an Ajax submit, for example, JavaScript event
         * handlers may submit the form with a "get" even when the form method is declared as "post."
         * Therefore this method should not be considered a guarantee of the HTTP method used, but a
         * value for the markup only. Override if you have a requirement to alter this behavior.
         *
         * @return the submit method specified in markup.
         */
        protected String getMethod()
        {
                String method = getMarkupAttributes().getString("method");
                return (method != null) ? method : METHOD_POST;
        }

        /**
         *
         * @see org.apache.wicket.Component#getStatelessHint()
         */
        @Override
        protected boolean getStatelessHint()
        {
                return false;
        }

        /**
         * @return True if is multipart
         */
        public boolean isMultiPart()
        {
                if (multiPart == 0)
                {
                        Boolean anyEmbeddedMultipart = visitChildren(Component.class,
                                        new IVisitor<Component, Boolean>()
                                        {
                                                @Override
                                                public void component(final Component component, final IVisit<Boolean> visit)
                                                {
                                                        boolean isMultiPart = false;
                                                        if (component instanceof Form<?>)
                                                        {
                                                                Form<?> form = (Form<?>)component;
                                                                if (form.isVisibleInHierarchy() && form.isEnabledInHierarchy())
                                                                {
                                                                        isMultiPart = (form.multiPart & MULTIPART_HARD) != 0;
                                                                }
                                                        }
                                                        else if (component instanceof FormComponent<?>)
                                                        {
                                                                FormComponent<?> fc = (FormComponent<?>)component;
                                                                if (fc.isVisibleInHierarchy() && fc.isEnabledInHierarchy())
                                                                {
                                                                        isMultiPart = fc.isMultiPart();
                                                                }
                                                        }

                                                        if (isMultiPart)
                                                        {
                                                                visit.stop(true);
                                                        }
                                                }

                                        });

                        if (Boolean.TRUE.equals(anyEmbeddedMultipart)) {
                                multiPart |= MULTIPART_HINT_YES;
                        } else {
                                multiPart |= MULTIPART_HINT_NO;
                        }
                }

                return (multiPart & (MULTIPART_HARD | MULTIPART_HINT_YES)) != 0;
        }

        /**
         * Handles multi-part processing of the submitted data.
         * <strong>WARNING</strong> If this method is overridden it can break {@link FileUploadField}s on this form
         *
         * @return false if form is multipart and upload failed
         */
        protected boolean handleMultiPart()
        {
                if (isMultiPart())
                {
                        // Change the request to a multipart web request so parameters are
                        // parsed out correctly
                        try
                        {
                                ServletWebRequest request = (ServletWebRequest)getRequest();
                                final MultipartServletWebRequest multipartWebRequest = request.newMultipartWebRequest(
                                        getMaxSize(), getPage().getId());
                                multipartWebRequest.setFileMaxSize(getFileMaxSize());
                                multipartWebRequest.setFileCountMax(getFileCountMax());
                                multipartWebRequest.parseFileParts();

                                // TODO: Can't this be detected from header?
                                getRequestCycle().setRequest(multipartWebRequest);
                        }
                        catch (final FileUploadException fux)
                        {
                                // Create model with exception and maximum size values
                                final Map<String, Object> model = new HashMap<>();
                                model.put("exception", fux);
                                model.put("maxSize", getMaxSize());
                                model.put("fileMaxSize", getFileMaxSize());
                                model.put("fileCountMax", getFileCountMax());

                                onFileUploadException(fux, model);

                                // don't process the form if there is a FileUploadException
                                return false;
                        }
                }
                return true;
        }

        /**
         * The default message may look like ".. may not exceed 10240 Bytes..". Which is ok, but
         * sometimes you may want something like "10KB". By subclassing this method you may replace
         * maxSize in the model or add you own property and use that in your error message.
         * <p>
         * Don't forget to call super.onFileUploadException(e, model) at the end of your method.
         *
         * @param e
         * @param model
         */
        protected void onFileUploadException(final FileUploadException e,
                final Map<String, Object> model)
        {
                if (e instanceof FileUploadBase.SizeLimitExceededException)
                {
                        String msg = getString(UPLOAD_TOO_LARGE_RESOURCE_KEY, Model.ofMap(model));
                        error(msg);
                }
                else if (e instanceof FileUploadBase.FileSizeLimitExceededException)
                {
                        String msg = getString(UPLOAD_SINGLE_FILE_TOO_LARGE_RESOURCE_KEY, Model.ofMap(model));
                        error(msg);
                }
                else if (e instanceof FileCountLimitExceededException)
                {
                        String msg = getString(UPLOAD_TOO_MANY_FILES_RESOURCE_KEY, Model.ofMap(model));
                        error(msg);
                }
                else
                {
                        String msg = getString(UPLOAD_FAILED_RESOURCE_KEY, Model.ofMap(model));
                        error(msg);

                        log.warn(msg, e);
                }
        }

        /**
         * @see org.apache.wicket.Component#internalOnModelChanged()
         */
        @Override
        protected void internalOnModelChanged()
        {
                // Visit all the form components and validate each
                visitFormComponentsPostOrder(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                // If form component is using form model
                                if (formComponent.sameInnermostModel(Form.this))
                                {
                                        formComponent.modelChanged();
                                }
                        }
                });
        }

        /**
         * Mark each form component on this form invalid.
         */
        protected final void markFormComponentsInvalid()
        {
                // call invalidate methods of all nested form components
                visitFormComponentsPostOrder(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                if (formComponent.isVisibleInHierarchy())
                                {
                                        formComponent.invalid();
                                }
                        }
                });
        }

        /**
         * Mark each form component on this form and on nested forms valid.
         */
        protected final void markFormComponentsValid()
        {
                internalMarkFormComponentsValid();
                markNestedFormComponentsValid();
        }

        /**
         * Mark each form component on nested form valid.
         */
        private void markNestedFormComponentsValid()
        {
                visitChildren(Form.class, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(final Form<?> form, final IVisit<Void> visit)
                        {
                                if (form.isSubmitted())
                                {
                                        form.internalMarkFormComponentsValid();
                                }
                                else
                                {
                                        visit.dontGoDeeper();
                                }
                        }
                });
        }

        /**
         * Mark each form component on this form valid.
         */
        private void internalMarkFormComponentsValid()
        {
                // call valid methods of all nested form components
                visitFormComponentsPostOrder(new IVisitor<FormComponent<?>, Void>()
                {
                        @Override
                        public void component(final FormComponent<?> formComponent, IVisit<Void> visit)
                        {
                                if (formComponent.getForm() == Form.this && formComponent.isVisibleInHierarchy())
                                {
                                        formComponent.valid();
                                }
                        }
                });
        }

        /**
         * @see org.apache.wicket.Component#onComponentTag(ComponentTag)
         */
        @Override
        protected void onComponentTag(final ComponentTag tag)
        {
                super.onComponentTag(tag);

                if (isRootForm())
                {
                        checkComponentTag(tag, "form");

                        String method = getMethod().toLowerCase(Locale.ROOT);
                        tag.put("method", method);
                        String url = getActionUrl().toString();
                        if (encodeUrlInHiddenFields())
                        {
                                int i = url.indexOf('?');
                                String action = (i > -1) ? url.substring(0, i) : "";
                                tag.put("action", action);
                                // alternatively, we could just put an empty string here, so
                                // that mounted paths stay in good order. I decided against this
                                // as I'm not sure whether that could have side effects with
                                // other encoders
                        }
                        else
                        {
                                tag.put("action", url);
                        }

                        if (isMultiPart())
                        {
                                if (METHOD_GET.equalsIgnoreCase(method))
                                {
                                        log.warn("Form with id '{}' is multipart. It should use method 'POST'!",
                                                getId());
                                        tag.put("method", METHOD_POST.toLowerCase(Locale.ROOT));
                                }

                                tag.put("enctype", ENCTYPE_MULTIPART_FORM_DATA);
                                //
                                // require the application-encoding for multipart/form-data to be sure to
                                // get multipart-uploaded characters with the proper encoding on the following
                                // request.
                                //
                                // for details see: http://stackoverflow.com/questions/546365
                                //
                                tag.put("accept-charset", getApplication().getRequestCycleSettings()
                                        .getResponseRequestEncoding());
                        }
                        else
                        {
                                // sanity check
                                String enctype = (String)tag.getAttributes().get("enctype");
                                if (ENCTYPE_MULTIPART_FORM_DATA.equalsIgnoreCase(enctype))
                                {
                                        // though not set explicitly in Java, this is a multipart
                                        // form
                                        setMultiPart(true);
                                }
                        }
                }
                else
                {
                        adjustNestedTagName(tag);
                        tag.remove("method");
                        tag.remove("action");
                        tag.remove("enctype");
                }
        }

        // WICKET-6658 form is not allowed, anything else can stay as is
        private void adjustNestedTagName(ComponentTag tag) {
                if ("form".equalsIgnoreCase(tag.getName()))
                {
                        tag.setName("div");
                }
        }

        /**
         * Generates the action url for the form
         *
         * @return action url
         */
        protected CharSequence getActionUrl()
        {
                return urlForListener(new PageParameters());
        }

        /**
         * @see org.apache.wicket.Component#renderPlaceholderTag(org.apache.wicket.markup.ComponentTag,
         *      org.apache.wicket.request.Response)
         */
        @Override
        protected void renderPlaceholderTag(ComponentTag tag, Response response)
        {
                if (!isRootForm())
                {
                        // WICKET-2166
                        adjustNestedTagName(tag);
                }

                super.renderPlaceholderTag(tag, response);
        }

        /**
         * Should URL query parameters be encoded in hidden fields, by default <code>true</code>
         * for {@link #METHOD_GET} only.
         * <p>
         * In that case, the parameters must <em>not</em> be written as query parameters, as the browser
         * would strip them from the action url before appending the form values.
         *
         * @return true if form's method is 'get'
         *
         * @see #getMethod()
         */
        protected boolean encodeUrlInHiddenFields()
        {
                return METHOD_GET.equalsIgnoreCase(getMethod());
        }

        /**
         * Append an additional hidden input tag to support anchor tags that can submit a form.
         *
         * @param markupStream
         *            The markup stream
         * @param openTag
         *            The open tag for the body
         */
        @Override
        public void onComponentTagBody(final MarkupStream markupStream, final ComponentTag openTag)
        {
                if (isRootForm())
                {
                        // get the hidden field id
                        writeHiddenFields();
                }

                // do the rest of the processing
                super.onComponentTagBody(markupStream, openTag);
        }

        @Override
        public void renderHead(IHeaderResponse response)
        {
                super.renderHead(response);

                if (hasDefaultSubmittingComponent())
                {
                        addDefaultSubmitButtonHandler(response);
                }
        }

        /**
         * Writes the markup for the hidden input fields and default button field if applicable to the
         * current response.
         */
        public final void writeHiddenFields()
        {
                getResponse().write(String.format("<div id=\"%s\" hidden=\"\" class=\"%s\">",
                        getHiddenFieldsId(HIDDEN_FIELDS_PARAMS_IDX),
                        getString(HIDDEN_FIELDS_CSS_CLASS_KEY)));
                // if the parameters are not in the action attribute, they have to be written as hidden fields
                if (encodeUrlInHiddenFields())
                {
                        AppendingStringBuffer buffer = new AppendingStringBuffer();

                        String url = getActionUrl().toString();
                        int i = url.indexOf('?');
                        String queryString = (i > -1) ? url.substring(i + 1) : url;
                        String[] params = Strings.split(queryString, '&');

                        writeParamsAsHiddenFields(params, buffer);

                        getResponse().write(buffer);
                }
                getResponse().write("</div>");

                // if a default submitting component was set, handle the rendering of that
                if (hasDefaultSubmittingComponent())
                {
                        appendDefaultButtonField();
                }
        }

        private boolean hasDefaultSubmittingComponent()
        {
                if (defaultSubmittingComponent instanceof Component)
                {
                        final Component submittingComponent = (Component) defaultSubmittingComponent;
                        return submittingComponent.isVisibleInHierarchy()
                                && submittingComponent.isEnabledInHierarchy();
                }
                return false;
        }

        /**
         *
         * @param params
         * @param buffer
         */
        protected void writeParamsAsHiddenFields(String[] params, AppendingStringBuffer buffer)
        {
                for (String param : params)
                {
                        String[] pair = Strings.split(param, '=');

                        buffer.append("<input type=\"hidden\" name=\"")
                                .append(recode(pair[0]))
                                .append("\" value=\"")
                                .append(pair.length > 1 ? recode(pair[1]) : "")
                                .append("\" />");
                }
        }

        /**
         * Take URL-encoded query string value, decode it and return HTML-escaped version
         *
         * @param s
         *            value to decode
         * @return URL decoded and HTML escaped value
         */
        private String recode(String s)
        {
                String un = UrlDecoder.QUERY_INSTANCE.decode(s, getRequest().getCharset());
                return Strings.escapeMarkup(un).toString();
        }

        /**
         * @see org.apache.wicket.Component#onDetach()
         */
        @Override
        protected void onDetach()
        {
                setFlag(FLAG_SUBMITTED, false);

                super.onDetach();
        }

        /**
         * Method to override if you want to do something special when an error occurs (other than
         * simply displaying validation errors).
         */
        protected void onError()
        {
        }

        @Override
        public void onEvent(IEvent<?> event) {
                if (event.getPayload() instanceof AjaxRequestTarget) {
                        // WICKET-6171 clear multipart hint, it might change during Ajax requests without this form being rendered
                        this.multiPart &= MULTIPART_HARD;
                }
        }

        @Override
        protected void onBeforeRender()
        {
                // clear multipart hint, it will be reevaluated by #isMultiPart()
                this.multiPart &= MULTIPART_HARD;

                super.onBeforeRender();
        }

        /**
         * Implemented by subclasses to deal with form submits.
         */
        protected void onSubmit()
        {
        }

        /**
         * Update the model of all components on this form and nested forms using the fields that were
         * sent with the current request. This method only updates models when the Form.validate() is
         * called first that takes care of the conversion for the FormComponents.
         *
         * Normally this method will not be called when a validation error occurs in one of the form
         * components.
         *
         * @see org.apache.wicket.markup.html.form.FormComponent#updateModel()
         */
        protected final void updateFormComponentModels()
        {
                internalUpdateFormComponentModels();
                updateNestedFormComponentModels();
        }

        /**
         * Update the model of all components on nested forms.
         *
         * @see #updateFormComponentModels()
         */
        private void updateNestedFormComponentModels()
        {
                visitChildren(Form.class, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(final Form<?> form, final IVisit<Void> visit)
                        {
                                if (form.isSubmitted())
                                {
                                        form.internalUpdateFormComponentModels();
                                }
                                else
                                {
                                        visit.dontGoDeeper();
                                }
                        }
                });
        }

        /**
         * Update the model of all components on this form.
         *
         * @see #updateFormComponentModels()
         */
        private void internalUpdateFormComponentModels()
        {
                FormComponent.visitComponentsPostOrder(this, new FormModelUpdateVisitor(this));
        }

        /**
         * Validates the form by checking required fields, converting raw input and running validators
         * for every form component, and last running global form validators. This method is typically
         * called before updating any models.
         * <p>
         * NOTE: in most cases, custom validations on the form can be achieved using an IFormValidator
         * that can be added using addValidator().
         * </p>
         */
        protected final void validate()
        {
                // since this method can be called directly by users, this additional check is needed
                if (isEnabledInHierarchy() && isVisibleInHierarchy())
                {
                        validateNestedForms();
                        validateComponents();
                        validateFormValidators();
                        onValidate();
                }
        }

        /**
         * Callback during the validation stage of the form
         */
        protected void onValidate()
        {

        }

        /**
         * Calls {@linkplain #onValidateModelObjects()} on this form and all nested forms that are
         * visible and enabled
         */
        private void internalOnValidateModelObjects()
        {
                onValidateModelObjects();
                visitChildren(Form.class, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(Form<?> form, IVisit<Void> visit)
                        {
                                if (form.isSubmitted())
                                {
                                        form.onValidateModelObjects();
                                }
                                else
                                {
                                        visit.dontGoDeeper();
                                }
                        }
                });
        }

        /**
         * Called after form components have updated their models. This is a late-stage validation that
         * allows outside frameworks to validate any beans that the form is updating.
         *
         * This validation method is not preferred because at this point any errors will not unroll any
         * changes to the model object, so the model object is in a modified state potentially
         * containing illegal values. However, with external frameworks there may not be an alternate
         * way to validate the model object. A good example of this is a JSR303 Bean Validator
         * validating the model object to check any class-level constraints, in order to check such
         * constraints the model object must contain the values set by the user.
         */
        protected void onValidateModelObjects()
        {
        }

        /**
         * Triggers type conversion on form components
         */
        protected final void validateComponents()
        {
                visitFormComponentsPostOrder(new ValidationVisitor()
                {
                        @Override
                        public void validate(final FormComponent<?> formComponent)
                        {
                                final Form<?> form = formComponent.getForm();
                                if (form == Form.this && form.isEnabledInHierarchy() && form.isVisibleInHierarchy())
                                {
                                        formComponent.validate();
                                }
                        }
                });
        }

        /**
         * Checks if the specified form component visible and is attached to a page
         *
         * @param fc
         *            form component
         *
         * @return true if the form component and all its parents are visible and there component is in
         *         page's hierarchy
         */
        private boolean isFormComponentVisibleInPage(FormComponent<?> fc)
        {
                if (fc == null)
                {
                        throw new IllegalArgumentException("Argument `fc` cannot be null");
                }
                return fc.isVisibleInHierarchy();
        }


        /**
         * Validates form with the given form validator
         *
         * @param validator
         */
        protected final void validateFormValidator(final IFormValidator validator)
        {
                Args.notNull(validator, "validator");

                final FormComponent<?>[] dependents = validator.getDependentFormComponents();

                boolean validate = true;

                if (dependents != null)
                {
                        for (final FormComponent<?> dependent : dependents)
                        {
                                // check if the dependent component is valid
                                if (!dependent.isValid())
                                {
                                        validate = false;
                                        break;
                                }
                                // check if the dependent component is visible and is attached to
                                // the page
                                else if (!isFormComponentVisibleInPage(dependent))
                                {
                                        if (log.isWarnEnabled())
                                        {
                                                log.warn("IFormValidator in form `" +
                                                        getPageRelativePath() +
                                                        "` depends on a component that has been removed from the page or is no longer visible. " +
                                                        "Offending component id `" + dependent.getId() + "`.");
                                        }
                                        validate = false;
                                        break;
                                }
                        }
                }

                if (validate)
                {
                        validator.validate(this);
                }
        }

        /**
         * Triggers any added {@link IFormValidator}s.
         */
        protected final void validateFormValidators()
        {
                for (Behavior behavior : getBehaviors())
                {
                        if (behavior instanceof IFormValidator)
                        {
                                validateFormValidator((IFormValidator)behavior);
                        }
                }
        }

        /**
         * Validates {@link FormComponent}s as well as {@link IFormValidator}s in nested {@link Form}s.
         *
         * @see #validate()
         */
        private void validateNestedForms()
        {
                Visits.visitPostOrder(this, new IVisitor<Form<?>, Void>()
                {
                        @Override
                        public void component(final Form<?> form, final IVisit<Void> visit)
                        {
                                if (form == Form.this)
                                {
                                        // skip self, only process children
                                        visit.stop();
                                        return;
                                }

                                if (form.isSubmitted())
                                {
                                        form.validateComponents();
                                        form.validateFormValidators();
                                        form.onValidate();
                                }
                        }
                }, new ClassVisitFilter(Form.class));
        }

        /**
         * Allows to customize input names of form components inside this form.
         *
         * @return String that well be used as prefix to form component input names
         */
        protected String getInputNamePrefix()
        {
                return "";
        }

        /**
         * @param component
         * @return The parent form for component
         */
        public static Form<?> findForm(Component component)
        {
                return component.findParent(Form.class);
        }

        /**
         * Utility method to assemble an id to distinct form components from different nesting levels.
         * Useful to generate input names attributes.
         *
         * @param component
         * @return form relative identification string
         */
        public static String getRootFormRelativeId(Component component)
        {
                String id = component.getId();
                final PrependingStringBuffer inputName = new PrependingStringBuffer(id.length());
                Component c = component;
                while (true)
                {
                        inputName.prepend(id);
                        c = c.getParent();
                        if (c == null || (c instanceof Form<?> && ((Form<?>)c).isRootForm()) ||
                                c instanceof Page)
                        {
                                break;
                        }
                        inputName.prepend(Component.PATH_SEPARATOR);
                        id = c.getId();
                }

                /*
                 * Certain input names causes problems with JavaScript. If the input name would cause a
                 * problem, we create a replacement unique name by prefixing the name with a path that would
                 * otherwise never be used (blank id in path).
                 *
                 * Input names must start with [A-Za-z] according to HTML 4.01 spec. HTML 5 allows almost
                 * anything.
                 */
                if (JavaScriptReservedNames.isNameReserved(inputName.toString()))
                {
                        inputName.prepend(Component.PATH_SEPARATOR);
                        inputName.prepend(Component.PATH_SEPARATOR);
                        inputName.prepend("p");
                }
                return inputName.toString();
        }

        /**
         * Get the request parameters for a form submit,
         * according to the request's method or the form's method as fallback.
         *
         * @param component any component inside the form or the form itself
         * @return parameters
         */
        static IRequestParameters getRequestParameters(Component component) {
                String method = Form.METHOD_POST;
                final Request request = component.getRequest();
                if (request.getContainerRequest() instanceof HttpServletRequest)
                {
                        method = ((HttpServletRequest)request.getContainerRequest()).getMethod();
                }
                else
                {
                        final Form<?> form;
                        if (component instanceof Form) {
                                form = (Form<?>)component;
                        } else {
                                form = component.findParent(Form.class);
                        }

                        if (form != null)
                        {
                                method = form.getMethod();
                        }
                }

                final IRequestParameters parameters;
                switch (method.toLowerCase(Locale.ROOT))
                {
                        case Form.METHOD_POST:
                                parameters = request.getPostParameters();
                                break;
                        case Form.METHOD_GET:
                                parameters = request.getQueryParameters();
                                break;
                        default:
                                parameters = EmptyRequestParameters.INSTANCE;
                }

                return parameters;
        }

        /**
         * Response when a submission method mismatch is detected
         *
         * @see Form#getMethod()
         *
         * @author igor
         */
        public static enum MethodMismatchResponse {
                /**
                 * Continue processing.
                 */
                CONTINUE,

                /**
                 * Abort processing.
                 */
                ABORT
        }
}