/*
 * 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.request.resource.caching;

import java.util.regex.Pattern;

import org.apache.wicket.request.cycle.RequestCycle;
import org.apache.wicket.request.http.WebResponse;
import org.apache.wicket.request.resource.AbstractResource;
import org.apache.wicket.request.resource.caching.version.CachingResourceVersion;
import org.apache.wicket.request.resource.caching.version.IResourceVersion;
import org.apache.wicket.util.lang.Args;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * resource caching strategy that adds a version for the 
 * requested resource to the filename.
 * <p/>
 * versioned_filename := [basename][version-prefix][version](.extension)
 * <p/>
 * the <code>version</code> must not contain the <code>version-prefix</code> so
 * please use an unambiguous value for the <code>version-prefix</code>. The default
 * <code>version-prefix</code> is <code>{@value #DEFAULT_VERSION_PREFIX}</code>.
 * <p/> 
 * Since browsers and proxies use the versioned filename of the resource 
 * as a cache key a change to the version will also change the filename and 
 * cause a reliable cache miss. This enables us to set the caching duration
 * of the resource to a maximum and get best network performance.
 * <p/>
 * 
 * @author Peter Ertl
 * 
 * @since 1.5
 */
public class FilenameWithVersionResourceCachingStrategy implements IResourceCachingStrategy
{
        private static final Logger LOG = LoggerFactory.getLogger(FilenameWithVersionResourceCachingStrategy.class);

        private static final String DEFAULT_VERSION_PREFIX = "-ver-";
        
        /** string that marks the beginning the of the version in the decorated filename */
        private final String versionPrefix;

        /** resource version provider */
        private final IResourceVersion resourceVersion;

        /**
         * create filename caching strategy with given version provider and 
         * <code>version-prefix = '{@value #DEFAULT_VERSION_PREFIX}'</code>
         * 
         * @param resourceVersion
         *            version provider
         *            
         * @see #FilenameWithVersionResourceCachingStrategy(String, org.apache.wicket.request.resource.caching.version.IResourceVersion) 
         */
        public FilenameWithVersionResourceCachingStrategy(IResourceVersion resourceVersion)
        {
                this(DEFAULT_VERSION_PREFIX, resourceVersion);
        }

        /**
         * Constructor
         * 
         * @param versionPrefix
         *            string that marks the beginning the of the version in the decorated filename 
         * @param resourceVersion
         *            resource version object
         * 
         * @see #FilenameWithVersionResourceCachingStrategy(org.apache.wicket.request.resource.caching.version.IResourceVersion) 
         */
        public FilenameWithVersionResourceCachingStrategy(String versionPrefix,
                                                          IResourceVersion resourceVersion)
        {
                this.resourceVersion = Args.notNull(resourceVersion, "resourceVersion");
                this.versionPrefix = Args.notEmpty(versionPrefix, "versionPrefix");
        }

        /**
         * @return string appended to the filename before the version string
         */
        public final String getVersionPrefix()
        {
                return versionPrefix;
        }

        @Override
        public void decorateUrl(ResourceUrl url, IStaticCacheableResource resource)
        {
                // get version string for requested resource
                final String version = this.resourceVersion.getVersion(resource);

                // ignore resource if no version information is available
                if (version == null)
                {
                        return;
                }

                // get undecorated filename
                final String filename = url.getFileName();

                // check if resource name has extension
                final int extensionAt = filename.lastIndexOf('.');

                // create filename with version:
                //
                // filename :=
                // [basename][version-prefix][version](.extension)
                //
                final StringBuilder versionedFilename = new StringBuilder();
                
                // add filename
                if (extensionAt == -1)
                {
                        versionedFilename.append(filename);
                }
                else
                {
                        versionedFilename.append(filename.substring(0, extensionAt));
                }

                int pos = versionedFilename.indexOf(getVersionPrefix());
                if (pos != -1 && isVersion(versionedFilename.substring(pos + versionPrefix.length())))
                {
                        LOG.error("A resource with name '{}' contains the version prefix '{}' so the un-decoration will not work." +
                                        " Either use a different version prefix or rename this resource.", filename, getVersionPrefix());
                }

                // add version suffix
                versionedFilename.append(versionPrefix);
                
                // add version
                versionedFilename.append(version);

                // add extension if present
                if (extensionAt != -1)
                {
                        versionedFilename.append(filename.substring(extensionAt));
                }
                // set versioned filename
                url.setFileName(versionedFilename.toString());
        }

        @Override
        public void undecorateUrl(ResourceUrl url)
        {
                final String filename = url.getFileName();
                
                // check for extension
                int pos = filename.lastIndexOf('.');

                // get name of file without extension (but with version string)
                final String fullname = pos == -1 ? filename : filename.substring(0, pos);
                
                // get extension of file if present
                final String extension = pos == -1 ? null : filename.substring(pos);

                // get position of version string
                pos = fullname.lastIndexOf(versionPrefix);

                // remove version string if it exists
                if (pos != -1 && isVersion(fullname.substring(pos + versionPrefix.length())))
                {
                        // get filename before version string
                        final String basename = fullname.substring(0, pos);

                        // create filename without version string 
                        // (required for working resource lookup)
                        url.setFileName(extension == null? basename : basename + extension);

                        // store the version in the request cycle
                        RequestCycle requestCycle = RequestCycle.get();
                        if (requestCycle != null)
                        {
                                int idx = fullname.indexOf(versionPrefix);
                                String urlVersion = fullname.substring(idx + versionPrefix.length());
                                requestCycle.setMetaData(URL_VERSION, urlVersion);
                        }
                }
        }

        private boolean isVersion(String substring)
        {
                Pattern versionPattern = resourceVersion.getVersionPattern();
                return versionPattern == null || versionPattern.matcher(substring).matches();
        }

        /**
         * set resource caching to maximum and set cache-visibility to 'public'
         * 
         * @param response
         */
        @Override
        public void decorateResponse(AbstractResource.ResourceResponse response, IStaticCacheableResource resource)
        {
                String requestedVersion = RequestCycle.get().getMetaData(URL_VERSION);
                String calculatedVersion = this.resourceVersion.getVersion(resource);
                if (calculatedVersion != null && calculatedVersion.equals(requestedVersion))
                {
                        response.setCacheDurationToMaximum();
                        response.setCacheScope(WebResponse.CacheScope.PUBLIC);
                }
        }

        @Override
        public void clearCache()
        {
                if (resourceVersion instanceof CachingResourceVersion)
                {
                        ((CachingResourceVersion) resourceVersion).invalidateAll();
                }
        }
}