/*
 * 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.catalina;

import java.io.InputStream;
import java.net.URL;
import java.util.List;
import java.util.Set;

/**
 * Represents the complete set of resources for a web application. The resources for a web application comprise of
 * multiple ResourceSets and when looking for a Resource, the ResourceSets are processed in the following order:
 * <ol>
 * <li>Pre - Resources defined by the &lt;PreResource&gt; element in the web application's context.xml. Resources will
 * be searched in the order they were specified.</li>
 * <li>Main - The main resources for the web application - i.e. the WAR or the directory containing the expanded
 * WAR</li>
 * <li>JARs - Resource JARs as defined by the Servlet specification. JARs will be searched in the order they were added
 * to the ResourceRoot.</li>
 * <li>Post - Resources defined by the &lt;PostResource&gt; element in the web application's context.xml. Resources will
 * be searched in the order they were specified.</li>
 * </ol>
 * The following conventions should be noted:
 * <ul>
 * <li>Write operations (including delete) will only be applied to the main ResourceSet. The write operation will fail
 * if the presence of a Resource in one of the other ResourceSets effectively makes the operation on the main
 * ResourceSet a NO-OP.</li>
 * <li>A file in a ResourceSet will hide a directory of the same name (and all the contents of that directory) in a
 * ResourceSet that is later in the search order.</li>
 * <li>Only the main ResourceSet may define a META-INF/context.xml since that file defines the Pre- and
 * Post-Resources.</li>
 * <li>As per the Servlet specification, any META-INF or WEB-INF directories in a resource JAR will be ignored.</li>
 * <li>Pre- and Post-Resources may define WEB-INF/lib and WEB-INF/classes in order to make additional libraries and/or
 * classes available to the web application.
 * </ul>
 * This mechanism replaces and extends the following features that were present in earlier versions:
 * <ul>
 * <li>Aliases - Replaced by Post-Resources with the addition of support for single files as well as directories and
 * JARs.</li>
 * <li>VirtualWebappLoader - Replaced by Pre- and Post-Resources mapped to WEB-INF/lib and WEB-INF/classes</li>
 * <li>VirtualDirContext - Replaced by Pre- and Post-Resources</li>
 * <li>External repositories - Replaced by Pre- and Post-Resources mapped to WEB-INF/lib and WEB-INF/classes</li>
 * <li>Resource JARs - Same feature but implemented using the same mechanism as all the other additional resources.</li>
 * </ul>
 */
/*
 * A potential future enhancement is to allow writing to any ResourceSet, not just the main ResourceSet although that
 * adds all sorts complications including: - which ResourceSet to write to - unexpected behaviour when deleting a
 * resource from one ResourceSet since that may unmask a resource in a lower priority ResourceSet so what was a delete
 * looks like a replace with the user having no idea where the 'new' resource came from - how to handle PUT when the
 * target is read-only but it could be written to a higher priority ResourceSet that is read-write
 */
public interface WebResourceRoot extends Lifecycle {
    /**
     * Obtain the object that represents the resource at the given path. Note that the resource at that path may not
     * exist. If the resource does not exist, the WebResource returned will be associated with the main WebResourceSet.
     *
     * @param path The path for the resource of interest relative to the root of the web application. It must start with
     *                 '/'.
     *
     * @return The object that represents the resource at the given path
     */
    WebResource getResource(String path);

    /**
     * Obtain the objects that represent the resource at the given path. Note that the resource at that path may not
     * exist. If the resource does not exist, the WebResource returned will be associated with the main WebResourceSet.
     * This will include all matches even if the resource would not normally be accessible (e.g. because it was
     * overridden by another resource)
     *
     * @param path The path for the resource of interest relative to the root of the web application. It must start with
     *                 '/'.
     *
     * @return The objects that represents the resource at the given path
     */
    WebResource[] getResources(String path);

    /**
     * Obtain the object that represents the class loader resource at the given path. WEB-INF/classes is always searched
     * prior to searching JAR files in WEB-INF/lib. The search order for JAR files will be consistent across subsequent
     * calls to this method until the web application is reloaded. No guarantee is made as to what the search order for
     * JAR files may be.
     *
     * @param path The path of the class loader resource of interest relative to the the root of class loader resources
     *                 for this web application.
     *
     * @return The object that represents the class loader resource at the given path
     */
    WebResource getClassLoaderResource(String path);

    /**
     * Obtain the objects that represent the class loader resource at the given path. Note that the resource at that
     * path may not exist. If the path does not exist, the WebResource returned will be associated with the main
     * WebResourceSet. This will include all matches even if the resource would not normally be accessible (e.g. because
     * it was overridden by another resource)
     *
     * @param path The path for the class loader resource of interest relative to the root of the class loader resources
     *                 for the web application. It must start with '/'.
     *
     * @return The objects that represents the class loader resources at the given path. There will always be at least
     *             one element although that element may represent a resource that is not present.
     */
    WebResource[] getClassLoaderResources(String path);

    /**
     * Obtain the list of the names of all of the files and directories located in the specified directory.
     *
     * @param path The path for the resource of interest relative to the root of the web application. It must start with
     *                 '/'.
     *
     * @return The list of resources. If path does not refer to a directory then a zero length array will be returned.
     */
    String[] list(String path);

    /**
     * Obtain the Set of the web applications pathnames of all of the files and directories located in the specified
     * directory. Paths representing directories will end with a '/' character.
     *
     * @param path The path for the resource of interest relative to the root of the web application. It must start with
     *                 '/'.
     *
     * @return The Set of resources. If path does not refer to a directory then null will be returned.
     */
    Set<String> listWebAppPaths(String path);

    /**
     * Obtain the list of all of the WebResources in the specified directory.
     *
     * @param path The path for the resource of interest relative to the root of the web application. It must start with
     *                 '/'.
     *
     * @return The list of resources. If path does not refer to a directory then a zero length array will be returned.
     */
    WebResource[] listResources(String path);

    /**
     * Create a new directory at the given path.
     *
     * @param path The path for the new resource to create relative to the root of the web application. It must start
     *                 with '/'.
     *
     * @return <code>true</code> if the directory was created, otherwise <code>false</code>
     */
    boolean mkdir(String path);

    /**
     * Create a new resource at the requested path using the provided InputStream.
     *
     * @param path      The path to be used for the new Resource. It is relative to the root of the web application and
     *                      must start with '/'.
     * @param is        The InputStream that will provide the content for the new Resource.
     * @param overwrite If <code>true</code> and the resource already exists it will be overwritten. If
     *                      <code>false</code> and the resource already exists the write will fail.
     *
     * @return <code>true</code> if and only if the new Resource is written
     */
    boolean write(String path, InputStream is, boolean overwrite);

    /**
     * Creates a new {@link WebResourceSet} for this {@link WebResourceRoot} based on the provided parameters.
     *
     * @param type         The type of {@link WebResourceSet} to create
     * @param webAppMount  The path within the web application that the resources should be published at. It must start
     *                         with '/'.
     * @param url          The URL of the resource (must locate a JAR, file or directory)
     * @param internalPath The path within the resource where the content is to be found. It must start with '/'.
     */
    void createWebResourceSet(ResourceSetType type, String webAppMount, URL url, String internalPath);

    /**
     * Creates a new {@link WebResourceSet} for this {@link WebResourceRoot} based on the provided parameters.
     *
     * @param type         The type of {@link WebResourceSet} to create
     * @param webAppMount  The path within the web application that the resources should be published at. It must start
     *                         with '/'.
     * @param base         The location of the resources
     * @param archivePath  The path within the resource to the archive where the content is to be found. If there is no
     *                         archive then this should be <code>null</code>.
     * @param internalPath The path within the archive (or the resource if the archivePath is <code>null</code> where
     *                         the content is to be found. It must start with '/'.
     */
    void createWebResourceSet(ResourceSetType type, String webAppMount, String base, String archivePath,
            String internalPath);


    /**
     * Adds the provided WebResourceSet to this web application as a 'Pre' resource.
     *
     * @param webResourceSet the resource set to use
     */
    void addPreResources(WebResourceSet webResourceSet);

    /**
     * @return the list of WebResourceSet configured to this web application as a 'Pre' resource.
     */
    WebResourceSet[] getPreResources();

    /**
     * Adds the provided WebResourceSet to this web application as a 'Jar' resource.
     *
     * @param webResourceSet the resource set to use
     */
    void addJarResources(WebResourceSet webResourceSet);

    /**
     * @return the list of WebResourceSet configured to this web application as a 'Jar' resource.
     */
    WebResourceSet[] getJarResources();

    /**
     * Adds the provided WebResourceSet to this web application as a 'Post' resource.
     *
     * @param webResourceSet the resource set to use
     */
    void addPostResources(WebResourceSet webResourceSet);

    /**
     * @return the list of WebResourceSet configured to this web application as a 'Post' resource.
     */
    WebResourceSet[] getPostResources();

    /**
     * @return the web application this WebResourceRoot is associated with.
     */
    Context getContext();

    /**
     * Set the web application this WebResourceRoot is associated with.
     *
     * @param context the associated context
     */
    void setContext(Context context);

    /**
     * Configure if this resources allow the use of symbolic links.
     *
     * @param allowLinking <code>true</code> if symbolic links are allowed.
     */
    void setAllowLinking(boolean allowLinking);

    /**
     * Determine if this resources allow the use of symbolic links.
     *
     * @return <code>true</code> if symbolic links are allowed
     */
    boolean getAllowLinking();

    /**
     * Set whether or not caching is permitted for this web application.
     *
     * @param cachingAllowed <code>true</code> to enable caching, else <code>false</code>
     */
    void setCachingAllowed(boolean cachingAllowed);

    /**
     * @return <code>true</code> if caching is permitted for this web application.
     */
    boolean isCachingAllowed();

    /**
     * Set the Time-To-Live (TTL) for cache entries.
     *
     * @param ttl TTL in milliseconds
     */
    void setCacheTtl(long ttl);

    /**
     * Get the Time-To-Live (TTL) for cache entries.
     *
     * @return TTL in milliseconds
     */
    long getCacheTtl();

    /**
     * Set the maximum permitted size for the cache.
     *
     * @param cacheMaxSize Maximum cache size in kilobytes
     */
    void setCacheMaxSize(long cacheMaxSize);

    /**
     * Get the maximum permitted size for the cache.
     *
     * @return Maximum cache size in kilobytes
     */
    long getCacheMaxSize();

    /**
     * Set the maximum permitted size for a single object in the cache. Note that the maximum size in bytes may not
     * exceed {@link Integer#MAX_VALUE}.
     *
     * @param cacheObjectMaxSize Maximum size for a single cached object in kilobytes
     */
    void setCacheObjectMaxSize(int cacheObjectMaxSize);

    /**
     * Get the maximum permitted size for a single object in the cache. Note that the maximum size in bytes may not
     * exceed {@link Integer#MAX_VALUE}.
     *
     * @return Maximum size for a single cached object in kilobytes
     */
    int getCacheObjectMaxSize();

    /**
     * Controls whether the track locked files feature is enabled. If enabled, all calls to methods that return objects
     * that lock a file and need to be closed to release that lock (e.g. {@link WebResource#getInputStream()} will
     * perform a number of additional tasks.
     * <ul>
     * <li>The stack trace at the point where the method was called will be recorded and associated with the returned
     * object.</li>
     * <li>The returned object will be wrapped so that the point where close() (or equivalent) is called to release the
     * resources can be detected. Tracking of the object will cease once the resources have been released.</li>
     * <li>All remaining locked resources on web application shutdown will be logged and then closed.</li>
     * </ul>
     *
     * @param trackLockedFiles {@code true} to enable it, {@code false} to disable it
     */
    void setTrackLockedFiles(boolean trackLockedFiles);

    /**
     * Has the track locked files feature been enabled?
     *
     * @return {@code true} if it has been enabled, otherwise {@code false}
     */
    boolean getTrackLockedFiles();

    /**
     * Set the strategy to use for the resources archive lookup.
     *
     * @param archiveIndexStrategy The strategy to use for the resources archive lookup
     */
    void setArchiveIndexStrategy(String archiveIndexStrategy);

    /**
     * Get the strategy to use for the resources archive lookup.
     *
     * @return The strategy to use for the resources archive lookup
     */
    String getArchiveIndexStrategy();

    /**
     * Get the strategy to use for the resources archive lookup.
     *
     * @return The strategy to use for the resources archive lookup
     */
    ArchiveIndexStrategy getArchiveIndexStrategyEnum();

    /**
     * This method will be invoked by the context on a periodic basis and allows the implementation a method that
     * executes periodic tasks, such as purging expired cache entries.
     */
    void backgroundProcess();

    /**
     * Add a specified resource to track to be able to later release resources on stop.
     *
     * @param trackedResource the resource that will be tracked
     */
    void registerTrackedResource(TrackedWebResource trackedResource);

    /**
     * Stop tracking specified resource, once it no longer needs to free resources.
     *
     * @param trackedResource the resource that was tracked
     */
    void deregisterTrackedResource(TrackedWebResource trackedResource);

    /**
     * @return the set of {@link WebResourceSet#getBaseUrl()} for all {@link WebResourceSet}s used by this root.
     */
    List<URL> getBaseUrls();

    /**
     * Implementations may cache some information to improve performance. This method triggers the clean-up of those
     * resources.
     */
    void gc();

    /**
     * Obtain the current caching strategy.
     * <p>
     * The default implementation returns {@code null}. Sub-classes wishing to utilise a {@link CacheStrategy} should
     * provide an appropriate implementation.
     *
     * @return the current caching strategy or {@code null} if no strategy has been configured
     */
    default CacheStrategy getCacheStrategy() {
        return null;
    }

    /**
     * Set the current caching strategy.
     * <p>
     * The default implementation is a NO-OP. Sub-classes wishing to utilise a {@link CacheStrategy} should provide an
     * appropriate implementation.
     *
     * @param strategy The new strategy to use or {@code null} for no strategy
     */
    default void setCacheStrategy(CacheStrategy strategy) {
        // NO-OP
    }

    /**
     * Set if the main resources are read only.
     *
     * @param readOnly the value
     */
    default void setReadOnly(boolean readOnly) {
        // NO-OP
    }

    /**
     * @return {@code true} if the main resources are read only, otherwise {@code false}. The default implementation
     *             returns {@code false}.
     */
    default boolean isReadOnly() {
        return false;
    }

    enum ResourceSetType {
        PRE,
        RESOURCE_JAR,
        POST,
        CLASSES_JAR
    }

    enum ArchiveIndexStrategy {
        SIMPLE(false, false),
        BLOOM(true, true),
        PURGED(true, false);

        private final boolean usesBloom;
        private final boolean retain;

        ArchiveIndexStrategy(boolean usesBloom, boolean retain) {
            this.usesBloom = usesBloom;
            this.retain = retain;
        }

        public boolean getUsesBloom() {
            return usesBloom;
        }

        public boolean getRetain() {
            return retain;
        }
    }

    /**
     * Provides a mechanism to modify the caching behaviour.
     */
    interface CacheStrategy {

        /**
         * Should the result of looking up the resource at the given path be excluded from caching?
         *
         * @param path The path to check against the strategy to see if the result should be cached
         *
         * @return {@code true} if the result should not be cached, otherwise {@code false}
         */
        boolean noCache(String path);
    }
}
