Copyright (c) 2000, 2017 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.team.internal.core;

import java.io.File;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.eclipse.core.runtime.IPath;
import org.eclipse.core.runtime.jobs.ILock;
import org.eclipse.core.runtime.jobs.Job;
import org.eclipse.osgi.util.NLS;
import org.eclipse.team.core.TeamException;
import org.eclipse.team.core.variants.CachedResourceVariant;

This class implements a caching facility that can be used by TeamProviders to cache contents
/**
 * This class implements a caching facility that can be used by TeamProviders to cache contents
 */
public class ResourceVariantCache {

	// Directory to cache file contents
	private static final String CACHE_DIRECTORY = ".cache"; //$NON-NLS-1$
	// Maximum lifespan of local cache file, in milliseconds
	private static final long CACHE_FILE_LIFESPAN = 60*60*1000; // 1hr

	// Map of registered caches indexed by local name of a QualifiedName
	private static Map<String, ResourceVariantCache> caches = new HashMap<>(); // String (local name) > RemoteContentsCache

	private String name;
	private Map<String, ResourceVariantCacheEntry> cacheEntries;
	private long lastCacheCleanup;
	private int cacheDirSize;

	// Lock used to serialize the writing of cache contents
	private ILock lock = Job.getJobManager().newLock();

	
Enables the use of remote contents caching for the given cacheId. The cache ID must be unique.
A good candidate for this ID is the plugin ID of the plugin performing the caching.
Params:
cacheId – the unique Id of the cache being enabled/**
	 * Enables the use of remote contents caching for the given cacheId. The cache ID must be unique.
	 * A good candidate for this ID is the plugin ID of the plugin performing the caching.
	 *
	 * @param cacheId the unique Id of the cache being enabled
	 */
	public static synchronized void enableCaching(String cacheId) {
		if (isCachingEnabled(cacheId)) return;
		ResourceVariantCache cache = new ResourceVariantCache(cacheId);
		cache.createCacheDirectory();
		caches.put(cacheId, cache);
	}

	
Returns whether caching has been enabled for the given Id. A cache should only be enabled once.
It is conceivable that a cache be persisted over workbench invocations thus leading to a cache that
is enabled on startup without intervention by the owning plugin.
Params:
cacheId – the unique Id of the cache
Returns:
true if caching for the given Id is enabled/**
	 * Returns whether caching has been enabled for the given Id. A cache should only be enabled once.
	 * It is conceivable that a cache be persisted over workbench invocations thus leading to a cache that
	 * is enabled on startup without intervention by the owning plugin.
	 *
	 * @param cacheId the unique Id of the cache
	 * @return true if caching for the given Id is enabled
	 */
	public static boolean isCachingEnabled(String cacheId) {
		return getCache(cacheId) != null;
	}

	
Disable the cache, disposing of any file contents in the cache.
Params:
cacheId – the unique Id of the cache/**
	 * Disable the cache, disposing of any file contents in the cache.
	 *
	 * @param cacheId the unique Id of the cache
	 */
	public static void disableCache(String cacheId) {
		ResourceVariantCache cache = getCache(cacheId);
		if (cache == null) {
			// There is no cache to dispose of
			return;
		}
		caches.remove(cacheId);
		cache.deleteCacheDirectory();
	}

	
Return the cache for the given id or null if caching is not enabled for the given id.
Params:
cacheId – 
Returns:
the cache/**
	 * Return the cache for the given id or null if caching is not enabled for the given id.
	 * @param cacheId
	 * @return the cache
	 */
	public static synchronized ResourceVariantCache getCache(String cacheId) {
		return caches.get(cacheId);
	}

	public static synchronized void shutdown() {
		String[] keys = caches.keySet().toArray(new String[caches.size()]);
		for (String id : keys) {
			disableCache(id);
		}
	}

	private ResourceVariantCache(String name) {
		this.name = name;
	}

	
Return whether the cache contains an entry for the given id. Register a hit if it does.
Params:
id – the id of the cache entry
Returns:
true if there are contents cached for the id/**
	 * Return whether the cache contains an entry for the given id. Register a hit if it does.
	 * @param id the id of the cache entry
	 * @return true if there are contents cached for the id
	 */
	public boolean hasEntry(String id) {
		return internalGetCacheEntry(id) != null;
	}

	protected IPath getCachePath() {
		return getStateLocation().append(CACHE_DIRECTORY).append(name);
	}

	private IPath getStateLocation() {
		return TeamPlugin.getPlugin().getStateLocation();
	}

	private synchronized void clearOldCacheEntries() {
		long current = new Date().getTime();
		if ((lastCacheCleanup!=-1) && (current - lastCacheCleanup < CACHE_FILE_LIFESPAN)) return;
		List<ResourceVariantCacheEntry> stale = new ArrayList<>();
		for (ResourceVariantCacheEntry entry : cacheEntries.values()) {
			long lastHit = entry.getLastAccessTimeStamp();
			if ((current - lastHit) > CACHE_FILE_LIFESPAN){
				stale.add(entry);
			}
		}
		for (ResourceVariantCacheEntry entry : stale) {
			entry.dispose();
		}
	}

	private synchronized void purgeFromCache(String id) {
		ResourceVariantCacheEntry entry = cacheEntries.get(id);
		File f = entry.getFile();
		try {
			deleteFile(f);
		} catch (TeamException e) {
			// Ignore the deletion failure.
			// A failure only really matters when purging the directory on startup
		}
		cacheEntries.remove(id);
	}

	private synchronized void createCacheDirectory() {
		IPath cacheLocation = getCachePath();
		File file = cacheLocation.toFile();
		if (file.exists()) {
			try {
				deleteFile(file);
			} catch (TeamException e) {
				// Check to see if were in an acceptable state
				File[] fileList = file.listFiles();
				if (file.exists() && (!file.isDirectory() || (fileList != null && fileList.length != 0))) {
					TeamPlugin.log(e);
				}
			}
		}
		if (! file.exists() && ! file.mkdirs()) {
			TeamPlugin.log(new TeamException(NLS.bind(Messages.RemoteContentsCache_fileError, new String[] { file.getAbsolutePath() })));
		}
		cacheEntries = new HashMap<>();
		lastCacheCleanup = -1;
		cacheDirSize = 0;
	}

	private synchronized void deleteCacheDirectory() {
		cacheEntries = null;
		lastCacheCleanup = -1;
		cacheDirSize = 0;
		IPath cacheLocation = getCachePath();
		File file = cacheLocation.toFile();
		if (file.exists()) {
			try {
				deleteFile(file);
			} catch (TeamException e) {
				// Don't worry about problems deleting.
				// The only case that matters is when the cache directory is created
			}
		}
	}

	private void deleteFile(File file) throws TeamException {
		if (file.isDirectory()) {
			File[] children = file.listFiles();
			if(children == null) {
				throw new TeamException(NLS.bind(Messages.RemoteContentsCache_fileError, new String[] { file.getAbsolutePath() }));
			}
			for (File f : children) {
				deleteFile(f);
			}
		}
		if (! file.delete()) {
			throw new TeamException(NLS.bind(Messages.RemoteContentsCache_fileError, new String[] { file.getAbsolutePath() }));
		}
	}

	
Purge the given cache entry from the cache. This method should only be invoked from
an instance of ResourceVariantCacheEntry after it has set it's state to DISPOSED.
Params:
entry – /**
	 * Purge the given cache entry from the cache. This method should only be invoked from
	 * an instance of ResourceVariantCacheEntry after it has set it's state to DISPOSED.
	 * @param entry
	 */
	protected void purgeFromCache(ResourceVariantCacheEntry entry) {
		purgeFromCache(entry.getId());
	}

	private synchronized ResourceVariantCacheEntry internalGetCacheEntry(String id) {
		if (cacheEntries == null) {
			// This probably means that the cache has been disposed
			throw new IllegalStateException(NLS.bind(Messages.RemoteContentsCache_cacheDisposed, new String[] { name }));
		}
		ResourceVariantCacheEntry entry = cacheEntries.get(id);
		if (entry != null) {
			entry.registerHit();
		}
		return entry;
	}

	
Params:
id – the id that uniquely identifies the remote resource that is cached.
Returns:
the cache entry/**
	 * @param id the id that uniquely identifies the remote resource that is cached.
	 * @return the cache entry
	 */
	public ResourceVariantCacheEntry getCacheEntry(String id) {
		return internalGetCacheEntry(id);
	}

	public synchronized ResourceVariantCacheEntry add(String id, CachedResourceVariant resource) {
		clearOldCacheEntries();
		String filePath = String.valueOf(cacheDirSize++);
		ResourceVariantCacheEntry entry = new ResourceVariantCacheEntry(this, lock, id, filePath);
		entry.setResourceVariant(resource);
		cacheEntries.put(id, entry);
		return entry;
	}

	public String getName() {
		return name;
	}

	/*
	 * Method used for testing only
	 */
	public ResourceVariantCacheEntry[] getEntries() {
		return cacheEntries.values().toArray(new ResourceVariantCacheEntry[cacheEntries.size()]);
	}

}