var SYNC_PERIOD = 30000;
var SYNC_PROVIDER_GDRIVE = "sync.gdrive.";
var syncGoogleDrive = false;

var synchronizer = (function() {
	var synchronizer = {};

	// A synchronization queue containing fileIndex that has to be synchronized
	var syncUpQueue = undefined;
	synchronizer.init = function() {
		syncUpQueue = ";";
		// Load the queue from localStorage in case a previous synchronization
		// was aborted
		if (localStorage["sync.queue"]) {
			syncUpQueue = localStorage["sync.queue"];
		}
		if (localStorage["sync.current"]) {
			this.addFileForUpload(localStorage["sync.current"]);
		}
	};

	// Add a file to the synchronization queue
	synchronizer.addFileForUpload = function(fileIndex) {
		if (syncUpQueue.indexOf(";" + fileIndex + ";") === -1) {
			syncUpQueue += fileIndex + ";";
			localStorage["sync.queue"] = syncUpQueue;
		}
	};

	// Recursive function to upload a single file on multiple locations
	function fileUp(fileSyncIndexList, content, title, callback) {
		if (fileSyncIndexList.length === 0) {
			localStorage.removeItem("sync.current");
			// run the next file synchronization
			syncUp(callback);
			return;
		}
		var fileSyncIndex = fileSyncIndexList.pop();

		// Try to find the provider
		if (fileSyncIndex.indexOf(SYNC_PROVIDER_GDRIVE) === 0) {
			var id = fileSyncIndex.substring(SYNC_PROVIDER_GDRIVE.length);
			gdrive.updateFile(id, title, content, function(result) {
				if (result === undefined && offline === true) {
					// If we detect offline mode we put the fileIndex back in
					// the queue
					synchronizer.addFileForUpload(localStorage["sync.current"]);
					localStorage.removeItem("sync.current");
					callback();
					return;
				}
				fileUp(fileSyncIndexList, content, title, callback);
			});
		} else {
			fileUp(fileSyncIndexList, content, title, callback);
		}
	}

	function syncUp(callback) {
		// If nothing to synchronize
		if (syncUpQueue.length === 1) {
			callback();
			return;
		}

		// Dequeue the fileIndex
		var separatorPos = syncUpQueue.indexOf(";", 1);
		var fileIndex = syncUpQueue.substring(1, separatorPos);
		localStorage["sync.current"] = fileIndex;
		syncUpQueue = syncUpQueue.substring(separatorPos);
		localStorage["sync.queue"] = syncUpQueue;

		var content = localStorage[fileIndex + ".content"];
		var title = localStorage[fileIndex + ".title"];

		// Parse the list of synchronized locations associated to the file
		var fileSyncIndexList = localStorage[fileIndex + ".sync"].split(";");
		fileUp(fileSyncIndexList, content, title, callback);
	};

	function syncDownGdrive(callback) {
		if (syncGoogleDrive === false) {
			callback();
			return;
		}
		var lastChangeId = parseInt(localStorage[SYNC_PROVIDER_GDRIVE
			+ "lastChangeId"]);
		gdrive.checkUpdates(lastChangeId, function(changes, newChangeId) {
			if (changes === undefined) {
				callback();
				return;
			}
			gdrive.downloadContent(changes, function(changes) {
				if (changes === undefined) {
					callback();
					return;
				}
				var updateFileTitles = false;
				for ( var i = 0; i < changes.length; i++) {
					var change = changes[i];
					var fileSyncIndex = SYNC_PROVIDER_GDRIVE + change.fileId;
					var fileIndexList = localStorage["file.list"].split(";");
					var fileIndex = undefined;
					// Look for local file associated to this synchronized location 
					for ( var i = 1; i < fileIndexList.length - 1; i++) {
						var tempFileIndex = fileIndexList[i];
						var sync = localStorage[tempFileIndex + ".sync"];
						if (sync.indexOf(";" + fileSyncIndex + ";") !== -1) {
							fileIndex = tempFileIndex;
							break;
						}
					}
					// No file corresponding (this should never happen...)
					if(fileIndex === undefined) {
						// We can remove the stored etag
						localStorage.removeItem(fileSyncIndex + ".etag");
						continue;
					}
					var title = localStorage[fileIndex + ".title"];
					// File deleted
					if (change.deleted === true) {
						fileManager.removeSync(fileSyncIndex);
						updateFileTitles = true;
						showMessage('"' + title + '" has been removed from Google Drive.');
						continue;
					}
					var content = localStorage[fileIndex + ".content"];
					var file = change.file;
					var titleChanged = title != file.title;
					var contentChanged = content != file.content;
					// If file is in the upload queue we have a conflict
					if ((titleChanged || contentChanged) && syncUpQueue.indexOf(";" + fileIndex + ";") !== -1) {
						fileManager.createFile(title + " (backup)", content);
						updateFileTitles = true;
						showMessage('Conflict detected on "' + title + '". A backup has been created locally.');
					}
					// If file title changed
					if(titleChanged) {
						localStorage[fileIndex + ".title"] = file.title;
						updateFileTitles = true;
						showMessage('"' + title + '" has been renamed to "' + file.title + '" on Google Drive.');
					}
					// If file content changed
					if(contentChanged) {
						localStorage[fileIndex + ".content"] = file.content;
						showMessage('"' + file.title + '" has been updated from Google Drive.');
						if(fileIndex == localStorage["file.current"]) {
							updateFileTitles = false; // Done by next function
							fileManager.selectFile();
						}
					}
					// Update file etag
					localStorage[fileSyncIndex + ".etag"] = file.etag;
					// Synchronize file to others locations
					synchronizer.addFileForUpload(fileIndex);
				}
				if(updateFileTitles) {
					fileManager.updateFileTitles();
				}
				localStorage[SYNC_PROVIDER_GDRIVE
				 			+ "lastChangeId"] = newChangeId;
				callback();
			});
		});
	}

	function syncDown(callback) {
		syncDownGdrive(callback);
	};
		
	var syncRunning = false;
	var lastSync = 0;
	synchronizer.sync = function() {
		// If sync is already running or timeout is not reached or offline
		if (syncRunning || lastSync + SYNC_PERIOD > currentTime || offline) {
			return;
		}
		syncRunning = true;
		lastSync = currentTime;

		syncDown(function() {
			syncUp(function() {
				syncRunning = false;
			});
		});
	};

	return synchronizer;
})();