define(["jquery", "async-runner"], function($, asyncRunner) {

	// Dependencies
	var core = undefined;

	var client = undefined;
	var authenticated = false;

	var dropboxHelper = {};

	// Try to connect dropbox by downloading client.js
	function connect(task) {
		task.onRun(function() {
			if(core.isOffline === true) {
				client = undefined;
				core.showMessage("Operation not available in offline mode.");
				task.error();
				return;
			}		
			if (client !== undefined) {
				task.chain();
				return;
			}
			$.ajax({
				url : "lib/dropbox.min.js",
				dataType : "script", timeout : AJAX_TIMEOUT
			}).done(function() {
				client = new Dropbox.Client({
				    key: DROPBOX_APP_KEY,
				    secret: DROPBOX_APP_SECRET
				});
				client.authDriver(new Dropbox.Drivers.Popup({
				    receiverUrl: BASE_URL + "dropbox-oauth-receiver.html",
				    rememberUser: true
				}));
				task.chain();
			}).fail(function() {
				core.setOffline();
				task.error(new Error("Network timeout"));
			});
		});
	}

	// Try to authenticate with Oauth
	function authenticate(task) {
		task.onRun(function() {
			if (authenticated === true) {
				task.chain();
				return;
			}
			var immediate = true;
			function localAuthenticate() {
				if (immediate === false) {
					core.showMessage("Please make sure the Dropbox authorization popup is not blocked by your browser.");
					// If not immediate we add time for user to enter his credentials
					task.timeout = ASYNC_TASK_LONG_TIMEOUT;
				}
				client.reset();
				client.authenticate({interactive: !immediate}, function(error, client) {
					// Success
					if (client.authState === Dropbox.Client.DONE) {
						authenticated = true;
						task.chain();
						return;
					}
					// If immediate did not work retry without immediate flag
					if (immediate === true) {
						immediate = false;
						task.chain(localAuthenticate);
						return;
					}
					// Error
					var errorMsg = "Access to Dropbox account is not authorized.";
					core.showError(errorMsg);
					task.error(new Error(errorMsg));
				});
			}
			task.chain(localAuthenticate);
		});
	}

	dropboxHelper.upload = function(path, content, callback) {
		callback = callback || core.doNothing;
		var result = undefined;
		var task = asyncRunner.createTask();
		connect(task);
		authenticate(task);
		task.onRun(function() {
			client.writeFile(path, content, function(error, stat) {
				if (!error) {
					result = stat;
					task.chain();
					return;
				}
				// Handle error
				if(error.status === Dropbox.ApiError.INVALID_PARAM) {
					error = 'Could not upload document into path "' + path + '".';
				}
				handleError(error, task, callback);
			});
		});
		task.onSuccess(function() {
			callback(undefined, result);
		});
		task.onError(function(error) {
			callback(error);
		});
		asyncRunner.addTask(task);
	};

	dropboxHelper.checkUpdates = function(lastChangeId, callback) {
		callback = callback || core.doNothing;
		var changes = [];
		var newChangeId = lastChangeId || 0;
		var task = asyncRunner.createTask();
		connect(task);
		authenticate(task);
		task.onRun(function() {
			function retrievePageOfChanges() {
				client.pullChanges(newChangeId, function(error, pullChanges) {
					if (error) {
						handleError(error, task, callback);
						return;
					}
					// Retrieve success
					newChangeId = pullChanges.cursor();
					if(pullChanges.changes !== undefined) {
						for(var i=0; i<pullChanges.changes.length; i++) {
							var item = pullChanges.changes[i];
							var version = localStorage[SYNC_PROVIDER_DROPBOX
							    + encodeURIComponent(item.path.toLowerCase()) + ".version"];
							if(version && (item.wasRemoved || item.stat.versionTag != version)) {
								changes.push(item);
							}
						}
					}
					if (pullChanges.shouldPullAgain) {
						task.chain(retrievePageOfChanges);
					} else {
						task.chain();
					}
				});
			}
			task.chain(retrievePageOfChanges);
		});
		task.onSuccess(function() {
			callback(undefined, changes, newChangeId);
		});
		task.onError(function(error) {
			callback(error);
		});
		asyncRunner.addTask(task);
	};

	dropboxHelper.downloadMetadata = function(paths, callback) {
		callback = callback || core.doNothing;
		var result = [];
		var task = asyncRunner.createTask();
		connect(task);
		authenticate(task);
		task.onRun(function() {
			function recursiveDownloadMetadata() {
				if(paths.length === 0) {
					task.chain();
					return;
				}
				var path = paths.pop();
				client.stat(path, function(error, stat) {
					if(stat) {
						result.push(stat);
						task.chain(recursiveDownloadMetadata);
						return;
					}
					handleError(error, task, callback);
				});
			}
			task.chain(recursiveDownloadMetadata);
		});
		task.onSuccess(function() {
			callback(undefined, result);
		});
		task.onError(function(error) {
			callback(error);
		});
		asyncRunner.addTask(task);
	};

	dropboxHelper.downloadContent = function(objects, callback) {
		callback = callback || core.doNothing;
		var result = [];
		var task = asyncRunner.createTask();
		connect(task);
		authenticate(task);
		task.onRun(function() {			
			function recursiveDownloadContent() {
				if(objects.length === 0) {
					task.chain();
					return;
				}
				var object = objects.pop();
				result.push(object);
				var file = undefined;
				// object may be a file
				if(object.isFile === true) {
					file = object;
				}
				// object may be a change
				else if(object.wasRemoved !== undefined) {
					file = object.stat;
				}
				if(!file) {
					task.chain(recursiveDownloadContent);
					return;
				}
				client.readFile(file.path, function(error, data) {
					if(data) {
						file.content = data;
						recursiveDownloadContent();
						return;
					}
					handleError(error, task, callback);
				});
			}
			task.chain(recursiveDownloadContent);
		});
		task.onSuccess(function() {
			callback(undefined, result);
		});
		task.onError(function(error) {
			callback(error);
		});
		asyncRunner.addTask(task);
	};
	
	function handleError(error, task, callback) {
		var errorMsg = true;
		if (error) {
			console.error(error);
			// Try to analyze the error
			if (typeof error === "string") {
				errorMsg = error;
			} else if (error.status === Dropbox.ApiError.INVALID_TOKEN
				|| error.status === Dropbox.ApiError.OAUTH_ERROR) {
				authenticated = false;
				task.retry();
				return;
			} else if(error.status === Dropbox.ApiError.INVALID_PARAM && error.responseText
					.indexOf("oauth_nonce") !== -1) {
				// A bug I guess...
				_.each(_.keys(localStorage), function(key) {
					// We have to remove the Oauth cache from the localStorage
					if(key.indexOf("dropbox-auth") === 0) {
						localStorage.removeItem(key);
					}
				});
				authenticated = false;
				task.retry();
				return;
			} else if (error.status === Dropbox.ApiError.NETWORK_ERROR) {
				client = undefined;
				authenticated = false;
				core.setOffline();
			} else {
				errorMsg = "Dropbox error ("
					+ error.status + ").";
			}
			core.showError(errorMsg);
		}
		task.error(new Error(errorMsg));
	}

	var pickerLoaded = false;
	function loadPicker(task) {
		task.onRun(function() {
			if (pickerLoaded === true) {
				task.chain();
				return;
			}
			$.ajax({
				url : "https://www.dropbox.com/static/api/1/dropbox.js",
				dataType : "script", timeout : AJAX_TIMEOUT
			}).done(function() {
				pickerLoaded = true;
				task.chain();
			}).fail(function() {
				core.setOffline();
				task.error();
			});
		});
	}
	
	dropboxHelper.picker = function(callback) {
		callback = callback || core.doNothing;
		var paths = [];
		var task = asyncRunner.createTask();
		// Add some time for user to choose his files
		task.timeout = ASYNC_TASK_LONG_TIMEOUT;
		connect(task);
		loadPicker(task);
		task.onRun(function() {			
			var options = {};
			options.multiselect = true;
			options.linkType = "direct";
			options.success = function(files) {
				for(var i=0; i<files.length; i++) {
					var path = files[i].link;
					path = path.replace(/.*\/view\/[^\/]*/, "");
					paths.push(decodeURI(path));
				}
				task.chain();
            };
            options.cancel = function() {
				task.chain();
            };
			Dropbox.choose(options);
			core.showMessage("Please make sure the Dropbox chooser popup is not blocked by your browser.");
		});
		task.onSuccess(function() {
			callback(undefined, paths);
		});
		task.onError(function(error) {
			callback(error);
		});
		asyncRunner.addTask(task);
	};

	dropboxHelper.init = function(coreModule) {
		core = coreModule;
	};
	
	return dropboxHelper;
});