/**
 * High level crypto api that invokes native crypto (if available) and
 * gracefully degrades to JS crypto (if unavailable)
 */
app.crypto.Crypto = function(window, util) {
	'use strict';

	var symmetricUserKey = null, // the user's secret key used to encrypt item-keys
		aes = new app.crypto.AesCCM(sjcl); // use authenticated AES-CCM mode by default

	/**
	 * Initializes the crypto modules by fetching the user's
	 * encrypted secret key from storage and storing it in memory.
	 */
	this.init = function(emailAddress, password, keySize, ivSize, callback) {
		this.emailAddress = emailAddress;
		this.keySize = keySize;
		this.ivSize = ivSize;

		// derive PBKDF2 from password in web worker thread
		this.deriveKey(password, keySize, function(pbkdf2) {

			// fetch user's encrypted secret key from keychain/storage
			var keyStore = new app.dao.LocalStorageDAO(window);
			var storageId = emailAddress + '_encryptedSymmetricKey';
			var storedKey = keyStore.read(storageId);

			// check if key exists
			if (!storedKey) {
				// generate key, encrypt and persist if none exists
				symmetricUserKey = util.random(keySize);
				var iv = util.random(ivSize);
				var key = aes.encrypt(symmetricUserKey, pbkdf2, iv);
				keyStore.persist(storageId, {
					_id: util.UUID(),
					userId: emailAddress,
					encryptedKey: key,
					keyIV: iv
				});
			} else {
				// decrypt key
				symmetricUserKey = aes.decrypt(storedKey.encryptedKey, pbkdf2, storedKey.keyIV);
			}

			callback();
		});
	};

	/**
	 * Do PBKDF2 key derivation in a WebWorker thread
	 */
	this.deriveKey = function(password, keySize, callback) {
		// check for WebWorker support
		if (window.Worker) {

			// init webworker thread
			var worker = new Worker(app.config.workerPath + '/crypto/pbkdf2-worker.js');

			worker.onmessage = function(e) {
				// return derived key from the worker
				callback(e.data);
			};

			// send plaintext data to the worker
			worker.postMessage({
				password: password,
				keySize: keySize
			});

		} else {
			// no WebWorker support... do synchronous call
			var pbkdf2 = new app.crypto.PBKDF2();
			var key = pbkdf2.getKey(password, keySize);
			callback(key);
		}
	};

	/**
	 * Derive an asymmetric keypait from the user's secret
	 */
	this.deriveKeyPair = function(naclCrypto, id) {
		var keys = naclCrypto.generateKeypair(symmetricUserKey);
		if (id) {
			keys.id = id;
		}
		return keys;
	};

	//
	// En/Decrypts single item
	//

	this.aesEncrypt = function(plaintext, key, iv, callback) {
		if (window.Worker) {

			var worker = new Worker(app.config.workerPath + '/crypto/aes-worker.js');
			worker.onmessage = function(e) {
				callback(e.data);
			};
			worker.postMessage({
				type: 'encrypt',
				plaintext: plaintext,
				key: key,
				iv: iv
			});

		} else {
			var ct = this.aesEncryptSync(plaintext, key, iv);
			callback(ct);
		}
	};

	this.aesDecrypt = function(ciphertext, key, iv, callback) {
		if (window.Worker) {

			var worker = new Worker(app.config.workerPath + '/crypto/aes-worker.js');
			worker.onmessage = function(e) {
				callback(e.data);
			};
			worker.postMessage({
				type: 'decrypt',
				ciphertext: ciphertext,
				key: key,
				iv: iv
			});

		} else {
			var pt = this.aesDecryptSync(ciphertext, key, iv);
			callback(pt);
		}
	};

	this.aesEncryptSync = function(plaintext, key, iv) {
		return aes.encrypt(plaintext, key, iv);
	};

	this.aesDecryptSync = function(ciphertext, key, iv) {
		return aes.decrypt(ciphertext, key, iv);
	};

	//
	// En/Decrypt a list of items with AES in a WebWorker thread
	//

	this.aesEncryptList = function(list, callback) {
		if (window.Worker) {

			var worker = new Worker(app.config.workerPath + '/crypto/aes-batch-worker.js');
			worker.onmessage = function(e) {
				callback(e.data);
			};
			worker.postMessage({
				type: 'encrypt',
				list: list
			});

		} else {
			var encryptedList = util.encryptList(aes, list);
			callback(encryptedList);
		}
	};

	this.aesDecryptList = function(list, callback) {
		if (window.Worker) {

			var worker = new Worker(app.config.workerPath + '/crypto/aes-batch-worker.js');
			worker.onmessage = function(e) {
				callback(e.data);
			};
			worker.postMessage({
				type: 'decrypt',
				list: list
			});

		} else {
			var decryptedList = util.decryptList(aes, list);
			callback(decryptedList);
		}
	};

	//
	// En/Decrypt something speficially using the user's secret key
	//

	this.aesEncryptForUser = function(plaintext, iv, callback) {
		var ciphertext = aes.encrypt(plaintext, symmetricUserKey, iv);
		callback(ciphertext);
	};
	this.aesDecryptForUser = function(ciphertext, iv, callback) {
		var decrypted = aes.decrypt(ciphertext, symmetricUserKey, iv);
		callback(decrypted);
	};
	this.aesEncryptForUserSync = function(plaintext, iv) {
		return aes.encrypt(plaintext, symmetricUserKey, iv);
	};
	this.aesDecryptForUserSync = function(ciphertext, iv) {
		return aes.decrypt(ciphertext, symmetricUserKey, iv);
	};

	this.aesEncryptListForUser = function(list, callback) {
		var i, envelope, envelopes = [],
			self = this;

		// package objects into batchable envelope format
		for (i = 0; i < list.length; i++) {
			envelope = {
				id: list[i].id,
				plaintext: list[i],
				key: util.random(self.keySize),
				iv: util.random(self.ivSize)
			};
			envelopes.push(envelope);
		}

		// encrypt list
		this.aesEncryptList(envelopes, function(encryptedList) {

			// encrypt keys for user
			for (i = 0; i < encryptedList.length; i++) {
				// process new values
				encryptedList[i].itemIV = encryptedList[i].iv;
				encryptedList[i].keyIV = util.random(self.ivSize);
				encryptedList[i].encryptedKey = self.aesEncryptForUserSync(encryptedList[i].key, encryptedList[i].keyIV);
				// delete old ones
				delete encryptedList[i].iv;
				delete encryptedList[i].key;
			}

			callback(encryptedList);
		});
	};

	this.aesDecryptListForUser = function(encryptedList, callback) {
		var i, list = [];

		// decrypt keys for user
		for (i = 0; i < encryptedList.length; i++) {
			// decrypt item key
			encryptedList[i].key = this.aesDecryptForUserSync(encryptedList[i].encryptedKey, encryptedList[i].keyIV);
			encryptedList[i].iv = encryptedList[i].itemIV;
			// delete old values
			delete encryptedList[i].keyIV;
			delete encryptedList[i].itemIV;
			delete encryptedList[i].encryptedKey;
		}

		// decrypt list
		this.aesDecryptList(encryptedList, function(decryptedList) {
			// add plaintext to list
			for (i = 0; i < decryptedList.length; i++) {
				list.push(decryptedList[i].plaintext);
			}

			callback(list);
		});
	};

};