/**
 * A high-level Data-Access Api for handling Keypair synchronization
 * between the cloud service and the device's local storage
 */
define(function(require) {
    'use strict';

    var _ = require('underscore'),
        util = require('js/crypto/util'),
        config = require('js/app-config').config;

    var DB_PUBLICKEY = 'publickey',
        DB_PRIVATEKEY = 'privatekey',
        DB_DEVICENAME = 'devicename',
        DB_DEVICE_SECRET = 'devicesecret';

    var KeychainDAO = function(localDbDao, publicKeyDao, privateKeyDao, crypto, pgp) {
        this._localDbDao = localDbDao;
        this._publicKeyDao = publicKeyDao;
        this._privateKeyDao = privateKeyDao;
        this._crypto = crypto;
        this._pgp = pgp;
    };

    //
    // Public key functions
    //

    /**
     * Verifies the public key of a user o nthe public key store
     * @param {String} uuid The uuid to verify the key
     * @param {Function} callback(error) Callback with an optional error object when the verification is done. If the was an error, the error object contains the information for it.
     */
    KeychainDAO.prototype.verifyPublicKey = function(uuid, callback) {
        this._publicKeyDao.verify(uuid, callback);
    };

    /**
     * Get an array of public keys by looking in local storage and
     * fetching missing keys from the cloud service.
     * @param ids [Array] the key ids as [{_id, userId}]
     * @return [PublicKeyCollection] The requiested public keys
     */
    KeychainDAO.prototype.getPublicKeys = function(ids, callback) {
        var self = this,
            after, already, pubkeys = [];

        // return empty array if key ids are emtpy
        if (ids.length < 1) {
            callback(null, pubkeys);
            return;
        }

        after = _.after(ids.length, function() {
            callback(null, pubkeys);
        });

        _.each(ids, function(i) {
            // lookup locally and in storage
            self.lookupPublicKey(i._id, function(err, pubkey) {
                if (err || !pubkey) {
                    callback({
                        errMsg: 'Error looking up public key!',
                        err: err
                    });
                    return;
                }

                // check if public key with that id has already been fetched
                already = null;
                already = _.findWhere(pubkeys, {
                    _id: i._id
                });
                if (!already) {
                    pubkeys.push(pubkey);
                }

                after(); // asynchronously iterate through objects
            });
        });
    };

    /**
     * Checks for public key updates of a given user id
     * @param {String} userId The user id (email address) for which to check the key
     * @param {Function} callback(error, key) Invoked when the key has been updated or an error occurred
     */
    KeychainDAO.prototype.refreshKeyForUserId = function(userId, callback) {
        var self = this;

        // get the public key corresponding to the userId
        self.getReceiverPublicKey(userId, function(err, localKey) {
            if (!localKey || !localKey._id) {
                // there is no key available, no need to refresh
                callback();
                return;
            }

            // no need to refresh manually imported public keys
            if (localKey.imported) {
                callback(null, localKey);
                return;
            }

            // check if the key id still exists on the key server
            checkKeyExists(localKey);
        });

        // checks if the user's key has been revoked by looking up the key id
        function checkKeyExists(localKey) {
            self._publicKeyDao.get(localKey._id, function(err, cloudKey) {
                if (err && err.code === 42) {
                    // we're offline, we're done checking the key
                    callback(null, localKey);
                    return;
                }

                if (err) {
                    // there was an error, exit and inform
                    callback(err);
                    return;
                }

                if (cloudKey && cloudKey._id === localKey._id) {
                    // the key is present on the server, all is well
                    callback(null, localKey);
                    return;
                }

                // the key has changed, update the key
                updateKey(localKey);
            });
        }

        function updateKey(localKey) {
            // look for an updated key for the user id
            self._publicKeyDao.getByUserId(userId, function(err, newKey) {
                // offline?
                if (err && err.code === 42) {
                    callback(null, localKey);
                    return;
                }

                if (err) {
                    callback(err);
                    return;
                }

                // the public key has changed, we need to ask for permission to update the key
                self.requestPermissionForKeyUpdate({
                    userId: userId,
                    newKey: newKey
                }, function(granted) {
                    if (!granted) {
                        // permission was not given to update the key, so don't overwrite the old one!
                        callback(null, localKey);
                        return;
                    }

                    // permission to update the key was given, so delete the old one and persist the new one
                    self.removeLocalPublicKey(localKey._id, function(err) {
                        if (err || !newKey) {
                            // error or no new key to save
                            callback(err);
                            return;
                        }

                        // persist the new key and return it
                        self.saveLocalPublicKey(newKey, function(err) {
                            callback(err, err ? undefined : newKey);
                        });
                    });
                });

            });
        }
    };

    /**
     * Look up a reveiver's public key by user id
     * @param userId [String] the receiver's email address
     */
    KeychainDAO.prototype.getReceiverPublicKey = function(userId, callback) {
        var self = this;

        // search local keyring for public key
        self._localDbDao.list(DB_PUBLICKEY, 0, null, function(err, allPubkeys) {
            if (err) {
                callback(err);
                return;
            }

            // query primary email address
            var pubkey = _.findWhere(allPubkeys, {
                userId: userId
            });

            // query mutliple userIds (for imported public keys)
            if (!pubkey) {
                for (var i = 0, match; i < allPubkeys.length; i++) {
                    match = _.findWhere(allPubkeys[i].userIds, {
                        emailAddress: userId
                    });
                    if (match) {
                        pubkey = allPubkeys[i];
                        break;
                    }
                }
            }

            if (pubkey && pubkey._id) {
                // that user's public key is already in local storage
                callback(null, pubkey);
                return;
            }

            // no public key by that user id in storage
            // find from cloud by email address
            self._publicKeyDao.getByUserId(userId, onKeyReceived);
        });

        function onKeyReceived(err, cloudPubkey) {
            if (err && err.code === 42) {
                // offline
                callback();
                return;
            }

            if (err) {
                callback(err);
                return;
            }

            if (!cloudPubkey) {
                // public key has been deleted without replacement
                callback();
                return;
            }

            self.saveLocalPublicKey(cloudPubkey, function(err) {
                if (err) {
                    callback(err);
                    return;
                }

                callback(null, cloudPubkey);
            });
        }
    };

    //
    // Device registration functions
    //

    /**
     * Set the device's memorable name e.g 'iPhone Work'
     * @param {String}   deviceName The device name
     * @param {Function} callback(error)
     */
    KeychainDAO.prototype.setDeviceName = function(deviceName, callback) {
        if (!deviceName) {
            callback(new Error('Please set a device name!'));
            return;
        }

        this._localDbDao.persist(DB_DEVICENAME, deviceName, callback);
    };

    /**
     * Get the device' memorable name from local storage. Throws an error if not set
     * @param  {Function} callback(error, deviceName)
     * @return {String} The device name
     */
    KeychainDAO.prototype.getDeviceName = function(callback) {
        // check if deviceName is already persisted in storage
        this._localDbDao.read(DB_DEVICENAME, function(err, deviceName) {
            if (err) {
                callback(err);
                return;
            }

            if (!deviceName) {
                callback(new Error('Device name not set!'));
                return;
            }

            callback(null, deviceName);
        });
    };

    /**
     * Geneate a device specific key and secret to authenticate to the private key service.
     * @param {Function} callback(error, deviceSecret:[base64 encoded string])
     */
    KeychainDAO.prototype.getDeviceSecret = function(callback) {
        var self = this;

        // generate random deviceSecret or get from storage
        self._localDbDao.read(DB_DEVICE_SECRET, function(err, storedDevSecret) {
            if (err) {
                callback(err);
                return;
            }

            if (storedDevSecret) {
                // a device key is already available locally
                callback(null, storedDevSecret);
                return;
            }

            // generate random deviceSecret
            var deviceSecret = util.random(config.symKeySize);
            // persist deviceSecret to local storage (in plaintext)
            self._localDbDao.persist(DB_DEVICE_SECRET, deviceSecret, function(err) {
                if (err) {
                    callback(err);
                    return;
                }

                callback(null, deviceSecret);
            });
        });
    };

    /**
     * Register the device on the private key server. This will give the device access to upload an encrypted private key.
     * @param  {String}   options.userId The user's email address
     * @param  {Function} callback(error)
     */
    KeychainDAO.prototype.registerDevice = function(options, callback) {
        var self = this,
            devName;

        // check if deviceName is already persisted in storage
        self.getDeviceName(function(err, deviceName) {
            if (err) {
                callback(err);
                return;
            }

            requestDeviceRegistration(deviceName);
        });

        function requestDeviceRegistration(deviceName) {
            devName = deviceName;

            // request device registration session key
            self._privateKeyDao.requestDeviceRegistration({
                userId: options.userId,
                deviceName: deviceName
            }, function(err, regSessionKey) {
                if (err) {
                    callback(err);
                    return;
                }

                if (!regSessionKey.encryptedRegSessionKey) {
                    callback(new Error('Invalid format for session key!'));
                    return;
                }

                decryptSessionKey(regSessionKey);
            });
        }

        function decryptSessionKey(regSessionKey) {
            // TODO: fetch public key for service to verify response
            self.lookupPublicKey(config.serverPrivateKeyId, function(err, serverPubkey) {
                if (err) {
                    callback(err);
                    return;
                }

                if (!serverPubkey || !serverPubkey.publicKey) {
                    callback(new Error('Server public key for device registration not found!'));
                    return;
                }

                // decrypt the session key
                var ct = regSessionKey.encryptedRegSessionKey;
                self._pgp.decrypt(ct, serverPubkey.publicKey, function(err, decrypedSessionKey) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    uploadDeviceSecret(decrypedSessionKey);
                });
            });
        }

        function uploadDeviceSecret(regSessionKey) {
            // read device secret from local storage
            self.getDeviceSecret(function(err, deviceSecret) {
                if (err) {
                    callback(err);
                    return;
                }

                // generate iv
                var iv = util.random(config.symIvSize);
                // encrypt deviceSecret
                self._crypto.encrypt(deviceSecret, regSessionKey, iv, function(err, encryptedDeviceSecret) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    // upload encryptedDeviceSecret
                    self._privateKeyDao.uploadDeviceSecret({
                        userId: options.userId,
                        deviceName: devName,
                        encryptedDeviceSecret: encryptedDeviceSecret,
                        iv: iv
                    }, callback);
                });
            });
        }
    };

    //
    // Private key functions
    //

    /**
     * Authenticate to the private key server (required before private PGP key upload).
     * @param  {String}   userId The user's email address
     * @param  {Function} callback(error, authSessionKey)
     * @return {Object} {sessionId:String, sessionKey:[base64 encoded]}
     */
    KeychainDAO.prototype._authenticateToPrivateKeyServer = function(userId, callback) {
        var self = this,
            sessionId;

        // request auth session key required for upload
        self._privateKeyDao.requestAuthSessionKey({
            userId: userId
        }, function(err, authSessionKey) {
            if (err) {
                callback(err);
                return;
            }

            if (!authSessionKey.encryptedAuthSessionKey || !authSessionKey.encryptedChallenge || !authSessionKey.sessionId) {
                callback(new Error('Invalid format for session key!'));
                return;
            }

            // remember session id for verification
            sessionId = authSessionKey.sessionId;

            decryptSessionKey(authSessionKey);
        });

        function decryptSessionKey(authSessionKey) {
            // TODO: fetch public key for service to verify response
            self.lookupPublicKey(config.serverPrivateKeyId, function(err, serverPubkey) {
                if (err) {
                    callback(err);
                    return;
                }

                if (!serverPubkey || !serverPubkey.publicKey) {
                    callback(new Error('Server public key for authentication not found!'));
                    return;
                }

                // decrypt the session key
                var ct1 = authSessionKey.encryptedAuthSessionKey;
                self._pgp.decrypt(ct1, serverPubkey.publicKey, function(err, decryptedSessionKey) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    // decrypt the challenge
                    var ct2 = authSessionKey.encryptedChallenge;
                    self._pgp.decrypt(ct2, serverPubkey.publicKey, function(err, decryptedChallenge) {
                        if (err) {
                            callback(err);
                            return;
                        }

                        encryptChallenge(decryptedSessionKey, decryptedChallenge);
                    });
                });
            });
        }

        function encryptChallenge(sessionKey, challenge) {
            // get device secret
            self.getDeviceSecret(function(err, deviceSecret) {
                if (err) {
                    callback(err);
                    return;
                }

                var iv = util.random(config.symIvSize);
                // encrypt the challenge
                self._crypto.encrypt(challenge, sessionKey, iv, function(err, encryptedChallenge) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    // encrypt the device secret
                    self._crypto.encrypt(deviceSecret, sessionKey, iv, function(err, encryptedDeviceSecret) {
                        if (err) {
                            callback(err);
                            return;
                        }

                        replyChallenge({
                            encryptedChallenge: encryptedChallenge,
                            encryptedDeviceSecret: encryptedDeviceSecret,
                            iv: iv
                        }, sessionKey);
                    });
                });
            });
        }

        function replyChallenge(response, sessionKey) {
            // respond to challenge by uploading the with the session key encrypted challenge
            self._privateKeyDao.verifyAuthentication({
                userId: userId,
                sessionId: sessionId,
                encryptedChallenge: response.encryptedChallenge,
                encryptedDeviceSecret: response.encryptedDeviceSecret,
                iv: response.iv
            }, function(err) {
                if (err) {
                    callback(err);
                    return;
                }

                callback(null, {
                    sessionId: sessionId,
                    sessionKey: sessionKey
                });
            });
        }
    };

    /**
     * Encrypt and upload the private PGP key to the server.
     * @param  {String}   options.userId   The user's email address
     * @param  {String}   options.code     The randomly generated or self selected code used to derive the key for the encryption of the private PGP key
     * @param  {Function} callback(error)
     */
    KeychainDAO.prototype.uploadPrivateKey = function(options, callback) {
        var self = this,
            keySize = config.symKeySize,
            salt;

        if (!options.userId || !options.code) {
            callback(new Error('Incomplete arguments!'));
            return;
        }

        deriveKey(options.code);

        function deriveKey(code) {
            // generate random salt
            salt = util.random(keySize);
            // derive key from the code using PBKDF2
            self._crypto.deriveKey(code, salt, keySize, function(err, key) {
                if (err) {
                    callback(err);
                    return;
                }

                encryptPrivateKey(key);
            });
        }

        function encryptPrivateKey(encryptionKey) {
            // get private key from local storage
            self.getUserKeyPair(options.userId, function(err, keypair) {
                if (err) {
                    callback(err);
                    return;
                }

                var privkeyId = keypair.privateKey._id,
                    pgpBlock = keypair.privateKey.encryptedKey;

                // encrypt the private key with the derived key
                var iv = util.random(config.symIvSize);
                self._crypto.encrypt(pgpBlock, encryptionKey, iv, function(err, ct) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    var payload = {
                        _id: privkeyId,
                        userId: options.userId,
                        encryptedPrivateKey: ct,
                        salt: salt,
                        iv: iv
                    };

                    uploadPrivateKey(payload);
                });
            });
        }

        function uploadPrivateKey(payload) {
            // authenticate to server for upload
            self._authenticateToPrivateKeyServer(options.userId, function(err, authSessionKey) {
                if (err) {
                    callback(err);
                    return;
                }

                // encrypt encryptedPrivateKey again using authSessionKey
                var pt = payload.encryptedPrivateKey,
                    iv = payload.iv,
                    key = authSessionKey.sessionKey;
                self._crypto.encrypt(pt, key, iv, function(err, ct) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    // replace the encryptedPrivateKey with the double wrapped ciphertext
                    payload.encryptedPrivateKey = ct;
                    // set sessionId
                    payload.sessionId = authSessionKey.sessionId;

                    // upload the encrypted priavet key
                    self._privateKeyDao.upload(payload, callback);
                });
            });
        }
    };

    /**
     * Request downloading the user's encrypted private key. This will initiate the server to send the recovery token via email/sms to the user.
     * @param  {String}   options.userId    The user's email address
     * @param  {String}   options.keyId     The private PGP key id
     * @param  {Function} callback(error)
     */
    KeychainDAO.prototype.requestPrivateKeyDownload = function(options, callback) {
        this._privateKeyDao.requestDownload(options, callback);
    };

    /**
     * Download the encrypted private PGP key from the server using the recovery token.
     * @param  {String}   options.userId The user's email address
     * @param  {String}   options.keyId The user's email address
     * @param  {String}   options.recoveryToken The recovery token acquired via email/sms from the key server
     * @param  {Function} callback(error, encryptedPrivateKey)
     */
    KeychainDAO.prototype.downloadPrivateKey = function(options, callback) {
        this._privateKeyDao.download(options, callback);
    };

    /**
     * This is called after the encrypted private key has successfully been downloaded and it's ready to be decrypted and stored in localstorage.
     * @param  {String}   options._id The private PGP key id
     * @param  {String}   options.userId The user's email address
     * @param  {String}   options.code The randomly generated or self selected code used to derive the key for the decryption of the private PGP key
     * @param  {String}   options.encryptedPrivateKey The encrypted private PGP key
     * @param  {String}   options.salt The salt required to derive the code derived key
     * @param  {String}   options.iv The iv used to encrypt the private PGP key
     * @param  {Function} callback(error, keyObject)
     */
    KeychainDAO.prototype.decryptAndStorePrivateKeyLocally = function(options, callback) {
        var self = this,
            code = options.code,
            salt = options.salt,
            keySize = config.symKeySize;

        if (!options._id || !options.userId || !options.code || !options.salt || !options.encryptedPrivateKey || !options.iv) {
            callback(new Error('Incomplete arguments!'));
            return;
        }

        // derive key from the code and the salt using PBKDF2
        self._crypto.deriveKey(code, salt, keySize, function(err, key) {
            if (err) {
                callback(err);
                return;
            }

            decryptAndStore(key);
        });

        function decryptAndStore(derivedKey) {
            // decrypt the private key with the derived key
            var ct = options.encryptedPrivateKey,
                iv = options.iv;

            self._crypto.decrypt(ct, derivedKey, iv, function(err, privateKeyArmored) {
                if (err) {
                    callback(new Error('Invalid keychain code!'));
                    return;
                }

                // validate pgp key
                var keyParams;
                try {
                    keyParams = self._pgp.getKeyParams(privateKeyArmored);
                } catch (e) {
                    callback(new Error('Error parsing private PGP key!'));
                    return;
                }

                if (keyParams._id !== options._id || keyParams.userId !== options.userId) {
                    callback(new Error('Private key parameters don\'t match with public key\'s!'));
                    return;
                }

                var keyObject = {
                    _id: options._id,
                    userId: options.userId,
                    encryptedKey: privateKeyArmored
                };

                // store private key locally
                self.saveLocalPrivateKey(keyObject, function(err) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    callback(null, keyObject);
                });
            });
        }
    };

    //
    // Keypair functions
    //

    /**
     * Gets the local user's key either from local storage
     * or fetches it from the cloud. The private key is encrypted.
     * If no key pair exists, null is returned.
     * return [Object] The user's key pair {publicKey, privateKey}
     */
    KeychainDAO.prototype.getUserKeyPair = function(userId, callback) {
        var self = this;

        // search for user's public key locally
        self._localDbDao.list(DB_PUBLICKEY, 0, null, function(err, allPubkeys) {
            if (err) {
                callback(err);
                return;
            }

            var pubkey = _.findWhere(allPubkeys, {
                userId: userId
            });

            if (pubkey && pubkey._id) {
                // that user's public key is already in local storage...
                // sync keypair to the cloud
                syncKeypair(pubkey._id);
                return;
            }

            // no public key by that user id in storage
            // find from cloud by email address
            self._publicKeyDao.getByUserId(userId, function(err, cloudPubkey) {
                if (err) {
                    callback(err);
                    return;
                }

                if (cloudPubkey && cloudPubkey._id) {
                    // there is a public key for that user already in the cloud...
                    // sync keypair to local storage
                    syncKeypair(cloudPubkey._id);
                    return;
                }

                // continue without keypair... generate in crypto.js
                callback();
            });
        });

        function syncKeypair(keypairId) {
            // persist key pair in local storage
            self.lookupPublicKey(keypairId, function(err, savedPubkey) {
                if (err) {
                    callback(err);
                    return;
                }

                // persist private key in local storage
                self.lookupPrivateKey(keypairId, function(err, savedPrivkey) {
                    var keys = {};

                    if (err) {
                        callback(err);
                        return;
                    }

                    if (savedPubkey && savedPubkey.publicKey) {
                        keys.publicKey = savedPubkey;
                    }

                    if (savedPrivkey && savedPrivkey.encryptedKey) {
                        keys.privateKey = savedPrivkey;
                    }

                    callback(null, keys);
                });
            });
        }
    };

    /**
     * Checks to see if the user's key pair is stored both
     * locally and in the cloud and persist arccordingly
     * @param [Object] The user's key pair {publicKey, privateKey}
     */
    KeychainDAO.prototype.putUserKeyPair = function(keypair, callback) {
        var self = this;

        // validate input
        if (!keypair || !keypair.publicKey || !keypair.privateKey || !keypair.publicKey.userId || keypair.publicKey.userId !== keypair.privateKey.userId) {
            callback({
                errMsg: 'Incorrect input!'
            });
            return;
        }

        // store public key locally
        self.saveLocalPublicKey(keypair.publicKey, function(err) {
            if (err) {
                callback(err);
                return;
            }

            // persist public key in cloud storage
            self._publicKeyDao.put(keypair.publicKey, function(err) {
                // validate result
                if (err) {
                    callback(err);
                    return;
                }

                // store private key locally
                self.saveLocalPrivateKey(keypair.privateKey, callback);
            });
        });
    };

    //
    // Helper functions
    //

    KeychainDAO.prototype.lookupPublicKey = function(id, callback) {
        var self = this;

        if (!id) {
            callback({
                errMsg: 'ID must be set for public key query!'
            });
            return;
        }

        // lookup in local storage
        self._localDbDao.read(DB_PUBLICKEY + '_' + id, function(err, pubkey) {
            if (err) {
                callback(err);
                return;
            }

            if (pubkey) {
                callback(null, pubkey);
                return;
            }

            // fetch from cloud storage
            self._publicKeyDao.get(id, function(err, cloudPubkey) {
                if (err) {
                    callback(err);
                    return;
                }

                // cache public key in cache
                self.saveLocalPublicKey(cloudPubkey, function(err) {
                    if (err) {
                        callback(err);
                        return;
                    }

                    callback(null, cloudPubkey);
                });
            });
        });
    };

    /**
     * List all the locally stored public keys
     */
    KeychainDAO.prototype.listLocalPublicKeys = function(callback) {
        // search local keyring for public key
        this._localDbDao.list(DB_PUBLICKEY, 0, null, callback);
    };

    KeychainDAO.prototype.removeLocalPublicKey = function(id, callback) {
        this._localDbDao.remove(DB_PUBLICKEY + '_' + id, callback);
    };

    KeychainDAO.prototype.lookupPrivateKey = function(id, callback) {
        // lookup in local storage
        this._localDbDao.read(DB_PRIVATEKEY + '_' + id, callback);
    };

    KeychainDAO.prototype.saveLocalPublicKey = function(pubkey, callback) {
        // persist public key (email, _id)
        var pkLookupKey = DB_PUBLICKEY + '_' + pubkey._id;
        this._localDbDao.persist(pkLookupKey, pubkey, callback);
    };

    KeychainDAO.prototype.saveLocalPrivateKey = function(privkey, callback) {
        // persist private key (email, _id)
        var prkLookupKey = DB_PRIVATEKEY + '_' + privkey._id;
        this._localDbDao.persist(prkLookupKey, privkey, callback);
    };

    return KeychainDAO;
});