/**
 * A Wrapper for Forge's RSA encryption
 */
var RSA = function(forge, util) {
	'use strict';

	var utl = forge.util;

	var keypair = {};

	/**
	 * Initializes the RSA module by passing the user's keypair
	 * The private key is option and required only for decryption
	 * and signing
	 */
	this.init = function(pubkeyPem, privkeyPem, keyId) {
		if (pubkeyPem) {
			keypair.publicKey = forge.pki.publicKeyFromPem(pubkeyPem);
		}
		if (privkeyPem) {
			keypair.privateKey = forge.pki.privateKeyFromPem(privkeyPem);
		}
		if (keyId) {
			keypair._id = keyId;
		}
	};

	/**
	 * Generate RSA keypair with the corresponding keysize
	 */
	this.generateKeypair = function(keySize, callback) {
		forge.rsa.generateKeyPair({
			bits: keySize,
			workerScript: (typeof app !== 'undefined') ? (app.config.workerPath + '/../lib/forge/prime.worker.js') : undefined
		}, function(err, newKeypair) {
			if (err || !newKeypair || !newKeypair.publicKey || !newKeypair.privateKey) {
				callback({
					errMsg: 'RSA keygeneration failed!',
					err: err
				});
				return;
			}

			keypair = newKeypair;
			// generate unique keypair ID
			keypair._id = util.UUID();

			callback(null, {
				_id: keypair._id,
				pubkeyPem: forge.pki.publicKeyToPem(keypair.publicKey),
				privkeyPem: forge.pki.privateKeyToPem(keypair.privateKey)
			});
		});
	};

	/**
	 * Exports user's keypair as PEMs
	 */
	this.exportKeys = function() {
		return {
			_id: keypair._id,
			pubkeyPem: forge.pki.publicKeyToPem(keypair.publicKey),
			privkeyPem: forge.pki.privateKeyToPem(keypair.privateKey)
		};
	};

	/**
	 * Encrypt a String using RSA with PKCS#1 v1.5 padding
	 * @param plaintext [String] The input string in UTF-16
	 * @return [String] The base64 encoded ciphertext
	 */
	this.encrypt = function(plaintext) {
		// encode plaintext to utf8 and encrypt
		var ct = keypair.publicKey.encrypt(utl.encodeUtf8(plaintext));
		// encode ciphtext to base64
		return utl.encode64(ct);
	};

	/**
	 * Decrypt a String using RSA with PKCS#1 v1.5 padding
	 * @param ciphertext [String] The base64 encoded ciphertext
	 * @return [String] The decrypted plaintext in UTF-16
	 */
	this.decrypt = function(ciphertext) {
		// decode base64 ciphertext to utf8
		var ctUtf8 = utl.decode64(ciphertext);
		// decrypt and decode to utf16
		return utl.decodeUtf8(keypair.privateKey.decrypt(ctUtf8));
	};

	/**
	 * Signs an Array of Base64 encoded parts with the private key
	 * @param parts [Array] Array of Base64 encoded parts
	 * @return [String] The Base64 encoded signature
	 */
	this.sign = function(parts) {
		var sha = forge.md.sha256.create();
		parts.forEach(function(i) {
			// decode base64 part and append to sha msg
			sha.update(utl.decode64(i));
		});

		// encode signature to base64
		return utl.encode64(keypair.privateKey.sign(sha));
	};

	/**
	 * Verifies an Array of Base64 encoded parts with the public key
	 * @param parts [Array] Array of Base64 encoded parts
	 * @param sig [String] The Base64 encoded signatrure
	 * @return [bool] if the verification was successful
	 */
	this.verify = function(parts, sig) {
		// decode base64 signature to utf8
		var sigUtf8 = utl.decode64(sig);

		var sha = forge.md.sha256.create();
		parts.forEach(function(i) {
			// decode base64 part and append to sha msg
			sha.update(utl.decode64(i));
		});

		return keypair.publicKey.verify(sha.digest().getBytes(), sigUtf8);
	};

};

if (typeof module !== 'undefined' && module.exports) {
	module.exports = RSA;
} else {
	app.crypto.RSA = RSA;
}