/* vim: ts=4:sw=4
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/* Web Crypto polyfill. TODO: replace with web crypto */
// All inputs/outputs are arraybuffers!
window.crypto.subtle = (function() {
	if (window.crypto.subtle !== undefined && window.crypto.subtle !== null) {
			return window.crypto.subtle;
	} else {
		var StaticArrayBufferProto = new ArrayBuffer().__proto__;
		function assertIsArrayBuffer(thing) {
			if (thing !== Object(thing) || thing.__proto__ != StaticArrayBufferProto)
				throw new Error("Needed a ArrayBuffer");
		}

		// private implementation functions
		function HmacSHA256(key, input) {
			assertIsArrayBuffer(key);
			assertIsArrayBuffer(input);
			return CryptoJS.HmacSHA256(
					CryptoJS.lib.WordArray.create(toArrayBuffer(input)),
					CryptoJS.enc.Latin1.parse(getString(key))
				).toString(CryptoJS.enc.Latin1);
		};

		function encryptAESCTR(plaintext, key, counter) {
			assertIsArrayBuffer(plaintext);
			assertIsArrayBuffer(key);
			assertIsArrayBuffer(counter);
				return CryptoJS.AES.encrypt(CryptoJS.enc.Latin1.parse(getString(plaintext)),
						CryptoJS.enc.Latin1.parse(getString(key)),
						{mode: CryptoJS.mode.CTR, iv: CryptoJS.enc.Latin1.parse(getString(counter)),
							padding: CryptoJS.pad.NoPadding})
					.ciphertext.toString(CryptoJS.enc.Latin1);
		};

		function decryptAESCTR(ciphertext, key, counter) {
			assertIsArrayBuffer(ciphertext);
			assertIsArrayBuffer(key);
			assertIsArrayBuffer(counter);
				return CryptoJS.AES.decrypt(btoa(getString(ciphertext)),
						CryptoJS.enc.Latin1.parse(getString(key)),
						{mode: CryptoJS.mode.CTR, iv: CryptoJS.enc.Latin1.parse(getString(counter)),
							padding: CryptoJS.pad.NoPadding})
					.toString(CryptoJS.enc.Latin1);
		};

		function decryptAESCBC(ciphertext, key, iv) {
			assertIsArrayBuffer(ciphertext);
			assertIsArrayBuffer(key);
			assertIsArrayBuffer(iv);
			return CryptoJS.AES.decrypt(btoa(getString(ciphertext)),
					CryptoJS.enc.Latin1.parse(getString(key)),
					{iv: CryptoJS.enc.Latin1.parse(getString(iv))})
				.toString(CryptoJS.enc.Latin1);
		};

		// utility function for connecting front and back ends via promises
		// Takes an implementation function and 0 or more arguments
		function promise(implementation) {
			var args = Array.prototype.slice.call(arguments);
			args.shift();
			return Promise.resolve(toArrayBuffer(implementation.apply(this, args)));
		}

		// public interface functions
		function encrypt(algorithm, key, data) {
			if (algorithm.name === "AES-CTR")
				return promise(encryptAESCTR, data, key, algorithm.counter);
		};
		function decrypt(algorithm, key, data) {
			if (algorithm.name === "AES-CTR")
				return promise(decryptAESCTR, data, key, algorithm.counter);
			if (algorithm.name === "AES-CBC")
				return promise(decryptAESCBC, data, key, algorithm.iv);
		};
		function sign(algorithm, key, data) {
			if (algorithm.name === "HMAC" && algorithm.hash === "SHA-256")
				return promise(HmacSHA256, key, data);
		};

		return {
			encrypt     : encrypt,
			decrypt     : decrypt,
			sign        : sign,
		}
	}
})();