Migration towards TypeScript

This is going to be 1.1.0. Remaining TODOs:
* "npm run tsc" should generate declarations
* Add (restrictive) TSLint configuration
* Add support for TSLint in "npm test"

src/subtitle/decode.ts

@@ -0,0 +1,75 @@
+'use strict';
+export = main;
+import crypto = require('crypto');
+import bigInt = require('big-integer');
+import zlib = require('zlib');
+
+/**
+ * Decodes the data.
+ */
+function main(id: number, iv: Buffer|string, data: Buffer|string, done: (err?: Error, result?: Buffer) => void) {
+  try {
+    decompress(decrypt(id, iv, data), done);
+  } catch (e) {
+    done(e);
+  }
+}
+
+/**
+ * Decrypts the data.
+ */
+function decrypt(id: number, iv: Buffer|string, data: Buffer|string) {
+  var ivBuffer = typeof iv === 'string' ? new Buffer(iv, 'base64') : iv;
+  var dataBuffer = typeof data === 'string' ? new Buffer(data, 'base64') : data;
+  var decipher = crypto.createDecipheriv('aes-256-cbc', key(id), ivBuffer);
+  decipher.setAutoPadding(false);
+  return Buffer.concat([decipher.update(dataBuffer), decipher.final()]);
+}
+
+/**
+ * Decompresses the data.
+ */
+function decompress(data: Buffer, done: (err: Error, result?: Buffer) => void) {
+  try {
+    zlib.inflate(data, done);
+  } catch (e) {
+    done(null, data);
+  }
+}
+
+/**
+ * Generates a key.
+ */
+function key(subtitleId: number): Buffer {
+  var hash = secret(20, 97, 1, 2) + magic(subtitleId);
+  var result = new Buffer(32);
+  result.fill(0);
+  crypto.createHash('sha1').update(hash).digest().copy(result);
+  return result;
+}
+
+/**
+ * Generates a magic number.
+ */
+function magic(subtitleId: number): number {
+  var base = Math.floor(Math.sqrt(6.9) * Math.pow(2, 25));
+  var hash = bigInt(base).xor(subtitleId).toJSNumber();
+  var multipliedHash = bigInt(hash).multiply(32).toJSNumber();
+  return bigInt(hash).xor(hash >> 3).xor(multipliedHash).toJSNumber();
+}
+
+/**
+ * Generates a secret string based on a Fibonacci sequence.
+ */
+function secret(size: number, modulo: number, firstSeed: number, secondSeed: number): string {
+  var currentValue = firstSeed + secondSeed;
+  var previousValue = secondSeed;
+  var result = '';
+  for (var i = 0; i < size; i += 1) {
+    var oldValue = currentValue;
+    result += String.fromCharCode(currentValue % modulo + 33);
+    currentValue += previousValue;
+    previousValue = oldValue;
+  }
+  return result;
+}