/**
 * Minimal MD5 implementation for bundle integrity verification.
 * Based on the RSA Data Security, Inc. MD5 Message-Digest Algorithm (RFC 1321).
 */

function _ff(a: number, b: number, c: number, d: number, x: number, s: number, ac: number): number {
  a = (a + ((b & c) | (~b & d)) + x + ac) | 0
  return (((a << s) | (a >>> (32 - s))) + b) | 0
}

function _gg(a: number, b: number, c: number, d: number, x: number, s: number, ac: number): number {
  a = (a + ((b & d) | (c & ~d)) + x + ac) | 0
  return (((a << s) | (a >>> (32 - s))) + b) | 0
}

function _hh(a: number, b: number, c: number, d: number, x: number, s: number, ac: number): number {
  a = (a + (b ^ c ^ d) + x + ac) | 0
  return (((a << s) | (a >>> (32 - s))) + b) | 0
}

function _ii(a: number, b: number, c: number, d: number, x: number, s: number, ac: number): number {
  a = (a + (c ^ (b | ~d)) + x + ac) | 0
  return (((a << s) | (a >>> (32 - s))) + b) | 0
}

function _toWords(input: string): number[] {
  const msg = unescape(encodeURIComponent(input))
  const len = msg.length
  const n = (((len + 8) >>> 6) << 4) + 16
  const words = new Array<number>(n).fill(0)
  for (let i = 0; i < len; i++) {
    words[i >> 2] |= (msg.charCodeAt(i) & 0xff) << ((i % 4) << 3)
  }
  words[len >> 2] |= 0x80 << ((len % 4) << 3)
  words[n - 2] = len << 3
  return words
}

function _hex(n: number): string {
  let s = ''
  for (let j = 0; j < 4; j++) {
    s += '0123456789abcdef'.charAt((n >> (j * 8 + 4)) & 0x0f) +
         '0123456789abcdef'.charAt((n >> (j * 8)) & 0x0f)
  }
  return s
}

export function md5(input: string): string {
  const x = _toWords(input)
  let a = 0x67452301, b = 0xefcdab89, c = 0x98badcfe, d = 0x10325476

  for (let i = 0; i < x.length; i += 16) {
    const oa = a, ob = b, oc = c, od = d

    a = _ff(a, b, c, d, x[i],      7, 0xd76aa478)
    d = _ff(d, a, b, c, x[i + 1],  12, 0xe8c7b756)
    c = _ff(c, d, a, b, x[i + 2], 17, 0x242070db)
    b = _ff(b, c, d, a, x[i + 3], 22, 0xc1bdceee)
    a = _ff(a, b, c, d, x[i + 4],  7, 0xf57c0faf)
    d = _ff(d, a, b, c, x[i + 5], 12, 0x4787c62a)
    c = _ff(c, d, a, b, x[i + 6], 17, 0xa8304613)
    b = _ff(b, c, d, a, x[i + 7], 22, 0xfd469501)
    a = _ff(a, b, c, d, x[i + 8],  7, 0x698098d8)
    d = _ff(d, a, b, c, x[i + 9], 12, 0x8b44f7af)
    c = _ff(c, d, a, b, x[i + 10],17, 0xffff5bb1)
    b = _ff(b, c, d, a, x[i + 11],22, 0x895cd7be)
    a = _ff(a, b, c, d, x[i + 12], 7, 0x6b901122)
    d = _ff(d, a, b, c, x[i + 13],12, 0xfd987193)
    c = _ff(c, d, a, b, x[i + 14],17, 0xa679438e)
    b = _ff(b, c, d, a, x[i + 15],22, 0x49b40821)

    a = _gg(a, b, c, d, x[i + 1],  5, 0xf61e2562)
    d = _gg(d, a, b, c, x[i + 6],  9, 0xc040b340)
    c = _gg(c, d, a, b, x[i + 11],14, 0x265e5a51)
    b = _gg(b, c, d, a, x[i],     20, 0xe9b6c7aa)
    a = _gg(a, b, c, d, x[i + 5],  5, 0xd62f105d)
    d = _gg(d, a, b, c, x[i + 10], 9, 0x02441453)
    c = _gg(c, d, a, b, x[i + 15],14, 0xd8a1e681)
    b = _gg(b, c, d, a, x[i + 4], 20, 0xe7d3fbc8)
    a = _gg(a, b, c, d, x[i + 9],  5, 0x21e1cde6)
    d = _gg(d, a, b, c, x[i + 14], 9, 0xc33707d6)
    c = _gg(c, d, a, b, x[i + 3], 14, 0xf4d50d87)
    b = _gg(b, c, d, a, x[i + 8], 20, 0x455a14ed)
    a = _gg(a, b, c, d, x[i + 13], 5, 0xa9e3e905)
    d = _gg(d, a, b, c, x[i + 2],  9, 0xfcefa3f8)
    c = _gg(c, d, a, b, x[i + 7], 14, 0x676f02d9)
    b = _gg(b, c, d, a, x[i + 12],20, 0x8d2a4c8a)

    a = _hh(a, b, c, d, x[i + 5],  4, 0xfffa3942)
    d = _hh(d, a, b, c, x[i + 8], 11, 0x8771f681)
    c = _hh(c, d, a, b, x[i + 11],16, 0x6d9d6122)
    b = _hh(b, c, d, a, x[i + 14],23, 0xfde5380c)
    a = _hh(a, b, c, d, x[i + 1],  4, 0xa4beea44)
    d = _hh(d, a, b, c, x[i + 4], 11, 0x4bdecfa9)
    c = _hh(c, d, a, b, x[i + 7], 16, 0xf6bb4b60)
    b = _hh(b, c, d, a, x[i + 10],23, 0xbebfbc70)
    a = _hh(a, b, c, d, x[i + 13], 4, 0x289b7ec6)
    d = _hh(d, a, b, c, x[i],     11, 0xeaa127fa)
    c = _hh(c, d, a, b, x[i + 3], 16, 0xd4ef3085)
    b = _hh(b, c, d, a, x[i + 6], 23, 0x04881d05)
    a = _hh(a, b, c, d, x[i + 9],  4, 0xd9d4d039)
    d = _hh(d, a, b, c, x[i + 12],11, 0xe6db99e5)
    c = _hh(c, d, a, b, x[i + 15],16, 0x1fa27cf8)
    b = _hh(b, c, d, a, x[i + 2], 23, 0xc4ac5665)

    a = _ii(a, b, c, d, x[i],      6, 0xf4292244)
    d = _ii(d, a, b, c, x[i + 7], 10, 0x432aff97)
    c = _ii(c, d, a, b, x[i + 14],15, 0xab9423a7)
    b = _ii(b, c, d, a, x[i + 5], 21, 0xfc93a039)
    a = _ii(a, b, c, d, x[i + 12], 6, 0x655b59c3)
    d = _ii(d, a, b, c, x[i + 3], 10, 0x8f0ccc92)
    c = _ii(c, d, a, b, x[i + 10],15, 0xffeff47d)
    b = _ii(b, c, d, a, x[i + 1], 21, 0x85845dd1)
    a = _ii(a, b, c, d, x[i + 8],  6, 0x6fa87e4f)
    d = _ii(d, a, b, c, x[i + 15],10, 0xfe2ce6e0)
    c = _ii(c, d, a, b, x[i + 6], 15, 0xa3014314)
    b = _ii(b, c, d, a, x[i + 13],21, 0x4e0811a1)
    a = _ii(a, b, c, d, x[i + 4],  6, 0xf7537e82)
    d = _ii(d, a, b, c, x[i + 11],10, 0xbd3af235)
    c = _ii(c, d, a, b, x[i + 2], 15, 0x2ad7d2bb)
    b = _ii(b, c, d, a, x[i + 9], 21, 0xeb86d391)

    a = (a + oa) | 0; b = (b + ob) | 0; c = (c + oc) | 0; d = (d + od) | 0
  }

  return _hex(a) + _hex(b) + _hex(c) + _hex(d)
}