// Pure-JS MD5 (RFC 1321), used to verify .seq [SIGNATURE] sections
// synchronously (WebCrypto has no MD5). Input is treated as a byte string.

export function md5Hex(input: string): string {
  const bytes: number[] = []
  for (let i = 0; i < input.length; i++) bytes.push(input.charCodeAt(i) & 0xff)

  const origLenBits = bytes.length * 8
  bytes.push(0x80)
  while (bytes.length % 64 !== 56) bytes.push(0)
  let len = origLenBits
  for (let i = 0; i < 8; i++) {
    bytes.push(len & 0xff)
    len = Math.floor(len / 256)
  }

  const S = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9,
    14, 20, 5, 9, 14, 20, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 6, 10, 15,
    21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21,
  ]
  const K = Array.from({ length: 64 }, (_, i) => Math.floor(Math.abs(Math.sin(i + 1)) * 4294967296) >>> 0)

  let a0 = 0x67452301
  let b0 = 0xefcdab89
  let c0 = 0x98badcfe
  let d0 = 0x10325476

  const rotl = (x: number, c: number) => ((x << c) | (x >>> (32 - c))) >>> 0

  for (let chunk = 0; chunk < bytes.length; chunk += 64) {
    const M = Array.from({ length: 16 }, (_, j) => {
      const o = chunk + j * 4
      return (bytes[o] | (bytes[o + 1] << 8) | (bytes[o + 2] << 16) | (bytes[o + 3] << 24)) >>> 0
    })
    let A = a0
    let B = b0
    let C = c0
    let D = d0
    for (let i = 0; i < 64; i++) {
      let F: number
      let g: number
      if (i < 16) {
        F = (B & C) | (~B & D)
        g = i
      } else if (i < 32) {
        F = (D & B) | (~D & C)
        g = (5 * i + 1) % 16
      } else if (i < 48) {
        F = B ^ C ^ D
        g = (3 * i + 5) % 16
      } else {
        F = C ^ (B | ~D)
        g = (7 * i) % 16
      }
      F = (F + A + K[i] + M[g]) >>> 0
      A = D
      D = C
      C = B
      B = (B + rotl(F, S[i])) >>> 0
    }
    a0 = (a0 + A) >>> 0
    b0 = (b0 + B) >>> 0
    c0 = (c0 + C) >>> 0
    d0 = (d0 + D) >>> 0
  }

  const le = (w: number) => {
    let s = ''
    for (let i = 0; i < 4; i++) s += ((w >>> (i * 8)) & 0xff).toString(16).padStart(2, '0')
    return s
  }
  return le(a0) + le(b0) + le(c0) + le(d0)
}