///|
let sha512_h0 : Array[UInt64] = [
  0x6a09e667f3bcc908UL, 0xbb67ae8584caa73bUL, 0x3c6ef372fe94f82bUL, 0xa54ff53a5f1d36f1UL,
  0x510e527fade682d1UL, 0x9b05688c2b3e6c1fUL, 0x1f83d9abfb41bd6bUL, 0x5be0cd19137e2179UL,
]

///|
let sha512_k : Array[UInt64] = [
  0x428a2f98d728ae22UL, 0x7137449123ef65cdUL, 0xb5c0fbcfec4d3b2fUL, 0xe9b5dba58189dbbcUL,
  0x3956c25bf348b538UL, 0x59f111f1b605d019UL, 0x923f82a4af194f9bUL, 0xab1c5ed5da6d8118UL,
  0xd807aa98a3030242UL, 0x12835b0145706fbeUL, 0x243185be4ee4b28cUL, 0x550c7dc3d5ffb4e2UL,
  0x72be5d74f27b896fUL, 0x80deb1fe3b1696b1UL, 0x9bdc06a725c71235UL, 0xc19bf174cf692694UL,
  0xe49b69c19ef14ad2UL, 0xefbe4786384f25e3UL, 0x0fc19dc68b8cd5b5UL, 0x240ca1cc77ac9c65UL,
  0x2de92c6f592b0275UL, 0x4a7484aa6ea6e483UL, 0x5cb0a9dcbd41fbd4UL, 0x76f988da831153b5UL,
  0x983e5152ee66dfabUL, 0xa831c66d2db43210UL, 0xb00327c898fb213fUL, 0xbf597fc7beef0ee4UL,
  0xc6e00bf33da88fc2UL, 0xd5a79147930aa725UL, 0x06ca6351e003826fUL, 0x142929670a0e6e70UL,
  0x27b70a8546d22ffcUL, 0x2e1b21385c26c926UL, 0x4d2c6dfc5ac42aedUL, 0x53380d139d95b3dfUL,
  0x650a73548baf63deUL, 0x766a0abb3c77b2a8UL, 0x81c2c92e47edaee6UL, 0x92722c851482353bUL,
  0xa2bfe8a14cf10364UL, 0xa81a664bbc423001UL, 0xc24b8b70d0f89791UL, 0xc76c51a30654be30UL,
  0xd192e819d6ef5218UL, 0xd69906245565a910UL, 0xf40e35855771202aUL, 0x106aa07032bbd1b8UL,
  0x19a4c116b8d2d0c8UL, 0x1e376c085141ab53UL, 0x2748774cdf8eeb99UL, 0x34b0bcb5e19b48a8UL,
  0x391c0cb3c5c95a63UL, 0x4ed8aa4ae3418acbUL, 0x5b9cca4f7763e373UL, 0x682e6ff3d6b2b8a3UL,
  0x748f82ee5defb2fcUL, 0x78a5636f43172f60UL, 0x84c87814a1f0ab72UL, 0x8cc702081a6439ecUL,
  0x90befffa23631e28UL, 0xa4506cebde82bde9UL, 0xbef9a3f7b2c67915UL, 0xc67178f2e372532bUL,
  0xca273eceea26619cUL, 0xd186b8c721c0c207UL, 0xeada7dd6cde0eb1eUL, 0xf57d4f7fee6ed178UL,
  0x06f067aa72176fbaUL, 0x0a637dc5a2c898a6UL, 0x113f9804bef90daeUL, 0x1b710b35131c471bUL,
  0x28db77f523047d84UL, 0x32caab7b40c72493UL, 0x3c9ebe0a15c9bebcUL, 0x431d67c49c100d4cUL,
  0x4cc5d4becb3e42b6UL, 0x597f299cfc657e2aUL, 0x5fcb6fab3ad6faecUL, 0x6c44198c4a475817UL,
]

///|
fn rotr64(x : UInt64, n : Int) -> UInt64 {
  (x >> n) | (x << (64 - n))
}

///|
fn sha512_sigma0(x : UInt64) -> UInt64 {
  rotr64(x, 28) ^ rotr64(x, 34) ^ rotr64(x, 39)
}

///|
fn sha512_sigma1(x : UInt64) -> UInt64 {
  rotr64(x, 14) ^ rotr64(x, 18) ^ rotr64(x, 41)
}

///|
fn sha512_small_sigma0(x : UInt64) -> UInt64 {
  rotr64(x, 1) ^ rotr64(x, 8) ^ (x >> 7)
}

///|
fn sha512_small_sigma1(x : UInt64) -> UInt64 {
  rotr64(x, 19) ^ rotr64(x, 61) ^ (x >> 6)
}

///|
fn sha512_ch(x : UInt64, y : UInt64, z : UInt64) -> UInt64 {
  (x & y) ^ (x.lnot() & z)
}

///|
fn sha512_maj(x : UInt64, y : UInt64, z : UInt64) -> UInt64 {
  (x & y) ^ (x & z) ^ (y & z)
}

///|
fn sha512_pad(msg : Array[Byte]) -> Array[Byte] {
  let orig_len = msg.length()
  let bit_len = orig_len * 8
  let padded : Array[Byte] = Array::new(capacity=orig_len + 136)
  for i = 0; i < orig_len; i = i + 1 {
    padded.push(msg[i])
  }
  padded.push(b'\x80')
  while padded.length() % 128 != 112 {
    padded.push(b'\x00')
  }
  // 128-bit length: upper 12 bytes zero, lower 4 bytes hold bit_len
  for _i = 0; _i < 12; _i = _i + 1 {
    padded.push(b'\x00')
  }
  padded.push(((bit_len >> 24) & 0xFF).to_byte())
  padded.push(((bit_len >> 16) & 0xFF).to_byte())
  padded.push(((bit_len >> 8) & 0xFF).to_byte())
  padded.push((bit_len & 0xFF).to_byte())
  padded
}

///|
fn sha512_process_block(
  block : Array[Byte],
  offset : Int,
  h : Array[UInt64],
) -> Unit {
  let w : Array[UInt64] = Array::make(80, 0UL)
  for i = 0; i < 16; i = i + 1 {
    let base = offset + i * 8
    w[i] = (block[base].to_int().reinterpret_as_uint().to_uint64() << 56) |
      (block[base + 1].to_int().reinterpret_as_uint().to_uint64() << 48) |
      (block[base + 2].to_int().reinterpret_as_uint().to_uint64() << 40) |
      (block[base + 3].to_int().reinterpret_as_uint().to_uint64() << 32) |
      (block[base + 4].to_int().reinterpret_as_uint().to_uint64() << 24) |
      (block[base + 5].to_int().reinterpret_as_uint().to_uint64() << 16) |
      (block[base + 6].to_int().reinterpret_as_uint().to_uint64() << 8) |
      block[base + 7].to_int().reinterpret_as_uint().to_uint64()
  }
  for i = 16; i < 80; i = i + 1 {
    w[i] = sha512_small_sigma1(w[i - 2]) +
      w[i - 7] +
      sha512_small_sigma0(w[i - 15]) +
      w[i - 16]
  }
  let mut a = h[0]
  let mut b = h[1]
  let mut c = h[2]
  let mut d = h[3]
  let mut e = h[4]
  let mut f = h[5]
  let mut g = h[6]
  let mut hh = h[7]
  for i = 0; i < 80; i = i + 1 {
    let t1 = hh + sha512_sigma1(e) + sha512_ch(e, f, g) + sha512_k[i] + w[i]
    let t2 = sha512_sigma0(a) + sha512_maj(a, b, c)
    hh = g
    g = f
    f = e
    e = d + t1
    d = c
    c = b
    b = a
    a = t1 + t2
  }
  h[0] = h[0] + a
  h[1] = h[1] + b
  h[2] = h[2] + c
  h[3] = h[3] + d
  h[4] = h[4] + e
  h[5] = h[5] + f
  h[6] = h[6] + g
  h[7] = h[7] + hh
}

///|
pub fn sha512(data : Array[Byte]) -> Array[Byte] {
  let padded = sha512_pad(data)
  let h : Array[UInt64] = Array::make(8, 0UL)
  for i = 0; i < 8; i = i + 1 {
    h[i] = sha512_h0[i]
  }
  let num_blocks = padded.length() / 128
  for i = 0; i < num_blocks; i = i + 1 {
    sha512_process_block(padded, i * 128, h)
  }
  let result : Array[Byte] = Array::make(64, b'\x00')
  for i = 0; i < 8; i = i + 1 {
    for j = 0; j < 8; j = j + 1 {
      result[i * 8 + j] = ((h[i] >> ((7 - j) * 8)) & 0xFFUL).to_byte()
    }
  }
  result
}

///|
pub fn sha512_bytes(data : Array[Byte]) -> Array[Byte] {
  sha512(data)
}

///|
pub fn string_to_utf8(s : String) -> Array[Byte] {
  let bytes : Array[Byte] = []
  for i = 0; i < s.length(); i = i + 1 {
    let c = s[i].to_int()
    if c < 0x80 {
      bytes.push(c.to_byte())
    } else if c < 0x800 {
      bytes.push(((0xC0 | (c >> 6)) & 0xFF).to_byte())
      bytes.push(((0x80 | (c & 0x3F)) & 0xFF).to_byte())
    } else if c < 0x10000 {
      bytes.push(((0xE0 | (c >> 12)) & 0xFF).to_byte())
      bytes.push(((0x80 | ((c >> 6) & 0x3F)) & 0xFF).to_byte())
      bytes.push(((0x80 | (c & 0x3F)) & 0xFF).to_byte())
    } else {
      bytes.push(((0xF0 | (c >> 18)) & 0xFF).to_byte())
      bytes.push(((0x80 | ((c >> 12) & 0x3F)) & 0xFF).to_byte())
      bytes.push(((0x80 | ((c >> 6) & 0x3F)) & 0xFF).to_byte())
      bytes.push(((0x80 | (c & 0x3F)) & 0xFF).to_byte())
    }
  }
  bytes
}