-- circular shift
local function ROTRIGHT(a, b)
  return ((a >> b) | (a << (32 - b))) & 0xFFFFFFFF
end

-- choose
local function CH(x, y, z)
  return ((x & y) ~ ((~x) & z)) & 0xFFFFFFFF
end

-- majority
local function MAJ(x, y, z)
  return ((x & y) ~ (x & z) ~ (y & z)) & 0xFFFFFFFF
end

-- Sigma0 (uppercase sigma)
local function EP0(x)
  return (ROTRIGHT(x, 2) ~ ROTRIGHT(x, 13) ~ ROTRIGHT(x, 22)) & 0xFFFFFFFF
end

-- Sigma1 (uppercase sigma)
local function EP1(x)
  return (ROTRIGHT(x, 6) ~ ROTRIGHT(x, 11) ~ ROTRIGHT(x, 25)) & 0xFFFFFFFF
end

-- sigma0 (lowercase sigma)
local function SIG0(x)
  return (ROTRIGHT(x, 7) ~ ROTRIGHT(x, 18) ~ (x >> 3)) & 0xFFFFFFFF
end

-- sigma1 (lowercase sigma)
local function SIG1(x)
  return (ROTRIGHT(x, 17) ~ ROTRIGHT(x, 19) ~ (x >> 10)) & 0xFFFFFFFF
end

local function sha256_transform(state, data)
  local k = {
    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
  }
    
  -- m = uint32_t[64]
  local m = {}
    
  -- convert to 32 bit BE words
  for i = 1, 16 do
    local j = (i - 1) * 4 + 1
    m[i] = (data[j] << 24) | (data[j+1] << 16) | (data[j+2] << 8) | data[j+3]
  end
  
  for i = 17, 64 do
    m[i] = (SIG1(m[i-2]) + m[i-7] + SIG0(m[i-15]) + m[i-16]) & 0xFFFFFFFF
  end
  
  local a = state[1]
  local b = state[2]
  local c = state[3]
  local d = state[4]
  local e = state[5]
  local f = state[6]
  local g = state[7]
  local h = state[8]
  
  for i = 1, 64 do
    local t1 = (h + EP1(e) + CH(e, f, g) + k[i] + m[i]) & 0xFFFFFFFF
    local t2 = (EP0(a) + MAJ(a, b, c)) & 0xFFFFFFFF
    h = g
    g = f
    f = e
    e = (d + t1) & 0xFFFFFFFF
    d = c
    c = b
    b = a
    a = (t1 + t2) & 0xFFFFFFFF
  end

  state[1] = (state[1] + a) & 0xFFFFFFFF
  state[2] = (state[2] + b) & 0xFFFFFFFF
  state[3] = (state[3] + c) & 0xFFFFFFFF
  state[4] = (state[4] + d) & 0xFFFFFFFF
  state[5] = (state[5] + e) & 0xFFFFFFFF
  state[6] = (state[6] + f) & 0xFFFFFFFF
  state[7] = (state[7] + g) & 0xFFFFFFFF
  state[8] = (state[8] + h) & 0xFFFFFFFF
end

local files = {...}
local fs = import("filesystem")
if not files or not files[1] then
  shell.run("help sha256sum")
  return
end

for _, file in ipairs(files) do
  if file:sub(1, 1) ~= "/" then
    file = fs.concat(shell.workingDirectory, file)
  end
  if not fs.exists(file) then
    print("\27[91mFile does not exist.")
  end
  local handle = fs.open(file, "r")

  local data = {}

  local state = {
    0x6a09e667,
    0xbb67ae85,
    0x3c6ef372,
    0xa54ff53a,
    0x510e527f,
    0x9b05688c,
    0x1f83d9ab,
    0x5be0cd19
  }

  local datalen = 1
  local bitlen = 0
  
  while true do
    local chunk = handle:read(256)
    if not chunk then break end
    
    for i = 1, #chunk do
      local byte = string.byte(chunk, i)
      data[datalen] = byte
      datalen = datalen + 1
      if (datalen == 65) then
        sha256_transform(state, data)
        bitlen = bitlen + 512
        datalen = 1
      end
    end
  end
  
  local i = datalen
  if datalen <= 56 then
    data[i] = 0x80
    i = i + 1
    while i <= 56 do
      data[i] = 0x00
      i = i + 1
    end
  else
    data[i] = 0x80
    i = i + 1
    while i <= 64 do
      data[i] = 0x00
      i = i + 1
    end
    sha256_transform(state, data)
    for i = 1, 56 do
      data[i] = 0x00
    end
  end
  
  bitlen = bitlen + (datalen - 1) * 8
  data[64] = (bitlen) & 0x000000ff
  data[63] = (bitlen >> 8) & 0x000000ff
  data[62] = (bitlen >> 16) & 0x000000ff
  data[61] = (bitlen >> 24) & 0x000000ff
  data[60] = (bitlen >> 32) & 0x000000ff
  data[59] = (bitlen >> 40) & 0x000000ff
  data[58] = (bitlen >> 48) & 0x000000ff
  data[57] = (bitlen >> 56) & 0x000000ff
  sha256_transform(state, data)
  local hash_parts = {}
  for i = 0, 3 do
    hash_parts[i + 1]      = (state[1] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 4 + 1]  = (state[2] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 8 + 1]  = (state[3] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 12 + 1] = (state[4] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 16 + 1] = (state[5] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 20 + 1] = (state[6] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 24 + 1] = (state[7] >> (24 - i * 8)) & 0x000000ff
    hash_parts[i + 28 + 1] = (state[8] >> (24 - i * 8)) & 0x000000ff
  end
  local hash = {}
  for i = 1, 32 do
    hash[i] = string.format("%02x", hash_parts[i])
  end
  termlib.write(table.concat(hash).."  "..file.."\n")
end