-- from https://github.com/mpeterv/sha1
-- by Enrique García Cota, Eike Decker, Jeffrey Friedl, Peter Melnichenko
-- (MIT license)

local sha1 = {}

-- Merges four bytes into a uint32 number.
local function bytes_to_uint32(a, b, c, d)
   return a * 0x1000000 + b * 0x10000 + c * 0x100 + d
end

-- Splits a uint32 number into four bytes.
local function uint32_to_bytes(a)
   local a4 = a % 256
   a = (a - a4) / 256
   local a3 = a % 256
   a = (a - a3) / 256
   local a2 = a % 256
   local a1 = (a - a2) / 256
   return a1, a2, a3, a4
end

local function uint32_lrot(a, bits)
   return ((a << bits) & 0xFFFFFFFF) | (a >> (32 - bits))
end

local function uint32_ternary(a, b, c)
   -- c ~ (a & (b ~ c)) has less bitwise operations than (a & b) | (~a & c).
   return c ~ (a & (b ~ c))
end

local function uint32_majority(a, b, c)
   -- (a & (b | c)) | (b & c) has less bitwise operations than (a & b) | (a & c) | (b & c).
   return (a & (b | c)) | (b & c)
end

local sbyte = string.byte
local schar = string.char
local sformat = string.format
local srep = string.rep

local function hex_to_binary(hex)
   return (hex:gsub("..", function(hexval)
      return schar(tonumber(hexval, 16))
   end))
end

-- Calculates SHA1 for a string, returns it encoded as 40 hexadecimal digits.
function sha1.sha1(str)
   -- Input preprocessing.
   -- First, append a `1` bit and seven `0` bits.
   local first_append = schar(0x80)

   -- Next, append some zero bytes to make the length of the final message a multiple of 64.
   -- Eight more bytes will be added next.
   local non_zero_message_bytes = #str + 1 + 8
   local second_append = srep(schar(0), -non_zero_message_bytes % 64)

   -- Finally, append the length of the original message in bits as a 64-bit number.
   -- Assume that it fits into the lower 32 bits.
   local third_append = schar(0, 0, 0, 0, uint32_to_bytes(#str * 8))

   str = str .. first_append .. second_append .. third_append
   assert(#str % 64 == 0)

   -- Initialize hash value.
   local h0 = 0x67452301
   local h1 = 0xEFCDAB89
   local h2 = 0x98BADCFE
   local h3 = 0x10325476
   local h4 = 0xC3D2E1F0

   local w = {}

   -- Process the input in successive 64-byte chunks.
   for chunk_start = 1, #str, 64 do
      -- Load the chunk into W[0..15] as uint32 numbers.
      local uint32_start = chunk_start

      for i = 0, 15 do
         w[i] = bytes_to_uint32(sbyte(str, uint32_start, uint32_start + 3))
         uint32_start = uint32_start + 4
      end

      -- Extend the input vector.
      for i = 16, 79 do
         w[i] = uint32_lrot(w[i - 3] ~ w[i - 8] ~ w[i - 14] ~ w[i - 16], 1)
      end

      -- Initialize hash value for this chunk.
      local a = h0
      local b = h1
      local c = h2
      local d = h3
      local e = h4

      -- Main loop.
      for i = 0, 79 do
         local f
         local k

         if i <= 19 then
            f = uint32_ternary(b, c, d)
            k = 0x5A827999
         elseif i <= 39 then
            f = b ~ c ~ d
            k = 0x6ED9EBA1
         elseif i <= 59 then
            f = uint32_majority(b, c, d)
            k = 0x8F1BBCDC
         else
            f = b ~ c ~ d
            k = 0xCA62C1D6
         end

         local temp = (uint32_lrot(a, 5) + f + e + k + w[i]) % 4294967296
         e = d
         d = c
         c = uint32_lrot(b, 30)
         b = a
         a = temp
      end

      -- Add this chunk's hash to result so far.
      h0 = (h0 + a) % 4294967296
      h1 = (h1 + b) % 4294967296
      h2 = (h2 + c) % 4294967296
      h3 = (h3 + d) % 4294967296
      h4 = (h4 + e) % 4294967296
   end

   return sformat("%08x%08x%08x%08x%08x", h0, h1, h2, h3, h4)
end

function sha1.binary(str)
   return hex_to_binary(sha1.sha1(str))
end

-- Precalculate replacement tables.
local xor_with_0x5c = {}
local xor_with_0x36 = {}

for i = 0, 0xff do
   xor_with_0x5c[schar(i)] = schar(0x5c ~ i)
   xor_with_0x36[schar(i)] = schar(0x36 ~ i)
end

-- 512 bits.
local BLOCK_SIZE = 64

function sha1.hmac(key, text)
   if #key > BLOCK_SIZE then
      key = sha1.binary(key)
   end

   local key_xord_with_0x36 = key:gsub('.', xor_with_0x36) .. srep(schar(0x36), BLOCK_SIZE - #key)
   local key_xord_with_0x5c = key:gsub('.', xor_with_0x5c) .. srep(schar(0x5c), BLOCK_SIZE - #key)

   return sha1.sha1(key_xord_with_0x5c .. sha1.binary(key_xord_with_0x36 .. text))
end

function sha1.hmac_binary(key, text)
   return hex_to_binary(sha1.hmac(key, text))
end

setmetatable(sha1, {__call = function(_, str) return sha1.sha1(str) end})

return sha1