local md5 = {}
-- local md5 = {
--     _VERSION     = "md5.lua 1.1.0",
--     _DESCRIPTION = "MD5 computation in Lua (5.1-3, LuaJIT)",
--     _URL         = "https://github.com/kikito/md5.lua",
--     _LICENSE     = [[
--     MIT LICENSE
--
--     Copyright (c) 2013 Enrique García Cota + Adam Baldwin + hanzao + Equi 4 Software
--
--     Permission is hereby granted, free of charge, to any person obtaining a
--     copy of this software and associated documentation files (the
--     "Software"), to deal in the Software without restriction, including
--     without limitation the rights to use, copy, modify, merge, publish,
--     distribute, sublicense, and/or sell copies of the Software, and to
--     permit persons to whom the Software is furnished to do so, subject to
--     the following conditions:
--
--     The above copyright notice and this permission notice shall be included
--     in all copies or substantial portions of the Software.
--
--     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
--     OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
--     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
--     IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
--     CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
--     TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
--     SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
--   ]]
-- }

-- bit lib implementions

local char, byte, format, rep, sub =
string.char, string.byte, string.format, string.rep, string.sub
local bit_or, bit_and, bit_not, bit_xor, bit_rshift, bit_lshift

local ok, bit = pcall(require, 'bit')
local ok_ffi, ffi = pcall(require, 'ffi')
if ok then
    bit_or, bit_and, bit_not, bit_xor, bit_rshift, bit_lshift = bit.bor, bit.band, bit.bnot, bit.bxor, bit.rshift,
        bit.lshift
else
    ok, bit = pcall(require, 'bit32')

    if ok then

        bit_not = bit.bnot

        local tobit = function(n)
            return n <= 0x7fffffff and n or -(bit_not(n) + 1)
        end

        local normalize = function(f)
            return function(a, b) return tobit(f(tobit(a), tobit(b))) end
        end

        bit_or, bit_and, bit_xor = normalize(bit.bor), normalize(bit.band), normalize(bit.bxor)
        bit_rshift, bit_lshift = normalize(bit.rshift), normalize(bit.lshift)

    else

        local function tbl2number(tbl)
            local result = 0
            local power = 1
            for i = 1, #tbl do
                result = result + tbl[i] * power
                power = power * 2
            end
            return result
        end

        local function expand(t1, t2)
            local big, small = t1, t2
            if (#big < #small) then
                big, small = small, big
            end
            -- expand small
            for i = #small + 1, #big do
                small[i] = 0
            end
        end

        local to_bits -- needs to be declared before bit_not

        bit_not = function(n)
            local tbl = to_bits(n)
            local size = math.max(#tbl, 32)
            for i = 1, size do
                if (tbl[i] == 1) then
                    tbl[i] = 0
                else
                    tbl[i] = 1
                end
            end
            return tbl2number(tbl)
        end

        -- defined as local above
        to_bits = function(n)
            if (n < 0) then
                -- negative
                return to_bits(bit_not(math.abs(n)) + 1)
            end
            -- to bits table
            local tbl = {}
            local cnt = 1
            local last
            while n > 0 do
                last     = n % 2
                tbl[cnt] = last
                n        = (n - last) / 2
                cnt      = cnt + 1
            end

            return tbl
        end

        bit_or = function(m, n)
            local tbl_m = to_bits(m)
            local tbl_n = to_bits(n)
            expand(tbl_m, tbl_n)

            local tbl = {}
            for i = 1, #tbl_m do
                if (tbl_m[i] == 0 and tbl_n[i] == 0) then
                    tbl[i] = 0
                else
                    tbl[i] = 1
                end
            end

            return tbl2number(tbl)
        end

        bit_and = function(m, n)
            local tbl_m = to_bits(m)
            local tbl_n = to_bits(n)
            expand(tbl_m, tbl_n)

            local tbl = {}
            for i = 1, #tbl_m do
                if (tbl_m[i] == 0 or tbl_n[i] == 0) then
                    tbl[i] = 0
                else
                    tbl[i] = 1
                end
            end

            return tbl2number(tbl)
        end

        bit_xor = function(m, n)
            local tbl_m = to_bits(m)
            local tbl_n = to_bits(n)
            expand(tbl_m, tbl_n)

            local tbl = {}
            for i = 1, #tbl_m do
                if (tbl_m[i] ~= tbl_n[i]) then
                    tbl[i] = 1
                else
                    tbl[i] = 0
                end
            end

            return tbl2number(tbl)
        end

        bit_rshift = function(n, bits)
            local high_bit = 0
            if (n < 0) then
                -- negative
                n = bit_not(math.abs(n)) + 1
                high_bit = 0x80000000
            end

            local floor = math.floor

            for i = 1, bits do
                n = n / 2
                n = bit_or(floor(n), high_bit)
            end
            return floor(n)
        end

        bit_lshift = function(n, bits)
            if (n < 0) then
                -- negative
                n = bit_not(math.abs(n)) + 1
            end

            for i = 1, bits do
                n = n * 2
            end
            return bit_and(n, 0xFFFFFFFF)
        end
    end
end

-- convert little-endian 32-bit int to a 4-char string
local lei2str
-- function is defined this way to allow full jit compilation (removing UCLO instruction in LuaJIT)
if ok_ffi then
    local ct_IntType = ffi.typeof("int[1]")
    lei2str = function(i) return ffi.string(ct_IntType(i), 4) end
else
    lei2str = function(i)
        local f = function(s) return char(bit_and(bit_rshift(i, s), 255)) end
        return f(0) .. f(8) .. f(16) .. f(24)
    end
end



-- convert raw string to big-endian int
local function str2bei(s)
    local v = 0
    for i = 1, #s do
        v = v * 256 + byte(s, i)
    end
    return v
end

-- convert raw string to little-endian int
local str2lei

if ok_ffi then
    local ct_constcharptr = ffi.typeof("const char*")
    local ct_constintptr = ffi.typeof("const int*")
    str2lei = function(s)
        local int = ct_constcharptr(s)
        return ffi.cast(ct_constintptr, int)[0]
    end
else
    str2lei = function(s)
        local v = 0
        for i = #s, 1, -1 do
            v = v * 256 + byte(s, i)
        end
        return v
    end
end


-- cut up a string in little-endian ints of given size
local function cut_le_str(s)
    return {
        str2lei(sub(s, 1, 4)),
        str2lei(sub(s, 5, 8)),
        str2lei(sub(s, 9, 12)),
        str2lei(sub(s, 13, 16)),
        str2lei(sub(s, 17, 20)),
        str2lei(sub(s, 21, 24)),
        str2lei(sub(s, 25, 28)),
        str2lei(sub(s, 29, 32)),
        str2lei(sub(s, 33, 36)),
        str2lei(sub(s, 37, 40)),
        str2lei(sub(s, 41, 44)),
        str2lei(sub(s, 45, 48)),
        str2lei(sub(s, 49, 52)),
        str2lei(sub(s, 53, 56)),
        str2lei(sub(s, 57, 60)),
        str2lei(sub(s, 61, 64)),
    }
end

-- An MD5 mplementation in Lua, requires bitlib (hacked to use LuaBit from above, ugh)
-- 10/02/2001 jcw@equi4.com

local CONSTS = {
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391,
    0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476
}

local f = function(x, y, z) return bit_or(bit_and(x, y), bit_and(-x - 1, z)) end
local g = function(x, y, z) return bit_or(bit_and(x, z), bit_and(y, -z - 1)) end
local h = function(x, y, z) return bit_xor(x, bit_xor(y, z)) end
local i = function(x, y, z) return bit_xor(y, bit_or(x, -z - 1)) end
local z = function(ff, a, b, c, d, x, s, ac)
    a = bit_and(a + ff(b, c, d) + x + ac, 0xFFFFFFFF)
    -- be *very* careful that left shift does not cause rounding!
    return bit_or(bit_lshift(bit_and(a, bit_rshift(0xFFFFFFFF, s)), s), bit_rshift(a, 32 - s)) + b
end

local function transform(A, B, C, D, X)
    local a, b, c, d = A, B, C, D
    local t = CONSTS

    a = z(f, a, b, c, d, X[0], 7, t[1])
    d = z(f, d, a, b, c, X[1], 12, t[2])
    c = z(f, c, d, a, b, X[2], 17, t[3])
    b = z(f, b, c, d, a, X[3], 22, t[4])
    a = z(f, a, b, c, d, X[4], 7, t[5])
    d = z(f, d, a, b, c, X[5], 12, t[6])
    c = z(f, c, d, a, b, X[6], 17, t[7])
    b = z(f, b, c, d, a, X[7], 22, t[8])
    a = z(f, a, b, c, d, X[8], 7, t[9])
    d = z(f, d, a, b, c, X[9], 12, t[10])
    c = z(f, c, d, a, b, X[10], 17, t[11])
    b = z(f, b, c, d, a, X[11], 22, t[12])
    a = z(f, a, b, c, d, X[12], 7, t[13])
    d = z(f, d, a, b, c, X[13], 12, t[14])
    c = z(f, c, d, a, b, X[14], 17, t[15])
    b = z(f, b, c, d, a, X[15], 22, t[16])

    a = z(g, a, b, c, d, X[1], 5, t[17])
    d = z(g, d, a, b, c, X[6], 9, t[18])
    c = z(g, c, d, a, b, X[11], 14, t[19])
    b = z(g, b, c, d, a, X[0], 20, t[20])
    a = z(g, a, b, c, d, X[5], 5, t[21])
    d = z(g, d, a, b, c, X[10], 9, t[22])
    c = z(g, c, d, a, b, X[15], 14, t[23])
    b = z(g, b, c, d, a, X[4], 20, t[24])
    a = z(g, a, b, c, d, X[9], 5, t[25])
    d = z(g, d, a, b, c, X[14], 9, t[26])
    c = z(g, c, d, a, b, X[3], 14, t[27])
    b = z(g, b, c, d, a, X[8], 20, t[28])
    a = z(g, a, b, c, d, X[13], 5, t[29])
    d = z(g, d, a, b, c, X[2], 9, t[30])
    c = z(g, c, d, a, b, X[7], 14, t[31])
    b = z(g, b, c, d, a, X[12], 20, t[32])

    a = z(h, a, b, c, d, X[5], 4, t[33])
    d = z(h, d, a, b, c, X[8], 11, t[34])
    c = z(h, c, d, a, b, X[11], 16, t[35])
    b = z(h, b, c, d, a, X[14], 23, t[36])
    a = z(h, a, b, c, d, X[1], 4, t[37])
    d = z(h, d, a, b, c, X[4], 11, t[38])
    c = z(h, c, d, a, b, X[7], 16, t[39])
    b = z(h, b, c, d, a, X[10], 23, t[40])
    a = z(h, a, b, c, d, X[13], 4, t[41])
    d = z(h, d, a, b, c, X[0], 11, t[42])
    c = z(h, c, d, a, b, X[3], 16, t[43])
    b = z(h, b, c, d, a, X[6], 23, t[44])
    a = z(h, a, b, c, d, X[9], 4, t[45])
    d = z(h, d, a, b, c, X[12], 11, t[46])
    c = z(h, c, d, a, b, X[15], 16, t[47])
    b = z(h, b, c, d, a, X[2], 23, t[48])

    a = z(i, a, b, c, d, X[0], 6, t[49])
    d = z(i, d, a, b, c, X[7], 10, t[50])
    c = z(i, c, d, a, b, X[14], 15, t[51])
    b = z(i, b, c, d, a, X[5], 21, t[52])
    a = z(i, a, b, c, d, X[12], 6, t[53])
    d = z(i, d, a, b, c, X[3], 10, t[54])
    c = z(i, c, d, a, b, X[10], 15, t[55])
    b = z(i, b, c, d, a, X[1], 21, t[56])
    a = z(i, a, b, c, d, X[8], 6, t[57])
    d = z(i, d, a, b, c, X[15], 10, t[58])
    c = z(i, c, d, a, b, X[6], 15, t[59])
    b = z(i, b, c, d, a, X[13], 21, t[60])
    a = z(i, a, b, c, d, X[4], 6, t[61])
    d = z(i, d, a, b, c, X[11], 10, t[62])
    c = z(i, c, d, a, b, X[2], 15, t[63])
    b = z(i, b, c, d, a, X[9], 21, t[64])

    return bit_and(A + a, 0xFFFFFFFF), bit_and(B + b, 0xFFFFFFFF),
        bit_and(C + c, 0xFFFFFFFF), bit_and(D + d, 0xFFFFFFFF)
end

----------------------------------------------------------------

local function md5_update(self, s)
    self.pos = self.pos + #s
    s = self.buf .. s
    for ii = 1, #s - 63, 64 do
        local X = cut_le_str(sub(s, ii, ii + 63))
        assert(#X == 16)
        X[0] = table.remove(X, 1) -- zero based!
        self.a, self.b, self.c, self.d = transform(self.a, self.b, self.c, self.d, X)
    end
    self.buf = sub(s, math.floor(#s / 64) * 64 + 1, #s)
    return self
end

local function md5_finish(self)
    local msgLen = self.pos
    local padLen = 56 - msgLen % 64

    if msgLen % 64 > 56 then padLen = padLen + 64 end

    if padLen == 0 then padLen = 64 end

    local s = char(128) ..
        rep(char(0), padLen - 1) .. lei2str(bit_and(8 * msgLen, 0xFFFFFFFF)) .. lei2str(math.floor(msgLen / 0x20000000))
    md5_update(self, s)

    assert(self.pos % 64 == 0)
    return lei2str(self.a) .. lei2str(self.b) .. lei2str(self.c) .. lei2str(self.d)
end

----------------------------------------------------------------

function md5.new()
    return { a = CONSTS[65], b = CONSTS[66], c = CONSTS[67], d = CONSTS[68],
        pos = 0,
        buf = '',
        update = md5_update,
        finish = md5_finish }
end

function md5.tohex(s)
    return format("%08x%08x%08x%08x", str2bei(sub(s, 1, 4)), str2bei(sub(s, 5, 8)), str2bei(sub(s, 9, 12)),
        str2bei(sub(s, 13, 16)))
end

function md5.sum(s)
    return md5.new():update(s):finish()
end

function md5.sumhexa(s)
    return md5.tohex(md5.sum(s))
end

return md5