local sha1 = {}

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

-- loading this file (takes a while but grants a boost of factor 13)
local PRELOAD_CACHE = true

local BLOCK_SIZE = 64 -- 512 bits

-- local storing of global functions (minor speedup)
local floor, modf = math.floor, math.modf
local char, format, rep = string.char, string.format, string.rep

-- merge 4 bytes to an 32 bit word
local function bytes_to_w32(a, b, c, d) return a * 0x1000000 + b * 0x10000 + c * 0x100 + d end
-- split a 32 bit word into four 8 bit numbers
local function w32_to_bytes(i)
    return floor(i / 0x1000000) % 0x100, floor(i / 0x10000) % 0x100, floor(i / 0x100) % 0x100, i % 0x100
end

-- shift the bits of a 32 bit word. Don't use negative values for "bits"
local function w32_rot(bits, a)
    local b2 = 2 ^ (32 - bits)
    local a, b = modf(a / b2)
    return a + b * b2 * (2 ^ (bits))
end

-- caching function for functions that accept 2 arguments, both of values between
-- 0 and 255. The function to be cached is passed, all values are calculated
-- during loading and a function is returned that returns the cached values (only)
local function cache2arg(fn)
    if not PRELOAD_CACHE then return fn end
    local lut = {}
    for i = 0, 0xffff do
        local a, b = floor(i / 0x100), i % 0x100
        lut[i] = fn(a, b)
    end
    return function(a, b)
        return lut[a * 0x100 + b]
    end
end

-- splits an 8-bit number into 8 bits, returning all 8 bits as booleans
local function byte_to_bits(b)
    local b = function(n)
        local b = floor(b / n)
        return b % 2 == 1
    end
    return b(1), b(2), b(4), b(8), b(16), b(32), b(64), b(128)
end

-- builds an 8bit number from 8 booleans
local function bits_to_byte(a, b, c, d, e, f, g, h)
    local function n(b, x) return b and x or 0 end
    return n(a, 1) + n(b, 2) + n(c, 4) + n(d, 8) + n(e, 16) + n(f, 32) + n(g, 64) + n(h, 128)
end

-- bitwise "and" function for 2 8bit number
local band = cache2arg(function(a, b)
    local A, B, C, D, E, F, G, H = byte_to_bits(b)
    local a, b, c, d, e, f, g, h = byte_to_bits(a)
    return bits_to_byte(
        A and a, B and b, C and c, D and d,
        E and e, F and f, G and g, H and h)
end)

-- bitwise "or" function for 2 8bit numbers
local bor = cache2arg(function(a, b)
    local A, B, C, D, E, F, G, H = byte_to_bits(b)
    local a, b, c, d, e, f, g, h = byte_to_bits(a)
    return bits_to_byte(
        A or a, B or b, C or c, D or d,
        E or e, F or f, G or g, H or h)
end)

-- bitwise "xor" function for 2 8bit numbers
local bxor = cache2arg(function(a, b)
    local A, B, C, D, E, F, G, H = byte_to_bits(b)
    local a, b, c, d, e, f, g, h = byte_to_bits(a)
    return bits_to_byte(
        A ~= a, B ~= b, C ~= c, D ~= d,
        E ~= e, F ~= f, G ~= g, H ~= h)
end)

-- bitwise complement for one 8bit number
local function bnot(x)
    return 255 - (x % 256)
end

-- creates a function to combine to 32bit numbers using an 8bit combination function
local function w32_comb(fn)
    return function(a, b)
        local aa, ab, ac, ad = w32_to_bytes(a)
        local ba, bb, bc, bd = w32_to_bytes(b)
        return bytes_to_w32(fn(aa, ba), fn(ab, bb), fn(ac, bc), fn(ad, bd))
    end
end

-- create functions for and, xor and or, all for 2 32bit numbers
local w32_and = w32_comb(band)
local w32_xor = w32_comb(bxor)
local w32_or = w32_comb(bor)

-- xor function that may receive a variable number of arguments
local function w32_xor_n(a, ...)
    local aa, ab, ac, ad = w32_to_bytes(a)
    for i = 1, select('#', ...) do
        local ba, bb, bc, bd = w32_to_bytes(select(i, ...))
        aa, ab, ac, ad = bxor(aa, ba), bxor(ab, bb), bxor(ac, bc), bxor(ad, bd)
    end
    return bytes_to_w32(aa, ab, ac, ad)
end

-- combining 3 32bit numbers through binary "or" operation
local function w32_or3(a, b, c)
    local aa, ab, ac, ad = w32_to_bytes(a)
    local ba, bb, bc, bd = w32_to_bytes(b)
    local ca, cb, cc, cd = w32_to_bytes(c)
    return bytes_to_w32(
        bor(aa, bor(ba, ca)), bor(ab, bor(bb, cb)), bor(ac, bor(bc, cc)), bor(ad, bor(bd, cd))
    )
end

-- binary complement for 32bit numbers
local function w32_not(a)
    return 4294967295 - (a % 4294967296)
end

-- adding 2 32bit numbers, cutting off the remainder on 33th bit
local function w32_add(a, b) return (a + b) % 4294967296 end

-- adding n 32bit numbers, cutting off the remainder (again)
local function w32_add_n(a, ...)
    for i = 1, select('#', ...) do
        a = (a + select(i, ...)) % 4294967296
    end
    return a
end
-- converting the number to a hexadecimal string
local function w32_to_hexstring(w) return format("%08x", w) end

local function hex_to_binary(hex)
    return hex:gsub('..', function(hexval)
        return string.char(tonumber(hexval, 16))
    end)
end

-- building the lookuptables ahead of time (instead of littering the source code
-- with precalculated values)
local xor_with_0x5c = {}
local xor_with_0x36 = {}
for i = 0, 0xff do
    xor_with_0x5c[char(i)] = char(bxor(i, 0x5c))
    xor_with_0x36[char(i)] = char(bxor(i, 0x36))
end

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

-- calculating the SHA1 for some text
function sha1.sha1(msg)
    local H0, H1, H2, H3, H4     = 0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0
    local msg_len_in_bits        = #msg * 8

    local first_append           = char(0x80) -- append a '1' bit plus seven '0' bits

    local non_zero_message_bytes = #msg + 1 + 8 -- the +1 is the appended bit 1, the +8 are for the final appended length
    local current_mod            = non_zero_message_bytes % 64
    local second_append          = current_mod > 0 and rep(char(0), 64 - current_mod) or ""

    -- now to append the length as a 64-bit number.
    local B1, R1                 = modf(msg_len_in_bits / 0x01000000)
    local B2, R2                 = modf(0x01000000 * R1 / 0x00010000)
    local B3, R3                 = modf(0x00010000 * R2 / 0x00000100)
    local B4                     = 0x00000100 * R3

    local L64                    = char(0) .. char(0) .. char(0) .. char(0) -- high 32 bits
        .. char(B1) .. char(B2) .. char(B3) .. char(B4)    --  low 32 bits

    msg                          = msg .. first_append .. second_append .. L64

    assert(#msg % 64 == 0)

    local chunks = #msg / 64

    local W = {}
    local start, A, B, C, D, E, f, K, TEMP
    local chunk = 0

    while chunk < chunks do
        --
        -- break chunk up into W[0] through W[15]
        --
        start, chunk = chunk * 64 + 1, chunk + 1

        for t = 0, 15 do
            W[t] = bytes_to_w32(msg:byte(start, start + 3))
            start = start + 4
        end

        --
        -- build W[16] through W[79]
        --
        for t = 16, 79 do
            -- For t = 16 to 79 let Wt = S1(Wt-3 XOR Wt-8 XOR Wt-14 XOR Wt-16).
            W[t] = w32_rot(1, w32_xor_n(W[t - 3], W[t - 8], W[t - 14], W[t - 16]))
        end

        A, B, C, D, E = H0, H1, H2, H3, H4

        for t = 0, 79 do
            if t <= 19 then
                -- (B AND C) OR ((NOT B) AND D)
                f = w32_or(w32_and(B, C), w32_and(w32_not(B), D))
                K = 0x5A827999
            elseif t <= 39 then
                -- B XOR C XOR D
                f = w32_xor_n(B, C, D)
                K = 0x6ED9EBA1
            elseif t <= 59 then
                -- (B AND C) OR (B AND D) OR (C AND D
                f = w32_or3(w32_and(B, C), w32_and(B, D), w32_and(C, D))
                K = 0x8F1BBCDC
            else
                -- B XOR C XOR D
                f = w32_xor_n(B, C, D)
                K = 0xCA62C1D6
            end

            -- TEMP = S5(A) + ft(B,C,D) + E + Wt + Kt;
            A, B, C, D, E = w32_add_n(w32_rot(5, A), f, E, W[t], K),
                A, w32_rot(30, B), C, D
        end
        -- Let H0 = H0 + A, H1 = H1 + B, H2 = H2 + C, H3 = H3 + D, H4 = H4 + E.
        H0, H1, H2, H3, H4 = w32_add(H0, A), w32_add(H1, B), w32_add(H2, C), w32_add(H3, D), w32_add(H4, E)
    end
    local f = w32_to_hexstring
    return f(H0) .. f(H1) .. f(H2) .. f(H3) .. f(H4)
end

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

function sha1.hmac(key, text)
    assert(type(key) == 'string', "key passed to sha1.hmac should be a string")
    assert(type(text) == 'string', "text passed to sha1.hmac should be a string")

    if #key > BLOCK_SIZE then
        key = sha1.binary(key)
    end

    local key_xord_with_0x36 = key:gsub('.', xor_with_0x36) .. string.rep(string.char(0x36), BLOCK_SIZE - #key)
    local key_xord_with_0x5c = key:gsub('.', xor_with_0x5c) .. string.rep(string.char(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(_, msg) return sha1.sha1(msg) end })

return sha1