-----------------------------------------------------------------------------
-- base64 convertion routines for the Lua language
-- Author: Diego Nehab
-- Date: 26/12/2000
-- Conforms to: RFC 1521
-----------------------------------------------------------------------------
-- Author: Hungpu DU
-- Date: 2014/04/06
-- ChangeLog:
--  * Taken from LuaSocket 1.1 and modified for Lua 5.1
--  * Modified to be suitable for b64 filter

local math = require("math")
local string = require("string")

module("resty.smtp.base64")



local t64 = {
	[0] = 'A', [1] = 'B', [2] = 'C', [3] = 'D', [4] = 'E', [5] = 'F', [6] = 'G',
	[7] = 'H', [8] = 'I', [9] = 'J', [10] = 'K', [11] = 'L', [12] = 'M',
	[13] = 'N', [14] = 'O', [15] = 'P', [16] = 'Q', [17] = 'R', [18] = 'S',
	[19] = 'T', [20] = 'U', [21] = 'V', [22] = 'W', [23] = 'X', [24] = 'Y',
	[25] = 'Z', [26] = 'a', [27] = 'b', [28] = 'c', [29] = 'd', [30] = 'e',
	[31] = 'f', [32] = 'g', [33] = 'h', [34] = 'i', [35] = 'j', [36] = 'k',
	[37] = 'l', [38] = 'm', [39] = 'n', [40] = 'o', [41] = 'p', [42] = 'q',
	[43] = 'r', [44] = 's', [45] = 't', [46] = 'u', [47] = 'v', [48] = 'w',
	[49] = 'x', [50] = 'y', [51] = 'z', [52] = '0', [53] = '1', [54] = '2',
	[55] = '3', [56] = '4', [57] = '5', [58] = '6', [59] = '7', [60] = '8',
	[61] = '9', [62] = '+', [63] = '/', 
}

local f64 = {
	['A'] = 0, ['B'] = 1, ['C'] = 2, ['D'] = 3, ['E'] = 4, ['F'] = 5, ['G'] = 6,
	['H'] = 7, ['I'] = 8, ['J'] = 9, ['K'] = 10, ['L'] = 11, ['M'] = 12,
	['N'] = 13, ['O'] = 14, ['P'] = 15, ['Q'] = 16, ['R'] = 17, ['S'] = 18,
	['T'] = 19, ['U'] = 20, ['V'] = 21, ['W'] = 22, ['X'] = 23, ['Y'] = 24,
	['Z'] = 25, ['a'] = 26, ['b'] = 27, ['c'] = 28, ['d'] = 29, ['e'] = 30,
	['f'] = 31, ['g'] = 32, ['h'] = 33, ['i'] = 34, ['j'] = 35, ['k'] = 36,
	['l'] = 37, ['m'] = 38, ['n'] = 39, ['o'] = 40, ['p'] = 41, ['q'] = 42,
	['r'] = 43, ['s'] = 44, ['t'] = 45, ['u'] = 46, ['v'] = 47, ['w'] = 48,
	['x'] = 49, ['y'] = 50, ['z'] = 51, ['0'] = 52, ['1'] = 53, ['2'] = 54,
	['3'] = 55, ['4'] = 56, ['5'] = 57, ['6'] = 58, ['7'] = 59, ['8'] = 60,
	['9'] = 61, ['+'] = 62, ['/'] = 63, 
}


local t2f = function(a, b, c)
	local s = a:byte() * 65536 + b:byte() * 256 + c:byte() 
	local ca, cb, cc, cd

	cd = math.fmod(s, 64)
	s = (s - cd) / 64
	cc = math.fmod(s, 64)
	s = (s - cc) / 64
	cb = math.fmod(s, 64)
	ca = (s - cb) / 64

	return t64[ca] .. t64[cb] .. t64[cc] .. t64[cd]
end


local f2t = function(a, b, c, d)
	local s, ca, cb, cc

    if d ~= "=" then
        s = f64[a] * 262144 + f64[b] * 4096 + f64[c] * 64 + f64[d] 

	    cc = math.fmod(s, 256)
	    s = (s - cc) / 256
	    cb = math.fmod(s, 256)
	    ca = (s - cb) / 256

	    return string.char(ca, cb, cc)

    elseif c ~= "=" then
        s = f64[a] * 1024 + f64[b] * 16 + f64[c] / 4
        cb = math.fmod(s, 256)
        ca = (s - cb) / 256

        return string.char(ca, cb)

    else
        s = f64[a] * 4 + f64[b] / 16
        ca = math.fmod(s, 256)
        return string.char(ca)
    end
end


function pad(chunk)
	local s, a, b, ca, cb, cc

    if #chunk == 0 then return "" end

	_, _, a, b = chunk:find("(.?)(.?)")
	if b == "" then 
		s = a:byte() * 16
		cb = math.fmod(s, 64)
		ca = (s - cb)/64
		return t64[ca] .. t64[cb] .. "=="

    else
        s = a:byte() * 1024 + b:byte() * 4
        cc = math.fmod(s, 64)
        s = (s - cc) / 64
        cb = math.fmod(s, 64)
        ca = (s - cb)/64
        return t64[ca] .. t64[cb] .. t64[cc] .. "="
	end
end


function encode(chunk)
    local l = #chunk
    local r = math.fmod(l, 3)

    l = l - r
    if l <= 0 then return "", chunk end

    return string.gsub(chunk:sub(1, l), "(.)(.)(.)", t2f), chunk:sub(l + 1)
end

function decode(chunk)
    local l = #chunk
    local r = math.fmod(l, 4)

    l = l - r
    if l <= 0 then return "", chunk end

    return string.gsub(chunk:sub(1, l), "(.)(.)(.)(.)", f2t), chunk:sub(l + 1)
end


-- for Encoded Word
--
function qencode(chunk) return encode(chunk) end
function qdecode(chunk) return decode(chunk) end
function qpad(chunk) return pad(chunk) end