-- $Id: api_base64.lua 3171 2008-11-06 09:06:29Z det $
-- Author: Alex Kloss
-- Contact: http://www.it-rfc.de
-- Date: 2006-2008
-- License: LGPL2

-- Public functions:
--  * Spring.Utilities.Base64Encode(string data) -> string
--  * Spring.Utilities.Base64Decode(string data) -> string

-- bitshift functions (<<, >> equivalent)
-- shift left

Spring.Utilities = Spring.Utilities or {}

local function lsh(value, shift)
	return (value * (2 ^ shift)) % 256
end

-- shift right
local function rsh(value, shift)
	return math.floor(value / 2 ^ shift) % 256
end

-- return single bit (for OR)
local function bit(x, b)
	return (x % 2 ^ b - x % 2 ^ (b - 1) > 0)
end

-- logic OR for number values
local function lor(x, y)
	local result = 0
	for p = 1, 8 do
		result = result + (((bit(x, p) or bit(y, p)) == true) and 2 ^ (p - 1) or 0)
	end
	return result
end

-- encoding table
local base64chars = {
	[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] = '_'
}

-- function encode
-- encodes input string to base64.
function Spring.Utilities.Base64Encode(data)
	local bytes = {}
	local result = {}
	for spos = 0, string.len(data) - 1, 3 do
		for byte = 1, 3 do
			bytes[byte] = string.byte(string.sub(data, (spos + byte), (spos + byte))) or 0
		end
		result[#result + 1] = base64chars[rsh(bytes[1], 2)] ..
			(base64chars[lor(lsh((bytes[1] % 4), 4), rsh(bytes[2], 4))] or "=") ..
			(((#data - spos) > 1) and base64chars[lor(lsh(bytes[2] % 16, 2), rsh(bytes[3], 6))] or "=") ..
			(((#data - spos) > 2) and base64chars[(bytes[3] % 64)] or "=")
	end
	result = table.concat(result)
	return result
end

-- decoding table
local base64bytes = {
	['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,
	['='] = nil,
}

-- function decode
-- decode base64 input to string
function Spring.Utilities.Base64Decode(data)
	local chars = {}
	local result = {}
	for dpos = 0, string.len(data) - 1, 4 do
		for char = 1, 4 do
			chars[char] = base64bytes[(string.sub(data, (dpos + char), (dpos + char)) or "=")]
		end
		result[#result + 1] = string.char(lor(lsh(chars[1], 2), rsh(chars[2], 4))) ..
			((chars[3] ~= nil) and string.char(lor(lsh(chars[2], 4), rsh(chars[3], 2))) or "") ..
			((chars[4] ~= nil) and string.char(lor(lsh(chars[3], 6), (chars[4]))) or "")
	end
	result = table.concat(result)
	return result
end
