-- Base64 Encoder / Decoder
-- By KillaVanilla
-- see: http://www.computercraft.info/forums2/index.php?/topic/12450-killavanillas-various-apis/

local Base64 = { }

local bit      = _G.bit
local _brshift = bit.brshift
local _bor     = bit.bor
local _blshift = bit.blshift
local _band    = bit.band
local _sub     = string.sub
local os       = _G.os

local alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

local function sixBitToBase64(input)
	return _sub(alphabet, input+1, input+1)
end

local function base64ToSixBit(input)
	for i=1, 64 do
		if input == _sub(alphabet, i, i) then
			return i-1
		end
	end
end

local function octetToBase64(o1, o2, o3)
	local i1 = sixBitToBase64(_brshift(_band(o1, 0xFC), 2))
	local i2
	local i3 = "="
	local i4 = "="
	if o2 then
		i2 = sixBitToBase64(_bor( _blshift(_band(o1, 3), 4), _brshift(_band(o2, 0xF0), 4) ))
		if not o3 then
			i3 = sixBitToBase64(_blshift(_band(o2, 0x0F), 2))
		else
			i3 = sixBitToBase64(_bor( _blshift(_band(o2, 0x0F), 2), _brshift(_band(o3, 0xC0), 6) ))
		end
	else
		i2 = sixBitToBase64(_blshift(_band(o1, 3), 4))
	end
	if o3 then
		i4 = sixBitToBase64(_band(o3, 0x3F))
	end

	return i1..i2..i3..i4
end

-- octet 1 needs characters 1/2
-- octet 2 needs characters 2/3
-- octet 3 needs characters 3/4

local function base64ToThreeOctet(s1)
	local c1 = base64ToSixBit(_sub(s1, 1, 1))
	local c2 = base64ToSixBit(_sub(s1, 2, 2))
	local c3
	local c4
	local o1
	local o2
	local o3
	if _sub(s1, 3, 3) == "=" then
		c3 = nil
		c4 = nil
	elseif _sub(s1, 4, 4) == "=" then
		c3 = base64ToSixBit(_sub(s1, 3, 3))
		c4 = nil
	else
		c3 = base64ToSixBit(_sub(s1, 3, 3))
		c4 = base64ToSixBit(_sub(s1, 4, 4))
	end
	o1 = _bor( _blshift(c1, 2), _brshift(_band( c2, 0x30 ), 4) )
	if c3 then
		o2 = _bor( _blshift(_band(c2, 0x0F), 4), _brshift(_band( c3, 0x3C ), 2) )
	else
		o2 = nil
	end
	if c4 then
		o3 = _bor( _blshift(_band(c3, 3), 6), c4 )
	else
		o3 = nil
	end
	return o1, o2, o3
end

local function splitIntoBlocks(bytes)
	local blockNum = 1
	local blocks = {}
	for i=1, #bytes, 3 do
		blocks[blockNum] = {bytes[i], bytes[i+1], bytes[i+2]}
		--[[
		if #blocks[blockNum] < 3 then
			for j=#blocks[blockNum]+1, 3 do
				table.insert(blocks[blockNum], 0)
			end
		end
		]]
		blockNum = blockNum+1
	end
	return blocks
end

function Base64.encode(bytes)
	local blocks = splitIntoBlocks(bytes)
	local output = ""
	for i=1, #blocks do
		output = output..octetToBase64( unpack(blocks[i]) )
	end
	return output
end

local function Throttle()
	local ts = os.clock()
	local timeout = .095
	return function()
		local nts = os.clock()
		if nts > ts + timeout then
			os.sleep(0)
			ts = os.clock()
		end
	end
end

function Base64.decode(str)
	local bytes = {}
	local blocks = {}
	local blockNum = 1
	local throttle = Throttle()
	for i=1, #str, 4 do
		blocks[blockNum] = _sub(str, i, i+3)
		blockNum = blockNum+1
	end
	for i=1, #blocks do
		local o1, o2, o3 = base64ToThreeOctet(blocks[i])
		table.insert(bytes, o1)
		table.insert(bytes, o2)
		table.insert(bytes, o3)
		throttle()
	end
	-- Remove padding:
	--[[
	for i=#bytes, 1, -1 do
		if bytes[i] ~= 0 then
			break
		else
			bytes[i] = nil
		end
	end
	]]
	return bytes
end

return Base64