local cb64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

b64 = {}

local function istr(p)
    return string.sub(cb64, p + 1, p + 1)
end

function b64.encodeblock(in_tab, len)
    local s1, s2, s3, s4
    
    in_tab[0] = in_tab[1] or 0
    in_tab[1] = in_tab[2] or 0
    in_tab[2] = in_tab[3] or 0
    
    s1 = istr(bin.rshift(in_tab[0], 2))
    s2 = istr(bin.bor(bin.lshift(bin.band(in_tab[0], 3), 4), bin.rshift(bin.band(in_tab[1], 240), 4)))
    s3 = (len > 1 and istr(bin.bor(bin.lshift(bin.band(in_tab[1], 15), 2), bin.rshift(bin.band(in_tab[2], 192), 6))) or "=")
    s4 = (len > 2 and istr( bin.band(in_tab[2], 63)) or "=")
    
    return s1..s2..s3..s4
end

function b64.encode(stream, stream_size)
    local encoded = ""
    local e_block
    local in_tab, len, i, s_pos
    
    s_pos = 0
    
    while stream_size > 0 do
	in_tab = {}
	
	len = stream_size >= 3 and 3 or stream_size
	
	for i = 1, len do
	    in_tab[i] = stream[s_pos + i]
	end
	
	e_block = b64.encodeblock(in_tab, len)
	
	encoded = encoded .. e_block
	
	s_pos = s_pos + 3
	stream_size = stream_size - 3
    end
    
    return encoded
end

local function stri(s)
    return s == "=" and -1 or (string.find(cb64, s) - 1)
end

function b64.decodeblock(s1, s2, s3, s4)
    local b1, b2, b3, len
    
    len = s3 == "=" and 1 or s4 == "=" and 2 or 3
    
    s3 = s3 == "=" and "A" or s3
    s4 = s4 == "=" and "A" or s4
    
    s1 = stri(s1)
    s2 = stri(s2)
    s3 = stri(s3)
    s4 = stri(s4)
    
    b1 = bin.bor(bin.lshift(s1, 2), bin.rshift(s2, 4))
    b2 = bin.bor(bin.band(bin.lshift(s2, 4), 255), bin.rshift(s3, 2))
    b3 = bin.bor(bin.band(bin.lshift(s3, 6), 240), s4)
    
    return {b1, b2, b3}, len    
end

function b64.decode(str_in)
    local s_len = string.len(str_in) / 4
    local out, len, i, j, t_out, s1, s2, s3, s4, t_len = {}, 0
    
    for i = 1, s_len do
	s1 = string.sub(str_in, i * 4 - 3, i * 4 - 3)
	s2 = string.sub(str_in, i * 4 - 2, i * 4 - 2)
	s3 = string.sub(str_in, i * 4 - 1, i * 4 - 1)
	s4 = string.sub(str_in, i * 4 - 0, i * 4 - 0)
	t_out, t_len = b64.decodeblock(s1, s2, s3, s4)
	
	for j = 1, t_len do
	    out[i * 3 - 3 + j] = t_out[j]
	end
	
	len = len + t_len
    end
    
    return out, len
end

--[[

b64_test_in = {
    48, 49, 50, 51, 52, 53, 54, 55, 56, 57
}

b64_test_enc = "MDEyMzQ1Njc4OQ=="

function test_b64()
    local enc, dec, i, len
    
    enc = b64.encode(b64_test_in, 10)
    assert(enc == b64_test_enc)
    dec, len = b64.decode(enc)
    assert(len == 10)
    for i = 1, len do
	assert(b64_test_in[i] == dec[i])
    end
end

]]