if not B64 then B64 = {} end
local encode, decode = {}, {
	[strbyte("=")] = false,
}
for value = 0, 63 do
	local char = strsub("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/", value + 1, value + 1)
	encode[value] = char
	decode[strbyte(char)] = value
end

local t = {}
function B64.Encode(str)
	local j = 1
	for i = 1, strlen(str), 3 do
		local a, b, c = strbyte(str, i, i + 2)
		t[j] = encode[bit.rshift(a, 2)]
		t[j + 1] = encode[bit.band(bit.lshift(a, 4) + bit.rshift(b or 0, 4), 0x3F)]
		t[j + 2] = b and encode[bit.band(bit.lshift(b, 2) + bit.rshift(c or 0, 6), 0x3F)] or "="
		t[j + 3] = c and encode[bit.band(c, 0x3F)] or "="
		j = j + 4
	end
	return table.concat(t, "", 1, j - 1)
end

function B64.Decode(str)
	local j = 1
	if strlen(str) % 4 ~= 0 then str = str .. string.rep("=", 4 - strlen(str) % 4) end
	assert(strlen(str) % 4 == 0, format("invalid data length: %d", strlen(str)))
	for i = 1, strlen(str), 4 do
		local ba, bb, bc, bd = strbyte(str, i, i + 3)
		local a, b, c, d = decode[ba], decode[bb], decode[bc], decode[bd]
		assert(a ~= nil, format("invalid data at position %d: '%s'", i, ba))
		assert(b ~= nil, format("invalid data at position %d: '%s'", i + 1, bb))
		assert(c ~= nil, format("invalid data at position %d: '%s'", i + 2, bc))
		assert(d ~= nil, format("invalid data at position %d: '%s'", i + 3, bd))
		t[j] = strchar(bit.lshift(a, 2) + bit.rshift(b, 4))
		t[j + 1] = c and strchar(bit.band(bit.lshift(b, 4) + bit.rshift(c, 2), 0xFF)) or ""
		t[j + 2] = d and strchar(bit.band(bit.lshift(c, 6) + d, 0xFF)) or ""
		j = j + 3
	end
	return table.concat(t, "", 1, j - 1)
end