import("std/list").
import("std/str").

charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".

_b64(n) ->
        list\map(\shift -> list\at(charset, (n >> shift) & 63),
                           [18, 12, 6, 0]).

f([]) -> [].
f(a :: b :: c :: xs) -> do
    v = (a << 16) | (b << 8) | c;
    _b64(v) + f(xs)
end.
f(a :: b :: []) -> do
        v = (a << 16) | (b << 8);
        list\take(3, _b64(v)) + ["="]
end.
f(a :: []) -> do
        v = a << 16;
        list\take(2, _b64(v)) + ["=="]
end.

base64_encode(s) -> do
    bytes = list\map(ord, s);
    str\concat(f(bytes))
end.