Erlang token bucket rate limiter

-module(token_bucket).
-export([new/2, allow/2]).

new(Rate, Burst) ->
    #{rate => Rate, burst => Burst, tokens => float(Burst), ts => now_ms()}.

allow(C = #{rate := Rate, burst := Burst, tokens := T, ts := Last}) ->
    Now = now_ms(),
    Tokens = min(float(Burst), T + (Now - Last) * Rate / 1000),
    case Tokens >= 1.0 of
        true -> {true, C#{tokens => Tokens - 1, ts => Now}};
        false -> {false, C#{tokens => Tokens, ts => Now}}
    end.

now_ms() -> erlang:monotonic_time(millisecond).