var error = require("http-error");

/**
 * In memory rate limiter as connect middleware
 */
module.exports = ratelimit;

function ratelimit(key, duration, max) {
    var limit = {};
    return function(req, res, next) {
        var handle = req.params[key];

        var lim = limit[handle] || (limit[handle] = []);
        var now = Date.now();
        for (var i = 0; i < lim.length; i++) {
            if (now - lim[i] > duration) {
                lim.splice(i, 1);
                i--;
            }
            else break;
        }
        if (lim.length > max) {
            var err = new error.TooManyRequests("Rate limit exceeded");
            err.retryIn = duration - (Date.now() - lim[0]);
            next(err);
            return;
        }
        lim.push(Date.now());
        
        return next();
    };
}