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

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

function ratelimit(key, duration, max) {
    var requests = {};
    setInterval(function() {
        _.forIn(requests, function (requestsForHandle, key) {
            var totalToSplice = 0;
            var expireTime = Date.now() - duration;  
            /* Requests are already sorted by date as they are appended, so we just loop 
                until we find one that shouldn't have expired and splice them from the list */
            for (var i = 0; i < requestsForHandle.length; i++)  {
                if (requestsForHandle[i] >= expireTime) break;
                totalToSplice++;
            }
            requests[key].splice(0, totalToSplice);
            if (requests[key].length == 0) {
                delete requests[key];
            }
        });
    }, 10);
    return function(req, res, next) {
        var handle = req.params[key];

        requests[handle] = requests[handle] || [];
        if (requests[handle].length >= max) {
            var err = new error.TooManyRequests("Rate limit exceeded");
            err.retryIn = Math.min(duration, 5000);
            return next(err);
        }
        
        requests[handle].push(Date.now());
        return next();
    };
}