var Ioredis = require('ioredis');
var redis = new Ioredis();

// Rolling window rate limiter
//
// key is a unique identifier for the process or function call being limited
// exp is the expiry in milliseconds
// maxnum is the number of function calls allowed before expiry
var redis_limiter_rolling = function(key, maxnum, exp, next) {
  redis.multi([
    ['incr', 'limiter:num:' + key],
    ['time']
  ]).exec(function(err, results) {
    if (err) {
      next(err);
    } else {
      // unique incremented list number for this key
      var listnum = results[0][1];
      // current time
      var tcur = (parseInt(results[1][1][0], 10) * 1000) + Math.floor(parseInt(results[1][1][1], 10) / 1000);
      // absolute time of expiry
      var texpiry = tcur - exp;
      // get number of transacation in the last expiry time
      var listkey = 'limiter:list:' + key;
      redis.multi([
        ['zadd', listkey, tcur.toString(), listnum],
        ['zremrangebyscore', listkey, '-inf', texpiry.toString()],
        ['zcard', listkey]
      ]).exec(function(err, results) {
        if (err) {
          next(err);
        } else {
          // num is the number of calls in the last expiry time window
          var num = parseInt(results[2][1], 10);
          if (num <= maxnum) {
            // does not reach limit
            next(null, false, num, exp);
          } else {
            // limit surpassed
            next(null, true, num, exp);
          }
        }
      });
    }
  });
};

// Lockout window rate limiter
//
// key is a unique identifier for the process or function call being limited
// exp is the expiry in milliseconds
// maxnum is the number of function calls allowed within expiry time
var util_limiter_lockout = function(key, maxnum, exp, next) {
  // lockout rate limiter
  var idkey = 'limiter:lock:' + key;
  redis.incr(idkey, function(err, result) {
    if (err) {
      next(err);
    } else {
      if (result <= maxnum) {
        // still within number of allowable calls
        // - reset expiry and allow next function call
        redis.expire(idkey, exp, function(err) {
          if (err) {
            next(err);
          } else {
            next(null, false, result);
          }
        });
      } else {
        // too many calls, user must wait for expiry of idkey
        next(null, true, result);
      }
    }
  });
};