Lua script analysis of Laravel delay queue implementation

    /**
     * Get the Lua script for computing the size of queue.
     *
     * KEYS[1] - The name of the primary queue
     * KEYS[2] - The name of the "delayed" queue
     * KEYS[3] - The name of the "reserved" queue
     *
     * @return string
     */
    public static function size()
    {
        return <<<&#39;LUA&#39;
             return redis.call(&#39;llen&#39;, KEYS[1]) + redis.call(&#39;zcard&#39;, KEYS[2]) + 
             redis.call(&#39;zcard&#39;, KEYS[3])
        LUA;
    }

    /**
     * Get the Lua script for popping the next job off of the queue.
     *
     * KEYS[1] - The queue to pop jobs from, for example: queues:foo
     * KEYS[2] - The queue to place reserved jobs on, for example: queues:foo:reserved
     * ARGV[1] - The time at which the reserved job will expire
     *
     * @return string
     */
    public static function pop()
    {
      return <<<&#39;LUA&#39;
          -- Pop the first job off of the queue...
         local job = redis.call(&#39;lpop&#39;, KEYS[1])
         local reserved = false

         if(job ~= false) then
            -- Increment the attempt count and place job on the reserved queue...
            reserved = cjson.decode(job)
            reserved[&#39;attempts&#39;] = reserved[&#39;attempts&#39;] + 1
            reserved = cjson.encode(reserved)
            redis.call(&#39;zadd&#39;, KEYS[2], ARGV[1], reserved)
         end
        return {job, reserved}
      LUA;
    }

    /**
     * Get the Lua script for releasing reserved jobs.
     *
     * KEYS[1] - The "delayed" queue we release jobs onto, for example: queues:foo:delayed
     * KEYS[2] - The queue the jobs are currently on, for example: queues:foo:reserved
     * ARGV[1] - The raw payload of the job to add to the "delayed" queue
     * ARGV[2] - The UNIX timestamp at which the job should become available
     *
     * @return string
     */
    public static function release()
    {
        return <<<&#39;LUA&#39;
           -- Remove the job from the current queue...
           redis.call(&#39;zrem&#39;, KEYS[2], ARGV[1])
           -- Add the job onto the "delayed" queue...
           redis.call(&#39;zadd&#39;, KEYS[1], ARGV[2], ARGV[1])
           return true
        LUA;
    }

    /**
     * Get the Lua script to migrate expired jobs back onto the queue.
     *
     * KEYS[1] - The queue we are removing jobs from, for example: queues:foo:reserved
     * KEYS[2] - The queue we are moving jobs to, for example: queues:foo
     * ARGV[1] - The current UNIX timestamp
     *
     * @return string
     */
    public static function migrateExpiredJobs()
    {
        return <<<&#39;LUA&#39;
        -- Get all of the jobs with an expired "score"...
           local val = redis.call(&#39;zrangebyscore&#39;, KEYS[1], &#39;-inf&#39;, ARGV[1])

        -- If we have values in the array, we will remove them from the first queue
        -- and add them onto the destination queue in chunks of 100, which moves
        -- all of the appropriate jobs onto the destination queue very safely.
           if(next(val) ~= nil) then
             redis.call(&#39;zremrangebyrank&#39;, KEYS[1], 0, #val - 1)

             for i = 1, #val, 100 do
               redis.call(&#39;rpush&#39;, KEYS[2], unpack(val, i, math.min(i+99, #val)))
             end
           end
          return val
        LUA;
}