using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SafeMobileLib.Modules
{
    public class AppServerMonitoring
    {
        public static int APP_SERVER_HEARTBEAT_SEC = 5;
#if DEBUG
        public int MISSED_INTERVALS = 240;
#else
        public int MISSED_INTERVALS = 24;
#endif
        // thread to check at periodic time 
        private Thread monitoringThread;
        // flag that the monitoring should be running or not
        private bool isRunning = false;
        private bool isUnreachable = false;


        private DateTime _lastAppServerHeartbeat;
        public DateTime lastAppServerHeartbeat
        {
            get { return _lastAppServerHeartbeat; }
            set { _lastAppServerHeartbeat = value; }
        }
       
        public AppServerMonitoring()
        {
            _lastAppServerHeartbeat = new DateTime(0);
        }

        public void NewHeartBeatReceived()
        {

            if (isUnreachable)
            {
                isUnreachable = false;
                OnAppServerReacheableAgain?.Invoke();
            }
            // set the last app server heartbeat to now
            lastAppServerHeartbeat = DateTime.Now;
        }


        /// <summary>
        /// Start the thread which will manage the monitoring of the usb device plug & unplug
        /// </summary>
        public void StartAppServerMonitoring()
        {
            if (this.isRunning)
                return;

            this.isRunning = true;
            monitoringThread = new Thread(new ThreadStart(MonitoringThreadHandler));
            monitoringThread.Start();
        }

        /// <summary>
        /// Stop the thread which is monitoring the detection of application server is on or off
        /// </summary>
        public void StopMonitoring()
        {
            this.isRunning = false;
        }


         /// <summary>
        /// Thread function
        /// </summary>
        private void MonitoringThreadHandler()
        {
            int count = -1;
            while (isRunning)
            {
                // wait until checking again
                Thread.Sleep(500);

                // trigger event if more than two interval are missed and it at least one App Server heartbeat was received
                if(lastAppServerHeartbeat.Year > 2015 &&
                    (new TimeSpan(DateTime.Now.Ticks - lastAppServerHeartbeat.Ticks)).TotalSeconds > APP_SERVER_HEARTBEAT_SEC * MISSED_INTERVALS
                    && !isUnreachable)
                {
                    isUnreachable = true;
                    OnAppServerUnreacheable?.Invoke();
                }
                    
            }
        }

        public delegate void AppServerUnreacheable();
        public event AppServerUnreacheable OnAppServerUnreacheable;

        public delegate void AppServerReacheableAgain();
        public event AppServerReacheableAgain OnAppServerReacheableAgain;

    }
}