using System;
using System.Threading;
using System.Collections.Generic;
using System.Linq;
using ln.logging;

namespace ln.threading
{
    public enum PoolThreadState { READY, WORKING, EXITED }
    public delegate void PoolJobFinished(Pool pool, PoolJob job);

    public enum PoolState
    {
        INITIALIZE,     // Pool Instanz erstellt
        RUN,            // Pool ist in Betrieb
        SHUTDOWN,       // Pool wird heruntergefahren (es warten noch laufende Jobs)
        STOPPED         // Pool wurde beendet, alle Resourcen freigegeben
    }

    public partial class Pool : IDisposable
    {
        public static bool DEBUG = false;

        public PoolState State { get; protected set; } = PoolState.INITIALIZE;

        public event PoolJobFinished PoolJobFinished;

        public PoolThread[] PoolThreads => ThreadHelpers.GetLockedValue(poolThreads, () => poolThreads.ToArray());

        public int PoolSize { get; }
        public int CurrentPoolSize => ThreadHelpers.GetLockedValue(poolThreads, () => poolThreads.Count);
        public PoolJob[] CurrentPoolJobs => ThreadHelpers.GetLockedValue(poolThreads, () => poolThreads.Select((t) => t.CurrentJob).Where((j) => j != null).ToArray());

        public PoolJob[] QueuedJobs => ThreadHelpers.GetLockedValue(waitingThreads, () => queuedJobs.ToArray());
        public int NumQueuedJobs => ThreadHelpers.GetLockedValue(waitingThreads, () => queuedJobs.Count);

        private List<PoolThread> poolThreads = new List<PoolThread>();

        protected HashSet<PoolThread> workingThreads = new HashSet<PoolThread>();
        protected HashSet<PoolThread> waitingThreads = new HashSet<PoolThread>();

        private Queue<PoolJob> queuedJobs = new Queue<PoolJob>();

        public Pool() : this(Environment.ProcessorCount){}
        public Pool(int numThreads)
        {
            PoolSize = numThreads;
        }

        public virtual void Start()
        {
            if ((State == PoolState.RUN) || (State == PoolState.SHUTDOWN))
                throw new NotSupportedException("Pool can only be started if not running");

            State = PoolState.RUN;

            for (int n = 0; n < PoolSize; n++)
            {
                CreatePoolThread();
            }
        }

        public virtual void Stop() => Stop(false);
        public virtual void Stop(bool abort)
        {
            if (State != PoolState.RUN)
                throw new NotSupportedException("Pool must be running to be able to stop");

            State = PoolState.SHUTDOWN;

            lock (waitingThreads)
            {
                queuedJobs.Clear();
            }

            if (abort)
                Abort();

            while (CurrentPoolSize > ((PoolThread.CurrentPoolThread.Value?.Pool == this) ? 1 : 0))
            {
                try
                {
                    lock (waitingThreads)
                        Monitor.PulseAll(waitingThreads);
                    Thread.Sleep(100);
                }
                catch (ThreadInterruptedException)
                { }
            }

            State = PoolState.STOPPED;
        }

        public void Enqueue(JobDelegate job) => Enqueue((poolJob) => job());
        public PoolJob Enqueue(ExtendedJobDelegate extendedJobDelegate) => Enqueue(extendedJobDelegate, "N/A");
        public PoolJob Enqueue(ExtendedJobDelegate extendedJobDelegate, string jobName) => EnqueuePoolJob(new PoolJob(jobName, extendedJobDelegate));
        public bool Enqueue(PoolJob poolJob) => EnqueuePoolJob(poolJob) != null;

        protected virtual PoolJob EnqueuePoolJob(PoolJob poolJob)
        {
            if (State != PoolState.RUN)
                throw new NotSupportedException("Pool not running");

            lock (waitingThreads)
            {
                if (queuedJobs.Contains(poolJob) || CurrentPoolJobs.Contains(poolJob))
                    return null;

                poolJob.Prepare();
                queuedJobs.Enqueue(poolJob);

                PulseWaitingThread();
            }

            return poolJob;
        }

        protected virtual void PulseWaitingThread()
        {
            lock (waitingThreads)
                Monitor.Pulse(waitingThreads);
        }

        public virtual int Enqueue(IEnumerable<PoolJob> poolJobs)
        {
            if (State != PoolState.RUN)
                throw new NotSupportedException("Pool not running");

            int count = 0;

            lock (waitingThreads)
            {
                HashSet<PoolJob> currentPoolJobs = new HashSet<PoolJob>(CurrentPoolJobs);
                foreach (PoolJob j in queuedJobs)
                    currentPoolJobs.Add(j);

                foreach (PoolJob poolJob in poolJobs)
                {
                    if (!currentPoolJobs.Contains(poolJob))
                    {
                        poolJob.Prepare();
                        queuedJobs.Enqueue(poolJob);
                        count++;
                    }
                }
                Monitor.PulseAll(waitingThreads);
            }

            return count;
        }

        protected virtual PoolJob Dequeue() => Dequeue(PoolThread.CurrentPoolThread?.Value);
        protected virtual PoolJob Dequeue(PoolThread poolThread)
        {
            if (poolThread == null)
                throw new NullReferenceException();

            if (State == PoolState.RUN)
            {
                lock (waitingThreads)
                {
                    if (queuedJobs.Count > 0)
                        return queuedJobs.Dequeue();
                }
            }
            return null;
        }

        protected virtual PoolJob WaitForJob(PoolThread poolThread)
        {
            while (State == PoolState.RUN)
            {
                lock (waitingThreads)
                {
                    PoolJob poolJob = Dequeue(poolThread);
                    if (poolJob != null)
                        return poolJob;

                    waitingThreads.Add(poolThread);
                    Monitor.Wait(waitingThreads);
                    waitingThreads.Remove(poolThread);
                }
            }
            return null;
        }


        protected virtual void WorkerThreadLoop()
        {
            PoolThread poolThread = PoolThread.CurrentPoolThread.Value;
            if (poolThread == null)
                throw new NotSupportedException("Pool.WorkerThreadLoop(): Must be called from PoolThread");

            lock (poolThreads)
                poolThreads.Add(poolThread);

            try
            {
                while (State == PoolState.RUN)
                {
                    PoolJob poolJob = WaitForJob(poolThread);
                    if (poolJob == null)
                    {
                        break;
                    }
                    else
                    {
                        lock (workingThreads)
                            workingThreads.Add(poolThread);

                        try
                        {
                            poolJob.Run(this);
                            if (PoolJobFinished != null)
                                PoolJobFinished(this,poolJob);
                        }
                        finally
                        {
                            lock (workingThreads)
                                workingThreads.Remove(poolThread);
                        }
                    }
                }
            }
            catch (PoolThreadMustExitException)
            {}
            catch (Exception e)
            {
                Logging.Log(e);
            }
            finally
            {
                lock (poolThreads)
                    poolThreads.Remove(poolThread);
            }
        }



        public void Abort()
        {
            lock (poolThreads)
            {
                foreach (PoolThread poolThread in poolThreads)
                    poolThread?.CurrentJob?.RequestAbort();
            }
        }

        private bool AmIPoolThread() => PoolThread.CurrentPoolThread.Value != null;

        public PoolThread FindPoolThread(PoolJob job)
        {
            lock (poolThreads)
            {
                foreach (PoolThread poolThread in poolThreads)
                {
                    if (poolThread.CurrentJob == job)
                        return poolThread;
                }
            }
            return null;
        }



        protected virtual PoolThread CreatePoolThread()
        {
            PoolThread poolThread = new PoolThread(WorkerThreadLoop);
            return poolThread;
        }

        public void Dispose()
        {
            if (State == PoolState.RUN)
                Stop();
        }
    }
}