using System;
using System.Security.Principal;
using System.Collections;
using System.Threading;
using log4net;

namespace Novell.Zenworks.Zmd {

    internal class PoolLog {

        private static readonly ILog log = LogManager.GetLogger (typeof (ZenThread));

        public static void Debug (string msg, params object[] args) {
            if (Environment.GetEnvironmentVariable ("ZMD_THREAD_POOL_DEBUG") == null)
                return;

            log.Info (String.Format (msg, args));
        }
    }

    internal struct ThreadInfo {
        public ThreadStart ThreadStart;
        public IPrincipal Principal;

        public WaitCallback WaitCallback;
        public object UserData;

        public static ThreadInfo Zero {
            get { return new ThreadInfo (); }
        }
    }

    internal class ZenThread {

        private static readonly ILog log = LogManager.GetLogger (typeof (ZenThread));

        private static int nextId = 500;
        
        private Thread thread;
        private ThreadInfo tinfo;
        private bool running;
        private DateTime finishTime = DateTime.MinValue;
        private int id;
        
        public event EventHandler Finished;

        public int Id {
            get { return id; }
        }
        
        public DateTime FinishTime {
            get { return finishTime; }
        }

        public ZenThread () {
            id = nextId++;
            running = true;
            thread = new Thread (new ThreadStart (WorkerLoop));
            thread.IsBackground = true;
            thread.Start ();
        }

        public void RunThread (ThreadInfo tinfo) {
            lock (this) {
                PoolLog.Debug ("Thread {0}: got new worker", id);
                this.tinfo = tinfo;
                Monitor.Pulse (this);
            }
        }

        public void Stop () {
            lock (this) {
                PoolLog.Debug ("Thread {0}: stopping", id);
                running = false;
                Monitor.Pulse (this);
            }
        }

        private void WorkerLoop () {
            while (running) {
                lock (this) {
                    if (tinfo.Equals (ThreadInfo.Zero)) {
                        PoolLog.Debug ("Thread {0}: waiting on job...", id);
                        Monitor.Wait (this);
                    }

                    if (!running) {
                        PoolLog.Debug ("Thread {0}: terminating", id);
                        break;
                    }

                    // set the principal
                    if (tinfo.Principal != null) {
                        Thread.CurrentPrincipal = tinfo.Principal;
                    }

                    try {
                        PoolLog.Debug ("Thread {0}: running job...", id);
                        if (tinfo.ThreadStart != null) {
                            tinfo.ThreadStart ();
                        } else {
                            tinfo.WaitCallback (tinfo.UserData);
                        }
                    } catch (Exception e) {
                        log.Info ("Unhandled exception: " + e);
                    } finally {
                        PoolLog.Debug ("Thread {0}: job finished", id);
                        tinfo = ThreadInfo.Zero;
                        finishTime = DateTime.Now;

                        if (Finished != null)
                            Finished (this, new EventArgs ());
                    }
                }
            }
        }
    }
    
    public class ZenThreadPool {

        private static TimeSpan ThreadTimeout = TimeSpan.FromMinutes (10);

        private ArrayList readyThreads = new ArrayList ();
        private ArrayList activeThreads = new ArrayList ();
        
        private Queue queue = new Queue ();
        private int max = 50;
        private int min = 3;
        
        private static ZenThreadPool sharedPool;

        public static ZenThreadPool SharedPool {
            get {
                lock (typeof (ZenThreadPool)) {
                    if (sharedPool == null)
                        sharedPool = new ZenThreadPool ();

                    return sharedPool;
                }
            }
        }

        public int MaxThreads {
            get { return max; }
            set { max = value; }
        }

        public int MinThreads {
            get { return min; }
            set { min = value; }
        }

        private int TotalThreads {
            get {
                lock (readyThreads) {
                    return readyThreads.Count + activeThreads.Count;
                }
            }
        }

        public ZenThreadPool () : this (3, 50) {
        }

        public ZenThreadPool (int min, int max) {
            this.min = min;
            this.max = max;

            for (int i = 0; i < min; i++) {
                AddThread (ThreadInfo.Zero);
            }
        }

        private void AddThread (ThreadInfo tinfo) {
            lock (readyThreads) {
                ZenThread thread = new ZenThread ();

                PoolLog.Debug ("Added a new thread ({0}), total count is {1}", thread.Id, (TotalThreads + 1));
                
                thread.Finished += OnThreadFinished;

                if (!tinfo.Equals (ThreadInfo.Zero)) {
                    activeThreads.Add (thread);
                    thread.RunThread (tinfo);
                } else {
                    readyThreads.Add (thread);
                }
            }
        }

        private void OnThreadFinished (object o, EventArgs args) {
            lock (readyThreads) {
                ZenThread thread = (ZenThread) o;

                if (queue.Count == 0) {
                    activeThreads.Remove (thread);
                    readyThreads.Add (thread);
                    return;
                }

                PoolLog.Debug ("Dequeuing job...");
                ThreadInfo tinfo = (ThreadInfo) queue.Dequeue ();
                thread.RunThread (tinfo);
            }
        }

        public void RunThread (WaitCallback cb) {
            RunThread (cb, null);
        }

        public void RunThread (WaitCallback cb, object data) {
            RunThread (cb, data, null);
        }

        public void RunThread (WaitCallback cb, object data, IPrincipal principal) {
            ThreadInfo tinfo = new ThreadInfo ();
            tinfo.WaitCallback = cb;
            tinfo.UserData = data;
            tinfo.Principal = principal;

            RunThread (tinfo);
        }

        public void RunThread (ThreadStart start) {
            RunThread (start, Thread.CurrentPrincipal);
        }

        public void RunThread (ThreadStart start, IPrincipal principal) {
            ThreadInfo tinfo = new ThreadInfo ();
            tinfo.ThreadStart = start;
            tinfo.Principal = principal;

            RunThread (tinfo);
        }

        private void RunThread (ThreadInfo tinfo) {
            lock (readyThreads) {

                CleanupThreads ();

                // find an unused thread if possible
                if (readyThreads.Count > 0) {
                    ZenThread thread = (ZenThread) readyThreads[0];
                    readyThreads.Remove (thread);
                    activeThreads.Add (thread);
                    
                    PoolLog.Debug ("Running job in inactive thread {0}", thread.Id);
                    thread.RunThread (tinfo);
                    return;
                }

                // no free threads, see if we can create a new one
                if (TotalThreads < max) {
                    PoolLog.Debug ("Running job on new thread");
                    AddThread (tinfo);
                    return;
                }

                PoolLog.Debug ("Queueing new job");
                // can't create a new one, queue it up
                queue.Enqueue (tinfo);
            }
        }

        private void CleanupThreads () {
            lock (readyThreads) {
                
                foreach (ZenThread thread in readyThreads.ToArray (typeof (ZenThread))) {
                    if (TotalThreads == min)
                        break;
                    
                    if (DateTime.Now - thread.FinishTime > ThreadTimeout || TotalThreads > max) {

                        PoolLog.Debug ("Stopping thread {0}", thread.Id);
                        thread.Stop ();
                        readyThreads.Remove (thread);
                    }
                }
            }
        }
    }
}