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

namespace Implab.Parallels {
    public class WorkerPool : DispatchPool<Action> {

        MTQueue<Action> m_queue = new MTQueue<Action>();
        int m_queueLength = 0;
        readonly int m_threshold = 1;

        public WorkerPool(int minThreads, int maxThreads, int threshold)
            : base(minThreads, maxThreads) {
            m_threshold = threshold;
            InitPool();
        }

        public WorkerPool(int minThreads, int maxThreads) :
            base(minThreads, maxThreads) {
            InitPool();
        }

        public WorkerPool(int threads)
            : base(threads) {
            InitPool();
        }

        public WorkerPool()
            : base() {
            InitPool();
        }

        public Promise<T> Invoke<T>(Func<T> task) {
            if (task == null)
                throw new ArgumentNullException("task");
            if (IsDisposed)
                throw new ObjectDisposedException(ToString());

            var promise = new Promise<T>();

            EnqueueTask(delegate() {
                try {
                    promise.Resolve(task());
                } catch (Exception e) {
                    promise.Reject(e);
                }
            });

            return promise;
        }

        protected void EnqueueTask(Action unit) {
            Debug.Assert(unit != null);
            var len = Interlocked.Increment(ref m_queueLength);
            m_queue.Enqueue(unit);

            ExtendPool();
        }

        protected override bool ExtendPool() {
            if (m_queueLength <= m_threshold*ActiveThreads)
                // in this case we are in active thread and it request for additional workers
                // satisfy it only when queue is longer than threshold
                return false;
            return base.ExtendPool();
        }

        protected override bool TryDequeue(out Action unit) {
            if (m_queue.TryDequeue(out unit)) {
                Interlocked.Decrement(ref m_queueLength);
                return true;
            }
            return false;
        }

        protected override void InvokeUnit(Action unit) {
            unit();
        }

        protected override bool Suspend() {
            if (m_queueLength == 0)
                return base.Suspend();
            else
                return true; // spin again without locks...
        }
    }
}