//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="PipeLineRunner"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. All rights reserved.
//     
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//     
// -----------------------------------------------------------------------
// -----------------------------------------------------------------------
using StgSharp.Threading;

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

using System.Threading.Tasks;

namespace StgSharp.PipeLine
{
    public static class PipeLineRunner
    {

        private static NodeRunner[] allAvailableTask = CreateBlueprintRunnerArray();
        private static CancellationTokenSource cts = new CancellationTokenSource();
        private static ConcurrentStack<PipelineScheduler> pipelineInWaiting 
            = new ConcurrentStack<PipelineScheduler>();
        private static int _callingThread;
        private static SemaphoreSlim pipelineLock = new SemaphoreSlim(0, 1);

        public static void Run(PipelineScheduler pipeline)
        {
            // Console.WriteLine();
            if (pipeline == null)
            {
                return;
            }
            if (pipeline.IsRunning) {
                throw new InvalidOperationException("Attempt to run a blueprint instance twice.");
            }
            if (!IsValidCalling()) {
                pipelineLock.Wait();
            }
            if (InterruptAndRunNewPipeline(pipeline))
            {
                while (InterruptAndRunNewPipeline(NodeRunner.CurrentPipeline!)) { }
            }
            pipelineLock.Release();
            Interlocked.Exchange(ref _callingThread, -1);
        }

        public static void SetMaxTaskCount(int size)
        {
            if (size < 1) {
                size = 1;
            }
            if (allAvailableTask.Length >= size)
            {
                for (int i = size; i < allAvailableTask.Length; i++)
                {
                    if (allAvailableTask[i] != null) {
                        allAvailableTask[i].Cancel();
                    }
                }
            }
            Array.Resize(ref allAvailableTask, size);
        }

        public static void Terminate()
        {
            cts.Cancel();
            if (NodeRunner.CurrentPipeline is null) {
                return;
            }
            NodeRunner.CurrentPipeline.Terminate();
            foreach (NodeRunner task in allAvailableTask) {
                task.Cts.Cancel();
            }
            foreach (PipelineScheduler bp in pipelineInWaiting) {
                bp.Terminate();
            }
            pipelineInWaiting.Clear();
        }

        internal static bool InterruptAndRunNewPipeline(PipelineScheduler newPipeline)
        {
            ArgumentNullException.ThrowIfNull(newPipeline);
            if ((newPipeline != NodeRunner.CurrentPipeline) && (NodeRunner.CurrentPipeline != null))
            {
                // if a running bp exists
                pipelineInWaiting.Push(NodeRunner.CurrentPipeline);
            }

            // load new bp to current bp
            NodeRunner.CurrentPipeline = newPipeline;
            Interlocked.Exchange(ref _callingThread, Environment.CurrentManagedThreadId);

            // run beginning node to init it first.
            if (!NodeRunner.CurrentPipeline.IsRunning)
            {
                (NodeRunner.CurrentPipeline.BeginLayer as BeginningNode)!.Run();
            }

            // refresh all tasks
            /*
            for( int i = 0; i < allAvailableTask.Length; i++ )
            {
                NodeRunner item = allAvailableTask[ i ];
                if( ( item is null ) || item.IsCompleted ) {
                    allAvailableTask[ i ] = NodeRunner.Run();
                }
            }
            /**/
            PipelineNode node;
            while (!cts.Token.IsCancellationRequested && NodeRunner.CurrentPipeline.RequestNextMainThreadNode(out node))
            {
                node.Run();
                if (!NodeRunner.CurrentPipeline.IsRunning)
                {
                    break;
                }
            }

            while ((NodeRunner.CurrentPipeline != null) &&
                   NodeRunner.CurrentPipeline.IsRunning &&
                   !cts.Token.IsCancellationRequested &&
                   NodeRunner.CurrentPipeline!.RequestNexConcurrentNode(out node))
            {
                node.Run();
                if (!NodeRunner.CurrentPipeline!.IsRunning)
                {
                    break;
                }
            }
            (NodeRunner.CurrentPipeline!.EndLayer as EndingNode)!.Run();
            bool isEmpty = pipelineInWaiting.TryPop(out PipelineScheduler? pipeline);
            NodeRunner.CurrentPipeline = pipeline!;
            return isEmpty;
        }

        /// <summary>
        ///   <para> Only the following occasions of calling are valid: </para> <para> 1. no bp is
        ///   running or the only bp is quitting. </para><para> 2. calling from the main thread or a
        ///   thread the current bp is running on.</para>
        /// </summary>
        internal static bool IsValidCalling()
        {
            if ((NodeRunner.CurrentPipeline == null) || //no bp running at all
                ((pipelineInWaiting.IsEmpty) && (NodeRunner.CurrentPipeline.IsRunning == false)))
            {
                // a bp is quitting
                // in case no bp is running
                return true;
            }
            int? id = Task.CurrentId;
            if (id is null)
            {
                // in case calling from main thread and current running bp
                return _callingThread == Environment.CurrentManagedThreadId;
            }
            foreach (NodeRunner item in allAvailableTask)
            {
                if (item.Id == id)
                {
                    // if calling from any bp running task
                    return true;
                }
            }
            return false;
        }

        private static NodeRunner[] CreateBlueprintRunnerArray()
        {
            int count = Environment.ProcessorCount;
            return new NodeRunner[ count < 2 ? count : count - 2];
        }

    }

    internal class NodeRunner : CancellableTask
    {

        private static volatile PipelineScheduler? _current;

        internal NodeRunner()
            : base()
        {
            _startup = InternalRun;
        }

        internal static PipelineScheduler? CurrentPipeline
        {
            get => _current;
            set => _current = value;
        }

        internal static NodeRunner Run()
        {
            NodeRunner ret = new NodeRunner
            {
                _startup = InternalRun
            };
            ret._internalTask = Task.Run(ret.InternalAction);
            return ret;
        }

        private static void InternalRun(CancellationToken token)
        {
            PipelineNode item;
            Console.WriteLine($"Global thread {Environment.CurrentManagedThreadId} starts.");
            while ((CurrentPipeline != null) &&
                   CurrentPipeline.IsRunning &&
                   !token.IsCancellationRequested &&
                   CurrentPipeline.RequestNexConcurrentNode(out item)) {
                item.Run();
            }
        }

    }//------------------------------------- End of Class ------------------------------------------
}