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.Logic
{
    public static class BlueprintRunner
    {
        private static ConcurrentStack<Blueprint> blueprintInWaiting = new ConcurrentStack<Blueprint>();
        private static NodeRunner[] allAvailableTask = new NodeRunner[1]; 
        private static ReaderWriterLockSlim bpLock = new ReaderWriterLockSlim();
        private static CancellationTokenSource cts = new CancellationTokenSource();

        public static void Run(Blueprint blueprint, Func<bool> terminateInstructor)
        {
            //Console.WriteLine();
            if (blueprint == null) return;
            if (terminateInstructor == null)
            {
                throw new ArgumentNullException(nameof(terminateInstructor));
            }
            if (blueprint.IsRunning)
            {
                throw new InvalidOperationException( $"Attempt to run a blueprint twice." );
            }
            blueprint.ShouldClose = terminateInstructor;
            if (IsInternalCalling)
            {
                if(InterruptAndRunNewBp(blueprint))
                    do { } while(InterruptAndRunNewBp(NodeRunner.CurrentBlueprint));
            }
            else
            {
                if (!bpLock.IsWriteLockHeld)
                {
                    bpLock.EnterWriteLock();
                }
                if (InterruptAndRunNewBp(blueprint))
                    do { } while (InterruptAndRunNewBp(NodeRunner.CurrentBlueprint));
                bpLock.ExitWriteLock();
            }
        }

        internal static bool IsInternalCalling
        {
            get 
            {
                int? id = Task.CurrentId;
                if (id is null) return false;
                foreach (var item in allAvailableTask)
                {
                    if (item.Id == id)
                    {
                        return true;
                    }
                }
                return false;
            }
        }

        internal static bool InterruptAndRunNewBp(Blueprint newBp)
        {
            Debug.Assert(newBp != null);
            if (newBp != NodeRunner.CurrentBlueprint && NodeRunner.CurrentBlueprint != null)
            {
                blueprintInWaiting.Push(NodeRunner.CurrentBlueprint);
            }
            Interlocked.Exchange(ref NodeRunner.CurrentBlueprint!, newBp);
            if (!NodeRunner.CurrentBlueprint.IsRunning)
            {
                (NodeRunner.CurrentBlueprint.BeginLayer as BeginningNode)!.Run();
            }
            for (int i = 0; i < allAvailableTask.Length; i++)
            {
                var item = allAvailableTask[i];
                if (item is null || item.IsCompleted)
                {
                    allAvailableTask[i] = NodeRunner.Run();
                }
            }
            BlueprintNode node;
            while (!cts.Token.IsCancellationRequested
                && NodeRunner.CurrentBlueprint.RequestNextNativeNode(out node)) 
            {
                node.Run();
                if (!NodeRunner.CurrentBlueprint.IsRunning)
                {
                    break;
                }
            }
            (NodeRunner.CurrentBlueprint.EndLayer as EndingNode)!.Run();
            return blueprintInWaiting.TryPeek(out NodeRunner.CurrentBlueprint);
        }


        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();
            NodeRunner.CurrentBlueprint.Terminate();
            foreach (var task in allAvailableTask)
            {
                task.Cts.Cancel();
            }
            foreach (var bp in blueprintInWaiting)
            {
                bp.Terminate();
            }
            blueprintInWaiting.Clear();
        }

    }

    internal class NodeRunner: CancellableTask
    {
        private static Blueprint _current;

        internal static ref Blueprint CurrentBlueprint 
        {
            get => ref _current;
        }

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

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

        private static void InternalRun(CancellationToken token)
        {
            //Console.WriteLine("Task Begin");
            BlueprintNode item;
            while (CurrentBlueprint != null && CurrentBlueprint.IsRunning && !token.IsCancellationRequested
                && CurrentBlueprint.RequestNexGlobalNode(out item))
            {
                //Console.WriteLine($"Get node of {item.Name}, going to run.");
                item.Run();
            }
            //Console.WriteLine("Task Completed");
        }
    }//------------------------------------- End of Class ------------------------------------------
}