using AsbCloudApp.Data;
using AsbCloudApp.Services;
using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace AsbCloudInfrastructure.Services
{
    /// <summary>
    /// Сервис выстраивает очередь из фоновых задач. Ограничивает количество одновременно выполняющихся задач.
    /// </summary>
    public class BackgroundWorkerService : IDisposable, IBackgroundWorkerService
    {
        private readonly Worker[] workers;
        private readonly Dictionary<string, Work> works = new Dictionary<string, Work>();
        private bool isRunning = false;
        private CancellationTokenSource cts;
        private Task task;

        public BackgroundWorkerService(IConfiguration configuration)
        {
            var workersCount = configuration.GetValue("BackgroundWorkersCount", 4);
            workers = new Worker[workersCount];
            for (int i = 0; i < workers.Length; i++)
                workers[i] = new Worker();
        }

        ~BackgroundWorkerService()
        {
            Dispose();
        }

        public string Enqueue(Func<string, CancellationToken, Task> func)
        {
            var work = new Work
            {
                ActionAsync = func
            };
            return Enqueue(work);
        }

        public string Enqueue(string id, Func<string, CancellationToken, Task> func)
        {
            var work = new Work(id, func);
            return Enqueue(work);
        }

        public string Enqueue(string id, Func<string, CancellationToken, Task> func, Func<string, Exception, CancellationToken, Task> onError)
        {
            var work = new Work(id, func)
            {
                OnErrorAsync = onError
            };
            return Enqueue(work);
        }

        string Enqueue(Work work)
        {
            works[work.Id] = work;
            if (!isRunning)
            {
                isRunning = true;
                cts = new CancellationTokenSource();
                task = Task.Run(() => ExecuteAsync(cts.Token), cts.Token);
            }
            return work.Id;
        }

        private Work Dequeue()
        {
            var item = works.First();
            works.Remove(item.Key);
            return item.Value;
        }

        public bool TryRemove(string id)
            => works.Remove(id);

        public bool Contains(string id)
            => works.ContainsKey(id);

        protected async Task ExecuteAsync(CancellationToken token)
        {
            while (works.Any() && !token.IsCancellationRequested)
            {
                var freeworker = workers.FirstOrDefault(w => !w.IsBusy);
                if (freeworker is not null)
                {
                    var work = Dequeue();
                    freeworker.Start(work);
                }
                else
                    await Task.Delay(10, token).ConfigureAwait(false);
            }
            isRunning = false;
        }

        public void Dispose()
        {
            cts?.Cancel();
            task?.Wait(1);
            task?.Dispose();
            cts?.Dispose();
            task = null;
            cts = null;
            GC.SuppressFinalize(this);
        }
    }

    class Worker : IDisposable
    {
        private CancellationTokenSource cts;
        private Task task;
        public bool IsBusy { get; private set; }

        ~Worker()
        {
            Dispose();
        }

        public void Dispose()
        {
            Stop();
            GC.SuppressFinalize(this);
        }

        public void Start(Work work)
        {
            IsBusy = true;
            cts = new CancellationTokenSource();
            task = Task.Run(async () =>
            {
                try
                {
                    var actionTask = work.ActionAsync(work.Id, cts.Token);                    
                    await actionTask.WaitAsync(TimeSpan.FromMinutes(2), cts.Token);
                }
                catch (Exception ex)
                {
                    Trace.TraceError(ex.Message);

                    if (work.OnErrorAsync is not null)
                    {
                        try
                        {
                            await work.OnErrorAsync(work.Id, ex, cts.Token).ConfigureAwait(false);
                        }
                        catch (Exception exOnErrorHandler)
                        {
                            Trace.TraceError(exOnErrorHandler.Message);
                        }
                    }
                }
                finally
                {
                    cts?.Dispose();
                    cts = null;
                    IsBusy = false;
                }
            }, cts.Token);
        }

        public void Stop()
        {
            cts?.Cancel();
            task?.Wait(1);
            task = null;
            cts?.Dispose();
            cts = null;
            IsBusy = false;
        }
    }
    class Work
    {
        public string Id { get; private set; }
        public Func<string, CancellationToken, Task> ActionAsync { get; set; }
        public Func<string, Exception, CancellationToken, Task> OnErrorAsync { get; set; }

        public Work()
        {
            Id = Guid.NewGuid().ToString();
        }

        public Work(string id, Func<string, CancellationToken, Task> actionAsync)
        {
            Id = id;
            ActionAsync = actionAsync;
        }
    }
}