using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace AsbCloudInfrastructure.Background;

/// <summary>
/// Сервис для фонового выполнения периодической работы
/// </summary>
public class PeriodicBackgroundWorker : BackgroundService
{
    private readonly TimeSpan executePeriod = TimeSpan.FromSeconds(10);
    private readonly TimeSpan minDelay = TimeSpan.FromSeconds(1);
    private readonly IServiceProvider serviceProvider;
    private readonly List<WorkPeriodic> works = new(8);
    private bool isRuning = false;

    /// <summary>
    /// Список периодических работ
    /// </summary>
    public IEnumerable<WorkPeriodic> Works => works;

    /// <summary>
    /// Работа выполняемая в данный момент
    /// </summary>
    public Work? CurrentWork;

    /// <summary>
    /// Ошибка в главном цикле, никогда не должна появляться
    /// </summary>
    public string MainLoopLastException { get; private set; } = string.Empty;

    public PeriodicBackgroundWorker(IServiceProvider serviceProvider)
    {
        this.serviceProvider = serviceProvider;
    }

    protected override async Task ExecuteAsync(CancellationToken token)
    {
        if (isRuning)
            return;
        isRuning = true;
        Trace.TraceInformation($"{GetType().Name} started");
        while (!token.IsCancellationRequested)
        {
            try
            {
                var periodicWork = GetNext();
                if (periodicWork is null)
                {
                    await Task.Delay(executePeriod, token);
                    continue;
                }

                CurrentWork = periodicWork.Work;
                
                using var scope = serviceProvider.CreateScope();
                
                var result = await periodicWork.Work.Start(scope.ServiceProvider, token);

                CurrentWork = null;
                await Task.Delay(minDelay, token);
            }
            catch (Exception ex)
            {
                MainLoopLastException = $"BackgroundWorker " +
                    $"MainLoopLastException: \r\n" +
                    $"date: {DateTime.Now:O}\r\n" +
                    $"message: {ex.Message}\r\n" +
                    $"inner: {ex.InnerException?.Message}\r\n" +
                    $"stackTrace: {ex.StackTrace}";
                Trace.TraceError(MainLoopLastException);
            }
        }
        isRuning = false;
    }

    /// <summary>
    /// Добавить фоновую работу выполняющуюся с заданным периодом
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="period"></param>
    public void Add<T>(TimeSpan period)
        where T : Work, new()
    {
        var work = new T();
        Add(work, period);
    }

    /// <summary>
    /// Добавить фоновую работу выполняющуюся с заданным периодом
    /// </summary>
    /// <param name="work"></param>
    /// <param name="period"></param>
    public void Add(Work work, TimeSpan period)
    {
        var periodic = new WorkPeriodic(work, period);
        works.Add(periodic);
        if (ExecuteTask is null || ExecuteTask.IsCompleted)
            StartAsync(CancellationToken.None);
    }

    private WorkPeriodic? GetNext()
    {
        var work = works
            .OrderBy(w => w.NextStart)
            .FirstOrDefault();

        if (work is null || work.NextStart > DateTime.Now)
            return null;

        return work;
    }
}