using Cronos;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Mirea.Api.Endpoint.Common.Services;
using Mirea.Api.Endpoint.Configuration.Model;
using Mirea.Api.Endpoint.Configuration.Model.GeneralSettings;
using Mirea.Api.Endpoint.Sync;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace Mirea.Api.Endpoint.Configuration.Core.BackgroundTasks;

public class ScheduleSyncService : IHostedService, IDisposable
{
    private Timer? _timer;
    private string _cronUpdate;
    private List<ScheduleSettings.CronUpdateSkip> _cronUpdateSkip;
    private readonly ILogger<ScheduleSyncService> _logger;
    private CancellationTokenSource _cancellationTokenSource = new();
    private readonly IServiceProvider _serviceProvider;
    private readonly IDisposable? _onChangeUpdateCron;

    public ScheduleSyncService(IOptionsMonitor<GeneralConfig> generalConfigMonitor, ILogger<ScheduleSyncService> logger, IServiceProvider serviceProvider)
    {
        _logger = logger;
        _serviceProvider = serviceProvider;
        _cronUpdate = generalConfigMonitor.CurrentValue.ScheduleSettings!.CronUpdateSchedule;
        _cronUpdateSkip = generalConfigMonitor.CurrentValue.ScheduleSettings!.CronUpdateSkipDateList;

        ScheduleSyncManager.OnForceSyncRequested += OnForceSyncRequested;
        _onChangeUpdateCron = generalConfigMonitor.OnChange((config) =>
        {
            var updated = false;
            if (config.ScheduleSettings?.CronUpdateSchedule != null && _cronUpdate != config.ScheduleSettings.CronUpdateSchedule)
            {
                _cronUpdate = config.ScheduleSettings.CronUpdateSchedule;
                updated = true;
            }

            if (config.ScheduleSettings?.CronUpdateSkipDateList != null && !config.ScheduleSettings.CronUpdateSkipDateList.SequenceEqual(_cronUpdateSkip))
            {
                _cronUpdateSkip = config.ScheduleSettings.CronUpdateSkipDateList
                    .OrderBy(x => x.End ?? x.Date)
                    .ToList();
                updated = true;
            }

            if (updated)
                OnUpdateIntervalRequested();
        });
    }

    private void OnForceSyncRequested()
    {
        _logger.LogInformation("It was requested to synchronize the data immediately.");
        StopAsync(CancellationToken.None).ContinueWith(_ =>
        {
            _cancellationTokenSource = new CancellationTokenSource();
            ExecuteTask(null);
        });
    }

    private void OnUpdateIntervalRequested()
    {
        _logger.LogInformation("It was requested to update the time interval immediately.");
        StopAsync(CancellationToken.None).ContinueWith(_ =>
        {
            StartAsync(CancellationToken.None);
        });
    }

    private void ScheduleNextRun()
    {
        if (string.IsNullOrEmpty(_cronUpdate))
        {
            _logger.LogWarning("Cron expression is not set. The scheduled task will not run.");
            return;
        }

        var expression = CronExpression.Parse(_cronUpdate);

        var nextRunTime = _cronUpdateSkip.GetNextTask(expression).FirstOrDefault();

        if (nextRunTime == default)
        {
            _logger.LogWarning("No next run time found. The task will not be scheduled. Timezone: {TimeZone}",
                TimeZoneInfo.Local.DisplayName);
            return;
        }

        _logger.LogInformation("Next task run in {Time}", nextRunTime.ToString("G"));

        var delay = (nextRunTime - DateTimeOffset.Now).TotalMilliseconds;

        // The chance is small, but it's better to check
        if (delay <= 0)
            delay = 1;

        _cancellationTokenSource = new CancellationTokenSource();
        _timer = new Timer(ExecuteTask, null, delay > int.MaxValue ? int.MaxValue : (int)delay, Timeout.Infinite);
    }

    private async void ExecuteTask(object? state)
    {
        try
        {
            using var scope = _serviceProvider.CreateScope();
            var syncService = ActivatorUtilities.GetServiceOrCreateInstance<ScheduleSynchronizer>(scope.ServiceProvider);
            await syncService.StartSync(_cancellationTokenSource.Token);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error occurred during schedule synchronization.");
        }
        finally
        {
            ScheduleNextRun();
        }
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        ScheduleNextRun();
        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _cancellationTokenSource.Cancel();
        _timer?.Change(Timeout.Infinite, 0);
        return Task.CompletedTask;
    }

    public void Dispose()
    {
        StopAsync(CancellationToken.None).GetAwaiter().GetResult();
        _timer?.Dispose();
        ScheduleSyncManager.OnForceSyncRequested -= OnForceSyncRequested;
        _onChangeUpdateCron?.Dispose();
        _cancellationTokenSource.Dispose();

        GC.SuppressFinalize(this);
    }
}