using System;
using System.Threading;
using MediaBrowser.Model.Tasks;
using Microsoft.Extensions.Logging;

namespace Emby.Server.Implementations.ScheduledTasks.Triggers;

/// <summary>
/// Represents a task trigger that fires on a weekly basis.
/// </summary>
public sealed class WeeklyTrigger : ITaskTrigger, IDisposable
{
    private readonly TimeSpan _timeOfDay;
    private readonly DayOfWeek _dayOfWeek;
    private Timer? _timer;
    private bool _disposed;

    /// <summary>
    /// Initializes a new instance of the <see cref="WeeklyTrigger"/> class.
    /// </summary>
    /// <param name="timeOfDay">The time of day to trigger the task to run.</param>
    /// <param name="dayOfWeek">The day of week.</param>
    /// <param name="taskOptions">The options of this task.</param>
    public WeeklyTrigger(TimeSpan timeOfDay, DayOfWeek dayOfWeek, TaskOptions taskOptions)
    {
        _timeOfDay = timeOfDay;
        _dayOfWeek = dayOfWeek;
        TaskOptions = taskOptions;
    }

    /// <inheritdoc />
    public event EventHandler<EventArgs>? Triggered;

    /// <inheritdoc />
    public TaskOptions TaskOptions { get; }

    /// <inheritdoc />
    public void Start(TaskResult? lastResult, ILogger logger, string taskName, bool isApplicationStartup)
    {
        DisposeTimer();

        var triggerDate = GetNextTriggerDateTime();

        _timer = new Timer(_ => OnTriggered(), null, triggerDate - DateTime.Now, TimeSpan.FromMilliseconds(-1));
    }

    /// <summary>
    /// Gets the next trigger date time.
    /// </summary>
    /// <returns>DateTime.</returns>
    private DateTime GetNextTriggerDateTime()
    {
        var now = DateTime.Now;

        // If it's on the same day
        if (now.DayOfWeek == _dayOfWeek)
        {
            // It's either later today, or a week from now
            return now.TimeOfDay < _timeOfDay ? now.Date.Add(_timeOfDay) : now.Date.AddDays(7).Add(_timeOfDay);
        }

        var triggerDate = now.Date;

        // Walk the date forward until we get to the trigger day
        while (triggerDate.DayOfWeek != _dayOfWeek)
        {
            triggerDate = triggerDate.AddDays(1);
        }

        // Return the trigger date plus the time offset
        return triggerDate.Add(_timeOfDay);
    }

    /// <inheritdoc />
    public void Stop()
    {
        DisposeTimer();
    }

    /// <summary>
    /// Disposes the timer.
    /// </summary>
    private void DisposeTimer()
    {
        _timer?.Dispose();
        _timer = null;
    }

    /// <summary>
    /// Called when [triggered].
    /// </summary>
    private void OnTriggered()
    {
        Triggered?.Invoke(this, EventArgs.Empty);
    }

    /// <inheritdoc />
    public void Dispose()
    {
        if (_disposed)
        {
            return;
        }

        DisposeTimer();

        _disposed = true;
    }
}