using System;
using System.Threading;

namespace Swan.Threading {
  /// <summary>
  /// Provides a Manual Reset Event factory with a unified API.
  /// </summary>
  /// <example>
  /// The following example shows how to use the WaitEventFactory class.
  /// <code>
  /// using Swan.Threading;
  /// 
  /// public class Example
  /// {
  ///     // create a WaitEvent using the slim version
  ///     private static readonly IWaitEvent waitEvent = WaitEventFactory.CreateSlim(false);
  ///     
  ///     public static void Main()
  ///     {
  ///         Task.Factory.StartNew(() =>
  ///         {
  ///             DoWork(1);
  ///         });
  ///             
  ///         Task.Factory.StartNew(() =>
  ///         {
  ///             DoWork(2);
  ///         });
  ///             
  ///         // send first signal 
  ///         waitEvent.Complete();
  ///         waitEvent.Begin();
  ///             
  ///         Thread.Sleep(TimeSpan.FromSeconds(2));
  ///             
  ///         // send second signal
  ///         waitEvent.Complete();
  ///             
  ///         Terminal.Readline();
  ///     }
  ///         
  ///     public static void DoWork(int taskNumber)
  ///     {
  ///         $"Data retrieved:{taskNumber}".WriteLine();
  ///         waitEvent.Wait();
  ///              
  ///         Thread.Sleep(TimeSpan.FromSeconds(2));
  ///         $"All finished up {taskNumber}".WriteLine();
  ///     }
  ///  }
  /// </code>
  /// </example>
  public static class WaitEventFactory {
    #region Factory Methods

    /// <summary>
    /// Creates a Wait Event backed by a standard ManualResetEvent.
    /// </summary>
    /// <param name="isCompleted">if initially set to completed. Generally true.</param>
    /// <returns>The Wait Event.</returns>
    public static IWaitEvent Create(Boolean isCompleted) => new WaitEvent(isCompleted);

    /// <summary>
    /// Creates a Wait Event backed by a ManualResetEventSlim.
    /// </summary>
    /// <param name="isCompleted">if initially set to completed. Generally true.</param>
    /// <returns>The Wait Event.</returns>
    public static IWaitEvent CreateSlim(Boolean isCompleted) => new WaitEventSlim(isCompleted);

    /// <summary>
    /// Creates a Wait Event backed by a ManualResetEventSlim.
    /// </summary>
    /// <param name="isCompleted">if initially set to completed. Generally true.</param>
    /// <param name="useSlim">if set to <c>true</c> creates a slim version of the wait event.</param>
    /// <returns>The Wait Event.</returns>
    public static IWaitEvent Create(Boolean isCompleted, Boolean useSlim) => useSlim ? CreateSlim(isCompleted) : Create(isCompleted);

    #endregion

    #region Backing Classes

    /// <summary>
    /// Defines a WaitEvent backed by a ManualResetEvent.
    /// </summary>
    private class WaitEvent : IWaitEvent {
      private ManualResetEvent _event;

      /// <summary>
      /// Initializes a new instance of the <see cref="WaitEvent"/> class.
      /// </summary>
      /// <param name="isCompleted">if set to <c>true</c> [is completed].</param>
      public WaitEvent(Boolean isCompleted) => this._event = new ManualResetEvent(isCompleted);

      /// <inheritdoc />
      public Boolean IsDisposed {
        get; private set;
      }

      /// <inheritdoc />
      public Boolean IsValid => this.IsDisposed || this._event == null ? false : this._event?.SafeWaitHandle?.IsClosed ?? true ? false : !(this._event?.SafeWaitHandle?.IsInvalid ?? true);

      /// <inheritdoc />
      public Boolean IsCompleted => this.IsValid == false ? true : this._event?.WaitOne(0) ?? true;

      /// <inheritdoc />
      public Boolean IsInProgress => !this.IsCompleted;

      /// <inheritdoc />
      public void Begin() => this._event?.Reset();

      /// <inheritdoc />
      public void Complete() => this._event?.Set();

      /// <inheritdoc />
      void IDisposable.Dispose() {
        if(this.IsDisposed) {
          return;
        }

        this.IsDisposed = true;

        _ = this._event?.Set();
        this._event?.Dispose();
        this._event = null;
      }

      /// <inheritdoc />
      public void Wait() => this._event?.WaitOne();

      /// <inheritdoc />
      public Boolean Wait(TimeSpan timeout) => this._event?.WaitOne(timeout) ?? true;
    }

    /// <summary>
    /// Defines a WaitEvent backed by a ManualResetEventSlim.
    /// </summary>
    private class WaitEventSlim : IWaitEvent {
      private ManualResetEventSlim _event;

      /// <summary>
      /// Initializes a new instance of the <see cref="WaitEventSlim"/> class.
      /// </summary>
      /// <param name="isCompleted">if set to <c>true</c> [is completed].</param>
      public WaitEventSlim(Boolean isCompleted) => this._event = new ManualResetEventSlim(isCompleted);

      /// <inheritdoc />
      public Boolean IsDisposed {
        get; private set;
      }

      /// <inheritdoc />
      public Boolean IsValid => this.IsDisposed || this._event?.WaitHandle?.SafeWaitHandle == null ? false : !this._event.WaitHandle.SafeWaitHandle.IsClosed && !this._event.WaitHandle.SafeWaitHandle.IsInvalid;

      /// <inheritdoc />
      public Boolean IsCompleted => this.IsValid == false || this._event.IsSet;

      /// <inheritdoc />
      public Boolean IsInProgress => !this.IsCompleted;

      /// <inheritdoc />
      public void Begin() => this._event?.Reset();

      /// <inheritdoc />
      public void Complete() => this._event?.Set();

      /// <inheritdoc />
      void IDisposable.Dispose() {
        if(this.IsDisposed) {
          return;
        }

        this.IsDisposed = true;

        this._event?.Set();
        this._event?.Dispose();
        this._event = null;
      }

      /// <inheritdoc />
      public void Wait() => this._event?.Wait();

      /// <inheritdoc />
      public Boolean Wait(TimeSpan timeout) => this._event?.Wait(timeout) ?? true;
    }

    #endregion
  }
}