using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

using Swan;

namespace Unosquare.RaspberryIO.Camera {
  /// <summary>
  /// The Raspberry Pi's camera controller wrapping raspistill and raspivid programs.
  /// This class is a singleton.
  /// </summary>
  public class CameraController : SingletonBase<CameraController> {
    #region Private Declarations

    private static readonly ManualResetEventSlim OperationDone = new ManualResetEventSlim(true);
    private static readonly Object SyncRoot = new Object();
    private static CancellationTokenSource _videoTokenSource = new CancellationTokenSource();
    private static Task<Task>? _videoStreamTask;

    #endregion

    #region Properties

    /// <summary>
    /// Gets a value indicating whether the camera module is busy.
    /// </summary>
    /// <value>
    ///   <c>true</c> if this instance is busy; otherwise, <c>false</c>.
    /// </value>
    public Boolean IsBusy => OperationDone.IsSet == false;

    #endregion

    #region Image Capture Methods

    /// <summary>
    /// Captures an image asynchronously.
    /// </summary>
    /// <param name="settings">The settings.</param>
    /// <param name="ct">The ct.</param>
    /// <returns>The image bytes.</returns>
    /// <exception cref="InvalidOperationException">Cannot use camera module because it is currently busy.</exception>
    public async Task<Byte[]> CaptureImageAsync(CameraStillSettings settings, CancellationToken ct = default) {
      if(Instance.IsBusy) {
        throw new InvalidOperationException("Cannot use camera module because it is currently busy.");
      }

      if(settings.CaptureTimeoutMilliseconds <= 0) {
        throw new ArgumentException($"{nameof(settings.CaptureTimeoutMilliseconds)} needs to be greater than 0");
      }

      try {
        OperationDone.Reset();

        using MemoryStream output = new MemoryStream();
        Int32 exitCode = await ProcessRunner.RunProcessAsync(settings.CommandName, settings.CreateProcessArguments(), (data, proc) => output.Write(data, 0, data.Length), null, true, ct).ConfigureAwait(false);

        return exitCode != 0 ? Array.Empty<Byte>() : output.ToArray();
      } finally {
        OperationDone.Set();
      }
    }

    /// <summary>
    /// Captures an image.
    /// </summary>
    /// <param name="settings">The settings.</param>
    /// <returns>The image bytes.</returns>
    public Byte[] CaptureImage(CameraStillSettings settings) => this.CaptureImageAsync(settings).GetAwaiter().GetResult();

    /// <summary>
    /// Captures a JPEG encoded image asynchronously at 90% quality.
    /// </summary>
    /// <param name="width">The width.</param>
    /// <param name="height">The height.</param>
    /// <param name="ct">The ct.</param>
    /// <returns>The image bytes.</returns>
    public Task<Byte[]> CaptureImageJpegAsync(Int32 width, Int32 height, CancellationToken ct = default) {
      CameraStillSettings settings = new CameraStillSettings {
        CaptureWidth = width,
        CaptureHeight = height,
        CaptureJpegQuality = 90,
        CaptureTimeoutMilliseconds = 300,
      };

      return this.CaptureImageAsync(settings, ct);
    }

    /// <summary>
    /// Captures a JPEG encoded image at 90% quality.
    /// </summary>
    /// <param name="width">The width.</param>
    /// <param name="height">The height.</param>
    /// <returns>The image bytes.</returns>
    public Byte[] CaptureImageJpeg(Int32 width, Int32 height) => this.CaptureImageJpegAsync(width, height).GetAwaiter().GetResult();

    #endregion

    #region Video Capture Methods

    /// <summary>
    /// Opens the video stream with a timeout of 0 (running indefinitely) at 1080p resolution, variable bitrate and 25 FPS.
    /// No preview is shown.
    /// </summary>
    /// <param name="onDataCallback">The on data callback.</param>
    /// <param name="onExitCallback">The on exit callback.</param>
    public void OpenVideoStream(Action<Byte[]> onDataCallback, Action? onExitCallback = null) {
      CameraVideoSettings settings = new CameraVideoSettings {
        CaptureTimeoutMilliseconds = 0,
        CaptureDisplayPreview = false,
        CaptureWidth = 1920,
        CaptureHeight = 1080,
      };

      this.OpenVideoStream(settings, onDataCallback, onExitCallback);
    }

    /// <summary>
    /// Opens the video stream with the supplied settings. Capture Timeout Milliseconds has to be 0 or greater.
    /// </summary>
    /// <param name="settings">The settings.</param>
    /// <param name="onDataCallback">The on data callback.</param>
    /// <param name="onExitCallback">The on exit callback.</param>
    /// <exception cref="InvalidOperationException">Cannot use camera module because it is currently busy.</exception>
    /// <exception cref="ArgumentException">CaptureTimeoutMilliseconds.</exception>
    public void OpenVideoStream(CameraVideoSettings settings, Action<Byte[]> onDataCallback, Action? onExitCallback = null) {
      if(Instance.IsBusy) {
        throw new InvalidOperationException("Cannot use camera module because it is currently busy.");
      }

      if(settings.CaptureTimeoutMilliseconds < 0) {
        throw new ArgumentException($"{nameof(settings.CaptureTimeoutMilliseconds)} needs to be greater than or equal to 0");
      }

      try {
        OperationDone.Reset();
        _videoStreamTask = Task.Factory.StartNew(() => VideoWorkerDoWork(settings, onDataCallback, onExitCallback), _videoTokenSource.Token);
      } catch {
        OperationDone.Set();
        throw;
      }
    }

    /// <summary>
    /// Closes the video stream of a video stream is open.
    /// </summary>
    public void CloseVideoStream() {
      lock(SyncRoot) {
        if(this.IsBusy == false) {
          return;
        }
      }

      if(_videoTokenSource.IsCancellationRequested == false) {
        _videoTokenSource.Cancel();
        _videoStreamTask?.Wait();
      }

      _videoTokenSource = new CancellationTokenSource();
    }

    private static async Task VideoWorkerDoWork(CameraVideoSettings settings, Action<Byte[]> onDataCallback, Action? onExitCallback) {
      try {
        _ = await ProcessRunner.RunProcessAsync(settings.CommandName, settings.CreateProcessArguments(), (data, proc) => onDataCallback?.Invoke(data), null, true, _videoTokenSource.Token).ConfigureAwait(false);

        onExitCallback?.Invoke();
      } catch {
        // swallow
      } finally {
        Instance.CloseVideoStream();
        OperationDone.Set();
      }
    }
    #endregion
  }
}