using System;

using UnityEngine;

using Framework.Services;

namespace Framework.Cameras {

  /// <summary>Fades a camea in and out</summary>
  public class CameraFader : ScriptComponent {

    /// <summary>How long it takes for the camera to fade in or out</summary>
    /// <remarks>
    ///   Used when the camera is told to automatically fade in or out.
    /// </remarks>
    public float AutoFadeTimeSeconds = 2.0f;
    
    /// <summary>Whether the camera is currently doing an automatic fade</summary>
    public bool IsAutoFading = false;

    /// <summary>Whether the camera should be faded out</summary>
    public bool Faded = false;

    /// <summary>How far the camera is currently faded</summary>
    public float FadeLevel;                           

    /// <summary>Material that is used for fading the camera</summary>
    /// <remarks>
    ///   If this is not set, the camera will be faded using old-style GUI
    ///   code. This however doesn't work for VR applications.
    /// </remarks>
    public Material FadeMaterial;

    /// <summary>Fades the view out</summary>
    /// <param name="instantaneous">Whether to fade out with no delay</param>
    public void FadeOut(bool instantaneous) {
      this.Faded = true;
      if(instantaneous) {
        this.FadeLevel = 1.0f;
        this.IsAutoFading = false;
      } else {
        this.IsAutoFading = true;
      }
    }

    /// <summary>Fades the view in</summary>
    /// <param name="instantaneous">Whether to fade in with no delay</param>
    public void FadeIn(bool instantaneous) {
      this.Faded = false;
      if(instantaneous) {
        this.FadeLevel = 0.0f;
        this.IsAutoFading = false;
      } else {
        this.IsAutoFading = true;
      }
    }

    /// <summary>Called when the script component gets loaded into a game object</summary>
    protected override void Awake() {
      base.Awake();

      if(this.FadeMaterial == null) {
        this.fadeTexture = new Texture2D(1, 1, TextureFormat.RGB24, false);
        this.fadeTexture.SetPixel(0, 0, Color.black);
      }
    }

    /// <summary>Called after the scene had been rendered</summary>
    protected void OnPostRender() {
      if(this.FadeMaterial != null) {
        if(this.FadeLevel > 0.0f) {
          this.FadeMaterial.SetPass(0);
          this.FadeMaterial.SetColor("_Color", new Color(0.0f, 0.0f, 0.0f, this.FadeLevel));
          
          GL.PushMatrix();
          GL.LoadOrtho();
          GL.Color(this.FadeMaterial.color);
          GL.Begin(GL.QUADS);
          GL.Vertex3(0f, 0f, -12f);
          GL.Vertex3(0f, 1f, -12f);
          GL.Vertex3(1f, 1f, -12f);
          GL.Vertex3(1f, 0f, -12f);
          GL.End();
          GL.PopMatrix();
        }
      }
    }
    
    /// <summary>Called once per visual frame</summary>
    protected virtual void Update() {
      if(this.IsAutoFading) {
        float fadeAmount = Time.deltaTime * (1.0f / this.AutoFadeTimeSeconds);

        if(this.Faded) {
          this.FadeLevel += fadeAmount;
          if(this.FadeLevel >= 1.0f) {
            this.FadeLevel = 1.0f;
            this.IsAutoFading = false;
          }
        } else {
          this.FadeLevel -= fadeAmount;
          if(this.FadeLevel <= 0.0f) {
            this.FadeLevel = 0.0f;
            this.IsAutoFading = false;
          }
        }
      }
    }

    /// <summary>Called when Unity wants to draw its GUI</summary>
    protected virtual void OnGUI() {
      if(this.FadeMaterial == null) {
        if(this.FadeLevel > 0.0f) {
          Color previousColor = GUI.color;

          // This should be easier on resources then writing to the texture in
          // order to change its alpha value.
          GUI.color = new Color(0.0f, 0.0f, 0.0f, this.FadeLevel);
          try {
            GUI.DrawTexture(
              new Rect(0, 0, Screen.width, Screen.height),
              this.fadeTexture
            );
          }
          finally {
            GUI.color = previousColor;
          }
        }
      }
    }

    /// <summary>Camera manager to which the camera reports</summary>
    private ICameraManager cameraManager;

    /// <summary>Texture that will be used to fade the screen in and out</summary>
    private Texture2D fadeTexture;

  }

} // namespace Framework.Cameras