#if HAVE_SLATE

using System;
using System.Collections.Generic;

using UnityEngine;

using Slate;

using Framework.Cameras;
using Framework.Support;

namespace Framework.Cinematics {

  /// <summary>Helper methods for dealing with cutscenes</summary>
  public static class CutsceneHelper {

    #region class CameraParenter

    /// <summary>Temporarily changes the parent of a game object</summary>
    private class CameraParenter : IDisposable {

      /// <summary>Initializes a new instance that does nothing</summary>
      public CameraParenter() {
        this.onCutsceneStoppedDelegate = new Action<Cutscene>(onCutsceneStopped);
      }

      /// <summary>
      ///   Assigns a new parent to the camera and remembers the previous one
      /// </summary>
      /// <param name="newParentGameObject">New parent for the camera</param>
      /// <param name="cameraGameObject">Camera that will be reparented</param>
      public CameraParenter(
        GameObject newParentGameObject, GameObject cameraGameObject
      ) : this() {
        Initialize(newParentGameObject, cameraGameObject);
      }

      /// <summary>
      ///   Assigns a new parent to the camera and remembers the previous one
      /// </summary>
      /// <param name="newParentGameObject">New parent for the camera</param>
      /// <param name="cameraGameObject">Camera that will be reparented</param>
      public void Initialize(
        GameObject newParentGameObject, GameObject cameraGameObject
      ) {
        this.cameraGameObject = cameraGameObject;

        Transform cameraTransform = cameraGameObject.transform;
        this.previousPosition = cameraTransform.localPosition;
        this.previousOrientation = cameraTransform.localRotation;

        Transform parentTransform = cameraTransform.parent;
        if(parentTransform == null) {
          this.previousParentGameObject = null;
        } else {
          this.previousParentGameObject = parentTransform.gameObject;
        }

        GameObjectHelper.SetAsChild(newParentGameObject, cameraGameObject);
        cameraTransform.localPosition = Vector3.zero;
        cameraTransform.localRotation = Quaternion.identity;
      }

      /// <summary>Restores the original parent of the camera</summary>
      public void Dispose() {
        WatchCutsceneForRecycling(null);

        if(this.cameraGameObject != null) {
          GameObjectHelper.SetAsChild(this.previousParentGameObject, this.cameraGameObject);

          Transform cameraTransform = this.cameraGameObject.transform;
          cameraTransform.localPosition = this.previousPosition;
          cameraTransform.localRotation = this.previousOrientation;

          this.cameraGameObject = null;
        }
      }

      /// <summary>Sets the parenter up for recycling after a cutscene finishes</summary>
      /// <param name="cutscene">Cutscene that will be watched for completion</param>
      public void WatchCutsceneForRecycling(Cutscene cutscene) {
        if(this.cutsceneForUnsubscribe != null) {
          Cutscene.OnCutsceneStopped -= this.onCutsceneStoppedDelegate;
          this.cutsceneForUnsubscribe = null;
        }
        if(cutscene != null) {
          Cutscene.OnCutsceneStopped += this.onCutsceneStoppedDelegate;
          this.cutsceneForUnsubscribe = cutscene;
        }
      }

      /// <summary>Recycles the parenter when the cutscene stops playing</summary>
      /// <param name="cutscene">Cutscene that has stopped playing</param>
      private void onCutsceneStopped(Cutscene cutscene) {
        if(ReferenceEquals(this.cutsceneForUnsubscribe, cutscene)) {
          Dispose();

          CutsceneHelper.recyclableCameraParenters.Add(this);
        }
      }

      /// <summary>Game object that will be reparented</summary>
      private GameObject cameraGameObject;
      /// <summary>Game object that was the camera's previous parent</summary>
      private GameObject previousParentGameObject;
      /// <summary>Previous position of the camera</summary>
      private Vector3 previousPosition;
      /// <summary>Previous orientation of the camera</summary>
      private Quaternion previousOrientation;

      /// <summary>Cutscene this camera parenter is watching for completion</summary>
      private Cutscene cutsceneForUnsubscribe;
      /// <summary>Delegate for the onCutsceneStopped() method</summary>
      private Action<Cutscene> onCutsceneStoppedDelegate;

    }

    #endregion // class CameraParenter

    /// <summary>Starts playing a cutscene using the specified camera</summary>
    /// <param name="cutscene">Cutscene that will be played</param>
    /// <param name="cameraController">Camera on which the cutscene will be played</param>
    /// <param name="callback">Callback to invoke when the cutscene ends</param>
    public static void PlayCutsceneOnCamera(
      Cutscene cutscene, CameraController cameraController, System.Action callback = null
    ) {

      // Stop the DirectorCamera from messing with our camera settings
      DirectorCamera.setMainWhenActive = false;
      DirectorCamera.matchMainWhenActive = false;
      DirectorCamera.autoHandleActiveState = false;
      DirectorCamera.dontDestroyOnLoad = false;

      // Parent our render camera to the director camera root
      CameraParenter parenter = recycleOrCreateCameraParenter();
      parenter.Initialize(DirectorCamera.current.gameObject, cameraController.gameObject);

      // Set up the parenter to recycle (and unparent) when the cutscene ends,
      // then play the cutscene (in this order in case of a zero-length cutscene)
      parenter.WatchCutsceneForRecycling(cutscene);

      // Start the cutscene. This will disable the active camera, but we'll undo
      // that little mishap right away.
      cutscene.Play(0.0f, callback);

      // Switch to our own render camera
      CameraHelper.ActivateCamera(cameraController.Camera);

    }

    /// <summary>Starts playing a cutscene using the director camera</summary>
    /// <param name="cutscene">Cutscene that will be played</param>
    /// <param name="cameraController">Camera that will be active when the cutscene starts</param>
    /// <param name="callback">Callback to invoke when the cutscene ends</param>
    public static void PlayCutsceneOnDirectorCamera(
      Cutscene cutscene, CameraController cameraController, System.Action callback = null
    ) {

      // In this mode, we want the DirectorCamera to copy the camera's settings
      DirectorCamera.setMainWhenActive = true;
      DirectorCamera.matchMainWhenActive = true;
      DirectorCamera.autoHandleActiveState = true;
      DirectorCamera.dontDestroyOnLoad = false;

      // Active the camera from which the DirectorCamera should copy its settings
      CameraHelper.ActivateCamera(cameraController.Camera);

      // Start the cutscene
      cutscene.Play(0.0f, callback);

    }

    /// <summary>
    ///   Returns a recycled instance of a camera parenter or creates a new one
    /// </summary>
    /// <returns>An unused instance of a camera parenter</returns>
    private static CameraParenter recycleOrCreateCameraParenter() {
      if(recyclableCameraParenters == null) {
        recyclableCameraParenters = new List<CameraParenter>();
        return new CameraParenter();
      }

      int parenterCount = recyclableCameraParenters.Count;
      if(parenterCount == 0) {
        return new CameraParenter();
      }

      CameraParenter parenter = recyclableCameraParenters[parenterCount - 1];
      recyclableCameraParenters.RemoveAt(parenterCount - 1);
      return parenter;
    }

    /// <summary>Camera parenters that are ready for reuse</summary>
    private static IList<CameraParenter> recyclableCameraParenters;

  }

} // namespace Framework.Cinematics

#endif // HAVE_SLATE