/* Copyright (c) 2019-present Evereal. All rights reserved. */

// Credit: https://github.com/keijiro/FFmpegOut

using UnityEngine;
using UnityEngine.Rendering;

namespace Evereal.VideoCapture
{
  sealed class Blitter : MonoBehaviour
  {
    #region Factory method

    static System.Type[] _initialComponents =
        { typeof(Camera), typeof(Blitter) };

    public static GameObject CreateInstance(Camera source)
    {
      var go = new GameObject("Blitter", _initialComponents);
      go.hideFlags = HideFlags.HideInHierarchy;

      var camera = go.GetComponent<Camera>();
      camera.cullingMask = 1 << UILayer;
      camera.targetDisplay = source.targetDisplay;

      var blitter = go.GetComponent<Blitter>();
      blitter._sourceTexture = source.targetTexture;

      return go;
    }

    #endregion

    #region Private members

    // Assuming that the 5th layer is "UI". #badcode
    const int UILayer = 5;

    Texture _sourceTexture;
    Mesh _mesh;
    Material _material;

    void PreCull(Camera camera)
    {
      if (_mesh == null || camera != GetComponent<Camera>()) return;

      Graphics.DrawMesh(
          _mesh, transform.localToWorldMatrix,
          _material, UILayer, camera
      );
    }

#if UNITY_2019_1_OR_NEWER
    void BeginCameraRendering(ScriptableRenderContext context, Camera camera)
    {
      PreCull(camera);
    }
#endif

    #endregion

    #region MonoBehaviour implementation

    void Update()
    {
      if (_mesh == null)
      {
        // Index-only triangle mesh
        _mesh = new Mesh();
        _mesh.vertices = new Vector3[3];
        _mesh.triangles = new int[] { 0, 1, 2 };
        _mesh.bounds = new Bounds(Vector3.zero, Vector3.one);
        _mesh.UploadMeshData(true);

        // Blitter shader material
        var shader = Shader.Find("VideoCapture/Blitter");
        _material = new Material(shader);
        _material.SetTexture("_MainTex", _sourceTexture);

        // Register the camera render callback.
#if UNITY_2019_1_OR_NEWER
        RenderPipelineManager.beginCameraRendering += BeginCameraRendering; // SRP
#endif
        Camera.onPreCull += PreCull; // Legacy
      }
    }

    void OnDisable()
    {
      if (_mesh != null)
      {
        // Unregister the camera render callback.
#if UNITY_2019_1_OR_NEWER
        RenderPipelineManager.beginCameraRendering -= BeginCameraRendering; // SRP
#endif
        Camera.onPreCull -= PreCull; // Legacy

        // Destroy temporary objects.
        Destroy(_mesh);
        Destroy(_material);
        _mesh = null;
        _material = null;
      }
    }

    #endregion
  }
}