using UnityEngine;
using UnityEngine.Rendering;

[ExecuteInEditMode]
[ImageEffectAllowedInSceneView]
[RequireComponent(typeof(Camera))]
public class CommandBufferBlur : MonoBehaviour
{
    Shader _shader;

    Material _material = null;

    Camera _camera = null;
    CommandBuffer _commandBuffer = null;

    Vector2 _screenResolution = Vector2.zero;
    RenderTextureFormat _textureFormat = RenderTextureFormat.ARGB32;

    public void Cleanup()
    {
        if (!Initialized)
            return;

        _camera.RemoveCommandBuffer(CameraEvent.BeforeForwardAlpha, _commandBuffer);
        _commandBuffer = null;
        Object.DestroyImmediate(_material);
    }

    public void OnEnable()
    {
        Cleanup();
        Initialize();
    }

    public void OnDisable()
    {
        Cleanup();
    }

    public bool Initialized
    {
        get { return _commandBuffer != null; }
    }

    void Initialize()
    {
        if (Initialized)
            return;

        if (!_shader)
        {
            _shader = Shader.Find("Hidden/SeparableGlassBlur");

            if (!_shader)
                throw new MissingReferenceException("Unable to find required shader \"Hidden/SeparableGlassBlur\"");
        }

        if (!_material)
        {
            _material = new Material(_shader);
            _material.hideFlags = HideFlags.HideAndDontSave;
        }

        _camera = GetComponent<Camera>();

        if (_camera.allowHDR && SystemInfo.SupportsRenderTextureFormat(RenderTextureFormat.DefaultHDR))
            _textureFormat = RenderTextureFormat.DefaultHDR;

        _commandBuffer = new CommandBuffer();
        _commandBuffer.name = "Blur screen";

        int numIterations = 4;

        Vector2[] sizes = {
            new Vector2(Screen.width, Screen.height),
            new Vector2(Screen.width / 2, Screen.height / 2),
            new Vector2(Screen.width / 4, Screen.height / 4),
            new Vector2(Screen.width / 8, Screen.height / 8),
        };

        for (int i = 0; i < numIterations; ++i)
        {
            int screenCopyID = Shader.PropertyToID("_ScreenCopyTexture");
            _commandBuffer.GetTemporaryRT(screenCopyID, -1, -1, 0, FilterMode.Bilinear, _textureFormat);
            _commandBuffer.Blit(BuiltinRenderTextureType.CurrentActive, screenCopyID);

            int blurredID = Shader.PropertyToID("_Grab" + i + "_Temp1");
            int blurredID2 = Shader.PropertyToID("_Grab" + i + "_Temp2");
            _commandBuffer.GetTemporaryRT(blurredID, (int)sizes[i].x, (int)sizes[i].y, 0, FilterMode.Bilinear, _textureFormat);
            _commandBuffer.GetTemporaryRT(blurredID2, (int)sizes[i].x, (int)sizes[i].y, 0, FilterMode.Bilinear, _textureFormat);

            _commandBuffer.Blit(screenCopyID, blurredID);
            _commandBuffer.ReleaseTemporaryRT(screenCopyID);

            _commandBuffer.SetGlobalVector("offsets", new Vector4(2.0f / sizes[i].x, 0, 0, 0));
            _commandBuffer.Blit(blurredID, blurredID2, _material);
            _commandBuffer.SetGlobalVector("offsets", new Vector4(0, 2.0f / sizes[i].y, 0, 0));
            _commandBuffer.Blit(blurredID2, blurredID, _material);

            _commandBuffer.SetGlobalTexture("_GrabBlurTexture_" + i, blurredID);
        }

        _camera.AddCommandBuffer(CameraEvent.BeforeForwardAlpha, _commandBuffer);

        _screenResolution = new Vector2(Screen.width, Screen.height);
    }

    void OnPreRender()
    {
        if (_screenResolution != new Vector2(Screen.width, Screen.height))
            Cleanup();

        Initialize();
    }
}