using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using FidelityFX;
using UnityEngine;
using UnityEngine.Rendering;

/// <summary>
/// This class is responsible for hooking into various Unity events and translating them to the FSR2 subsystem.
/// This includes creation and destruction of the FSR2 context, as well as dispatching commands at the right time.
/// This class also exposes various FSR2 parameters to the Unity inspector.
/// </summary>
public class Fsr2Controller : MonoBehaviour
{
    [SerializeField]
    private bool performSharpenPass = true;

    [SerializeField, Range(0, 1)]
    private float sharpness = 0.8f;
    
    [SerializeField]
    private bool reset;
    
    [HideInInspector]
    public Camera gameCamera;

    [HideInInspector]
    public Camera outputCamera;

    [HideInInspector]
    public float renderScale;

    private bool _started;
    
    private Vector2Int DisplaySize => new Vector2Int(Screen.width, Screen.height);
    private Vector2Int RenderSize => new Vector2Int(Mathf.FloorToInt(Screen.width * renderScale), Mathf.FloorToInt(Screen.height * renderScale));

    private Fsr2Context _context;
    private readonly Fsr2.DispatchDescription _dispatchDescription = new Fsr2.DispatchDescription();

    private RenderTexture _upscaledOutput;

    private Material _copyMotionMat;
    private Material CopyMotionVectorsMaterial
    {
        get
        {
            if (_copyMotionMat == null)
            {
                var copyMotionShader = Fsr2.GlobalCallbacks.LoadShader("Shaders/FSR2_CopyMotionVectors");
                _copyMotionMat = new Material(copyMotionShader);
            }

            return _copyMotionMat;
        }
    }

    private void Start()
    {
        _started = true;
        OnEnable();
    }

    private void OnEnable()
    {
        // Delay OnEnable until we're sure all fields and properties are set
        if (!_started)
            return;
        
        _context = Fsr2.CreateContext(DisplaySize, RenderSize, Fsr2.InitializationFlags.EnableMotionVectorsJitterCancellation);

        // TODO: do we need a depth buffer for the output? We will need depth & motion vectors for subsequent post-FX. How should FSR2 output these?
        // TODO: can probably be a temporary RT
        _upscaledOutput = new RenderTexture(DisplaySize.x, DisplaySize.y, 0, RenderTextureFormat.ARGBHalf) { name = "FSR2 Upscaled Output", enableRandomWrite = true };
        _upscaledOutput.Create();
    }

    private void OnDisable()
    {
        if (_upscaledOutput != null)
        {
            _upscaledOutput.Release();
            _upscaledOutput = null;
        }

        if (_context != null)
        {
            _context.Destroy();
            _context = null;
        }
    }

    public void SetJitterOffset(Vector2 jitterOffset)
    {
        _dispatchDescription.JitterOffset = jitterOffset;
    }

    // For legacy built-in render pipeline
    private void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        var renderBuffer = gameCamera.targetTexture;
        
        // I hate having to allocate extra RTs just to duplicate already existing Unity render buffers, but AFAIK there is no way to directly address motion vectors from code
        var motionVectors = RenderTexture.GetTemporary(renderBuffer.width, renderBuffer.height, 0, RenderTextureFormat.RGHalf);
        Graphics.Blit(renderBuffer, motionVectors, CopyMotionVectorsMaterial);

        // TODO: if `dest` is null, we are rendering straight to the backbuffer and should use a temporary RT as the output buffer for FSR2
        // TODO: if `dest` it NOT null, we have more image effects lined up after this one, and we should be able to have FSR2 output straight to `dest` without an intermediary temp RT 
        
        _dispatchDescription.ColorDepth = renderBuffer;
        _dispatchDescription.MotionVectors = motionVectors;
        _dispatchDescription.Output = _upscaledOutput;
        _dispatchDescription.Exposure = null;
        _dispatchDescription.Reactive = null;
        _dispatchDescription.PreExposure = 0;
        _dispatchDescription.EnableSharpening = performSharpenPass;
        _dispatchDescription.Sharpness = sharpness;
        _dispatchDescription.MotionVectorScale.x = -gameCamera.pixelWidth;
        _dispatchDescription.MotionVectorScale.y = -gameCamera.pixelHeight;
        _dispatchDescription.RenderSize = RenderSize;
        _dispatchDescription.FrameTimeDelta = Time.unscaledDeltaTime;
        _dispatchDescription.CameraNear = gameCamera.nearClipPlane;
        _dispatchDescription.CameraFar = gameCamera.farClipPlane;
        _dispatchDescription.CameraFovAngleVertical = gameCamera.fieldOfView * Mathf.Deg2Rad;
        _dispatchDescription.ViewSpaceToMetersFactor = 1.0f;    // 1 unit is 1 meter in Unity
        _dispatchDescription.Reset = reset;
        reset = false;

        _context.Dispatch(_dispatchDescription);
        
        // Output upscaled image to screen
        // TODO: we should probably use a shader to include depth & motion vectors into the output
        // TODO: if `dest` is null, we likely don't care about the depth & motion vectors anymore
        Graphics.Blit(_upscaledOutput, dest);
        
        RenderTexture.ReleaseTemporary(motionVectors);
    }
}