using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using FidelityFX;
using UnityEngine;
using UnityEngine.Experimental.Rendering;
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;
    
    [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 _outputRT;

    private Material _copyDepthMat;
    private Material CopyDepthMaterial
    {
        get
        {
            if (_copyDepthMat == null)
            {
                var copyDepthShader = Fsr2.GlobalCallbacks.LoadShader("Shaders/FSR2_CopyDepth");
                _copyDepthMat = new Material(copyDepthShader);
            }

            return _copyDepthMat;
        }
    }

    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;
        
        RenderPipelineManager.endContextRendering += OnEndContextRendering;

        // TODO: destroy and recreate context on screen resolution and/or quality mode change
        // TODO: enable motion vector jitter cancellation or not?
        _context = Fsr2.CreateContext(DisplaySize, RenderSize);

        // 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
        _outputRT = new RenderTexture(DisplaySize.x, DisplaySize.y, 24, RenderTextureFormat.ARGBHalf) { enableRandomWrite = true };
        _outputRT.Create();
    }

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

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

        RenderPipelineManager.endContextRendering -= OnEndContextRendering;
    }

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

    // For scriptable rendering pipeline
    private void OnEndContextRendering(ScriptableRenderContext context, List<Camera> cameras)
    {
        Debug.Log($"OnEndContentRendering, cameras = {string.Join(", ", cameras.Select(c => c.name))}");
    }

    // For legacy built-in render pipeline
    private void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        var color = 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 these buffers individually from code
        var depth = RenderTexture.GetTemporary(color.width, color.height, 0, RenderTextureFormat.RFloat);
        var motionVectors = RenderTexture.GetTemporary(color.width, color.height, 0, RenderTextureFormat.RGHalf);
        
        // TODO: might be able to combine color + depth into a single RT and separate them out using RenderTextureSubElement
        // TODO: we can copy to all RTs at the same time using a multi-target blit, requiring only a single shader + material
        Graphics.Blit(color, depth, CopyDepthMaterial);
        Graphics.Blit(color, motionVectors, CopyMotionVectorsMaterial);

        _dispatchDescription.Color = color;
        _dispatchDescription.Depth = depth;
        _dispatchDescription.MotionVectors = motionVectors;
        _dispatchDescription.Output = _outputRT;
        _dispatchDescription.Exposure = null;
        _dispatchDescription.Reactive = null;
        _dispatchDescription.PreExposure = 1.0f;
        _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;

        _context.Dispatch(_dispatchDescription);
        
        RenderTexture.ReleaseTemporary(depth);
        RenderTexture.ReleaseTemporary(motionVectors);
        
        // Output upscaled image to screen
        Graphics.Blit(_outputRT, dest);
    }
}