using System.Reflection;
using Cysharp.Threading.Tasks;
using HarmonyLib;
using UnityEngine;

namespace ADOFAIRenderer.Core;

/// <summary>
/// Per-frame hook attached to the scrCamera GameObject by RenderManager when the game scene of a render has loaded,
/// and destroyed again when a render is cancelled or fails.
/// Execution order int.MaxValue: its LateUpdate runs after every other script's LateUpdate of the frame.
/// Each frame it calls RenderManager.OnLastUpdate (LateUpdate) and, after the frame has been rendered
/// (end of frame), RenderManager.OnPostFrame with the texture shown on scrCamera's camera quad, which is the frame
/// that gets captured.
/// Reference: https://docs.unity3d.com/ScriptReference/DefaultExecutionOrder.html
/// </summary>
[DefaultExecutionOrder(int.MaxValue)]
internal class PostRenderHook : MonoBehaviour
{
    /// <summary>Private field scrCamera.camQuadMesh: the MeshRenderer of the quad that displays the camera RenderTexture.</summary>
    private FieldInfo? _camQuadMeshField;

    /// <summary>Cached value of camQuadMesh for the current scrCamera instance. Looked up again while it is null or destroyed.</summary>
    private MeshRenderer? _camQuadMeshRenderer;

    private void Awake()
    {
        _camQuadMeshField = AccessTools.Field(typeof(scrCamera), "camQuadMesh");
    }
        
    /// <summary>
    /// Main thread, once per frame after all other LateUpdate calls. Runs the last-update work of RenderManager
    /// (OnLastUpdate callbacks of the session) and schedules the end-of-frame capture.
    /// </summary>
    private void LateUpdate()
    {
        if (RenderManager.Instance)
            RenderManager.Instance.OnLastUpdate();
            
        PostFrameAsync().Forget();
    }

    /// <summary>
    /// Waits until the end of the current frame (after the cameras have rendered) and passes the camera quad's main
    /// texture to RenderManager.OnPostFrame. The wait is cancelled when this component is destroyed.
    /// The texture is null when the quad's material has no RenderTexture; OnPostFrame then only updates the audio.
    /// </summary>
    private async UniTaskVoid PostFrameAsync()
    {
        await UniTask.WaitForEndOfFrame(this, destroyCancellationToken);
            
        if (!_camQuadMeshRenderer && scrCamera.instance)
            _camQuadMeshRenderer = _camQuadMeshField?.GetValue(scrCamera.instance) as MeshRenderer;

        if (RenderManager.Instance && _camQuadMeshRenderer)
            RenderManager.Instance.OnPostFrame(_camQuadMeshRenderer.sharedMaterial.mainTexture as RenderTexture);
    }
}