using System;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;

namespace Escape_Room_Engine.Portal
{
    public class Portal : MonoBehaviour
    {
        private static readonly Matrix4x4 HalfRotation = Matrix4x4.Rotate(Quaternion.Euler(0, 180, 0));
        
        /// <summary>
        /// The portal that is connected with this one.
        /// </summary>
        public Portal other;
        /// <summary>
        /// The main camera to take the position for the portal camera from.
        /// </summary>
        [SerializeField] private Camera playerCamera;
        /// <summary>
        /// The camera that will draw the view for this portal.
        /// </summary>
        [SerializeField] private Camera portalCamera;
        /// <summary>
        /// The quad where the rendered texture will be drawn on.
        /// </summary>
        [SerializeField] private MeshRenderer portalQuad;

        private RenderTexture _texture;

        private void Awake()
        {
            // check whether the other portal is set up
            if (!other || other.other != this) throw new Exception("Other Portal not set up correctly.");
            // check whether the player camera is set up
            if (!playerCamera) throw new Exception("No camera initialised.");
            
            // create render texture
            if (!_texture) _texture = new RenderTexture(Screen.width, Screen.height, 24, RenderTextureFormat.ARGB32);
        }

        private void Start()
        {
            // assign render texture
            portalCamera.targetTexture = _texture;
            other.portalQuad.material.mainTexture = _texture;
        }

        private void OnEnable()
        {
            RenderPipelineManager.beginCameraRendering += Render;
        }

        private void OnDisable()
        {
            RenderPipelineManager.beginCameraRendering -= Render;
        }

        private void Render(ScriptableRenderContext scriptableRenderContext, Camera camera)
        {
            var t = transform;
            
            // position portal camera
            var portalCameraMatrix = t.localToWorldMatrix * HalfRotation * other.transform.worldToLocalMatrix *
                                     playerCamera.transform.localToWorldMatrix;
            portalCamera.transform.SetPositionAndRotation(portalCameraMatrix.GetPosition(), portalCameraMatrix.rotation);
            
            // set camera clip plane to portal (otherwise the wall behind the portal would be rendered)
            // calculating the clip plane: https://computergraphics.stackexchange.com/a/1506
            var n = -t.forward; // clip plane normal
            var portalPlane = new Plane(n, t.position); // clip plane in world space
            var clipPlane = portalCamera.worldToCameraMatrix.inverse.transpose *
                            new Vector4(n.x, n.y, n.z, portalPlane.distance); // vector format clip plane in camera space
            portalCamera.projectionMatrix = playerCamera.CalculateObliqueMatrix(clipPlane);
            
            // render portal view
            UniversalRenderPipeline.RenderSingleCamera(scriptableRenderContext, portalCamera);
        }
    }
}