using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.UIElements;
using UnityUtils;

// https://discussions.unity.com/t/uitoolkit-world-space-support-status/887441/22
// https://gist.github.com/katas94/7b220a591215efc36110860a0b1125eb
public class WorldSpaceUIDocument : MonoBehaviour {
    #region Fields

    const string k_transparentShader = "Unlit/Transparent";
    const string k_textureShader = "Unlit/Texture";
    const string k_mainTex = "_MainTex";
    static readonly int MainTex = Shader.PropertyToID(k_mainTex);
    
    [Header("Panel Configuration")]
    [Tooltip("Width of the panel in pixels.")] 
    [SerializeField] int panelWidth = 1280;

    [Tooltip("Height of the panel in pixels.")] 
    [SerializeField] int panelHeight = 720;

    [Tooltip("Scale of the panel (like zoom in a browser).")] 
    [SerializeField] float panelScale = 1.0f;

    [Tooltip("Pixels per world unit. Determines the real-world size of the panel.")] 
    [SerializeField] float pixelsPerUnit = 500.0f;

    [Header("Dependencies")]
    [Tooltip("Visual tree asset for this panel.")] 
    [SerializeField] VisualTreeAsset visualTreeAsset;

    [Tooltip("PanelSettings prefab instance.")] 
    [SerializeField] PanelSettings panelSettingsAsset;

    [Tooltip("RenderTexture prefab instance.")] 
    [SerializeField] RenderTexture renderTextureAsset;
    
    MeshRenderer meshRenderer;
    UIDocument uiDocument;
    PanelSettings panelSettings;
    RenderTexture renderTexture;
    Material material;

    #endregion

    void Awake() {
        InitializeComponents();
        BuildPanel();
    }

    public void SetLabelText(string label, string text) {
        if (uiDocument.rootVisualElement == null) {
            uiDocument.visualTreeAsset = visualTreeAsset;
        }
        
        // Consider caching the label element for better performance
        uiDocument.rootVisualElement.Q<Label>(label).text = text;
    }

    void InitializeComponents() {
        InitializeMeshRenderer();
        
        // Optionally add a box collider to the object
        // BoxCollider boxCollider = gameObject.GetOrAdd<BoxCollider>();
        // boxCollider.size = new Vector3(1, 1, 0);
        
        MeshFilter meshFilter = gameObject.GetOrAdd<MeshFilter>();
        meshFilter.sharedMesh = GetQuadMesh();
    }

    void InitializeMeshRenderer() {
        meshRenderer = gameObject.GetOrAdd<MeshRenderer>();
        meshRenderer.sharedMaterial = null;
        meshRenderer.shadowCastingMode = ShadowCastingMode.Off;
        meshRenderer.receiveShadows = false;
        meshRenderer.motionVectorGenerationMode = MotionVectorGenerationMode.ForceNoMotion;
        meshRenderer.lightProbeUsage = LightProbeUsage.Off;
        meshRenderer.reflectionProbeUsage = ReflectionProbeUsage.Off;
    }

    void BuildPanel() {
        CreateRenderTexture();
        CreatePanelSettings();
        CreateUIDocument();
        CreateMaterial();
        
        SetMaterialToRenderer();
        SetPanelSize();
    }

    void CreateRenderTexture() {
        RenderTextureDescriptor descriptor = renderTextureAsset.descriptor;
        descriptor.width = panelWidth;
        descriptor.height = panelHeight;
        renderTexture = new RenderTexture(descriptor) {
            name = $"{name} - RenderTexture"
        };
    }

    void CreatePanelSettings() {
        panelSettings = Instantiate(panelSettingsAsset);
        panelSettings.targetTexture = renderTexture;
        panelSettings.clearColor = true;
        panelSettings.scaleMode = PanelScaleMode.ConstantPixelSize;
        panelSettings.scale = panelScale;
        panelSettings.name = $"{name} - PanelSettings";
    }

    void CreateUIDocument() {
        uiDocument = gameObject.GetOrAdd<UIDocument>();
        uiDocument.panelSettings = panelSettings;
        uiDocument.visualTreeAsset = visualTreeAsset;
    }

    void CreateMaterial() {
        string shaderName = panelSettings.colorClearValue.a < 1.0f ? k_transparentShader : k_textureShader;
        material = new Material(Shader.Find(shaderName));
        material.SetTexture(MainTex, renderTexture);
    }

    void SetMaterialToRenderer() {
        if (meshRenderer != null) {
            meshRenderer.sharedMaterial = material;
        }
    }

    void SetPanelSize() {
        if (renderTexture != null && (renderTexture.width != panelWidth || renderTexture.height != panelHeight)) {
            renderTexture.Release();
            renderTexture.width = panelWidth;
            renderTexture.height = panelHeight;
            renderTexture.Create();
            
            uiDocument?.rootVisualElement?.MarkDirtyRepaint();
        }
        
        transform.localScale = new Vector3(panelWidth / pixelsPerUnit, panelHeight / pixelsPerUnit, 1.0f);
    }

    static Mesh GetQuadMesh() {
        GameObject tempQuad = GameObject.CreatePrimitive(PrimitiveType.Quad);
        Mesh quadMesh = tempQuad.GetComponent<MeshFilter>().sharedMesh;
        Destroy(tempQuad);
        
        return quadMesh;
    }
    
    void DestroyGeneratedAssets () {
        if (uiDocument) Destroy(uiDocument);
        if (renderTexture) Destroy(renderTexture);
        if (panelSettings) Destroy(panelSettings);
        if (material) Destroy(material);
    }

    void OnDestroy () {
        DestroyGeneratedAssets();
    }   
}