// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

using Microsoft.MixedReality.Toolkit.Rendering;
using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

namespace Microsoft.MixedReality.Toolkit.Utilities
{
    /// <summary>
    /// An abstract primitive component to animate and visualize a clipping primitive that can be 
    /// used to drive per pixel based clipping.
    /// </summary>
    [ExecuteAlways]
    [HelpURL("https://docs.microsoft.com/windows/mixed-reality/mrtk-unity/features/rendering/clipping-primitive")]
    public abstract class ClippingPrimitive : MonoBehaviour, IMaterialInstanceOwner
    {
        /// <summary>
        /// The renderer(s) that should be affected by the primitive.
        /// </summary>
        protected readonly Dictionary<Renderer, MaterialInstance> rendererDict =
            new Dictionary<Renderer, MaterialInstance>();

        [Tooltip("The renderer(s) that should be affected by the primitive.")]
        [SerializeField]
        protected List<Renderer> renderers = new List<Renderer>();
        public enum Side
        {
            Inside = 1,
            Outside = -1
        }

        [Tooltip("Which side of the primitive to clip pixels against.")]
        [SerializeField]
        protected Side clippingSide = Side.Inside;

        /// <summary>
        /// The renderer(s) that should be affected by the primitive.
        /// </summary>
        public Side ClippingSide
        {
            get => clippingSide;
            set => clippingSide = value;
        }

        [SerializeField]
        [Tooltip("Toggles whether the primitive will use the Camera OnPreRender event")]
        private bool useOnPreRender;

        [SerializeField, Tooltip("Controls clipping features on the shared materials rather than material instances.")]
        private bool applyToSharedMaterial = false;

        /// <summary>
        /// Toggles whether the clipping features will apply to shared materials or material instances (default).
        /// </summary>
        /// <remarks>
        /// Applying to shared materials will allow for GPU instancing to batch calls between Renderers that interact with the same clipping primitives.
        /// </remarks>
        public bool ApplyToSharedMaterial
        {
            get => applyToSharedMaterial;
            set
            {
                if (value != applyToSharedMaterial)
                {
                    if (renderers.Count > 0)
                    {
                        throw new InvalidOperationException("Cannot change material applied to after renderers have been added.");
                    }
                    applyToSharedMaterial = value;
                }
            }
        }

        /// <summary>
        /// Toggles whether the primitive will use the Camera OnPreRender event.
        /// </summary>
        /// <remarks>
        /// This is especially helpful if you're trying to clip dynamically created objects that may be added to the scene after LateUpdate such as OnWillRender 
        /// </remarks>
        public bool UseOnPreRender
        {
            get => useOnPreRender;
            set
            {
                if (cameraMethods == null)
                {
                    cameraMethods = CameraCache.Main.gameObject.EnsureComponent<CameraEventRouter>();
                }

                if (useOnPreRender != value)
                {
                    if (value)
                    {
                        cameraMethods.OnCameraPreRender += OnCameraPreRender;
                    }
                    else if (!value)
                    {
                        cameraMethods.OnCameraPreRender -= OnCameraPreRender;
                    }

                    useOnPreRender = value;
                }
            }
        }

        [SerializeField]
        [Tooltip("Whether to let managed MaterialInstances use a cached copy of cachedRenderer.sharedMaterials or call sharedMaterials on the Renderer directly. " +
            "Enabling the option will lead to better performance but you must turn it off before modifying sharedMaterials of the Renderer.")]
        private bool cacheSharedMaterialsFromRenderer = false;

        /// <summary>
        /// Whether to let managed MaterialInstances use a cached copy of cachedRenderer.sharedMaterials or call sharedMaterials on the Renderer directly.
        /// Enabling the option will lead to better performance but you must turn it off before modifying sharedMaterials of the Renderer.
        /// </summary>
        public bool CacheSharedMaterialsFromRenderer
        {
            get => cacheSharedMaterialsFromRenderer;
            set => cacheSharedMaterialsFromRenderer = value;
        }

        protected abstract string Keyword { get; }
        protected abstract string ClippingSideProperty { get; }

        protected MaterialPropertyBlock materialPropertyBlock;

        private int clippingSideID;
        private CameraEventRouter cameraMethods;

        private Material[] AcquireMaterials(Renderer renderer, bool instance = true)
        {
            if (renderer == null)
            {
                return null;
            }

            if (applyToSharedMaterial)
            {
                return renderer.sharedMaterials;
            }
            else
            {
                return renderer.EnsureComponent<MaterialInstance>().AcquireMaterials(this, instance);
            }
        }

        private bool isDirty;

        /// <summary>
        /// Keeping track of any field, property or transformation changes to optimize material property block setting.
        /// </summary>
        public bool IsDirty
        {
            get => isDirty;
            set => isDirty = value;
        }

        /// <summary>
        /// Adds a renderer to the list of objects this clipping primitive clips.
        /// </summary>
        /// <param name="renderer">The renderer to add.</param>
        public void AddRenderer(Renderer renderer)
        {
            if (renderer != null)
            {
                if (!rendererDict.ContainsKey(renderer))
                {
                    Material[] materials;
                    if (applyToSharedMaterial)
                    {
                        rendererDict.Add(renderer, null);

                        materials = renderer.sharedMaterials;
                    }
                    else
                    {
                        var materialInstance = renderer.EnsureComponent<MaterialInstance>();
                        if (!materialInstance)
                        {
                            return;
                        }

                        materialInstance.CacheSharedMaterialsFromRenderer = CacheSharedMaterialsFromRenderer;
                        rendererDict.Add(renderer, materialInstance);

                        materials = materialInstance.AcquireMaterials(this);
                    }
                    renderers.Add(renderer);
                    ToggleClippingFeature(materials, gameObject.activeInHierarchy);
                    IsDirty = true;
                }
            }
        }

        /// <summary>
        /// Removes a renderer from the list of objects this clipping primitive clips.
        /// </summary>
        public void RemoveRenderer(Renderer _renderer, bool autoDestroyMaterial = true)
        {
            int index = renderers.IndexOf(_renderer);
            if (index >= 0)
            {
                RemoveRenderer(index, autoDestroyMaterial);
            }
        }

        /// <summary>
        /// Removes a renderer from the list of objects this clipping primitive clips based on index.
        /// </summary>
        private void RemoveRenderer(int rendererIndex, bool autoDestroyMaterial = true)
        {
            var _renderer = renderers[rendererIndex];
            renderers.RemoveAt(rendererIndex);
            if (rendererDict.TryGetValue(_renderer, out MaterialInstance materialInstance))
            {
                rendererDict.Remove(_renderer);
                // There is no need to acquire new instances if ones do not already exist since we are
                // in the process of removing.
                ToggleClippingFeature(AcquireMaterials(_renderer, instance: false), false);
                if (materialInstance != null)
                {
                    materialInstance.ReleaseMaterial(this, autoDestroyMaterial);
                }
            }
        }

        /// <summary>
        /// Removes all renderers in the list of objects this clipping primitive clips.
        /// </summary>
        public void ClearRenderers(bool autoDestroyMaterial = true)
        {
            while (renderers.Count != 0)
            {
                RemoveRenderer(renderers.Count - 1, autoDestroyMaterial);
            }
        }

        /// <summary>
        /// Returns a copy of the current list of renderers.
        /// </summary>
        /// <returns>The current list of renderers.</returns>
        public IEnumerable<Renderer> GetRenderersCopy()
        {
            return renderers.AsReadOnly();
        }

        #region MonoBehaviour Implementation

        protected void Awake()
        {
            if (renderers.Count != rendererDict.Count)
            {
                rendererDict.Clear();
                foreach (var renderer in renderers)
                {
                    if (applyToSharedMaterial)
                    {
                        rendererDict[renderer] = null;
                    }
                    else
                    {
                        MaterialInstance materialInstance = renderer.EnsureComponent<MaterialInstance>();
                        rendererDict[renderer] = materialInstance;
                        materialInstance.CacheSharedMaterialsFromRenderer = CacheSharedMaterialsFromRenderer;
                    }
                }
            }
            if (renderers.Count != rendererDict.Count)
            {
                renderers.Clear();
                renderers.AddRange(rendererDict.Keys);
            }
        }

        protected void OnEnable()
        {
            Initialize();
            UpdateRenderers();

#if UNITY_EDITOR
            if (!Application.isPlaying)
            {
                EditorApplication.update += EditorUpdate;
            }
#endif

            ToggleClippingFeature(true);

            if (useOnPreRender)
            {
                cameraMethods = CameraCache.Main.gameObject.EnsureComponent<CameraEventRouter>();
                cameraMethods.OnCameraPreRender += OnCameraPreRender;
            }
        }

        protected void OnDisable()
        {
#if UNITY_EDITOR
            EditorApplication.update -= EditorUpdate;
#endif

            UpdateRenderers();
            ToggleClippingFeature(false);

            if (cameraMethods != null)
            {
                UseOnPreRender = false;
            }
        }

#if UNITY_EDITOR
        // We need this class to be updated once per frame even when in edit mode. Ideally this would 
        // occur after all other objects are updated in LateUpdate(), but because the ExecuteInEditMode 
        // attribute only invokes Update() we handle edit mode updating here and runtime updating 
        // in LateUpdate().
        protected void EditorUpdate()
        {
            Initialize();
            UpdateRenderers();
        }
#endif

        protected void LateUpdate()
        {
            // Deferring the LateUpdate() call to OnCameraPreRender()
            if (!useOnPreRender)
            {
                UpdateRenderers();
            }
        }

        protected void OnCameraPreRender(CameraEventRouter router)
        {
            // Only subscribed to via UseOnPreRender property setter
            UpdateRenderers();
        }

        protected void OnDestroy()
        {
            ClearRenderers();
        }

        #endregion MonoBehaviour Implementation

        #region IMaterialInstanceOwner Implementation

        /// <inheritdoc />
        public void OnMaterialChanged(MaterialInstance materialInstance)
        {
            if (materialInstance != null)
            {
                ToggleClippingFeature(materialInstance.AcquireMaterials(this), gameObject.activeInHierarchy);
            }

            UpdateRenderers();
        }

        #endregion IMaterialInstanceOwner Implementation

        protected virtual void Initialize()
        {
            materialPropertyBlock = new MaterialPropertyBlock();
            clippingSideID = Shader.PropertyToID(ClippingSideProperty);
        }

        protected virtual void UpdateRenderers()
        {
            if (renderers == null || renderers.Count == 0) { return; }

            CheckTransformChange();
            if (!IsDirty) { return; }

            BeginUpdateShaderProperties();
            for (int i = renderers.Count - 1; i >= 0; --i)
            {
                var _renderer = renderers[i];
                if (_renderer == null)
                {
                    if (Application.isPlaying)
                    {
                        RemoveRenderer(i);
                    }
                    continue;
                }

                _renderer.GetPropertyBlock(materialPropertyBlock);
                materialPropertyBlock.SetFloat(clippingSideID, (float)clippingSide);
                UpdateShaderProperties(materialPropertyBlock);
                _renderer.SetPropertyBlock(materialPropertyBlock);
            }

            EndUpdateShaderProperties();
            IsDirty = false;
        }

        protected virtual void BeginUpdateShaderProperties() { }
        protected abstract void UpdateShaderProperties(MaterialPropertyBlock materialPropertyBlock);
        protected virtual void EndUpdateShaderProperties() { }

        protected void ToggleClippingFeature(bool keywordOn)
        {
            if (renderers.Count > 0)
            {
                foreach (var cachedRenderer in renderers)
                {
                    if (cachedRenderer != null)
                    {
                        ToggleClippingFeature(AcquireMaterials(cachedRenderer), keywordOn);
                    }
                }
            }
        }

        protected void ToggleClippingFeature(Material[] materials, bool keywordOn)
        {
            if (materials != null)
            {
                foreach (var material in materials)
                {
                    ToggleClippingFeature(material, keywordOn);
                }
            }
        }

        protected void ToggleClippingFeature(Material material, bool keywordOn)
        {
            if (material != null)
            {
                if (keywordOn)
                {
                    material.EnableKeyword(Keyword);
                }
                else
                {
                    material.DisableKeyword(Keyword);
                }
            }
        }

        private void CheckTransformChange()
        {
            if (transform.hasChanged)
            {
                IsDirty = true;
                transform.hasChanged = false;
            }
        }
    }
}