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

using System.Collections.Generic;
using UnityEngine;

namespace Microsoft.MixedReality.GraphicsTools
{
    /// <summary>
    /// Utility component to animate and visualize a light that can be used with the GraphicsTools/Standard and 
    /// GraphicsTools/Standard Canvas shaders that have the "_HOVER_LIGHT" keyword enabled.
    /// </summary>
    [ExecuteInEditMode]
    [AddComponentMenu("Scripts/GraphicsTools/HoverLight")]
    public class HoverLight : BaseLight
    {
        // The Graphics Tools/Standard and Graphics Tools/Standard Canvas shaders supports up to four (4) hover lights.
        private const int hoverLightCount = 4;
        private const int hoverLightDataSize = 2;

        private static List<HoverLight> activeHoverLights = new List<HoverLight>(hoverLightCount);
        private static Vector4[] hoverLightData = new Vector4[hoverLightDataSize * hoverLightCount];
        private static int _HoverLightDataID;
        private static int lastHoverLightUpdate = -1;

        [Tooltip("Specifies the radius of the HoverLight effect.")]
        [SerializeField, Min(0.0f)]
        private float radius = 0.15f;

        /// <summary>
        /// Specifies the Radius of the HoverLight effect.
        /// </summary>
        public float Radius
        {
            get => radius;
            set => radius = Mathf.Max(0.0f, value);
        }

        [Tooltip("Specifies the highlight color.")]
        [SerializeField]
        private Color color = new Color(0.3f, 0.3f, 0.3f, 1.0f);

        /// <summary>
        /// Specifies the highlight color.
        /// </summary>
        public Color Color
        {
            get => color;
            set => color = value;
        }

        #region BaseLight Implementation

        /// <inheritdoc/>
        protected override void Initialize()
        {
            _HoverLightDataID = Shader.PropertyToID("_HoverLightData");
        }

        /// <inheritdoc/>
        protected override void AddLight()
        {
            if (activeHoverLights.Count == hoverLightCount)
            {
                Debug.LogWarningFormat("Max hover light count {0} exceeded. {1} will not be considered by the Graphics Tools/Standard shader until other lights are removed.", hoverLightCount, gameObject.name);
            }

            activeHoverLights.Add(this);
        }

        /// <inheritdoc/>
        protected override void RemoveLight()
        {
            activeHoverLights.Remove(this);
        }

        /// <inheritdoc/>
        protected override void UpdateLights(bool forceUpdate = false)
        {
            if (lastHoverLightUpdate == -1)
            {
                Initialize();
            }

            if (!forceUpdate && (Time.frameCount == lastHoverLightUpdate))
            {
                return;
            }

            for (int i = 0; i < hoverLightCount; ++i)
            {
                HoverLight light = (i >= activeHoverLights.Count) ? null : activeHoverLights[i];
                int dataIndex = i * hoverLightDataSize;

                if (light)
                {
                    hoverLightData[dataIndex] = new Vector4(light.transform.position.x,
                                                            light.transform.position.y,
                                                            light.transform.position.z,
                                                            1.0f);
                    hoverLightData[dataIndex + 1] = new Vector4(light.Color.r,
                                                                light.Color.g,
                                                                light.Color.b,
                                                                1.0f / Mathf.Clamp(light.Radius, 0.001f, 1.0f));
                }
                else
                {
                    hoverLightData[dataIndex] = Vector4.zero;
                }
            }

            Shader.SetGlobalVectorArray(_HoverLightDataID, hoverLightData);

            lastHoverLightUpdate = Time.frameCount;
        }

        #endregion BaseLight Implementation
    }
}