using System;
using UnityEditor;
using UnityEngine;

public abstract class LightweightShaderGUI : ShaderGUI
{
    public enum SurfaceType
    {
        Opaque,
        Transparent
    }

    public enum BlendMode
    {
        Alpha,   // Old school alpha-blending mode, fresnel does not affect amount of transparency
        Premultiply, // Physically plausible transparency mode, implemented as alpha pre-multiply
        Additive,
        Multiply
    }

    private static class Styles
    {
        public static string renderingOptionsLabel = "Rendering Options";
        public static string surfaceType = "Surface Type";
        public static string blendingMode = "Blending Mode";
        public static GUIContent twoSidedText = new GUIContent("Two Sided", "Render front and back faces");
        public static GUIContent alphaClipText = new GUIContent("Alpha Clip", "Enable Alpha Clip");
        public static GUIContent alphaClipThresholdText = new GUIContent("Clip Threshold", "Threshold for alpha clip");
        public static GUIContent receiveShadowText = new GUIContent("Receive Shadows", "Enables this material to receive shadows if there is at least one shadow casting light affecting it.");
        public static readonly string[] surfaceNames = Enum.GetNames(typeof(SurfaceType));
        public static readonly string[] blendNames = Enum.GetNames(typeof(BlendMode));
    }

    protected MaterialEditor m_MaterialEditor;
    protected MaterialProperty surfaceTypeProp;
    protected MaterialProperty blendModeProp;
    protected MaterialProperty cullingProp;
    protected MaterialProperty alphaClipProp;
    protected MaterialProperty alphaCutoffProp;
    protected MaterialProperty receiveShadowsProp;
    private bool m_FirstTimeApply = true;

    public abstract void MaterialChanged(Material material);

    public virtual void FindProperties(MaterialProperty[] properties)
    {
        surfaceTypeProp = FindProperty("_Surface", properties);
        blendModeProp = FindProperty("_Blend", properties);
        cullingProp = FindProperty("_Cull", properties);
        alphaClipProp = FindProperty("_AlphaClip", properties);
        alphaCutoffProp = FindProperty("_Cutoff", properties);
        receiveShadowsProp = FindProperty("_ReceiveShadows", properties);
    }

    public virtual void ShaderPropertiesGUI(Material material)
    {
        DoPopup(Styles.surfaceType, surfaceTypeProp, Styles.surfaceNames);
        if ((SurfaceType)material.GetFloat("_Surface") == SurfaceType.Transparent)
            DoPopup(Styles.blendingMode, blendModeProp, Styles.blendNames);

        EditorGUI.BeginChangeCheck();
        bool twoSidedEnabled = EditorGUILayout.Toggle(Styles.twoSidedText, cullingProp.floatValue == 0);
        if (EditorGUI.EndChangeCheck())
            cullingProp.floatValue = twoSidedEnabled ? 0 : 2;

        EditorGUI.BeginChangeCheck();
        bool alphaClipEnabled = EditorGUILayout.Toggle(Styles.alphaClipText, alphaClipProp.floatValue == 1);
        if (EditorGUI.EndChangeCheck())
            alphaClipProp.floatValue = alphaClipEnabled ? 1 : 0;

        if (alphaClipProp.floatValue == 1)
            m_MaterialEditor.ShaderProperty(alphaCutoffProp, Styles.alphaClipThresholdText, MaterialEditor.kMiniTextureFieldLabelIndentLevel + 1);

        EditorGUI.BeginChangeCheck();
        bool receiveShadows = EditorGUILayout.Toggle(Styles.receiveShadowText, receiveShadowsProp.floatValue == 1.0f);
        if (EditorGUI.EndChangeCheck())
            receiveShadowsProp.floatValue = receiveShadows ? 1.0f : 0.0f;

        EditorGUILayout.Space();
    }

    public override void OnGUI(MaterialEditor materialEditor, MaterialProperty[] properties)
    {
        FindProperties(properties); // MaterialProperties can be animated so we do not cache them but fetch them every event to ensure animated values are updated correctly
        m_MaterialEditor = materialEditor;
        Material material = materialEditor.target as Material;

        // Make sure that needed setup (ie keywords/renderqueue) are set up if we're switching some existing
        // material to a lightweight shader.
        if (m_FirstTimeApply)
        {
            MaterialChanged(material);
            m_FirstTimeApply = false;
        }

        ShaderPropertiesGUI(material);
    }

    public static void SetupMaterialBlendMode(Material material)
    {
        bool alphaClip = material.GetFloat("_AlphaClip") == 1;
        if (alphaClip)
            material.EnableKeyword("_ALPHATEST_ON");
        else
            material.DisableKeyword("_ALPHATEST_ON");

        SurfaceType surfaceType = (SurfaceType)material.GetFloat("_Surface");
        if (surfaceType == SurfaceType.Opaque)
        {
            material.SetOverrideTag("RenderType", "");
            material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.One);
            material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.Zero);
            material.SetInt("_ZWrite", 1);
            material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
            material.renderQueue = -1;
            material.SetShaderPassEnabled("ShadowCaster", true);
        }
        else
        {
            BlendMode blendMode = (BlendMode)material.GetFloat("_Blend");
            switch (blendMode)
            {
                case BlendMode.Alpha:
                    material.SetOverrideTag("RenderType", "Transparent");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.SrcAlpha);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha);
                    material.SetInt("_ZWrite", 0);
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
                    material.SetShaderPassEnabled("ShadowCaster", false);
                    break;
                case BlendMode.Premultiply:
                    material.SetOverrideTag("RenderType", "Transparent");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.One);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha);
                    material.SetInt("_ZWrite", 0);
                    material.EnableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
                    material.SetShaderPassEnabled("ShadowCaster", false);
                    break;
                case BlendMode.Additive:
                    material.SetOverrideTag("RenderType", "Transparent");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.One);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.One);
                    material.SetInt("_ZWrite", 0);
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
                    material.SetShaderPassEnabled("ShadowCaster", false);
                    break;
                case BlendMode.Multiply:
                    material.SetOverrideTag("RenderType", "Transparent");
                    material.SetInt("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.DstColor);
                    material.SetInt("_DstBlend", (int)UnityEngine.Rendering.BlendMode.Zero);
                    material.SetInt("_ZWrite", 0);
                    material.DisableKeyword("_ALPHAPREMULTIPLY_ON");
                    material.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
                    material.SetShaderPassEnabled("ShadowCaster", false);
                    break;
            }
        }
    }

    protected void DoPopup(string label, MaterialProperty property, string[] options)
    {
        EditorGUI.showMixedValue = property.hasMixedValue;

        var mode = property.floatValue;
        EditorGUI.BeginChangeCheck();
        mode = EditorGUILayout.Popup(label, (int)mode, options);
        if (EditorGUI.EndChangeCheck())
        {
            m_MaterialEditor.RegisterPropertyChangeUndo(label);
            property.floatValue = (float)mode;
        }

        EditorGUI.showMixedValue = false;
    }

    protected void DoMaterialRenderingOptions()
    {
        EditorGUILayout.Space();
        GUILayout.Label(Styles.renderingOptionsLabel, EditorStyles.boldLabel);
        m_MaterialEditor.EnableInstancingField();
        m_MaterialEditor.DoubleSidedGIField();
    }
}