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
    }

    public abstract void FindProperties(MaterialProperty[] props);
    public abstract void ShaderPropertiesGUI(Material material);
    public abstract void MaterialChanged(Material material);

    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);
    }

    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;
    }

    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 MaterialEditor m_MaterialEditor;
    private bool m_FirstTimeApply = true;
}