// BlendUnlitShaderGUI.cs
// Custom Material Inspector for Soullies/BlendUnlit
// Drives the GPU Blend equation based on the user-selected Blend Mode.

using UnityEditor;
using UnityEngine;
using UnityEngine.Rendering;

public class BlendUnlitShaderGUI : ShaderGUI
{
    // -------------------------------------------------------------------------
    // Blend mode definitions
    // -------------------------------------------------------------------------
    enum BlendMode
    {
        Alpha         = 0, // SrcAlpha, OneMinusSrcAlpha  – standard transparency
        Additive      = 1, // SrcAlpha, One               – additive / glow, black = invisible
        Multiply      = 2, // DstColor, Zero              – darkens below
        Premultiplied = 3, // One,      OneMinusSrcAlpha  – pre-multiplied alpha / HDR
    }

    static readonly string[] BlendModeNames =
    {
        "Alpha (SrcAlpha, 1-SrcAlpha)",
        "Additive (SrcAlpha, One)",
        "Multiply (DstColor, Zero)",
        "Premultiplied (One, 1-SrcAlpha)",
    };

    // Src / Dst for each BlendMode entry
    static readonly (UnityEngine.Rendering.BlendMode src, UnityEngine.Rendering.BlendMode dst)[] BlendEquations =
    {
        (UnityEngine.Rendering.BlendMode.SrcAlpha,  UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha), // Alpha
        (UnityEngine.Rendering.BlendMode.SrcAlpha,  UnityEngine.Rendering.BlendMode.One),              // Additive
        (UnityEngine.Rendering.BlendMode.DstColor,  UnityEngine.Rendering.BlendMode.Zero),             // Multiply
        (UnityEngine.Rendering.BlendMode.One,       UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha), // Premultiplied
    };

    // -------------------------------------------------------------------------
    // GUI
    // -------------------------------------------------------------------------
    public override void OnGUI(MaterialEditor editor, MaterialProperty[] props)
    {
        Material mat = editor.target as Material;

        EditorGUI.BeginChangeCheck();

        // Draw all standard properties EXCEPT our hidden blend props
        foreach (var prop in props)
        {
            // Hide internal blend-equation float props from inspector
            if (prop.name == "_SrcBlendRGB" || prop.name == "_DstBlendRGB")
                continue;

            // Replace the raw _BlendMode float with our friendly enum popup
            if (prop.name == "_BlendMode")
            {
                EditorGUILayout.Space(4);
                DrawBlendModePopup(editor, mat, prop);
                EditorGUILayout.Space(4);
                continue;
            }

            editor.ShaderProperty(prop, prop.displayName);
        }

        if (EditorGUI.EndChangeCheck())
        {
            // Apply blend equations to all selected materials
            foreach (Object obj in editor.targets)
            {
                ApplyBlendMode((Material)obj);
            }
        }

        EditorGUILayout.Space(8);
        editor.RenderQueueField();
        editor.EnableInstancingField();
        editor.DoubleSidedGIField();
    }

    // -------------------------------------------------------------------------
    // Helpers
    // -------------------------------------------------------------------------
    static void DrawBlendModePopup(MaterialEditor editor, Material mat, MaterialProperty prop)
    {
        int current = (int)prop.floatValue;
        current = Mathf.Clamp(current, 0, BlendModeNames.Length - 1);

        EditorGUI.BeginChangeCheck();
        int selected = EditorGUILayout.Popup("Blend Mode", current, BlendModeNames);
        if (EditorGUI.EndChangeCheck())
        {
            editor.RegisterPropertyChangeUndo("Blend Mode");
            prop.floatValue = selected;
        }
    }

    static void ApplyBlendMode(Material mat)
    {
        int index = Mathf.Clamp((int)mat.GetFloat("_BlendMode"), 0, BlendEquations.Length - 1);
        BlendMode mode = (BlendMode)index;

        // Disable all keyword variants, then enable the correct one
        mat.DisableKeyword("_BLENDMODE_ALPHA");
        mat.DisableKeyword("_BLENDMODE_ADDITIVE");
        mat.DisableKeyword("_BLENDMODE_MULTIPLY");
        mat.DisableKeyword("_BLENDMODE_PREMULTIPLIED");

        switch (mode)
        {
            case BlendMode.Alpha:
                mat.EnableKeyword("_BLENDMODE_ALPHA");
                break;
            case BlendMode.Additive:
                mat.EnableKeyword("_BLENDMODE_ADDITIVE");
                break;
            case BlendMode.Multiply:
                mat.EnableKeyword("_BLENDMODE_MULTIPLY");
                break;
            case BlendMode.Premultiplied:
                mat.EnableKeyword("_BLENDMODE_PREMULTIPLIED");
                break;
        }

        // Write the actual Blend equation floats that the Shader reads
        var (src, dst) = BlendEquations[index];
        mat.SetFloat("_SrcBlendRGB", (float)src);
        mat.SetFloat("_DstBlendRGB", (float)dst);

        // Adjust RenderQueue hint for Multiply mode
        // (Multiply should typically not write ZBuffer and renders as transparent)
        if (mode == BlendMode.Multiply)
        {
            mat.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
        }
        else
        {
            // Keep queue at Transparent for all other modes (default)
            if (mat.renderQueue < (int)UnityEngine.Rendering.RenderQueue.Transparent)
                mat.renderQueue = (int)UnityEngine.Rendering.RenderQueue.Transparent;
        }

        EditorUtility.SetDirty(mat);
    }

    // Called when the Shader is assigned to a material for the first time
    public override void AssignNewShaderToMaterial(Material mat, Shader oldShader, Shader newShader)
    {
        base.AssignNewShaderToMaterial(mat, oldShader, newShader);
        ApplyBlendMode(mat);
    }
}