Shader "Custom/PBR_FresnelRim"
{
    Properties
    {
        _Color       ("Base Color", Color) = (1,1,1,1)
        _MainTex     ("Albedo (RGB) Alpha (A)", 2D) = "white" {}
        _Metallic    ("Metallic", Range(0,1)) = 0.0
        _Glossiness  ("Smoothness", Range(0,1)) = 0.5

        [NoScaleOffset]_BumpMap ("Normal Map", 2D) = "bump" {}
        _BumpScale   ("Normal Scale", Range(0,2)) = 1.0

        [HDR]_RimColor   ("Fresnel Edge Color (HDR)", Color) = (4,4,4,1)
        _RimPower    ("Fresnel Power (falloff)", Range(0.1, 8)) = 3.0
        _RimStrength ("Fresnel Strength (intensity)", Range(0, 10)) = 1.0
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" "Queue"="Geometry" }
        LOD 300

        CGPROGRAM
        #pragma surface surf Standard fullforwardshadows
        #pragma target 3.0
        #pragma multi_compile_instancing

        sampler2D _MainTex;
        fixed4 _Color;
        half _Metallic;
        half _Glossiness;

        sampler2D _BumpMap;
        half _BumpScale;

        fixed4 _RimColor;
        half _RimPower;
        half _RimStrength;

        struct Input
        {
            float2 uv_MainTex;
            float2 uv_BumpMap;
            float3 worldPos;
            float3 viewDir;   // Unity provides world-space view direction
        };

        UNITY_INSTANCING_BUFFER_START(Props)
        UNITY_INSTANCING_BUFFER_END(Props)

        inline float3 UnpackNormalScaled(sampler2D nmap, float2 uv, float scale)
        {
            float3 n = UnpackNormal(tex2D(nmap, uv));
            n.xy *= scale;
            n = normalize(n);
            return n;
        }

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            fixed4 albedo = tex2D(_MainTex, IN.uv_MainTex) * _Color;
            o.Albedo     = albedo.rgb;
            o.Metallic   = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha      = albedo.a;

            // Normal mapping (optional)
            float3 N = float3(0,0,1);
            if (_BumpScale > 0.0001)
                N = UnpackNormalScaled(_BumpMap, IN.uv_BumpMap, _BumpScale);
            else
                N = normalize(o.Normal);

            // Fresnel rim: pow(1 - N·V, power)
            float3 V = normalize(IN.viewDir);
            float ndotv = saturate(dot(N, V));
            float rim   = pow(1.0 - ndotv, _RimPower);

            // Emission drives the glow; HDR color recommended
            o.Emission = _RimColor.rgb * rim * _RimStrength;
        }
        ENDCG
    }

    FallBack "Diffuse"
}