Shader "Custom/InteriorReflectionShader"
{
    Properties
    {
        _ReflectionIntensity ("Reflection Intensity", Range(0, 1)) = 1.0
    }
    
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 300

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            float _ReflectionIntensity;

            // Use built-in cubemap sampler (unity_SpecCube0) for reflection probe
            // UNITY_DECLARE_TEXCUBE(unity_SpecCube0);

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                float3 worldPos : TEXCOORD0;
                float3 worldNormal : TEXCOORD1;
            };

            v2f vert (appdata v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                o.worldNormal = normalize(mul((float3x3)unity_ObjectToWorld, v.normal));
                return o;
            }

            half3 ComputeBoxProjectedReflection(float3 worldPos, float3 worldNormal)
            {
                // Calculate direction from the object to the reflection probe position
                float3 probeToPixel = worldPos - unity_SpecCube0_ProbePosition;

                // Calculate inverse box scale manually
                float3 boxSize = unity_SpecCube0_BoxMax - unity_SpecCube0_BoxMin;
                float3 invBoxSize = 1.0 / boxSize;

                // Transform the position into the box projection space
                float3 localPos = probeToPixel * invBoxSize + 0.5;

                // Calculate reflection direction
                float3 reflectionDir = normalize(worldPos - _WorldSpaceCameraPos);

                // Sample the cubemap using the adjusted reflection direction
                return UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, reflectionDir).rgb;
            }

            half4 frag (v2f i) : SV_Target
            {
                // Calculate reflection using box projection
                half3 reflectionColor = ComputeBoxProjectedReflection(i.worldPos, i.worldNormal);
                return half4(reflectionColor, 1.0);
            }
            ENDCG
        }
    }
    
    FallBack "Diffuse"
}