// Original code from https://gist.github.com/josephbk117/a43f5335cea9b3e12a44f196dc81f30f
Shader "Custom/InteriorReflectionShader"
{
    Properties
    {
        // TODO: Implement me!
        _Opacity("Opacity", Range(0.0, 1.0)) = 1.0
    }

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

            float _Opacity;  // TODO: Implement me!

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

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

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

            // ChatGPT snippet
            float3 BoxProjectReflectionDir(float3 worldPos, float3 worldRefl)
            {
                // Calculate relative position within the box
                float3 boxMin = unity_SpecCube0_BoxMin.xyz;
                float3 boxMax = unity_SpecCube0_BoxMax.xyz;
                float3 boxCenter = 0.5 * (boxMin + boxMax);
                float3 boxSize = boxMax - boxMin;

                float3 localPos = worldPos - boxCenter;
                float3 absLocalRefl = abs(worldRefl);

                // Scale the reflection vector based on which side of the box it hits
                float3 scale = boxSize / absLocalRefl;
                float scaleMin = min(min(scale.x, scale.y), scale.z);
                return localPos + worldRefl * scaleMin;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                half3 worldViewDir = normalize(UnityWorldSpaceViewDir(i.worldPos));  // Direction of ray from the camera towards the object surface
                half3 reflection = reflect(-worldViewDir, i.worldNormal);  // Direction of ray after hitting the surface of object
                reflection = BoxProjectReflectionDir(i.worldPos, reflection);
                half4 skyData = UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, reflection);
                half3 skyColor = DecodeHDR(skyData, unity_SpecCube0_HDR);  // This is done becasue the cubemap is stored HDR
                return half4(skyColor, 1.0);
            }
            ENDCG
        }
    }
}