Shader "Custom/VenusSurface"
{
    Properties
    {
        _MainTex("Surface Texture", 2D) = "white" {}
        _TroposphereLevel("Troposphere Level", Range(0, 1)) = 1
        _DayColor("Day Color", Color) = (1.0, 0.3, 0.05, 1)
        _NightColor("Night Color", Color) = (0.02, 0.02, 0.08, 1)
        _SunDirection("Sun Direction", Vector) = (1, 0, 0, 0)
    }

        SubShader
        {
            Tags { "RenderType" = "Opaque" "RenderPipeline" = "UniversalPipeline" }

            Pass
            {
                HLSLPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

                struct Attributes
                {
                    float4 positionOS : POSITION;
                    float3 normalOS   : NORMAL;
                    float2 uv         : TEXCOORD0;
                };

                struct Varyings
                {
                    float4 positionHCS : SV_POSITION;
                    float3 normalWS    : TEXCOORD0;
                    float2 uv          : TEXCOORD1;
                };

                TEXTURE2D(_MainTex);
                SAMPLER(sampler_MainTex);

                CBUFFER_START(UnityPerMaterial)
                    float4 _MainTex_ST;
                    float _TroposphereLevel;
                    half4 _DayColor;
                    half4 _NightColor;
                    float4 _SunDirection;
                CBUFFER_END

                Varyings vert(Attributes IN)
                {
                    Varyings OUT;
                    OUT.positionHCS = TransformObjectToHClip(IN.positionOS.xyz);
                    OUT.normalWS = TransformObjectToWorldNormal(IN.normalOS);
                    OUT.uv = TRANSFORM_TEX(IN.uv, _MainTex);
                    return OUT;
                }

                half4 frag(Varyings IN) : SV_Target
                {
                    half4 tex = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, IN.uv);

                    float3 normal = normalize(IN.normalWS);
                    float3 sunDir = normalize(_SunDirection.xyz);
                    float dayFactor = saturate(dot(normal, sunDir));

                    float heatBlend = saturate((1.0 - _TroposphereLevel) * 2.0);
                    float contrastFactor = saturate((1.0 - _TroposphereLevel) * 3.0);
                    dayFactor = saturate(dayFactor * (1.0 + contrastFactor * 2.0));

                    half3 heatColor = lerp(_NightColor.rgb, _DayColor.rgb, dayFactor);
                    half3 finalColor = lerp(tex.rgb, heatColor, heatBlend);

                    return half4(finalColor, 1.0);
                }
                ENDHLSL
            }
        }
}