Shader "Custom/WaterToggleURP"
{
    Properties
    {
        _NormalMap ("Normal Map", 2D) = "bump" {}
        _ReflectMap ("Reflection Map", 2D) = "white" {}
        _Strength ("Distortion Strength", Range(0, 0.2)) = 0.05
        _WaterTint ("Water Tint", Color) = (0.85, 0.85, 0.85, 1)
        _FacingColor ("Facing Color", Color) = (1,1,1,1)
        _GrazingColor ("Grazing Color", Color) = (0.5,0.5,0.5,1)
        _SpecColor ("Spec Color", Color) = (1,1,1,1)
        _SpecIntensity ("Spec Intensity", Range(0, 4)) = 1
        _RefractionStrength ("Refraction Strength", Range(0, 0.1)) = 0.02
    }

    SubShader
    {
        Tags { "Queue"="Transparent" "RenderType"="Transparent" }
        LOD 300

        Pass
        {
            Name "ForwardLit"
            Tags { "LightMode"="UniversalForward" }

            HLSLPROGRAM
            //-------------------------------------
            // Setup
            //-------------------------------------
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile _ _EXPENSIVE_WATER

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            TEXTURE2D(_NormalMap); SAMPLER(sampler_NormalMap);
            TEXTURE2D(_ReflectMap); SAMPLER(sampler_ReflectMap);
            TEXTURE2D(_CameraOpaqueTexture); SAMPLER(sampler_CameraOpaqueTexture);

            float _Strength;
            float4 _WaterTint;
            float4 _FacingColor;
            float4 _GrazingColor;
            float4 _SpecColor;
            float _SpecIntensity;
            float _RefractionStrength;

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

            struct Varyings {
                float4 positionHCS : SV_POSITION;
                float2 uv          : TEXCOORD0;
                float3 viewDirWS   : TEXCOORD1;
                float3 normalWS    : TEXCOORD2;
            };

            //-------------------------------------
            // Vertex shader
            //-------------------------------------
            Varyings vert(Attributes IN)
            {
                Varyings OUT;
                OUT.positionHCS = TransformObjectToHClip(IN.positionOS);

                VertexPositionInputs posInputs = GetVertexPositionInputs(IN.positionOS.xyz);
                VertexNormalInputs  nrmInputs =  GetVertexNormalInputs(IN.normalOS);

                OUT.uv = IN.uv;
                OUT.normalWS = nrmInputs.normalWS;
                OUT.viewDirWS = GetCameraPositionWS() - posInputs.positionWS;

                return OUT;
            }

            //-------------------------------------
            // Fresnel
            //-------------------------------------
            float ComputeFresnel(float3 view, float3 normal)
            {
                float NdotV = saturate(dot(normalize(view), normalize(normal)));
                return pow(1 - NdotV, 5);
            }

            //-------------------------------------
            // Fragment shader
            //-------------------------------------
            float4 frag(Varyings IN) : SV_Target
            {
                float3 Nmap = SAMPLE_TEXTURE2D(_NormalMap, sampler_NormalMap, IN.uv).xyz;
                Nmap = normalize(Nmap * 2 - 1);

                // Combine geometry normal + normal map
                float3 N = normalize(IN.normalWS + Nmap);

                //-------------------------------------
                // UV distortion
                //-------------------------------------
                float2 uvDistort = IN.uv + N.xy * _Strength;

                //-------------------------------------
                // Fresnel
                //-------------------------------------
                float fresnel = ComputeFresnel(IN.viewDirWS, N);

                //-------------------------------------
                // Reflection
                //-------------------------------------
                float3 reflectCol = SAMPLE_TEXTURE2D(_ReflectMap, sampler_ReflectMap, uvDistort).rgb;
                reflectCol *= _WaterTint.rgb;

                //-------------------------------------
                // Refraction (only if expensive mode)
                //-------------------------------------
                float3 refractCol = reflectCol;

                #ifdef _EXPENSIVE_WATER
                    float2 refractUV = IN.uv + N.xy * _RefractionStrength;
                    refractCol = SAMPLE_TEXTURE2D(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, refractUV).rgb;
                #endif

                //-------------------------------------
                // Fresnel blend (reflect vs refract)
                //-------------------------------------
                float3 combined = lerp(refractCol, reflectCol, fresnel);

                //-------------------------------------
                // Water color facing/grazing
                //-------------------------------------
                float3 waterCol = lerp(_FacingColor.rgb, _GrazingColor.rgb, fresnel);
                combined *= waterCol;

                //-------------------------------------
                // Specular
                //-------------------------------------
                float3 spec = _SpecColor.rgb * fresnel * _SpecIntensity;

                return float4(combined + spec, 1.0);
            }

            ENDHLSL
        }
    }
}