Shader "SLS/Postprocessing/HyperTunnel"
{
    SubShader
    {
        Tags
        {
            "RenderType" = "Opaque"
            "RenderPipeline" = "UniversalPipeline"
        }
        ZWrite Off Cull Off ZTest Always
        
        HLSLINCLUDE
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
        #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"

        float4 _HyperTunnelColor;
        // x: speed, y: intensity, z: radial blur amount, w: CA intensity
        float4 _HyperTunnelParams; 
        float2 _HyperTunnelCenter;

        // --- Fast Mobile-friendly Simplex Noise ---
        float3 mod2D289(float3 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
        float2 mod2D289(float2 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
        float3 permute(float3 x) { return mod2D289(((x * 34.0) + 1.0) * x); }
        
        float snoise(float2 v) 
        { 
            const float4 C = float4(0.211324865, 0.366025403, -0.577350269, 0.024390243);
            float2 i  = floor(v + dot(v, C.yy));
            float2 x0 = v - i + dot(i, C.xx); 
            float2 i1 = (x0.x > x0.y) ? float2(1.0, 0.0) : float2(0.0, 1.0);
            float4 x12 = x0.xyxy + C.xxzz; x12.xy -= i1;
            i = mod2D289(i);
            float3 p = permute(permute(i.y + float3(0.0, i1.y, 1.0)) + i.x + float3(0.0, i1.x, 1.0));
            float3 m = max(0.5 - float3(dot(x0, x0), dot(x12.xy, x12.xy), dot(x12.zw, x12.zw)), 0.0);
            m = m * m; m = m * m;
            float3 x = 2.0 * frac(p * C.www) - 1.0; 
            float3 h = abs(x) - 0.5;
            float3 ox = floor(x + 0.5); 
            float3 a0 = x - ox;
            m *= 1.792842914 - 0.85373472 * (a0 * a0 + h * h); 
            float3 g;
            g.x  = a0.x  * x0.x  + h.x  * x0.y; 
            g.yz = a0.yz * x12.xz + h.yz * x12.yw;
            return 130.0 * dot(m, g); 
        }

        half4 Fragment(Varyings input) : SV_Target
        {
            float2 uv = input.texcoord;
            
            // parameter unpacking setup
            float speed = _HyperTunnelParams.x;
            float lineIntensity = _HyperTunnelParams.y;
            float blurAmount = _HyperTunnelParams.z;
            float caIntensity = _HyperTunnelParams.w;
            float2 center = _HyperTunnelCenter;

            // distance vector from center
            float2 dir = uv - center;
            float dist = length(dir);
            float2 normDir = dir / (dist + 0.0001); // avoid div zero

            // Mask out the center (Tunnel illusion)
            // No blur or lines in the exact center focus point
            float centerMask = smoothstep(0.05, 0.4, dist);

            // ===================================
            // 1. Radial Blur + Chromatic Aberration 
            // ===================================
            // Mobile Optimization: Interleaved 4 loop calculation
            int samples = 4;
            float intensityMultiplier = centerMask; 
            
            half3 finalColor = half3(0, 0, 0);
            
            // Unroll loop for mobile shader registers
            UNITY_UNROLL
            for(int i = 0; i < 4; ++i)
            {
                float t = (float)i / (3.0); 
                float2 offsetBlur = dir * t * blurAmount * intensityMultiplier;
                
                // CA offsets are tangent along the line
                float2 uvR = uv - offsetBlur + normDir * caIntensity * intensityMultiplier * 0.005;
                float2 uvG = uv - offsetBlur;
                float2 uvB = uv - offsetBlur - normDir * caIntensity * intensityMultiplier * 0.005;

                half r = SAMPLE_TEXTURE2D_X(_BlitTexture, sampler_LinearClamp, uvR).r;
                half g = SAMPLE_TEXTURE2D_X(_BlitTexture, sampler_LinearClamp, uvG).g;
                half b = SAMPLE_TEXTURE2D_X(_BlitTexture, sampler_LinearClamp, uvB).b;
                
                finalColor += half3(r, g, b);
            }
            finalColor *= 0.25;

            // ===================================
            // 2. Hyper Speed Lines Overlay
            // ===================================
            // Convert to Polar coordinates
            float angle = atan2(dir.y, dir.x);
            float timeScaled = _Time.y * speed;
            
            float2 noiseUV = float2(angle * 15.0, timeScaled + dist * 5.0);
            float noiseVal = snoise(noiseUV) * 0.5 + 0.5; // [-1,1] to [0,1]
            
            // Power curve for intense sharp lines
            float lines = pow(noiseVal, 9.0) * lineIntensity;
            
            lines *= centerMask;

            half3 hcColor = _HyperTunnelColor.rgb * (_HyperTunnelColor.a * lines);
            
            return half4(finalColor + hcColor, 1.0);
        }
        ENDHLSL

        Pass
        {
            Name "Hyper Tunnel Pass"
            HLSLPROGRAM
            #pragma vertex Vert
            #pragma fragment Fragment
            ENDHLSL
        }
    }
}