Shader "BriarQueen/UI/Fog Reveal Haar"
{
    Properties
    {
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Color ("Tint", Color) = (1, 1, 1, 1)

        _FogAmount ("Fog Amount", Range(0, 1)) = 0
        _FogColor ("Fog Color", Color) = (0.18, 0.20, 0.26, 1)
        _FogIntensity ("Fog Intensity", Range(0, 1)) = 0.95
        _EdgeSoftness ("Edge Softness", Range(0.05, 1.0)) = 0.55
        _NoiseScale ("Noise Scale", Range(1, 20)) = 5
        _DriftSpeed ("Drift Speed", Range(0, 0.5)) = 0.04
        _DensityVariation ("Density Variation", Range(0, 1)) = 0.28
        _AspectRatio ("Aspect Ratio", Float) = 1.777
        [Toggle] _FogMotion ("Fog Motion", Float) = 1
        [Toggle] _UseSprite ("Use Sprite", Float) = 0

        _StencilComp ("Stencil Comparison", Float) = 8
        _Stencil ("Stencil ID", Float) = 0
        _StencilOp ("Stencil Operation", Float) = 0
        _StencilWriteMask ("Stencil Write Mask", Float) = 255
        _StencilReadMask ("Stencil Read Mask", Float) = 255
        _ColorMask ("Color Mask", Float) = 15

        [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
            "PreviewType" = "Plane"
            "CanUseSpriteAtlas" = "True"
        }

        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp]
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }

        Cull Off
        Lighting Off
        ZWrite Off
        ZTest [unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask [_ColorMask]

        Pass
        {
            Name "Default"
            CGPROGRAM
            #pragma vertex Vert
            #pragma fragment Frag
            #pragma target 3.0

            #include "UnityCG.cginc"
            #include "UnityUI.cginc"

            #pragma multi_compile_local _ UNITY_UI_CLIP_RECT
            #pragma multi_compile_local _ UNITY_UI_ALPHACLIP

            struct AppData
            {
                float4 vertex   : POSITION;
                float4 color    : COLOR;
                float2 texcoord : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 vertex        : SV_POSITION;
                fixed4 color         : COLOR;
                float2 uv            : TEXCOORD0;
                float4 worldPosition : TEXCOORD1;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            sampler2D _MainTex;
            fixed4 _Color;
            fixed4 _TextureSampleAdd;
            float4 _ClipRect;

            fixed4 _FogColor;
            float  _FogAmount;
            float  _FogIntensity;
            float  _EdgeSoftness;
            float  _NoiseScale;
            float  _DriftSpeed;
            float  _DensityVariation;
            float  _AspectRatio;
            float  _FogMotion;
            float  _UseSprite;

            // ── Noise ─────────────────────────────────────────────────

            float2 Hash22(float2 p)
            {
                p = float2(dot(p, float2(127.1, 311.7)),
                           dot(p, float2(269.5, 183.3)));
                return -1.0 + 2.0 * frac(sin(p) * 43758.5453);
            }

            float GradientNoise(float2 uv)
            {
                float2 i = floor(uv);
                float2 f = frac(uv);
                float2 u = f * f * f * (f * (f * 6.0 - 15.0) + 10.0);

                return lerp(
                    lerp(dot(Hash22(i + float2(0, 0)), f - float2(0, 0)),
                         dot(Hash22(i + float2(1, 0)), f - float2(1, 0)), u.x),
                    lerp(dot(Hash22(i + float2(0, 1)), f - float2(0, 1)),
                         dot(Hash22(i + float2(1, 1)), f - float2(1, 1)), u.x),
                    u.y);
            }

            float HaarFBM(float2 uv, float2 drift)
            {
                float2 p = uv * _NoiseScale;

                float2 uvA = p + drift;
                float n  = GradientNoise(uvA)              * 0.500;
                      n += GradientNoise(uvA * 2.01 + 3.7) * 0.250;
                      n += GradientNoise(uvA * 4.03 + 7.3) * 0.125;
                      n += GradientNoise(uvA * 8.07 + 1.9) * 0.063;

                float2 uvB = p + drift * float2(0.7, -0.4) + float2(17.3, 5.8);
                float m  = GradientNoise(uvB)              * 0.500;
                      m += GradientNoise(uvB * 2.05 + 9.1) * 0.250;
                      m += GradientNoise(uvB * 4.11 + 2.6) * 0.125;

                float combined = lerp(n, m, 0.4);
                return saturate(combined * 0.5 + 0.5);
            }

            // ── Vertex ────────────────────────────────────────────────

            Varyings Vert(AppData input)
            {
                Varyings output;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);

                output.worldPosition = input.vertex;
                output.vertex        = UnityObjectToClipPos(input.vertex);
                output.uv            = input.texcoord;
                output.color         = input.color * _Color;
                return output;
            }

            // ── Fragment ──────────────────────────────────────────────

            fixed4 Frag(Varyings input) : SV_Target
            {
                #ifdef UNITY_UI_CLIP_RECT
                float clipAlpha = UnityGet2DClipping(input.worldPosition.xy, _ClipRect);
                #else
                float clipAlpha = 1.0;
                #endif

                fixed4 texColor = (tex2D(_MainTex, input.uv) + _TextureSampleAdd) * input.color;

                float2 centredUv = input.uv - 0.5;
                centredUv.x *= _AspectRatio;
                float dist = length(centredUv) * 2.0;

                float2 drift = _FogMotion > 0.5
                    ? float2(_Time.y * _DriftSpeed, _Time.y * _DriftSpeed * 0.3)
                    : float2(0.0, 0.0);

                float fogNoise = HaarFBM(input.uv, drift);

                float noiseBias = (fogNoise - 0.5) * _EdgeSoftness * 2.5;
                float softEdge  = _EdgeSoftness * 0.8;

                float threshold = lerp(-_EdgeSoftness * 2.0, 2.5, _FogAmount);

                float fogMask = 1.0 - smoothstep(
                    threshold - softEdge + noiseBias,
                    threshold + softEdge + noiseBias,
                    dist
                );
                fogMask = saturate(fogMask);

                fixed4 result;

                if (_UseSprite > 0.5)
                {
                    // Sprite mode — fog mask directly gates the sprite's alpha
                    // Pixels outside the fog are fully transparent
                    // Pixels inside the fog draw the sprite normally
                    // The fog edge produces a soft natural reveal with noise
                    result.rgb = texColor.rgb;
                    result.a   = texColor.a * fogMask * clipAlpha;
                }
                else
                {
                    // Transparent mode — purely procedural fog colour
                    float density = 1.0 - fogNoise * _DensityVariation;
                    result.rgb = _FogColor.rgb * density;
                    result.a   = fogMask * _FogIntensity * clipAlpha;
                }

                #ifdef UNITY_UI_ALPHACLIP
                clip(result.a - 0.001);
                #endif

                return result;
            }
            ENDCG
        }
    }
}