//
// CRT-Pi Fragment Shader - Metal Shading Language
// Portado desde GLSL a MSL para macOS
//

#include <metal_stdlib>
using namespace metal;

// Configuración (equivalente a los #define en GLSL)
constant bool SCANLINES = true;
constant bool MULTISAMPLE = true;
constant bool GAMMA = true;
constant bool FAKE_GAMMA = false;
constant bool CURVATURE = false;
constant bool SHARPER = false;
constant int MASK_TYPE = 2;  // 0=none, 1=green/magenta, 2=trinitron

constant float CURVATURE_X = 0.05;
constant float CURVATURE_Y = 0.1;
constant float MASK_BRIGHTNESS = 0.80;
constant float SCANLINE_WEIGHT = 6.0;
constant float SCANLINE_GAP_BRIGHTNESS = 0.12;
constant float BLOOM_FACTOR = 3.5;
constant float INPUT_GAMMA = 2.4;
constant float OUTPUT_GAMMA = 2.2;

// Estructura de entrada (salida del vertex shader)
struct VertexOut {
    float4 position [[position]];
    float2 texCoord;
    float filterWidth;
    // float2 screenScale;  // Solo si CURVATURE está activo
};

// Uniforms
struct Uniforms {
    float2 textureSize;
};

// Función para calcular el peso de la scanline
float CalcScanLineWeight(float dist) {
    return max(1.0 - dist * dist * SCANLINE_WEIGHT, SCANLINE_GAP_BRIGHTNESS);
}

// Función para calcular scanline con multisampling
float CalcScanLine(float dy, float filterWidth) {
    float scanLineWeight = CalcScanLineWeight(dy);
    if (MULTISAMPLE) {
        scanLineWeight += CalcScanLineWeight(dy - filterWidth);
        scanLineWeight += CalcScanLineWeight(dy + filterWidth);
        scanLineWeight *= 0.3333333;
    }
    return scanLineWeight;
}

// Entry point del fragment shader
fragment float4 fragment_main(VertexOut in [[stage_in]],
                              texture2d<float> colorTexture [[texture(0)]],
                              constant Uniforms& uniforms [[buffer(1)]],
                              sampler textureSampler [[sampler(0)]]) {

    float2 texcoord = in.texCoord;

    // Si CURVATURE estuviera activo, aquí iría la función Distort()

    float2 texcoordInPixels = texcoord * uniforms.textureSize;

    float2 tc;
    float scanLineWeight;

    if (!SHARPER) {
        // Modo normal (no SHARPER)
        float tempY = floor(texcoordInPixels.y) + 0.5;
        float yCoord = tempY / uniforms.textureSize.y;
        float dy = texcoordInPixels.y - tempY;
        scanLineWeight = CalcScanLine(dy, in.filterWidth);
        float signY = sign(dy);
        dy = dy * dy;
        dy = dy * dy;
        dy *= 8.0;
        dy /= uniforms.textureSize.y;
        dy *= signY;
        tc = float2(texcoord.x, yCoord + dy);
    } else {
        // Modo SHARPER
        float2 tempCoord = floor(texcoordInPixels) + 0.5;
        float2 coord = tempCoord / uniforms.textureSize;
        float2 deltas = texcoordInPixels - tempCoord;
        scanLineWeight = CalcScanLine(deltas.y, in.filterWidth);
        float2 signs = sign(deltas);
        deltas.x *= 2.0;
        deltas = deltas * deltas;
        deltas.y = deltas.y * deltas.y;
        deltas.x *= 0.5;
        deltas.y *= 8.0;
        deltas /= uniforms.textureSize;
        deltas *= signs;
        tc = coord + deltas;
    }

    // Muestrear textura (texture() en GLSL = sample() en MSL)
    float3 colour = colorTexture.sample(textureSampler, tc).rgb;

    if (SCANLINES) {
        if (GAMMA) {
            if (FAKE_GAMMA) {
                colour = colour * colour;
            } else {
                colour = pow(colour, float3(INPUT_GAMMA));
            }
        }
        scanLineWeight *= BLOOM_FACTOR;
        colour *= scanLineWeight;

        if (GAMMA) {
            if (FAKE_GAMMA) {
                colour = sqrt(colour);
            } else {
                colour = pow(colour, float3(1.0 / OUTPUT_GAMMA));
            }
        }
    }

    // Aplicar máscara CRT
    if (MASK_TYPE == 0) {
        return float4(colour, 1.0);
    } else if (MASK_TYPE == 1) {
        // Máscara verde/magenta
        float whichMask = fract(in.position.x * 0.5);
        float3 mask;
        if (whichMask < 0.5) {
            mask = float3(MASK_BRIGHTNESS, 1.0, MASK_BRIGHTNESS);
        } else {
            mask = float3(1.0, MASK_BRIGHTNESS, 1.0);
        }
        return float4(colour * mask, 1.0);
    } else if (MASK_TYPE == 2) {
        // Máscara trinitron
        float whichMask = fract(in.position.x * 0.3333333);
        float3 mask = float3(MASK_BRIGHTNESS, MASK_BRIGHTNESS, MASK_BRIGHTNESS);
        if (whichMask < 0.3333333) {
            mask.x = 1.0;
        } else if (whichMask < 0.6666666) {
            mask.y = 1.0;
        } else {
            mask.z = 1.0;
        }
        return float4(colour * mask, 1.0);
    }

    return float4(colour, 1.0);
}