#include <flutter/runtime_effect.glsl>

// Output surface size in pixels.
uniform vec2 uResolution;
// One source-texel step in UV space: (1/width, 1/height).
uniform vec2 uTexel;
// 1.0 enables CRT post-process effects, 0.0 keeps only base AA.
uniform float uEffectsEnabled;
// Engine time in seconds used to animate scanline travel.
uniform float uTime;
// Source frame produced by the software renderer.
uniform sampler2D uTexture;

out vec4 fragColor;

// Perceptual brightness approximation used for edge detection.
float luma(vec3 color) {
  return dot(color, vec3(0.299, 0.587, 0.114));
}

void main() {
  // Convert fragment coordinates to normalized UV coordinates.
  vec2 uv = FlutterFragCoord().xy / uResolution;

  if (uEffectsEnabled > 0.5) {
    // Barrel-like warp to emulate curved CRT glass.
    vec2 centered = uv * 2.0 - 1.0;
    float radius2 = dot(centered, centered);
    centered *= 1.0 + radius2 * 0.045;
    uv = centered * 0.5 + 0.5;

    // Fill outside warped bounds with a subtle gray plastic TV bezel.
    if (uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0) {
      vec2 clampedUv = clamp(uv, 0.0, 1.0);
      vec2 edgeDelta = abs(uv - clampedUv);
      float overflow = max(edgeDelta.x, edgeDelta.y);

      float verticalShade = 0.96 + 0.06 * (1.0 - (FlutterFragCoord().y / uResolution.y));
      float depthShade = 1.0 - smoothstep(0.0, 0.06, overflow) * 0.18;
      float grain = sin(FlutterFragCoord().x * 0.21 + FlutterFragCoord().y * 0.11) * 0.01;

      vec3 bezelColor = vec3(0.46, 0.46, 0.44) * verticalShade * depthShade + vec3(grain);
      fragColor = vec4(bezelColor, 1.0);
      return;
    }
  }

  // Read the base color from the source frame.
  vec4 centerSample = texture(uTexture, uv);

  // Sample 4-neighborhood (N/S/E/W) around the current pixel.
  vec3 sampleN = texture(uTexture, uv + vec2(0.0, -uTexel.y)).rgb;
  vec3 sampleS = texture(uTexture, uv + vec2(0.0, uTexel.y)).rgb;
  vec3 sampleE = texture(uTexture, uv + vec2(uTexel.x, 0.0)).rgb;
  vec3 sampleW = texture(uTexture, uv + vec2(-uTexel.x, 0.0)).rgb;

  // Compute local luma range; wider range means a stronger edge.
  float lumaCenter = luma(centerSample.rgb);
  float lumaMin = min(
    lumaCenter,
    min(min(luma(sampleN), luma(sampleS)), min(luma(sampleE), luma(sampleW)))
  );
  float lumaMax = max(
    lumaCenter,
    max(max(luma(sampleN), luma(sampleS)), max(luma(sampleE), luma(sampleW)))
  );

  float edgeSpan = max(lumaMax - lumaMin, 0.0001);
  // Convert raw edge strength into a smooth 0..1 blending amount.
  float edgeAmount = smoothstep(0.03, 0.18, edgeSpan);

  // Average neighbors and blend toward that average only near edges.
  // This acts like a lightweight edge-aware anti-aliasing pass.
  vec3 neighborhoodAvg = (sampleN + sampleS + sampleE + sampleW) * 0.25;
  vec3 aaColor = mix(centerSample.rgb, neighborhoodAvg, edgeAmount * 0.45);

  // Preserve source alpha and output the anti-aliased color.
  vec3 outColor = aaColor;

  if (uEffectsEnabled > 0.5) {
    // Horizontal scanline modulation.
    float scanlineBand = 0.88 + 0.12 * sin(uv.y * uResolution.y * 3.14159265);

    // Slow bright line crawling down the screen.
    float sweepPos = fract(uTime * 0.08);
    float sweepBand = 1.0 + 0.16 * exp(-pow((uv.y - sweepPos) * 120.0, 2.0));

    // Slight center brightening and edge falloff (CRT phosphor + lens feel).
    vec2 centeredUv = uv * 2.0 - 1.0;
    float vignette = smoothstep(1.15, 0.25, length(centeredUv));
    float centerLift = 1.0 + 0.08 * (1.0 - length(centeredUv));

    outColor *= scanlineBand * sweepBand * centerLift;
    outColor *= mix(0.62, 1.0, vignette);
  }

  fragColor = vec4(outColor, centerSample.a);
}