#define PI 3.141592653589793

vec2 pxToNdc(vec2 p, float isPosition) {
    return (p * 2.0 - iResolution.xy * isPosition) / iResolution.y;
}

float segPos(vec2 p, vec2 a, vec2 b) {
    vec2 ba = b - a;
    return clamp(dot(p - a, ba) / max(dot(ba, ba), 0.000001), 0.0, 1.0);
}

float segDist(vec2 p, vec2 a, vec2 b) {
    float h = segPos(p, a, b);
    return length(p - (a + (b - a) * h));
}

float diamond(vec2 p, vec2 c, float r) {
    float d = abs(p.x - c.x) + abs(p.y - c.y);
    return 1.0 - smoothstep(r * 0.25, r, d);
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec4 base = texture(iChannel0, uv);
    vec3 col = base.rgb;

    vec2 p = pxToNdc(fragCoord.xy, 1.0);

    // Ghostty cursor rect: xy is the top-left-ish corner, zw is width/height.
    vec2 curPx = vec2(
        iCurrentCursor.x + iCurrentCursor.z * 0.5,
        iCurrentCursor.y - iCurrentCursor.w * 0.5
    );

    vec2 prevPx = vec2(
        iPreviousCursor.x + iPreviousCursor.z * 0.5,
        iPreviousCursor.y - iPreviousCursor.w * 0.5
    );

    vec2 cur = pxToNdc(curPx, 1.0);
    vec2 prev = pxToNdc(prevPx, 1.0);

    float cell = max(0.008, max(iCurrentCursor.z, iCurrentCursor.w) * 2.0 / iResolution.y);
    float age = clamp(iTime - iTimeCursorChange, 0.0, 2.0);
    float pulse = exp(-age * 4.5);

    float moved = smoothstep(cell * 1.2, cell * 5.0, distance(cur, prev));

    // Orange-gold trail after cursor jumps.
    float h = segPos(p, prev, cur);
    float trailD = segDist(p, prev, cur);
    float trail = (1.0 - smoothstep(cell * 0.18, cell * 0.85, trailD));
    trail *= sin(h * PI) * moved * pulse;

    col += trail * vec3(1.0, 0.36, 0.05) * 0.90;

    // Gold glow around current cursor.
    float d = length(p - cur);
    float shimmer = 0.75 + 0.25 * sin(iTime * 9.0 + d * 90.0);
    float glow = exp(-d / (cell * 4.0)) * 0.28 * shimmer;
    col += glow * vec3(1.0, 0.62, 0.12);

    // Expanding diamond ring when cursor moves.
    float ringRadius = cell * (1.30 + 2.20 * pulse);
    float ring = 1.0 - smoothstep(cell * 0.10, cell * 0.35, abs(d - ringRadius));
    col += ring * vec3(1.0, 0.92, 0.65) * (0.42 + 0.75 * pulse);

    // Tiny orbiting diamonds: pinky ring / grill sparkle.
    float orbit = 0.0;
    for (int k = 0; k < 8; k++) {
        float fi = float(k);
        float dir = mix(-1.0, 1.0, step(0.5, mod(fi, 2.0)));
        float a = fi * PI * 2.0 / 8.0 + iTime * (1.5 + 0.1 * fi) * dir;
        float rad = cell * (2.4 + 0.45 * sin(iTime * 2.0 + fi * 1.7));
        vec2 q = cur + vec2(cos(a), sin(a)) * rad;

        float tw = 0.65 + 0.35 * sin(iTime * 7.0 + fi * 2.0);
        orbit += diamond(p, q, cell * 0.45) * tw;
    }

    col += orbit * vec3(1.0, 0.86, 0.50) * 0.70;

    // Cross flare directly on cursor.
    float flareX = (1.0 - smoothstep(0.0, cell * 0.035, abs(p.y - cur.y))) *
                   (1.0 - smoothstep(0.0, cell * 4.5, abs(p.x - cur.x)));
    float flareY = (1.0 - smoothstep(0.0, cell * 0.035, abs(p.x - cur.x))) *
                   (1.0 - smoothstep(0.0, cell * 4.5, abs(p.y - cur.y)));
    col += (flareX + flareY) * vec3(1.0, 0.92, 0.60) * 0.11;

    fragColor = vec4(clamp(col, 0.0, 1.0), base.a);
}