// Onsets become places. The song does not move the agents directly; it puts
// food down, and the agents grow on it.
//
// Three rules make the geography legible:
//   - the voice picks the ring: kick near the centre, body in the middle,
//     air at the rim, so a track's mix is visible as an annulus;
//   - the dominant pitch picks the angle, so twelve pitch classes become
//     twelve sectors and harmony becomes direction;
//   - strength sets how much food and how wide, so a hit is a place and a
//     fill is a region.

const TAU = Math.PI * 2;
const RINGS = [0.24, 0.54, 0.82];

export function buildEvents(analysis, rng) {
    const events = [];
    const keys = analysis.summary.chroma ? 12 : 0;
    for (const o of analysis.onsets.all) {
        const f = o.frame;
        const hz = analysis.dominantHz[f] || 440;
        const semis = Math.round(12 * Math.log2(hz / 440));
        const pc = ((semis % 12) + 12 + 9) % 12;
        // A quiet, noisy band has an unstable dominant bin. Pull the angle
        // toward the event's own hash when the band is flat.
        const confidence = 0.55 + 0.45 * (1 - (analysis.flatness[f] ?? 0.3));
        const angle = ((pc / (keys || 12)) * TAU) * confidence +
            rng.range(-0.16, 0.16) +
            (o.voice - 1) * 0.05;
        const radius = RINGS[o.voice] * (0.82 + 0.36 * rng.next());
        const strength = Math.max(0, Math.min(1, 0.18 + 0.82 * o.strength));

        events.push({
            frame: f,
            t: o.t,
            voice: o.voice,
            strength,
            x: 0.5 + Math.cos(angle) * radius * 0.5,
            y: 0.5 + Math.sin(angle) * radius * 0.5,
            // World units. A wide event is a region, not a point.
            spread: 0.014 + 0.040 * strength * strength,
            // Food units. Scaled so a dense arrangement supports roughly a
            // thousand agents and a sparse one a few hundred; see the report.
            amount: (10 + 34 * strength * strength) * 0.11,
            // Strong events seed life as well as food.
            spawn: strength > 0.62 ? (o.voice === 0 ? 3 : o.voice === 1 ? 2 : 1) : 0,
            born: 0,
        });
    }
    return events;
}

/** Frame -> events, so the world steps in O(events this frame). */
export function indexEvents(events, frames) {
    const index = Array.from({ length: frames }, () => []);
    for (const e of events) {
        if (e.frame >= 0 && e.frame < frames) index[e.frame].push(e);
    }
    return index;
}