export type MomentAsset = {
  id: string;
  capture_ts_utc: string;
};

export type MomentCluster = {
  day: string;
  start: string;
  end: string;
  count: number;
  assets: MomentAsset[];
};

const MOMENT_WINDOW_MINUTES = 30;
const MOMENT_WINDOW_MS = MOMENT_WINDOW_MINUTES * 60 * 1000;

function dayKeyFromIso(iso: string) {
  const d = new Date(iso);
  const yyyy = d.getUTCFullYear();
  const mm = String(d.getUTCMonth() + 1).padStart(2, "0");
  const dd = String(d.getUTCDate()).padStart(2, "0");
  return `${yyyy}-${mm}-${dd}`;
}

export function clusterMoments(input: MomentAsset[]): MomentCluster[] {
  const byDay = new Map<string, MomentAsset[]>();

  for (const asset of input) {
    if (!asset.capture_ts_utc) continue;
    const key = dayKeyFromIso(asset.capture_ts_utc);
    const list = byDay.get(key);
    if (list) list.push(asset);
    else byDay.set(key, [asset]);
  }

  const clusters: MomentCluster[] = [];

  for (const [day, assets] of byDay) {
    const sorted = [...assets].sort((a, b) =>
      a.capture_ts_utc.localeCompare(b.capture_ts_utc),
    );

    let current: MomentAsset[] = [];
    let lastTs: number | null = null;

    for (const asset of sorted) {
      const ts = new Date(asset.capture_ts_utc).getTime();
      if (!Number.isFinite(ts)) continue;

      if (lastTs === null || ts - lastTs <= MOMENT_WINDOW_MS) {
        current.push(asset);
      } else {
        const start = current[0]?.capture_ts_utc;
        const end = current[current.length - 1]?.capture_ts_utc;
        if (start && end) {
          clusters.push({
            day,
            start,
            end,
            count: current.length,
            assets: current,
          });
        }
        current = [asset];
      }

      lastTs = ts;
    }

    if (current.length) {
      const start = current[0].capture_ts_utc;
      const end = current[current.length - 1].capture_ts_utc;
      clusters.push({
        day,
        start,
        end,
        count: current.length,
        assets: current,
      });
    }
  }

  return clusters;
}