4D schedule dates and status

export function parseDay(s) {
  const m = /^(\d{4})-(\d{2})-(\d{2})$/.exec(String(s ?? '').trim());
  if (!m) return null;
  const d = Date.UTC(+m[1], +m[2] - 1, +m[3]);
  const back = new Date(d);
  if (back.getUTCFullYear() !== +m[1] || back.getUTCMonth() !== +m[2] - 1 || back.getUTCDate() !== +m[3]) return null;   // 2026-02-30
  return Math.round(d / 86400000);
}

export function statusAt(matched, day) {
  const all = new Map();   // key → [built, progress, waiting] counts over its tasks
  for (const t of matched) {
    const i = day > t.finish ? 0 : day >= t.start ? 1 : 2;   // in progress from Start through Finish, built the day after
    for (const k of t.keys) { let c = all.get(k); if (!c) all.set(k, (c = [0, 0, 0])); c[i]++; }
  }
  const st = new Map();
  for (const [k, c] of all) st.set(k, c[1] || (c[0] && c[2]) ? 'progress' : c[0] ? 'built' : 'waiting');   // built in one task, not started in another: still being worked on
  return st;
}

export function groupState(tasks, day) {
  const n = { done: 0, now: 0, todo: 0 };
  for (const t of tasks) n[day > t.finish ? 'done' : day >= t.start ? 'now' : 'todo']++;
  return n;
}