import { Timestamp, type DocumentReference } from 'firebase-admin/firestore';
import { dayKey } from '../core/time.js';

/**
 * 2026-09-16 EC02·EC05: 누락된 집계를 0으로 채우지 않는다.
 * 원장 C-26 `target = max(1, ceil(avgDau × rate))` · C-27 생성 후 완료 집계일 ≤ [windowDays] 일 평균 ·
 * C-21 집계 기간은 운영값(기본 7일).
 */
export async function eclipseTarget(
  fandom: DocumentReference,
  createdAt: unknown,
  day: string,
  rate = 0.05,
  windowDays = 7,
): Promise<
  { target: number; averageDau: number | null; dauDays: string[] }
  | { result: 'cancelled_error'; cancelReason: string }
> {
  const invalid = (cancelReason: string) => ({ result: 'cancelled_error' as const, cancelReason });
  if (!Number.isFinite(rate) || rate <= 0 || rate > 1) return invalid('INVALID_TARGET_RATE');
  if (!Number.isSafeInteger(windowDays) || windowDays < 1) return invalid('INVALID_DAU_WINDOW');
  if (!(createdAt instanceof Timestamp)) return invalid('MISSING_FANDOM_CREATED_AT');
  // 기존 scheduler/dayKey와 같은 날짜 키로 완료된 일별 집계를 조회한다.
  const createdDay = dayKey(createdAt.toDate());
  if (createdDay > day) return invalid('FUTURE_FANDOM_CREATED_AT');
  if (createdDay === day) return { target: 1, averageDau: null, dauDays: [] };
  const days: string[] = [];
  for (let i = 1; i <= windowDays; i++) {
    const previous = new Date(`${day}T00:00:00Z`);
    previous.setUTCDate(previous.getUTCDate() - i);
    const key = previous.toISOString().slice(0, 10);
    if (key < createdDay) break;
    days.push(key);
  }
  const docs = await fandom.firestore.getAll(
    ...days.map((key) => fandom.collection('fandomDailyStats').doc(key)),
  );
  if (docs.some((doc) => !doc.exists || !Number.isSafeInteger(doc.get('dau')) || doc.get('dau') < 0)) {
    return invalid('MISSING_OR_INVALID_DAU');
  }
  const sum = docs.reduce((total, doc) => total + (doc.get('dau') as number), 0);
  if (!Number.isSafeInteger(sum)) return invalid('INVALID_DAU_TOTAL');
  const averageDau = sum / days.length;
  return { target: Math.max(1, Math.ceil(averageDau * rate)), averageDau, dauDays: days };
}