const admin = require("firebase-admin");
const { onSchedule } = require("firebase-functions/v2/scheduler");
const { refList } = require("../index");
const firestore = refList.projects.firestore;

function buildMonthContext(referenceDate) {
  const current = referenceDate ? new Date(referenceDate) : new Date();
  current.setHours(0, 0, 0, 0);
  current.setDate(1);

  const target = new Date(current);
  target.setMonth(target.getMonth() - 1);

  const month = target.getMonth();
  const year = target.getFullYear();
  const monthKey = `${year}-${String(month + 1).padStart(2, "0")}`;
  const rangeStart = new Date(year, month, 1, 0, 0, 0, 0);
  const rangeEnd = new Date(year, month + 1, 0, 23, 59, 59, 999);

  return {
    year,
    month: month + 1,
    monthKey,
    rangeStart,
    rangeEnd,
  };
}

exports.snapshotMonthlyTopSongs = onSchedule(
  {
    schedule: "5 0 1 * *",
    timeZone: "Europe/Paris",
  },
  async (event) => {
    const { scheduleTime } = event;
    const context = buildMonthContext(
      scheduleTime ? new Date(scheduleTime) : new Date()
    );

    const topProjectsSnap = await refList.projects
      .orderBy("views", "desc")
      .limit(3)
      .get();

    const topProjects = topProjectsSnap.docs.map((doc, index) => {
      const data = doc.data() || {};
      return {
        rank: index + 1,
        projectId: doc.id,
        title: data.title || null,
        userId: data.userId || null,
        userName: data.userName || null,
        coverUrl: data.coverUrl || null,
        songUrl: data.songUrl || null,
        views: data.views || 0,
      };
    });

    const docRef = firestore
      .collection("monthlyTopSongs")
      .doc(context.monthKey);

    const existingSnapshot = await docRef.get();
    const payload = {
      monthKey: context.monthKey,
      month: context.month,
      year: context.year,
      range: {
        start: admin.firestore.Timestamp.fromDate(context.rangeStart),
        end: admin.firestore.Timestamp.fromDate(context.rangeEnd),
      },
      topProjects,
      totalProjects: topProjects.length,
      updatedAt: admin.firestore.FieldValue.serverTimestamp(),
    };

    if (!existingSnapshot.exists) {
      payload.createdAt = admin.firestore.FieldValue.serverTimestamp();
    }

    await docRef.set(payload, { merge: true });
  }
);