import { NextResponse } from "next/server";
import prisma from "@/lib/prisma";

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

export async function GET() {
  // 전체 출석 누적 상위 (Top 10)
  const overallGroups = await prisma.attendance.groupBy({
    by: ["userId"],
    _count: { _all: true },
    orderBy: { _count: { _all: "desc" } },
    take: 20,
  });
  const overallUserIds = overallGroups.map((g) => g.userId);
  const overallUsers = await prisma.user.findMany({
    where: { userId: { in: overallUserIds } },
    select: { userId: true, nickname: true, profileImage: true, grade: true },
  });
  const userMeta = new Map(overallUsers.map((u) => [u.userId, u]));
  const overall = overallGroups.map((g) => ({
    userId: g.userId,
    nickname: userMeta.get(g.userId)?.nickname ?? "회원",
    count: g._count._all,
    profileImage: userMeta.get(g.userId)?.profileImage ?? null,
    grade: userMeta.get(g.userId)?.grade ?? 0,
  }));

  // 연속 출석 상위 (Top 10, 현재 연속 기준)
  const now = new Date();
  const todayUTC = new Date(Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate(), 0, 0, 0, 0));
  const past = new Date(todayUTC);
  past.setUTCDate(past.getUTCDate() - 60); // 최근 60일 데이터만으로 streak 계산
  const recent = await prisma.attendance.findMany({
    where: { date: { gte: past } },
    select: { userId: true, date: true },
    orderBy: { userId: "asc" },
  });
  const map = new Map<string, Set<string>>();
  for (const r of recent) {
    const set = map.get(r.userId) ?? new Set<string>();
    set.add(toYmdUTC(new Date(r.date)));
    map.set(r.userId, set);
  }
  const streakArr: { userId: string; streak: number }[] = [];
  for (const [userId, set] of map.entries()) {
    let streak = 0;
    let cursor = new Date(todayUTC);
    while (streak < 60) {
      const ymd = toYmdUTC(cursor);
      if (set.has(ymd)) {
        streak += 1;
        cursor.setUTCDate(cursor.getUTCDate() - 1);
      } else {
        break;
      }
    }
    if (streak > 0) streakArr.push({ userId, streak });
  }
  streakArr.sort((a, b) => b.streak - a.streak);
  const topStreak = streakArr.slice(0, 20);
  const streakUserIds = topStreak.map((s) => s.userId);
  const streakUsers = await prisma.user.findMany({
    where: { userId: { in: streakUserIds } },
    select: { userId: true, nickname: true, profileImage: true, grade: true },
  });
  const streakMeta = new Map(streakUsers.map((u) => [u.userId, u]));
  const streak = topStreak.map((s) => ({
    userId: s.userId,
    nickname: streakMeta.get(s.userId)?.nickname ?? "회원",
    streak: s.streak,
    profileImage: streakMeta.get(s.userId)?.profileImage ?? null,
    grade: streakMeta.get(s.userId)?.grade ?? 0,
  }));

  return NextResponse.json({ overall, streak });
}