import { prisma } from "@/lib/prisma";
import Link from "next/link";

export default async function AdminDashboard() {
  const now = new Date();
  const dayAgo = new Date(now.getTime() - 24 * 60 * 60 * 1000);
  const weekAgo = new Date(now.getTime() - 7 * 24 * 60 * 60 * 1000);
  const monthAgo = new Date(now.getTime() - 30 * 24 * 60 * 60 * 1000);

  const [
    totalStudents,
    newStudentsMonth,
    totalCourses,
    publishedCourses,
    activeEnrollments,
    expiringWeek,
    homeworkPending,
    homeworkTotal,
    progressTotal,
    balanceAggregate,
    activeLast24h,
  ] = await Promise.all([
    prisma.user.count({ where: { role: "student" } }),
    prisma.user.count({ where: { role: "student", createdAt: { gte: monthAgo } } }),
    prisma.course.count(),
    prisma.course.count({ where: { published: true } }),
    prisma.courseEnrollment.count({
      where: { OR: [{ expiresAt: null }, { expiresAt: { gt: now } }] },
    }),
    prisma.courseEnrollment.count({
      where: { expiresAt: { gt: now, lte: new Date(now.getTime() + 7 * 24 * 60 * 60 * 1000) } },
    }),
    prisma.homeworkSubmission.count({ where: { status: { in: ["PENDING", "REVIEWING"] } } }),
    prisma.homeworkSubmission.count(),
    prisma.lessonProgress.count(),
    prisma.balanceTransaction.aggregate({ _sum: { amount: true } }),
    prisma.session.findMany({
      where: { createdAt: { gte: dayAgo } },
      select: { userId: true },
      distinct: ["userId"],
    }).then((rows) => rows.length),
  ]);

  const totalBalance = Number(balanceAggregate._sum.amount ?? 0);

  // Recent enrollments
  const recentEnrollments = await prisma.courseEnrollment.findMany({
    orderBy: { enrolledAt: "desc" },
    take: 8,
    include: {
      user: { select: { name: true, email: true } },
      course: { select: { title: true } },
    },
  });

  // Most active courses (by enrollment count)
  const topCourses = await prisma.course.findMany({
    where: { published: true },
    include: { _count: { select: { enrollments: true, modules: true } } },
    orderBy: { enrollments: { _count: "desc" } },
    take: 5,
  });

  return (
    <div className="p-8 max-w-5xl">
      <h1 className="text-2xl font-bold mb-1">Обзор</h1>
      <p className="text-sm mb-8" style={{ color: "var(--muted-foreground)" }}>
        Платформа Second Brain · {now.toLocaleDateString("ru-RU", { day: "numeric", month: "long", year: "numeric" })}
      </p>

      {/* Stats grid */}
      <div className="grid grid-cols-2 md:grid-cols-4 gap-4 mb-8">
        <StatCard
          label="Студентов"
          value={totalStudents}
          sub={`+${newStudentsMonth} за месяц`}
          href="/admin/users"
        />
        <StatCard
          label="Курсов"
          value={totalCourses}
          sub={`${publishedCourses} опубликовано`}
          href="/admin/courses"
        />
        <StatCard
          label="Активных доступов"
          value={activeEnrollments}
          sub={expiringWeek > 0 ? `${expiringWeek} истекает на неделе` : "нет истекающих"}
          subAccent={expiringWeek > 0}
          href="/admin/courses"
        />
        <StatCard
          label="ДЗ на проверку"
          value={homeworkPending}
          sub={`${homeworkTotal} всего сдано`}
          subAccent={homeworkPending > 0}
          href="/curator/homework?status=pending"
        />
      </div>

      <div className="grid md:grid-cols-2 gap-6">
        {/* Recent enrollments */}
        <div className="card-aubade p-5">
          <div className="flex items-center justify-between mb-4">
            <p className="text-xs font-bold uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
              Последние зачисления
            </p>
            <Link href="/admin/users" className="text-xs underline" style={{ color: "var(--muted-foreground)" }}>
              Все →
            </Link>
          </div>
          {recentEnrollments.length === 0 ? (
            <p className="text-sm" style={{ color: "var(--muted-foreground)" }}>Нет зачислений</p>
          ) : (
            <div className="space-y-2">
              {recentEnrollments.map((e) => (
                <div key={`${e.userId}-${e.courseId}`} className="flex items-center gap-3 text-sm">
                  <div className="flex-1 min-w-0">
                    <p className="font-medium truncate">{e.user.name}</p>
                    <p className="text-xs truncate" style={{ color: "var(--muted-foreground)" }}>{e.course.title}</p>
                  </div>
                  <span className="text-xs shrink-0" style={{ color: "var(--muted-foreground)" }}>
                    {new Date(e.enrolledAt).toLocaleDateString("ru-RU")}
                  </span>
                </div>
              ))}
            </div>
          )}
        </div>

        {/* Top courses + progress stat */}
        <div className="space-y-6">
          <div className="card-aubade p-5">
            <div className="flex items-center justify-between mb-4">
              <p className="text-xs font-bold uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>
                Популярные курсы
              </p>
              <Link href="/admin/courses" className="text-xs underline" style={{ color: "var(--muted-foreground)" }}>
                Все →
              </Link>
            </div>
            {topCourses.length === 0 ? (
              <p className="text-sm" style={{ color: "var(--muted-foreground)" }}>Нет курсов</p>
            ) : (
              <div className="space-y-3">
                {topCourses.map((c) => (
                  <div key={c.id} className="flex items-center gap-3 text-sm">
                    <div className="flex-1 min-w-0">
                      <p className="font-medium truncate">{c.title}</p>
                      <p className="text-xs" style={{ color: "var(--muted-foreground)" }}>
                        {c._count.modules} модулей
                      </p>
                    </div>
                    <div className="text-right shrink-0">
                      <p className="font-bold">{c._count.enrollments}</p>
                      <p className="text-xs" style={{ color: "var(--muted-foreground)" }}>студентов</p>
                    </div>
                  </div>
                ))}
              </div>
            )}
          </div>

          <div className="card-aubade p-5">
            <p className="text-xs font-bold uppercase tracking-widest mb-3" style={{ color: "var(--muted-foreground)" }}>
              Активность
            </p>
            <div className="flex items-end gap-6">
              <div>
                <p className="text-3xl font-bold">{progressTotal}</p>
                <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>уроков пройдено</p>
              </div>
              <div>
                <p className="text-3xl font-bold">{homeworkTotal}</p>
                <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>работ сдано</p>
              </div>
            </div>
          </div>

          <Link href="/admin/users?balance=nonzero" className="card-aubade p-5 block">
            <p className="text-xs font-bold uppercase tracking-widest mb-3" style={{ color: "var(--muted-foreground)" }}>
              На балансах
            </p>
            <p className="text-3xl font-bold">
              {totalBalance.toLocaleString("ru-RU", { minimumFractionDigits: 2, maximumFractionDigits: 2 })} ₽
            </p>
            <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>сумма по всем пользователям</p>
          </Link>

          <div className="card-aubade p-5">
            <p className="text-xs font-bold uppercase tracking-widest mb-3" style={{ color: "var(--muted-foreground)" }}>
              Авторизации за 24 часа
            </p>
            <p className="text-3xl font-bold">{activeLast24h}</p>
            <p className="text-xs mt-0.5" style={{ color: "var(--muted-foreground)" }}>уникальных пользователей</p>
          </div>
        </div>
      </div>
    </div>
  );
}

function StatCard({
  label,
  value,
  sub,
  subAccent,
  href,
}: {
  label: string;
  value: number | string;
  sub?: string;
  subAccent?: boolean;
  href?: string;
}) {
  const content = (
    <div className="card-aubade p-4">
      <p className="text-3xl font-bold">{value}</p>
      <p className="text-xs font-bold uppercase tracking-widest mt-1" style={{ color: "var(--muted-foreground)" }}>
        {label}
      </p>
      {sub && (
        <p className="text-xs mt-1.5" style={{ color: subAccent ? "oklch(0.577 0.245 27.325)" : "var(--muted-foreground)" }}>
          {sub}
        </p>
      )}
    </div>
  );

  return href ? <Link href={href}>{content}</Link> : content;
}