import { useEffect, useState } from "react";
import { apiGet, apiPut, apiDelete } from "../../lib/api";

type Tab = "overview" | "teachers" | "sessions" | "students";

interface Stats {
  teachers: number;
  students: number;
  quizzes: number;
  reports: number;
  student_results: number;
  prompts: number;
  schema_version: string | null;
}

interface TeacherRow {
  id: number;
  email: string;
  full_name: string;
  school: string;
  is_admin: boolean;
  created_at: string;
  quiz_count: number;
  student_count: number;
}

interface SessionRow {
  id: number;
  title: string;
  subject: string | null;
  status: string;
  teacher_email: string;
  report_count: number;
  created_at: string;
}

interface StudentRow {
  id: number;
  name: string;
  teacher_email: string;
  result_count: number;
  avg_score: number | null;
}

interface TimelineEntry {
  quiz_title: string;
  quiz_subject: string | null;
  quiz_created_at: string;
  total_questions: number;
  correct_count: number;
  score: number;
}

const TABS: { key: Tab; label: string }[] = [
  { key: "overview", label: "總覽" },
  { key: "teachers", label: "教師" },
  { key: "sessions", label: "測驗" },
  { key: "students", label: "學生" },
];

export function AdminDashboard() {
  const [tab, setTab] = useState<Tab>("overview");

  return (
    <main className="max-w-6xl mx-auto px-4 pb-12">
      <div className="text-center mb-6">
        <h2 className="font-display text-2xl font-bold text-[var(--color-text)]">管理後台</h2>
        <p className="text-[var(--color-text-muted)] mt-1">資料庫管理與使用分析</p>
      </div>

      <div className="flex justify-center gap-2 mb-6">
        {TABS.map((t) => (
          <button
            key={t.key}
            onClick={() => setTab(t.key)}
            className={`px-4 py-2 text-sm font-medium rounded-lg transition-colors ${
              tab === t.key
                ? "bg-[var(--color-primary)] text-white"
                : "text-[var(--color-text-muted)] hover:text-[var(--color-text)] border border-[var(--color-border)]"
            }`}
          >
            {t.label}
          </button>
        ))}
      </div>

      {tab === "overview" && <Overview />}
      {tab === "teachers" && <Teachers />}
      {tab === "sessions" && <Sessions />}
      {tab === "students" && <Students />}
    </main>
  );
}

function useFetch<T>(path: string, deps: unknown[] = []) {
  const [data, setData] = useState<T | null>(null);
  const [error, setError] = useState("");
  const [loading, setLoading] = useState(true);
  const [nonce, setNonce] = useState(0);
  const reload = () => setNonce((n) => n + 1);

  useEffect(() => {
    let active = true;
    setLoading(true);
    apiGet<T>(path)
      .then((d) => active && setData(d))
      .catch((e) => active && setError(e instanceof Error ? e.message : "Error"))
      .finally(() => active && setLoading(false));
    return () => {
      active = false;
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [path, nonce, ...deps]);

  return { data, error, loading, reload };
}

function StatCard({ label, value }: { label: string; value: number | string }) {
  return (
    <div className="card p-6 text-center">
      <div className="text-3xl font-bold text-[var(--color-primary)]">{value}</div>
      <div className="text-sm text-[var(--color-text-muted)] mt-1">{label}</div>
    </div>
  );
}

function Overview() {
  const { data, loading, error } = useFetch<Stats>("/api/admin/stats");
  if (loading) return <Spinner />;
  if (error || !data) return <ErrorBox msg={error} />;
  return (
    <div>
      <div className="grid grid-cols-2 md:grid-cols-3 gap-4">
        <StatCard label="教師" value={data.teachers} />
        <StatCard label="學生" value={data.students} />
        <StatCard label="測驗" value={data.quizzes} />
        <StatCard label="已生成報告" value={data.reports} />
        <StatCard label="學生成績紀錄" value={data.student_results} />
        <StatCard label="提示詞" value={data.prompts} />
      </div>
      <p className="text-center text-xs text-[var(--color-text-muted)] mt-6">
        資料庫結構版本：{data.schema_version ?? "未知"}
      </p>
    </div>
  );
}

function Teachers() {
  const { data, loading, error, reload } = useFetch<{ users: TeacherRow[] }>("/api/admin/users");
  if (loading) return <Spinner />;
  if (error || !data) return <ErrorBox msg={error} />;

  const toggleAdmin = async (u: TeacherRow) => {
    await apiPut(`/api/admin/users/${u.id}/admin`, { is_admin: !u.is_admin });
    reload();
  };
  const remove = async (u: TeacherRow) => {
    if (!confirm(`刪除教師 ${u.email}？此操作會一併刪除其所有測驗與報告。`)) return;
    await apiDelete(`/api/admin/users/${u.id}`);
    reload();
  };

  return (
    <Table headers={["Email", "姓名", "學校", "測驗", "學生", "管理員", ""]}>
      {data.users.map((u) => (
        <tr key={u.id} className="border-t border-[var(--color-border)]">
          <Td>{u.email}</Td>
          <Td>{u.full_name || "—"}</Td>
          <Td>{u.school || "—"}</Td>
          <Td>{u.quiz_count}</Td>
          <Td>{u.student_count}</Td>
          <Td>
            <button onClick={() => toggleAdmin(u)} className="text-sm underline text-[var(--color-primary)]">
              {u.is_admin ? "是" : "否"}
            </button>
          </Td>
          <Td>
            <button onClick={() => remove(u)} className="text-sm text-red-400 hover:underline">
              刪除
            </button>
          </Td>
        </tr>
      ))}
    </Table>
  );
}

function Sessions() {
  const { data, loading, error, reload } = useFetch<{ sessions: SessionRow[] }>("/api/admin/sessions");
  if (loading) return <Spinner />;
  if (error || !data) return <ErrorBox msg={error} />;

  const remove = async (s: SessionRow) => {
    if (!confirm(`刪除測驗「${s.title}」？`)) return;
    await apiDelete(`/api/admin/sessions/${s.id}`);
    reload();
  };

  return (
    <Table headers={["標題", "科目", "教師", "狀態", "報告", "建立時間", ""]}>
      {data.sessions.map((s) => (
        <tr key={s.id} className="border-t border-[var(--color-border)]">
          <Td>{s.title}</Td>
          <Td>{s.subject || "—"}</Td>
          <Td>{s.teacher_email}</Td>
          <Td>{s.status}</Td>
          <Td>{s.report_count}</Td>
          <Td>{new Date(s.created_at).toLocaleDateString()}</Td>
          <Td>
            <button onClick={() => remove(s)} className="text-sm text-red-400 hover:underline">
              刪除
            </button>
          </Td>
        </tr>
      ))}
    </Table>
  );
}

function Students() {
  const { data, loading, error } = useFetch<{ students: StudentRow[] }>("/api/admin/students");
  const [selected, setSelected] = useState<number | null>(null);

  if (loading) return <Spinner />;
  if (error || !data) return <ErrorBox msg={error} />;

  if (selected !== null) {
    return <StudentDetail studentId={selected} onBack={() => setSelected(null)} />;
  }

  return (
    <Table headers={["姓名", "教師", "測驗次數", "平均分數", ""]}>
      {data.students.map((s) => (
        <tr key={s.id} className="border-t border-[var(--color-border)]">
          <Td>{s.name}</Td>
          <Td>{s.teacher_email}</Td>
          <Td>{s.result_count}</Td>
          <Td>{s.avg_score ?? "—"}</Td>
          <Td>
            <button onClick={() => setSelected(s.id)} className="text-sm underline text-[var(--color-primary)]">
              查看歷程
            </button>
          </Td>
        </tr>
      ))}
    </Table>
  );
}

function StudentDetail({ studentId, onBack }: { studentId: number; onBack: () => void }) {
  const { data, loading, error } = useFetch<{
    student: { name: string };
    timeline: TimelineEntry[];
  }>(`/api/admin/students/${studentId}`);

  if (loading) return <Spinner />;
  if (error || !data) return <ErrorBox msg={error} />;

  return (
    <div>
      <button onClick={onBack} className="text-sm text-[var(--color-text-muted)] hover:underline mb-4">
        ← 返回學生列表
      </button>
      <h3 className="font-display text-xl font-semibold mb-4 text-[var(--color-text)]">
        {data.student.name} 的跨測驗歷程
      </h3>
      {data.timeline.length === 0 ? (
        <p className="text-[var(--color-text-muted)]">尚無成績紀錄</p>
      ) : (
        <Table headers={["測驗", "科目", "日期", "答對", "總題數", "分數"]}>
          {data.timeline.map((t, i) => (
            <tr key={i} className="border-t border-[var(--color-border)]">
              <Td>{t.quiz_title}</Td>
              <Td>{t.quiz_subject || "—"}</Td>
              <Td>{new Date(t.quiz_created_at).toLocaleDateString()}</Td>
              <Td>{t.correct_count}</Td>
              <Td>{t.total_questions}</Td>
              <Td>
                <span className="font-semibold text-[var(--color-primary)]">{t.score}</span>
              </Td>
            </tr>
          ))}
        </Table>
      )}
    </div>
  );
}

function Table({ headers, children }: { headers: string[]; children: React.ReactNode }) {
  return (
    <div className="card overflow-x-auto">
      <table className="w-full text-sm">
        <thead>
          <tr className="text-left text-[var(--color-text-muted)]">
            {headers.map((h, i) => (
              <th key={i} className="px-4 py-3 font-medium">
                {h}
              </th>
            ))}
          </tr>
        </thead>
        <tbody className="text-[var(--color-text)]">{children}</tbody>
      </table>
    </div>
  );
}

function Td({ children }: { children: React.ReactNode }) {
  return <td className="px-4 py-3">{children}</td>;
}

function Spinner() {
  return (
    <div className="flex justify-center py-12">
      <div className="w-6 h-6 border-2 border-[var(--color-primary)] border-t-transparent rounded-full animate-spin" />
    </div>
  );
}

function ErrorBox({ msg }: { msg: string }) {
  return <div className="card p-6 text-center text-red-400">{msg || "載入失敗"}</div>;
}