Add login gate, calculation history, and AI markdown download.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/auth/auth-provider.tsx

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+"use client";
+
+import {
+  createContext,
+  useCallback,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+} from "react";
+
+interface AuthState {
+  loading: boolean;
+  authEnabled: boolean;
+  loggedIn: boolean;
+  username?: string;
+  refresh: () => Promise<void>;
+  logout: () => Promise<void>;
+}
+
+const AuthContext = createContext<AuthState | null>(null);
+
+export function AuthProvider({ children }: { children: React.ReactNode }) {
+  const [loading, setLoading] = useState(true);
+  const [authEnabled, setAuthEnabled] = useState(false);
+  const [loggedIn, setLoggedIn] = useState(true);
+  const [username, setUsername] = useState<string>();
+
+  const refresh = useCallback(async () => {
+    try {
+      const res = await fetch("/api/auth/me", { cache: "no-store" });
+      const data = await res.json();
+      setAuthEnabled(!!data.authEnabled);
+      setLoggedIn(!!data.loggedIn);
+      setUsername(data.username);
+    } catch {
+      setAuthEnabled(false);
+      setLoggedIn(true);
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    refresh();
+  }, [refresh]);
+
+  const logout = useCallback(async () => {
+    await fetch("/api/auth/logout", { method: "POST" });
+    await refresh();
+    window.location.href = "/";
+  }, [refresh]);
+
+  const value = useMemo(
+    () => ({ loading, authEnabled, loggedIn, username, refresh, logout }),
+    [loading, authEnabled, loggedIn, username, refresh, logout],
+  );
+
+  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>;
+}
+
+export function useAuth() {
+  const ctx = useContext(AuthContext);
+  if (!ctx) {
+    throw new Error("useAuth must be used within AuthProvider");
+  }
+  return ctx;
+}
+
+export function useRequireAuthForPath(path: string): boolean {
+  const { authEnabled, loggedIn } = useAuth();
+  if (!authEnabled) {
+    return true;
+  }
+  const protectedPaths = ["/liuyao", "/bazi", "/combined", "/history"];
+  if (!protectedPaths.some((p) => path === p || path.startsWith(`${p}/`))) {
+    return true;
+  }
+  return loggedIn;
+}

components/auth/login-form.tsx

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+"use client";
+
+import { useState } from "react";
+import { useRouter, useSearchParams } from "next/navigation";
+import { Button } from "@/components/ui/button";
+import { useAuth } from "@/components/auth/auth-provider";
+
+export default function LoginForm() {
+  const router = useRouter();
+  const searchParams = useSearchParams();
+  const { refresh } = useAuth();
+  const [username, setUsername] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [loading, setLoading] = useState(false);
+
+  async function handleSubmit(e: React.FormEvent) {
+    e.preventDefault();
+    setError("");
+    setLoading(true);
+    try {
+      const res = await fetch("/api/auth/login", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ username, password }),
+      });
+      const data = await res.json();
+      if (!res.ok) {
+        setError(data.error ?? "登录失败");
+        return;
+      }
+      await refresh();
+      const next = searchParams.get("next") || "/liuyao";
+      router.push(next);
+      router.refresh();
+    } catch {
+      setError("网络错误，请稍后重试");
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="mx-auto w-full max-w-sm space-y-4">
+      <div className="space-y-2">
+        <label className="text-sm font-medium">用户名</label>
+        <input
+          type="text"
+          autoComplete="username"
+          className="w-full rounded-md border bg-background px-3 py-2 text-sm"
+          value={username}
+          onChange={(e) => setUsername(e.target.value)}
+          required
+        />
+      </div>
+      <div className="space-y-2">
+        <label className="text-sm font-medium">密码</label>
+        <input
+          type="password"
+          autoComplete="current-password"
+          className="w-full rounded-md border bg-background px-3 py-2 text-sm"
+          value={password}
+          onChange={(e) => setPassword(e.target.value)}
+          required
+        />
+      </div>
+      {error && <p className="text-sm text-destructive">{error}</p>}
+      <Button type="submit" className="w-full" disabled={loading}>
+        {loading ? "登录中…" : "登录"}
+      </Button>
+      <p className="text-center text-xs text-muted-foreground">
+        登录后可使用六爻算卦、生辰八字、综合测算与测算历史
+      </p>
+    </form>
+  );
+}