"use client";

import React, { createContext, useCallback, useContext, useEffect, useMemo, useState } from "react";
import { apiFetch, ApiError } from "@/lib/api";
import { AuthResponse, AuthUser, TwoFactorChallenge, clearToken, getDeviceToken, getToken, isTwoFactorChallenge, saveDeviceToken, saveToken } from "@/lib/auth";

export type AuthContextValue = {
  user: AuthUser | null;
  token: string | null;
  loading: boolean;
  login: (email: string, password: string) => Promise<AuthUser | (TwoFactorChallenge & { twoFactorRequired: true })>;
  verifyTwoFactor: (challengeId: string, code: string, rememberDevice: boolean) => Promise<AuthUser>;
  resendTwoFactor: (challengeId: string) => Promise<TwoFactorChallenge>;
  register: (data: { name: string; email: string; password: string; phoneNumber?: string; notificationPreference?: "email" | "whatsapp" | "both" }) => Promise<void>;
  logout: () => void;
  updateToken: (token: string) => void;
};

const AuthContext = createContext<AuthContextValue | undefined>(undefined);

// The last profile the server confirmed, so a page reloaded with no connection (e.g. the
// ticket scanner in offline mode) still knows who's signed in. The server checks the
// token on every API call regardless, so this never grants anything by itself.
const USER_CACHE_KEY = "hope_events_user_cache";
function cacheUser(u: AuthUser | null) {
  try {
    if (u) localStorage.setItem(USER_CACHE_KEY, JSON.stringify(u));
    else localStorage.removeItem(USER_CACHE_KEY);
  } catch { /* storage unavailable */ }
}
function cachedUser(): AuthUser | null {
  try {
    const raw = localStorage.getItem(USER_CACHE_KEY);
    return raw ? JSON.parse(raw) : null;
  } catch {
    return null;
  }
}

export function AuthProvider({ children }: { children: React.ReactNode }) {
  const [token, setToken] = useState<string | null>(null);
  const [user, setUser] = useState<AuthUser | null>(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    const init = async () => {
      try {
        const t = getToken();
        if (t) {
          // Validate the stored token by fetching the user profile.
          // Only update React state after a successful response so we never
          // hold a half-initialised (token set, user null) state.
          const me = await apiFetch<AuthUser>("/api/users/profile", { authToken: t });
          setToken(t);
          setUser(me);
          cacheUser(me);
        }
      } catch (e) {
        // Only wipe the stored token when the server explicitly rejects it (401).
        // Transient failures (network down, 5xx) should NOT log the user out — the
        // token stays in localStorage so the next page load can retry.
        if (e instanceof ApiError && e.status === 401) {
          clearToken();
          cacheUser(null);
          setToken(null);
          setUser(null);
        } else {
          // No connection: carry on as the last confirmed user.
          const t = getToken();
          const cached = cachedUser();
          if (t && cached) {
            setToken(t);
            setUser(cached);
          }
        }
      } finally {
        setLoading(false);
      }
    };
    init();
  }, []);

  const startSession = useCallback((res: AuthResponse) => {
    const { token, deviceToken, ...loggedInUser } = res;
    if (deviceToken) saveDeviceToken(deviceToken);
    saveToken(token);
    setToken(token);
    setUser(loggedInUser);
    cacheUser(loggedInUser);
    return loggedInUser;
  }, []);

  const login = useCallback(async (email: string, password: string) => {
    const res = await apiFetch<AuthResponse | TwoFactorChallenge>("/api/users/login", {
      method: "POST",
      body: { email, password, deviceToken: getDeviceToken() || undefined },
    });
    // 2FA accounts get a challenge back instead of a token — nothing is saved
    // until verifyTwoFactor exchanges the emailed/WhatsApp code for one.
    if (isTwoFactorChallenge(res)) return res;
    return startSession(res as AuthResponse);
  }, [startSession]);

  const verifyTwoFactor = useCallback(async (challengeId: string, code: string, rememberDevice: boolean) => {
    const res = await apiFetch<AuthResponse>("/api/users/login/2fa", {
      method: "POST",
      body: { challengeId, code, rememberDevice },
    });
    return startSession(res);
  }, [startSession]);

  const resendTwoFactor = useCallback((challengeId: string) => {
    return apiFetch<TwoFactorChallenge>("/api/users/login/2fa/resend", {
      method: "POST",
      body: { challengeId },
    });
  }, []);

  const register = useCallback(async (data: { name: string; email: string; password: string; phoneNumber?: string; notificationPreference?: "email" | "whatsapp" | "both" }) => {
    const res = await apiFetch<AuthResponse>("/api/users", {
      method: "POST",
      body: data,
    });
    const { token, ...registeredUser } = res;
    saveToken(token);
    setToken(token);
    setUser(registeredUser);
  }, []);

  const logout = useCallback(() => {
    clearToken();
    cacheUser(null);
    setToken(null);
    setUser(null);
  }, []);

  // Some endpoints (profile update, password change, session revocation) issue a
  // fresh token mid-session. Persist it AND update in-memory state so the app
  // keeps using a valid token without requiring a page refresh.
  const updateToken = useCallback((t: string) => {
    saveToken(t);
    setToken(t);
  }, []);

  const value = useMemo(
    () => ({ user, token, loading, login, verifyTwoFactor, resendTwoFactor, register, logout, updateToken }),
    [loading, login, logout, register, resendTwoFactor, token, updateToken, user, verifyTwoFactor]
  );

  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>;
}

export function useAuthContext() {
  const ctx = useContext(AuthContext);
  if (!ctx) throw new Error("useAuthContext must be used within AuthProvider");
  return ctx;
}