import { demoUser } from "@/lib/frontend-demo-data";
import { getPublicDemoMode, getPublicApiBaseUrl } from "@/lib/env";
import { apiFetch, apiJson, apiPatch, isApiError, normalizeApiError } from "@/lib/api/client";
import {
  clearAuthenticationRequired,
  markAuthenticationRequired,
} from "@/lib/auth/session-requirement";
import type {
  ApiUser,
  AccountDeleteRequest,
  AccountDeleteResponse,
  AuthLoginRequest,
  AuthSignupRequest,
  AuthSignupResponse,
  AuthTokenResponse,
  ApiErrorBody,
  UserUpdateRequest,
} from "@/lib/api/types";

export const DEMO_PREVIEW_TOKEN = "docdoe-demo-preview-token";
export const AUTH_SESSION_UPDATED_EVENT = "docdoe-auth-session-updated";

const TOKEN_KEY = "exam_success_access_token";
const USER_KEY = "exam_success_user";
const EXPIRES_AT_KEY = "exam_success_token_expires_at";
const REFRESH_TOKEN_KEY = "exam_success_refresh_token";
const REMEMBER_EMAIL_KEY = "docdoe_remember_email";
const STAY_SIGNED_IN_KEY = "docdoe_stay_signed_in";

function authStorage(preferLocal = true): Storage {
  if (typeof window === "undefined") {
    throw new Error("auth storage is browser-only");
  }
  if (preferLocal) return window.localStorage;
  return window.sessionStorage;
}

function readAuthItem(key: string) {
  if (typeof window === "undefined") return null;
  return window.localStorage.getItem(key) ?? window.sessionStorage.getItem(key);
}

function writeAuthItem(key: string, value: string, staySignedIn: boolean) {
  const primary = authStorage(staySignedIn);
  const secondary = authStorage(!staySignedIn);
  primary.setItem(key, value);
  secondary.removeItem(key);
}

export function isDemoPreviewSession() {
  return getAuthToken() === DEMO_PREVIEW_TOKEN;
}

/** The only route that may opt into the local, unauthenticated preview. */
export function isExplicitDemoPreviewPath() {
  return typeof window !== "undefined" && window.location.pathname === "/preview/tuition";
}

export function getAuthToken() {
  if (typeof window === "undefined") return null;
  const token = readAuthItem(TOKEN_KEY);
  const expiresAt = Number(readAuthItem(EXPIRES_AT_KEY));
  if (token && Number.isFinite(expiresAt) && expiresAt > 0 && Date.now() > expiresAt) {
    // Prefer refresh over hard wipe when a refresh_token is present.
    if (readAuthItem(REFRESH_TOKEN_KEY)) {
      return token;
    }
    clearAuthSession();
    markAuthenticationRequired();
    return null;
  }
  return token;
}

export function getStoredUser() {
  if (typeof window === "undefined") return null;
  const rawUser = readAuthItem(USER_KEY);
  if (!rawUser) return null;
  try {
    return JSON.parse(rawUser) as ApiUser;
  } catch {
    return null;
  }
}

export function getRememberedEmail() {
  if (typeof window === "undefined") return "";
  return window.localStorage.getItem(REMEMBER_EMAIL_KEY) ?? "";
}

export function setRememberedEmail(email: string | null) {
  if (typeof window === "undefined") return;
  if (!email?.trim()) {
    window.localStorage.removeItem(REMEMBER_EMAIL_KEY);
    return;
  }
  window.localStorage.setItem(REMEMBER_EMAIL_KEY, email.trim().toLowerCase());
}

export function getStaySignedInPreference() {
  if (typeof window === "undefined") return true;
  const raw = window.localStorage.getItem(STAY_SIGNED_IN_KEY);
  if (raw === null) return true;
  return raw === "1";
}

export function setStaySignedInPreference(staySignedIn: boolean) {
  if (typeof window === "undefined") return;
  window.localStorage.setItem(STAY_SIGNED_IN_KEY, staySignedIn ? "1" : "0");
}


export function getRefreshToken() {
  if (typeof window === "undefined") return null;
  return readAuthItem(REFRESH_TOKEN_KEY);
}

/** Exchange refresh_token for a new AuthTokenResponse. Returns null on failure. */
export async function refreshAuthSession(): Promise<AuthTokenResponse | null> {
  const refreshToken = getRefreshToken();
  if (!refreshToken || refreshToken === DEMO_PREVIEW_TOKEN) return null;
  try {
    const response = await apiJson<AuthTokenResponse, { refresh_token: string }>(
      "/auth/refresh",
      { refresh_token: refreshToken },
      { skipAuthClear: true },
    );
    setAuthSession(response);
    return response;
  } catch {
    return null;
  }
}

export function setAuthSession(
  response: AuthTokenResponse,
  options?: { staySignedIn?: boolean },
) {
  if (typeof window === "undefined") return;
  const staySignedIn = options?.staySignedIn ?? getStaySignedInPreference();
  setStaySignedInPreference(staySignedIn);
  writeAuthItem(TOKEN_KEY, response.access_token, staySignedIn);
  writeAuthItem(USER_KEY, JSON.stringify(response.user), staySignedIn);
  if (response.expires_in) {
    writeAuthItem(
      EXPIRES_AT_KEY,
      String(Date.now() + response.expires_in * 1000),
      staySignedIn,
    );
  }
  if (response.refresh_token) {
    writeAuthItem(REFRESH_TOKEN_KEY, response.refresh_token, staySignedIn);
  } else {
    // Google OAuth sessions are first-party backend JWTs and do not carry a
    // Supabase refresh token. Never let a previous Supabase account's token
    // survive an identity switch and later replace the Google session.
    window.localStorage.removeItem(REFRESH_TOKEN_KEY);
    window.sessionStorage.removeItem(REFRESH_TOKEN_KEY);
  }
  clearAuthenticationRequired();
  // OAuth finishes inside a child route while AuthProvider remains mounted.
  // Notify the provider immediately so client-side navigation cannot carry a
  // stale `user = null` into Home or Onboarding.
  window.dispatchEvent(new Event(AUTH_SESSION_UPDATED_EVENT));
}

function safeNextPath(nextPath: string) {
  if (!nextPath.startsWith("/") || nextPath.startsWith("//")) return "/study-chat";
  return nextPath;
}

export function startGoogleSignIn({
  nextPath = "/study-chat",
  inviteCode,
}: {
  nextPath?: string;
  inviteCode?: string;
} = {}) {
  const params = new URLSearchParams({
    next: safeNextPath(nextPath),
  });
  if (inviteCode?.trim()) {
    params.set("invite_code", inviteCode.trim());
  }
  window.location.assign(`${getPublicApiBaseUrl()}/auth/google/start?${params.toString()}`);
}

export function setStoredUser(user: ApiUser) {
  if (typeof window === "undefined") return;
  const staySignedIn = getStaySignedInPreference();
  writeAuthItem(USER_KEY, JSON.stringify(user), staySignedIn);
}

export function clearAuthSession() {
  if (typeof window === "undefined") return;
  for (const storage of [window.localStorage, window.sessionStorage]) {
    storage.removeItem(TOKEN_KEY);
    storage.removeItem(USER_KEY);
    storage.removeItem(EXPIRES_AT_KEY);
    storage.removeItem(REFRESH_TOKEN_KEY);
  }
}

/** Clear the server-scoped media cookie as well as client-managed credentials. */
export function logoutCurrentSession() {
  // Start the request before clearing storage: apiFetch reads the current
  // bearer token synchronously. Logout still completes locally if the network
  // is unavailable, so a stale browser view cannot keep using private APIs.
  void apiFetch<void>("/auth/logout", { method: "POST" }).catch(() => undefined);
  markAuthenticationRequired();
  clearAuthSession();
}

function isDocDoeAccountKey(key: string) {
  return (
    key.startsWith("docdoe") ||
    key.startsWith("exam_success_") ||
    key === "access_token" ||
    key === "auth_token"
  );
}

/** Remove only DocDoe-owned browser data after the backend confirms deletion. */
export function clearDeletedAccountLocalData() {
  if (typeof window === "undefined") return;
  for (const storage of [window.localStorage, window.sessionStorage]) {
    if (!storage) continue;
    const keys = Array.from({ length: storage.length }, (_, index) => storage.key(index))
      .filter((key): key is string => Boolean(key));
    for (const key of keys) {
      if (isDocDoeAccountKey(key)) storage.removeItem(key);
    }
  }
}

/** Local demo session for previewing the student workspace without backend auth. */
export function setDemoPreviewSession() {
  setAuthSession({
    access_token: DEMO_PREVIEW_TOKEN,
    token_type: "bearer",
    expires_in: 60 * 60 * 24 * 7,
    user: demoUser,
  });
}

function userSafeAuthError(error: unknown, action: "login" | "signup" | "resend" | "profile") {
  if (isApiError(error)) {
    const body = error.body as ApiErrorBody | null;
    const errorCode = body?.error?.code
      ?? (body?.detail && typeof body.detail === "object" && "code" in body.detail
        ? String(body.detail.code ?? "")
        : "");
    if (action === "login" && error.status === 401) {
      return "Could not sign in right now. Please check your email and password.";
    }
    if (action === "signup" && errorCode === "BETA_INVITE_ONLY") {
      return "DocDoe beta accounts are invitation-only. Sign in with the account prepared for you.";
    }
    if (action === "signup" && (error.status === 400 || error.status === 409)) {
      return "An account with this email already exists. Please sign in.";
    }
    if (action === "signup" && error.status === 403) {
      return "This invite code is not valid. Contact the DocDoe team for beta access.";
    }
    if (action === "signup" && error.status === 503) {
      return "Email account verification is being configured. Please try again later.";
    }
    if (action === "signup" && error.status === 429) {
      return "Too many signup attempts. Wait a moment, then try again.";
    }
    if (action === "signup" && error.status === 502) {
      return "We couldn't send your verification email. Please try again in a few minutes.";
    }
    if (action === "resend" && error.status === 429) {
      return "Too many code requests. Wait a moment before requesting another code.";
    }
    if (action === "resend" && error.status === 404) {
      return "Signup verification is not available on this deployment. Please sign in or contact the DocDoe team.";
    }
    if (action === "resend" && error.status === 502) {
      return "We couldn't send your verification code. Please try again shortly.";
    }
    if (action === "resend" && error.status === 503) {
      return "Email account verification is being configured. Please try again later.";
    }
    if (error.isAuthError) {
      return "Your session expired. Please sign in again.";
    }
    if (error.status == null) {
      return action === "signup"
        ? "Could not reach DocDoe to create your account. Check your connection and try again."
        : "Could not reach DocDoe right now. Check your connection and try again.";
    }
  }
  if (action === "signup") return "Could not create your account right now. Please try again.";
  if (action === "login") return "Could not sign in right now. Please try again.";
  if (action === "resend") return "Could not resend the verification code right now. Please try again.";
  return normalizeApiError(error);
}

export async function loginWithEmailPassword(
  payload: AuthLoginRequest,
  options?: { staySignedIn?: boolean; rememberEmail?: boolean },
) {
  try {
    const response = await apiJson<AuthTokenResponse, AuthLoginRequest>("/auth/login", payload);
    setAuthSession(response, { staySignedIn: options?.staySignedIn });
    if (options?.rememberEmail) {
      setRememberedEmail(payload.email);
    } else if (options?.rememberEmail === false) {
      setRememberedEmail(null);
    }
    return response;
  } catch (error) {
    throw new Error(userSafeAuthError(error, "login"));
  }
}

export async function requestLoginOtp(email: string) {
  try {
    return await apiJson<{ message: string }, { email: string }>(
      "/auth/login/otp/request",
      { email: email.trim().toLowerCase() },
      { timeoutMs: 30_000 },
    );
  } catch (error) {
    if (isApiError(error) && error.status === 429) {
      const wait = error.retryAfter ?? 60;
      throw new Error(`Please wait ${wait} seconds before requesting another code.`);
    }
    if (isApiError(error) && error.status === 503) {
      throw new Error("Email sign-in codes are temporarily unavailable. Use your password instead.");
    }
    throw new Error("We could not send a sign-in code right now. Please try again.");
  }
}

export async function verifyLoginOtp(
  payload: { email: string; code: string },
  options?: { staySignedIn?: boolean; rememberEmail?: boolean },
) {
  try {
    const response = await apiJson<
      AuthTokenResponse,
      { email: string; code: string }
    >("/auth/login/otp/verify", {
      email: payload.email.trim().toLowerCase(),
      code: payload.code.trim(),
    });
    setAuthSession(response, { staySignedIn: options?.staySignedIn });
    if (options?.rememberEmail) {
      setRememberedEmail(payload.email);
    } else if (options?.rememberEmail === false) {
      setRememberedEmail(null);
    }
    return response;
  } catch (error) {
    if (isApiError(error) && error.status === 401) {
      throw new Error("That code is invalid or expired. Request a new one.");
    }
    if (isApiError(error) && error.status === 503) {
      throw new Error("Email sign-in codes are temporarily unavailable. Use your password instead.");
    }
    if (isApiError(error) && error.status === 429) {
      throw new Error("Too many code attempts. Wait a moment, then request a new code.");
    }
    throw new Error("Could not verify the sign-in code. Please try again.");
  }
}

export async function signupWithEmailPassword(payload: AuthSignupRequest) {
  try {
    const response = await apiJson<AuthSignupResponse, AuthSignupRequest>("/auth/signup", {
      ...payload,
      name: payload.name.trim(),
      email: payload.email.trim().toLowerCase(),
    });
    if ("access_token" in response) setAuthSession(response);
    return response;
  } catch (error) {
    throw new Error(userSafeAuthError(error, "signup"));
  }
}

export async function verifySignupOtp(payload: { email: string; code: string }) {
  try {
    const response = await apiJson<
      AuthTokenResponse,
      { email: string; code: string }
    >("/auth/signup/otp/verify", {
      email: payload.email.trim().toLowerCase(),
      code: payload.code.trim(),
    });
    setAuthSession(response);
    return response;
  } catch (error) {
    if (isApiError(error) && error.status === 401) {
      throw new Error("That verification code is invalid or expired. Request a new one.");
    }
    if (isApiError(error) && error.status === 429) {
      throw new Error("Too many code attempts. Wait a moment, then request a new code.");
    }
    throw new Error("Could not verify your email right now. Please try again.");
  }
}

type ResendSignupOtpResponse = {
  sent: boolean;
};

/**
 * Re-request the signup verification code for an unconfirmed account.
 * The backend answers identically whether or not the address is registered,
 * so callers must not read the response as an account-existence signal.
 */
export async function resendSignupOtp(email: string) {
  try {
    return await apiJson<ResendSignupOtpResponse, { email: string }>(
      "/auth/signup/otp/resend",
      { email: email.trim().toLowerCase() },
      { timeoutMs: 30_000 },
    );
  } catch (error) {
    throw new Error(userSafeAuthError(error, "resend"));
  }
}

/** Keep the client aligned with the backend password rule before a request is sent. */
export function getPasswordPolicyError(password: string) {
  if (password.length < 8) {
    return "Use at least 8 characters.";
  }
  if (!/[A-Za-z]/.test(password) || !/\d/.test(password)) {
    return "Use at least one letter and one number.";
  }
  return null;
}

type PasswordRecoveryResponse = {
  message: string;
};

type PasswordResetResponse = {
  reset: boolean;
};

export async function requestPasswordRecovery(email: string) {
  try {
    return await apiJson<PasswordRecoveryResponse, { email: string }>(
      "/auth/forgot-password",
      { email },
      { timeoutMs: 30_000 },
    );
  } catch (error) {
    if (isApiError(error) && error.status === 503) {
      throw new Error("Password recovery is temporarily unavailable. Please try again shortly.");
    }
    throw new Error("We could not send a recovery link right now. Please try again.");
  }
}

export async function resetPasswordWithToken({
  token,
  password,
}: {
  token: string;
  password: string;
}) {
  try {
    return await apiJson<PasswordResetResponse, { token: string; password: string }>(
      "/auth/reset-password",
      { token, password },
      { timeoutMs: 30_000 },
    );
  } catch (error) {
    if (isApiError(error) && error.status === 503) {
      throw new Error("Password recovery is temporarily unavailable. Please try again shortly.");
    }
    if (isApiError(error) && error.status === 400) {
      throw new Error("This recovery link is invalid or has expired. Request a new one.");
    }
    throw new Error("We could not reset your password right now. Please request a new recovery link.");
  }
}

export async function fetchCurrentUser() {
  const token = getAuthToken();
  if (token === DEMO_PREVIEW_TOKEN) {
    if (getPublicDemoMode() === "live" || !isExplicitDemoPreviewPath()) {
      clearAuthSession();
      return null;
    }
    // A preview token represents a local, deliberately offline session. It is
    // not a server credential, so probing /auth/session can hold every
    // protected route behind the boot screen until the API request times out.
    // Real deployments never create this token because they run in live mode.
    return getStoredUser() ?? demoUser;
  }
  if (!token) {
    if (getPublicDemoMode() !== "live" && isExplicitDemoPreviewPath()) {
      setDemoPreviewSession();
      return demoUser;
    }
    return null;
  }

  try {
    const user = await apiFetch<ApiUser>("/auth/session", { skipAuthClear: true });
    // A request started before an OAuth callback may complete successfully
    // after the browser has switched to a replacement token. Do not let that
    // older identity overwrite the replacement session in storage.
    if (getAuthToken() !== token) {
      return getAuthToken() ? getStoredUser() : null;
    }
    setStoredUser(user);
    return user;
  } catch (error) {
    if (isApiError(error) && error.isAuthError) {
      // Try refresh before wiping — lasting sessions need refresh_token (#50).
      if (getAuthToken() === token || getRefreshToken()) {
        const refreshed = await refreshAuthSession();
        if (refreshed?.user) {
          return refreshed.user;
        }
      }
      // The request may have started with an older token while an OAuth
      // callback was completing. Never let that stale 401 clear the newly
      // persisted session (or make the provider render a guest state).
      if (getAuthToken() === token) {
        const stored = getStoredUser();
        // Soft-fail: keep a just-written login session if /auth/session 401s.
        if (stored) {
          return stored;
        }
        clearAuthSession();
        markAuthenticationRequired();
        return null;
      }
      return getAuthToken() ? getStoredUser() : null;
    }
    if (getPublicDemoMode() === "live") {
      return getStoredUser();
    }
    return getStoredUser() ?? demoUser;
  }
}

export async function updateCurrentUser(payload: UserUpdateRequest) {
  const token = getAuthToken();
  if (token === DEMO_PREVIEW_TOKEN) {
    const nextUser = {
      ...(getStoredUser() ?? demoUser),
      ...payload,
    };
    setStoredUser(nextUser);
    return nextUser;
  }
  if (!token) {
    if (getPublicDemoMode() === "live") {
      throw new Error("Authentication required to update profile.");
    }
    const nextUser = {
      ...(getStoredUser() ?? demoUser),
      ...payload,
    };
    setStoredUser(nextUser);
    return nextUser;
  }

  try {
    const user = await apiPatch<ApiUser, UserUpdateRequest>("/users/me", payload);
    setStoredUser(user);
    return user;
  } catch (error) {
    throw new Error(userSafeAuthError(error, "profile"));
  }
}

export async function deleteCurrentAccount(payload: AccountDeleteRequest) {
  const token = getAuthToken();
  if (!token || token === DEMO_PREVIEW_TOKEN) {
    throw new Error("The shared preview account cannot be deleted.");
  }
  try {
    return await apiFetch<AccountDeleteResponse>("/users/me", {
      method: "DELETE",
      body: JSON.stringify(payload),
      timeoutMs: 30_000,
    });
  } catch (error) {
    if (isApiError(error) && error.message.trim()) {
      throw new Error(error.message.trim());
    }
    throw new Error("Your account could not be deleted. Nothing was changed; please try again.");
  }
}