import { logger } from '../services/logging';

export interface AuthTokens {
  accessToken: string;
  refreshToken?: string | null;
}

const TOKEN_STORAGE_KEY = 'meds_auth_tokens';

let memoryTokens: AuthTokens | null = null;

function getStorage(): Storage | null {
  if (typeof window === 'undefined') {
    return null;
  }

  try {
    return window.localStorage;
  } catch (error) {
    // LocalStorage may be unavailable (e.g. Safari private mode); gracefully degrade.
    logger.warn('Token storage fallback to memory', 'AUTH_TOKENS', error);
    return null;
  }
}

function persist(tokens: AuthTokens | null): void {
  const storage = getStorage();

  if (!storage) {
    memoryTokens = tokens;
    return;
  }

  if (!tokens) {
    storage.removeItem(TOKEN_STORAGE_KEY);
    memoryTokens = null;
    return;
  }

  const payload: AuthTokens = {
    accessToken: tokens.accessToken,
    refreshToken: tokens.refreshToken ?? null,
  };

  storage.setItem(TOKEN_STORAGE_KEY, JSON.stringify(payload));
  memoryTokens = payload;
}

function readTokens(): AuthTokens | null {
  const storage = getStorage();

  if (!storage) {
    return memoryTokens;
  }

  try {
    const raw = storage.getItem(TOKEN_STORAGE_KEY);
    if (!raw) {
      memoryTokens = null;
      return null;
    }

    const parsed = JSON.parse(raw) as AuthTokens;
    memoryTokens = parsed;
    return parsed;
  } catch (error) {
    logger.warn(
      'Failed to parse stored tokens, clearing cache',
      'AUTH_TOKENS',
      error
    );
    storage.removeItem(TOKEN_STORAGE_KEY);
    memoryTokens = null;
    return null;
  }
}

export const tokenStorage = {
  save(tokens: AuthTokens): void {
    if (!tokens || !tokens.accessToken) {
      throw new Error('Token payload must include an access token');
    }

    persist(tokens);
  },

  getTokens(): AuthTokens | null {
    return readTokens();
  },

  getAccessToken(): string | null {
    const tokens = readTokens();
    return tokens?.accessToken ?? null;
  },

  clear(): void {
    persist(null);
  },
};

export default tokenStorage;