package com.example.myapp.service;

import com.example.myapp.model.User;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class UserService {
  private Map<String, User> users;
  private Map<String, String> usernameToEmail;
  private Map<String, String> registrationCodes;
  private Map<String, String> resetPasswordCodes;

  private final FileStorageService fileStorageService;
  private static final UserService instance = new UserService();

  public static UserService getInstance() {
    return instance;
  }

  private UserService() {
    this.fileStorageService = new FileStorageService();
    loadData();
  }

  private void loadData() {
    users = fileStorageService.readUsersData();
    registrationCodes = fileStorageService.readRegistrationCodesData();
    resetPasswordCodes = fileStorageService.readResetPasswordCodesData();

    usernameToEmail = new ConcurrentHashMap<>();
    if (users != null) {
      for (User user : users.values()) {
        if (user.getUsername() != null && !user.getUsername().trim().isEmpty()) {
          usernameToEmail.put(user.getUsername().toLowerCase(), user.getEmail());
        }
      }
    }

    if (users == null) users = new ConcurrentHashMap<>();
    if (registrationCodes == null) registrationCodes = new ConcurrentHashMap<>();
    if (resetPasswordCodes == null) resetPasswordCodes = new ConcurrentHashMap<>();
    if (usernameToEmail == null) usernameToEmail = new ConcurrentHashMap<>();
  }

  private void saveUsers() {
    fileStorageService.writeUsersData(users);
  }

  private void saveRegistrationCodes() {
    fileStorageService.writeRegistrationCodesData(registrationCodes);
  }

  private void saveResetPasswordCodes() {
    fileStorageService.writeResetPasswordCodesData(resetPasswordCodes);
  }

  public boolean emailExists(String email) {
    return users.containsKey(email);
  }

  public boolean usernameExists(String username) {
    return usernameToEmail.containsKey(username.toLowerCase());
  }

  public User getUserByIdentifier(String identifier) {
    if (identifier.contains("@")) {
      return users.get(identifier);
    } else {
      String email = usernameToEmail.get(identifier.toLowerCase());
      return email != null ? users.get(email) : null;
    }
  }

  public boolean userExists(String identifier) {
    if (identifier.contains("@")) {
      return emailExists(identifier);
    } else {
      return usernameExists(identifier);
    }
  }

  public boolean isUserRegistered(String email) {
    User user = users.get(email);
    return user != null && user.getPasswordHash() != null && !user.getPasswordHash().isEmpty();
  }

  public void createPendingUser(String email, String code) {
    if (users.containsKey(email)) {
      User existingUser = users.get(email);
      if (existingUser.getPasswordHash() == null || existingUser.getPasswordHash().isEmpty()) {
        registrationCodes.put(email, code);
        saveRegistrationCodes();
        return;
      }
    }

    users.putIfAbsent(email, new User(email, null));
    registrationCodes.put(email, code);
    saveUsers();
    saveRegistrationCodes();
  }

  public boolean setUsername(String email, String username) {
    if (username == null || username.trim().isEmpty()) {
      return false;
    }

    String usernameLower = username.toLowerCase();
    if (usernameToEmail.containsKey(usernameLower)) {
      return false;
    }

    User user = users.get(email);
    if (user != null) {
      if (user.getUsername() != null) {
        usernameToEmail.remove(user.getUsername().toLowerCase());
      }

      user.setUsername(username);
      usernameToEmail.put(usernameLower, email);
      saveUsers();
      return true;
    }
    return false;
  }

  public boolean verifyCode(String email, String code) {
    String storedCode = registrationCodes.get(email);
    if (storedCode != null && storedCode.equals(code)) {
      User u = users.get(email);
      if (u != null) {
        u.setVerified(true);
        registrationCodes.remove(email);
        saveUsers();
        saveRegistrationCodes();
        return true;
      }
    }
    return false;
  }

  // 忘记密码相关方法
  public void createResetPasswordCode(String email, String code) {
    resetPasswordCodes.put(email, code);
    saveResetPasswordCodes();
  }

  public boolean verifyResetPasswordCode(String email, String code) {
    String storedCode = resetPasswordCodes.get(email);
    if (storedCode != null && storedCode.equals(code)) {
      resetPasswordCodes.remove(email);
      saveResetPasswordCodes();
      return true;
    }
    return false;
  }

  public void setPassword(String email, String passwordHash) {
    User u = users.get(email);
    if (u != null) {
      u.setPasswordHash(passwordHash);
      u.setVerified(true);
      saveUsers();
    }
  }

  public boolean checkPassword(String identifier, String plain) {
    User user = getUserByIdentifier(identifier);
    if (user == null || user.getPasswordHash() == null) {
      return false;
    }

    return com.example.myapp.util.PasswordUtil.check(plain, user.getPasswordHash());
  }

  public String getDisplayName(String identifier) {
    User user = getUserByIdentifier(identifier);
    if (user == null) return identifier;
    return user.getUsername() != null ? user.getUsername() : user.getEmail();
  }
}