package com.mathgenerator.service;

import com.google.gson.Gson;
import java.util.Objects;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import com.mathgenerator.model.User;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Type;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ThreadLocalRandom;
import java.util.regex.Pattern;
import org.apache.commons.mail.Email;
import org.apache.commons.mail.EmailException;
import org.apache.commons.mail.SimpleEmail;


public class UserService {
    private static final Path USER_FILE_PATH = Paths.get("users.json");
    // 密码策略: 6-10位, 必须包含大小写字母和数字
    private static final Pattern PASSWORD_PATTERN =
            Pattern.compile("^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d).{6,10}$");
    private Map<String, User> userDatabase;
    private final Gson gson = new GsonBuilder().setPrettyPrinting().create();

    public UserService() {
        this.userDatabase = loadUsersFromFile();
    }

    private Map<String, User> loadUsersFromFile() {
        try {
            if (Files.exists(USER_FILE_PATH) && Files.size(USER_FILE_PATH) > 0) {
                try (FileReader reader = new FileReader(USER_FILE_PATH.toFile())) {
                    Type type = new TypeToken<Map<String, User>>() {}.getType();
                    Map<String, User> loadedUsers = gson.fromJson(reader, type);
                    return loadedUsers != null ? new ConcurrentHashMap<>(loadedUsers) : new ConcurrentHashMap<>();
                }
            }
        } catch (IOException e) {
            System.err.println("错误：加载用户文件失败 - " + e.getMessage());
        }
        return new ConcurrentHashMap<>();
    }

    private void saveUsers() {
        try (FileWriter writer = new FileWriter(USER_FILE_PATH.toFile())) {
            gson.toJson(this.userDatabase, writer);
        } catch (IOException e) {
            System.err.println("错误：保存用户文件失败 - " + e.getMessage());
        }
    }

    public Optional<User> findUserByUsername(String username) {
        return Optional.ofNullable(this.userDatabase.get(username));
    }

    public Optional<User> login(String username, String password) {
        return findUserByUsername(username)
                .filter(user -> user.password().equals(password));
    }

    /**
     * (已更新) 发送真实的邮件验证码。
     * @param email 用户的邮箱
     * @return 成功发送则返回生成的6位验证码, 失败则返回null
     */
    public String sendVerificationCode(String email) {
        String code = String.format("%06d", ThreadLocalRandom.current().nextInt(100000, 1000000));

        try {
            Email mail = new SimpleEmail();

            // 1. 设置SMTP服务器信息
            mail.setHostName(EmailConfig.getHost());
            mail.setSmtpPort(EmailConfig.getPort());
            mail.setAuthentication(EmailConfig.getUsername(), EmailConfig.getPassword());
            mail.setSSLOnConnect(true); // 开启SSL加密

            // 2. 设置邮件内容
            mail.setFrom(EmailConfig.getUsername()); // 发件人
            mail.setSubject("【数学学习软件】您的注册验证码"); // 邮件主题
            mail.setMsg("您好！\n\n感谢您注册数学学习软件。您的验证码是：" + code + "\n\n请在5分钟内使用。"); // 邮件正文
            mail.addTo(email); // 收件人

            // 3. 发送邮件
            mail.send();

            System.out.println("验证码邮件已成功发送至: " + email);
            return code;

        } catch (EmailException e) {
            System.err.println("错误：发送验证码邮件失败！请检查您的 config.properties 配置或网络连接。");
            e.printStackTrace();
            return null; // 发送失败
        }
    }

    /**
     * 注册新用户。
     * @return 成功返回true, 否则返回false
     */
    public boolean register(String username, String email, String password) {
        // 1. 基础校验：防止 null 或空白输入
        if (username == null || email == null || password == null ||
                username.trim().isEmpty() || email.trim().isEmpty() || password.trim().isEmpty()) {
            return false;
        }

        // 2. 检查用户名或邮箱是否已存在（使用 Objects.equals 安全比较）
        boolean usernameExists = userDatabase.containsKey(username);
        boolean emailExists = userDatabase.values().stream()
                .anyMatch(u -> Objects.equals(u.email(), email));

        if (usernameExists || emailExists) {
            return false; // 用户名或邮箱已存在
        }

        // 3. 创建新用户并保存
        User newUser = new User(username, email, password);
        userDatabase.put(username, newUser);
        saveUsers();
        return true;
    }

    /**
     * 验证密码是否符合复杂度要求。
     * @param password 待验证的密码
     * @return true如果符合要求
     */
    public static boolean isPasswordValid(String password) {
        return password != null && PASSWORD_PATTERN.matcher(password).matches();
    }

    /**
     * 修改密码。
     * @return 成功返回true
     */
    public boolean changePassword(String username, String oldPassword, String newPassword) {
        return findUserByUsername(username)
                .filter(user -> user.password().equals(oldPassword))
                .map(user -> {
                    User updatedUser = new User(user.username(), user.email(), newPassword);
                    userDatabase.put(username, updatedUser);
                    saveUsers();
                    return true;
                }).orElse(false);
    }
}