#适配器模式

// 每个渠道都写一个适配器类，最后变成了"适配器地狱"
class AlipayAdapter { void pay() {} }
class WechatPayAdapter { void pay() {} }
class UnionPayAdapter { void pay() {} }
class MeituanPayAdapter { void pay() {} }
class BaiduPayAdapter { void pay() {} }
// ... 8 个适配器，每个都不一样

// 目标接口
interface Target {
    void request();
}

// 被适配者
class Adaptee {
    public void specificRequest() {
        System.out.println("Adaptee: specific request");
    }
}

// 方式一：类适配器（通过继承）
class ClassAdapter extends Adaptee implements Target {
    @Override
    public void request() {
        // 调用父类方法
        specificRequest();
    }
}

// 方式二：对象适配器（通过组合）
class ObjectAdapter implements Target {
    private final Adaptee adaptee;

    public ObjectAdapter(Adaptee adaptee) {
        this.adaptee = adaptee;
    }

    @Override
    public void request() {
        adaptee.specificRequest();
    }
}

// Arrays.asList：数组 → List
String[] arr = {"a", "b", "c"};
List<String> list = Arrays.asList(arr); // 适配器

// Collections.enumeration：迭代器 → 枚举
Iterator<String> it = list.iterator();
Enumeration<String> enumeration = Collections.enumeration(it);

// InputStreamReader：字节流 → 字符流
Reader reader = new InputStreamReader(inputStream); // 适配器

// 外部第三方 API（接口不兼容）
class ThirdPartyLegacyAPI {
    public LegacyResponse getUserData(Map<String, Object> params) {
        // 返回 Map 结构的旧格式
        return null;
    }
}

// 目标接口
interface UserDataProvider {
    UserDTO getUserById(Long id);
}

// 适配器
class ThirdPartyAPIAdapter implements UserDataProvider {
    private final ThirdPartyLegacyAPI legacyAPI;

    @Override
    public UserDTO getUserById(Long id) {
        Map<String, Object> params = new HashMap<>();
        params.put("user_id", id);
        params.put("format", "json");

        LegacyResponse response = legacyAPI.getUserData(params);

        return new UserDTO(
            (String) response.get("user_name"),
            (String) response.get("email"),
            (Integer) response.get("age")
        );
    }
}

interface DataSource {
    User findUser(Long id);
    Order findOrder(Long id);
}

// MySQL 数据源适配
class MySQLDataSource implements DataSource {
    private final JdbcTemplate jdbcTemplate;

    @Override
    public User findUser(Long id) {
        return jdbcTemplate.queryForObject(
            "SELECT * FROM users WHERE id = ?",
            userRowMapper,
            id
        );
    }
}

// MongoDB 数据源适配
class MongoDataSource implements DataSource {
    private final MongoTemplate mongoTemplate;

    @Override
    public User findUser(Long id) {
        return mongoTemplate.findById(id, User.class);
    }
}

// ❌ 错误：直接抛出未转换的异常
class BadAdapter implements Target {
    @Override
    public void request() {
        try {
            adaptee.specificOperation();
        } catch (LegacyException e) {
            throw e; // 调用方无法处理
        }
    }
}

// ✅ 正确：转换为新异常
class GoodAdapter implements Target {
    @Override
    public void request() {
        try {
            adaptee.specificOperation();
        } catch (LegacyException e) {
            throw new ServiceUnavailableException(
                "External service failed: " + e.getMessage(), e
            );
        }
    }
}

// ❌ 错误：用适配器弥补 API 设计缺陷
// 如果原有接口设计有问题，应该重构而不是适配
class OverlyComplexAdapter implements Target {
    @Override
    public void request() {
        // 大量逻辑来弥合两个不兼容的接口
        // 说明接口设计本身就有问题
    }
}