FakeChatClient.java

import java.util.ArrayList;
import java.util.List;

/**
 * 「假的」客戶端：完全不碰網路，把所有訊息直接回送給監聽者。
 *
 * 用途：在伺服器還沒寫好之前，就能開發並「測試」UI——
 * 這正是「對介面寫程式」帶來的好處：任何 ChatClient 的實作都可以互換。
 */
public class FakeChatClient implements ChatClient {

    private final List<Listener> listeners = new ArrayList<>();
    private boolean connected = false;
    private String name;
    private final List<String> rooms = new ArrayList<>();

    @Override
    public void addListener(Listener listener) {
        this.listeners.add(listener);
    }

    @Override
    public void connect(String host, int port, String name) {
        if (this.connected) {
            throw new IllegalStateException("已經連線");
        }
        this.connected = true;
        this.name = name;
    }

    @Override
    public void join(String room) {
        requireConnected();
        this.rooms.add(room);
    }

    @Override
    public void say(String room, String text) {
        requireConnected();
        if (!this.rooms.contains(room)) {
            for (Listener l : this.listeners) {
                l.onError(403, "not in room " + room);   // 模擬伺服器回 ERR
            }
            return;
        }
        for (Listener l : this.listeners) {              // 模擬伺服器把訊息廣播回來
            l.onMessage(room, this.name, text);
        }
    }

    @Override
    public void disconnect() {
        requireConnected();
        this.connected = false;
        for (Listener l : this.listeners) {
            l.onDisconnected();
        }
    }

    @Override
    public boolean isConnected() {
        return this.connected;
    }

    private void requireConnected() {
        if (!this.connected) {
            throw new IllegalStateException("尚未連線");
        }
    }
}