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ahucoderahucoder
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The Command Pattern
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‎src/main/java/command/App.java‎

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package command;
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import command.service.command.Command;
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import command.service.command.impl.DelayedCommand;
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import command.service.command.impl.LightOffCommand;
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import command.service.command.impl.LightOnCommand;
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import command.service.command.impl.MacroCommand;
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import command.service.device.SmartDeviceController;
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import command.service.device.impl.LightDevice;
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import java.util.Arrays;
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import java.util.concurrent.TimeUnit;
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public class App {
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public static void main(String[] args) throws InterruptedException {
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// Create smart device controller
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SmartDeviceController controller = new SmartDeviceController();
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// Create device
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LightDevice livingRoomLight = new LightDevice("livingRoomLight");
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LightDevice bedroomLight = new LightDevice("bedroomLight");
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// Register device
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controller.registerDevice(livingRoomLight);
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controller.registerDevice(bedroomLight);
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// Create command
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Command livingRoomOn = new LightOnCommand(livingRoomLight);
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Command livingRoomOff = new LightOffCommand(livingRoomLight);
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Command bedroomOn = new LightOnCommand(bedroomLight);
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Command bedroomOff = new LightOffCommand(bedroomLight);
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// Create macro command
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Command homeArrival = new MacroCommand("Home Mode", Arrays.asList(
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livingRoomOn
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));
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Command bedtime = new MacroCommand("Sleep Mode", Arrays.asList(
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livingRoomOff,
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bedroomOn
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));
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// Create delay command
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Command delayedLightOff = new DelayedCommand(bedroomOff, 5000);
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// Assign commands to slots of controller
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controller.assignCommand("A1", livingRoomOn);
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controller.assignCommand("A2", livingRoomOff);
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controller.assignCommand("B1", bedroomOn);
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controller.assignCommand("B2", bedroomOff);
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controller.assignCommand("C1", homeArrival);
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controller.assignCommand("C2", bedtime);
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controller.assignCommand("D1", delayedLightOff);
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// Execute command
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System.out.println("===== Execute Home Mode =====");
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controller.pressButton("C1");
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TimeUnit.SECONDS.sleep(1);
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System.out.println("\n===== Current Status =====");
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System.out.println(controller.getStatusReport());
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TimeUnit.SECONDS.sleep(1);
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System.out.println("===== Execute Sleep Mode =====");
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controller.pressButton("C2");
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TimeUnit.SECONDS.sleep(1);
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System.out.println("\n===== Current Status =====");
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System.out.println(controller.getStatusReport());
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System.out.println("===== Delay By 5 Seconds To Turn Off The Bedroom Light =====");
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controller.pressButton("D1");
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System.out.println("\n===== Execute Undo Operation =====");
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controller.undo(); // Cancel delay command
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controller.undo(); // Cancel sleep mode
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System.out.println("\n===== Execute Redo Operation =====");
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controller.redo(); // Redo sleep mode
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TimeUnit.SECONDS.sleep(6); // Waiting for delayed command execution
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System.out.println("\n===== Final Status =====");
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System.out.println(controller.getStatusReport());
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System.out.println("\n===== Command History =====");
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System.out.println(controller.getCommandHistory());
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controller.shutdown();
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}
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}

‎src/main/java/command/listener/CommandListener.java‎

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package command.listener;
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import command.service.command.Command;
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public interface CommandListener {
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void onCommandAction(Command command, boolean executed);
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}

‎src/main/java/command/manager/CommandManager.java‎

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package command.manager;
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import com.google.common.collect.Lists;
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import command.listener.CommandListener;
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import command.service.command.Command;
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import command.service.command.impl.RedoCommand;
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import command.service.command.impl.UndoCommand;
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import java.util.ArrayDeque;
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import java.util.Deque;
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import java.util.List;
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import java.util.stream.Collectors;
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public class CommandManager {
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private final Deque<Command> history = new ArrayDeque<>();
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private final Deque<Command> redoStack = new ArrayDeque<>();
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private final List<Command> log = Lists.newArrayList();
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private final List<CommandListener> listeners = Lists.newArrayList();
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public void execute(Command command) {
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command.execute();
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history.push(command);
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redoStack.clear(); // Clear the redo stack when executing a new command
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log.add(command);
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notifyListeners(command, true);
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}
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public void undo() {
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if (!history.isEmpty()) {
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Command command = history.pop();
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command.undo();
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redoStack.push(command);
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log.add(new UndoCommand(command));
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notifyListeners(command, false);
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}
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}
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public void redo() {
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if (!redoStack.isEmpty()) {
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Command command = redoStack.pop();
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command.execute();
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history.push(command);
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log.add(new RedoCommand(command));
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notifyListeners(command, true);
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}
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}
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public void addListener(CommandListener listener) {
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listeners.add(listener);
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}
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public String getLog() {
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return log.stream()
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.map(Command::description)
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.collect(Collectors.joining("\n"));
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}
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private void notifyListeners(Command command, boolean executed) {
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listeners.forEach(l -> l.onCommandAction(command, executed));
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}
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}

‎src/main/java/command/service/command/Command.java‎

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package command.service.command;
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public interface Command {
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void execute();
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void undo();
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String description();
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}

‎src/main/java/command/service/command/impl/DelayedCommand.java‎

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package command.service.command.impl;
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import command.service.command.Command;
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import java.util.concurrent.Executors;
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import java.util.concurrent.ScheduledExecutorService;
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import java.util.concurrent.ScheduledFuture;
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import java.util.concurrent.TimeUnit;
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public class DelayedCommand implements Command {
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private final Command command;
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private final long delayMillis;
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private ScheduledFuture<?> future;
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private final ScheduledExecutorService scheduler;
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public DelayedCommand(Command command, long delayMillis) {
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this.command = command;
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this.delayMillis = delayMillis;
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this.scheduler = Executors.newSingleThreadScheduledExecutor();
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}
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@Override
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public void execute() {
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future = scheduler.schedule(() -> {
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System.out.println("[DELAY EXECUTE] " + command.description());
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command.execute();
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}, delayMillis, TimeUnit.MILLISECONDS);
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}
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@Override
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public void undo() {
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if (future != null && !future.isDone()) {
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future.cancel(true);
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System.out.println("[CANCEL DELAY EXECUTE COMMAND] " + command.description());
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} else {
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command.undo();
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}
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scheduler.shutdown();
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}
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@Override
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public String description() {
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return String.format("Delay execute after %.1fseconds: %s", delayMillis / 1000.0, command.description());
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}
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}

‎src/main/java/command/service/command/impl/LightOffCommand.java‎

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package command.service.command.impl;
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import command.service.command.Command;
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import command.service.device.impl.LightDevice;
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public class LightOffCommand implements Command {
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private final LightDevice light;
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private int previousBrightness;
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private boolean wasOn;
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public LightOffCommand(LightDevice light) {
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this.light = light;
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}
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@Override
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public void execute() {
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wasOn = light.isOn();
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previousBrightness = light.getBrightness();
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light.turnOff();
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}
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@Override
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public void undo() {
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if (wasOn) {
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light.turnOn();
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light.setBrightness(previousBrightness);
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}
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}
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@Override
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public String description() {
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return "turn off " + light.getName();
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}
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}

‎src/main/java/command/service/command/impl/LightOnCommand.java‎

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package command.service.command.impl;
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import command.service.command.Command;
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import command.service.device.impl.LightDevice;
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public class LightOnCommand implements Command {
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private final LightDevice light;
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private int previousBrightness;
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public LightOnCommand(LightDevice light) {
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this.light = light;
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}
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@Override
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public void execute() {
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previousBrightness = light.getBrightness();
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light.turnOn();
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light.setBrightness(100);
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}
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@Override
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public void undo() {
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light.turnOff();
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light.setBrightness(previousBrightness);
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}
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@Override
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public String description() {
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return "turn on " + light.getName() + " and set brightness to 100%";
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}
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}

‎src/main/java/command/service/command/impl/MacroCommand.java‎

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package command.service.command.impl;
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import com.google.common.collect.Lists;
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import command.service.command.Command;
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import java.util.List;
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import java.util.ListIterator;
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public class MacroCommand implements Command {
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private final String name;
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private final List<Command> commands;
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public MacroCommand(String name, List<Command> commands) {
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this.name = name;
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this.commands = Lists.newArrayList(commands);
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}
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@Override
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public void execute() {
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System.out.println("===== Execution Scene: " + name + " =====");
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commands.forEach(Command::execute);
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}
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@Override
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public void undo() {
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System.out.println("===== Cancel Scene: " + name + " =====");
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// Reverse execution revocation
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ListIterator<Command> iterator = commands.listIterator(commands.size());
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while (iterator.hasPrevious()) {
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iterator.previous().undo();
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}
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}
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@Override
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public String description() {
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return "Scene Mode: " + name + " (" + commands.size() + " Commands)";
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}
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}

‎src/main/java/command/service/command/impl/RedoCommand.java‎

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package command.service.command.impl;
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import command.service.command.Command;
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public class RedoCommand implements Command {
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private final Command command;
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public RedoCommand(Command command) {
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this.command = command;
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}
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@Override
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public void execute() {
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}
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@Override
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public void undo() {
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}
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@Override
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public String description() {
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return "[REDO]" + command.description();
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}
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}

‎src/main/java/command/service/command/impl/UndoCommand.java‎

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package command.service.command.impl;
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import command.service.command.Command;
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public class UndoCommand implements Command {
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private final Command command;
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public UndoCommand(Command command) {
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this.command = command;
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}
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@Override
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public void execute() {
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}
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@Override
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public void undo() {
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}
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@Override
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public String description() {
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return "[UNDO]" + command.description();
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}
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}

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