Add command design pattern with test case (#51)

Author: mperor

DesignPatterns/README.md

@@ -8,6 +8,7 @@ This project explores various design patterns and their implementations in moder
 
 ### Behavioral Design Patterns 💪
 
+- [Command](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command) 📝
 - [Strategy](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy) 🎯
 - [Execute Around Method (EAM)](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/eam) ⭕
 

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command/Account.java

@@ -0,0 +1,27 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+class Account {
+
+    private double balance;
+    private boolean active;
+
+    void deposit(double amount) {
+        balance += amount;
+    }
+
+    void withdraw(double amount) {
+        balance -= amount;
+    }
+
+    void changeActive() {
+        active = !active;
+    }
+
+    double getBalance() {
+        return balance;
+    }
+
+    boolean isActive() {
+        return active;
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command/AccountDepositCommand.java

@@ -0,0 +1,14 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+record AccountDepositCommand(Account account, double deposit) implements Command {
+
+    @Override
+    public void execute() {
+        account.deposit(deposit);
+    }
+
+    @Override
+    public Command reversed() {
+        return new AccountWithdrawCommand(account, deposit);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command/AccountWithdrawCommand.java

@@ -0,0 +1,14 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+record AccountWithdrawCommand(Account account, double withdraw) implements Command {
+
+    @Override
+    public void execute() {
+        account.withdraw(withdraw);
+    }
+
+    @Override
+    public Command reversed() {
+        return new AccountDepositCommand(account, withdraw);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command/Command.java

@@ -0,0 +1,11 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+@FunctionalInterface
+public interface Command {
+
+    void execute();
+
+    default Command reversed() {
+        return this;
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command/CommandRegister.java

@@ -0,0 +1,32 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+class CommandRegister {
+
+    private final Deque<Command> historyCommands = new LinkedList<>();
+    private final Deque<Command> redoCommands = new LinkedList<>();
+
+    void execute(Command command) {
+        command.execute();
+        historyCommands.push(command);
+        redoCommands.clear();
+    }
+
+    void undo() {
+        if (!historyCommands.isEmpty()) {
+            var command = historyCommands.pop();
+            redoCommands.push(command);
+            command.reversed().execute();
+        }
+    }
+
+    void redo() {
+        if (!redoCommands.isEmpty()) {
+            var command = redoCommands.pop();
+            historyCommands.push(command);
+            command.execute();
+        }
+    }
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/command/CommandRegistryTest.java

@@ -0,0 +1,51 @@
+package pl.mperor.lab.java.design.pattern.behavioral.command;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class CommandRegistryTest {
+
+    @Test
+    public void testUndoRedoImplementationWithCommandPattern() {
+        Account account = new Account();
+        CommandRegister commander = new CommandRegister();
+        commander.execute(account::changeActive);
+        commander.execute(new AccountDepositCommand(account, 10));
+        Assert.that(account).active(true).balance(10);
+
+        commander.undo();
+        Assert.that(account).active(true).balance(0);
+
+        commander.undo();
+        Assert.that(account).active(false).balance(0);
+
+        commander.redo();
+        Assert.that(account).active(true).balance(0);
+
+        commander.redo();
+        Assert.that(account).active(true).balance(10);
+    }
+
+    static class Assert {
+
+        private Account account;
+
+        Assert(Account account) {
+            this.account = account;
+        }
+
+        Assert active(boolean active) {
+            Assertions.assertEquals(active, account.isActive());
+            return this;
+        }
+
+        Assert balance(double balance) {
+            Assertions.assertEquals(balance, account.getBalance());
+            return this;
+        }
+
+        static Assert that(Account account) {
+            return new Assert(account);
+        }
+    }
+}