Add Command pattern implementation and tests

Implemented the Command design pattern with a `Light` receiver, `LightOnCommand` and `LightOffCommand` classes, and a `RemoteControl` invoker.

Updated `Program.cs` to include a demo showcasing command execution and undo functionality.

Introduced the `ICommand` interface to define the contract for commands.

Updated `README.md` to document the Command pattern, its purpose, usage, and related files.

Added `CommandTests.cs` to verify the functionality of the Command pattern, including execution and undo scenarios.

Author: froghramar

DesignPatterns/Command/ICommand.cs

@@ -0,0 +1,7 @@
+namespace DesignPatterns.Command;
+
+public interface ICommand
+{
+    void Execute();
+    void Undo();
+}

DesignPatterns/Command/Light.cs

@@ -0,0 +1,9 @@
+namespace DesignPatterns.Command;
+
+public class Light
+{
+    public bool IsOn { get; private set; }
+
+    public void On() => IsOn = true;
+    public void Off() => IsOn = false;
+}

DesignPatterns/Command/LightOffCommand.cs

@@ -0,0 +1,11 @@
+namespace DesignPatterns.Command;
+
+public class LightOffCommand : ICommand
+{
+    private readonly Light _light;
+
+    public LightOffCommand(Light light) => _light = light;
+
+    public void Execute() => _light.Off();
+    public void Undo() => _light.On();
+}

DesignPatterns/Command/LightOnCommand.cs

@@ -0,0 +1,11 @@
+namespace DesignPatterns.Command;
+
+public class LightOnCommand : ICommand
+{
+    private readonly Light _light;
+
+    public LightOnCommand(Light light) => _light = light;
+
+    public void Execute() => _light.On();
+    public void Undo() => _light.Off();
+}

DesignPatterns/Command/RemoteControl.cs

@@ -0,0 +1,24 @@
+namespace DesignPatterns.Command;
+
+public class RemoteControl
+{
+    private ICommand? _slot;
+    private readonly Stack<ICommand> _history = new();
+
+    public void SetCommand(ICommand command) => _slot = command;
+
+    public void PressButton()
+    {
+        _slot?.Execute();
+        if (_slot != null) _history.Push(_slot);
+    }
+
+    public void PressUndo()
+    {
+        if (_history.Any())
+        {
+            var cmd = _history.Pop();
+            cmd.Undo();
+        }
+    }
+}

DesignPatterns/Program.cs

@@ -66,6 +66,7 @@
 ITextProvider provider = new LegacyTextAdapter(legacy);
 Console.WriteLine(provider.GetText());
 
+
 // Bridge demo
 Console.WriteLine();
 Console.WriteLine("Bridge pattern demo:");
@@ -110,6 +111,28 @@
 Console.WriteLine(h1.Handle(new Request(2, "r2")));
 Console.WriteLine(h1.Handle(new Request(99, "r3")));
 
+// Command demo
+Console.WriteLine();
+Console.WriteLine("Command pattern demo:");
+var light = new DesignPatterns.Command.Light();
+var lightOn = new DesignPatterns.Command.LightOnCommand(light);
+var lightOff = new DesignPatterns.Command.LightOffCommand(light);
+var cmdRemote = new DesignPatterns.Command.RemoteControl();
+
+cmdRemote.SetCommand(lightOn);
+cmdRemote.PressButton();
+Console.WriteLine($"Light is on: {light.IsOn}");
+
+cmdRemote.SetCommand(lightOff);
+cmdRemote.PressButton();
+Console.WriteLine($"Light is on: {light.IsOn}");
+
+// demonstrate undo
+cmdRemote.SetCommand(lightOn);
+cmdRemote.PressButton();
+cmdRemote.PressUndo();
+Console.WriteLine($"After undo, light is on: {light.IsOn}");
+
 // Decorator demo
 Console.WriteLine();
 Console.WriteLine("Decorator pattern demo:");

README.md

@@ -3,7 +3,7 @@ Design Patterns Examples
 This solution demonstrates simple design pattern examples in C# targeting .NET 10 (C# 14).
 
 Projects
-- `DesignPatterns` - Console demo showing Factory, Singleton, Builder, Prototype, Abstract Factory, Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy, and Chain of Responsibility patterns.
+- `DesignPatterns` - Console demo showing Factory, Singleton, Builder, Prototype, Abstract Factory, Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy, Chain of Responsibility, and Command patterns.
   - Factory implementation: `DesignPatterns/Factories`
   - Singleton implementation: `DesignPatterns/Singleton/Logger.cs`
   - Builder implementation: `DesignPatterns/Builder/HouseBuilder.cs` and `DesignPatterns/Builder/House.cs`
@@ -17,6 +17,7 @@ Projects
   - Flyweight implementation: `DesignPatterns/Flyweight/*`
   - Proxy implementation: `DesignPatterns/Proxy/*`
   - Chain of Responsibility implementation: `DesignPatterns/Chain/*`
+  - Command implementation: `DesignPatterns/Command/*`
 - `Tests` - xUnit tests covering the examples.
 
 Included patterns and brief docs
@@ -173,6 +174,20 @@ Included patterns and brief docs
     Console.WriteLine(h1.Handle(new Request(99, "r3")));
     ```
 
+- Command Pattern
+  - Purpose: Encapsulate a request as an object, thereby letting you parameterize clients with queues, requests, and operations and support undoable operations.
+  - Example: `DesignPatterns/Command/*` contains `ICommand`, `Light`, `LightOnCommand`, `LightOffCommand`, and `RemoteControl` (invoker).
+  - Usage snippet:
+
+    ```csharp
+    var light = new Light();
+    var on = new LightOnCommand(light);
+    var remote = new RemoteControl();
+    remote.SetCommand(on);
+    remote.PressButton();
+    remote.PressUndo();
+    ```
+
 Tests
 - Tests are written with xUnit in the `Tests` project.
   - Factory tests: `Tests/ShapeFactoryTests.cs`
@@ -188,6 +203,7 @@ Tests
   - Flyweight tests: `Tests/FlyweightTests.cs`
   - Proxy tests: `Tests/ProxyTests.cs`
   - Chain tests: `Tests/ChainTests.cs`
+  - Command tests: `Tests/CommandTests.cs`
 
 Common commands
 - Build solution: `dotnet build`

Tests/CommandTests.cs

@@ -0,0 +1,39 @@
+using DesignPatterns.Command;
+
+namespace Tests;
+
+public class CommandTests
+{
+    [Fact]
+    public void LightOnCommand_ExecutesAndUndo()
+    {
+        var light = new Light();
+        var on = new LightOnCommand(light);
+
+        var remote = new RemoteControl();
+        remote.SetCommand(on);
+
+        remote.PressButton();
+        Assert.True(light.IsOn);
+
+        remote.PressUndo();
+        Assert.False(light.IsOn);
+    }
+
+    [Fact]
+    public void LightOffCommand_ExecutesAndUndo()
+    {
+        var light = new Light();
+        light.On();
+        var off = new LightOffCommand(light);
+
+        var remote = new RemoteControl();
+        remote.SetCommand(off);
+
+        remote.PressButton();
+        Assert.False(light.IsOn);
+
+        remote.PressUndo();
+        Assert.True(light.IsOn);
+    }
+}