Adds observer pattern and target framework 4.5

Core/Extensions/ConsoleExtensions.cs

@@ -1,5 +1,4 @@
-using System.Text;
-using Core.Console.Interfaces;
+using Core.Console.Interfaces;
 using Microsoft.Extensions.Logging;
 
 namespace Core.Extensions;
@@ -8,17 +7,6 @@ internal static class ConsoleExtensions
 {
     public static ILoggerFactory GetLoggerFactory() => LoggerFactory.Create(builder => { builder.AddConsole(); });
 
-    public static void Log<T>(this IConsoleLogger logger, string identifier, IEnumerable<T> options)
-    {
-        var message = new StringBuilder($"Please enter from following {identifier}: ");
-
-        var i = 0;
-        foreach (var option in options)
-            message.Append($"\n {++i}. {option} ");
-
-        logger.Log(message.ToString());
-    }
-
     public static TEnum AcceptInputEnum<TEnum>(this IInputReader inputReader, TEnum defaultValue)
     {
         var input = inputReader.AcceptInput();
@@ -31,4 +19,9 @@ public static decimal AcceptInputDecimal(this IInputReader inputReader)
         var input = inputReader.AcceptInput();
         return decimal.Parse(input);
     }
+
+    public static void LogInfoQuit(this IConsoleLogger logger)
+    {
+        logger.Log("Please provide 'quit' input in order to quit from the example.");
+    }
 }

Directory.Packages.props

@@ -1,19 +1,20 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
-    <PropertyGroup>
-        <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
-        <NoWarn>NU1507</NoWarn>
-    </PropertyGroup>
-    <ItemGroup Label="Microsoft Nugets">
-        <PackageVersion Include="coverlet.collector" Version="3.1.2" />
-        <PackageVersion Include="Microsoft.Extensions.Logging" Version="6.0.0" />
-        <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="6.0.0" />
-        <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="6.0.0" />
-        <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
-        <PackageVersion Include="Moq" Version="4.18.4" />
-        <PackageVersion Include="NUnit" Version="3.13.3" />
-        <PackageVersion Include="NUnit3TestAdapter" Version="4.2.1" />
-        <PackageVersion Include="NUnit.Analyzers" Version="3.3.0" />
-        <PackageVersion Include="YamlDotNet" Version="13.2.0" />
-    </ItemGroup>
+  <PropertyGroup>
+    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
+    <NoWarn>NU1507</NoWarn>
+  </PropertyGroup>
+  <ItemGroup Label="Microsoft Nugets">
+    <PackageVersion Include="coverlet.collector" Version="3.1.2" />
+    <PackageVersion Include="Microsoft.AspNet.WebApi.Client" Version="4.0.20505" />
+    <PackageVersion Include="Microsoft.Extensions.Logging" Version="6.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="6.0.0" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="6.0.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
+    <PackageVersion Include="Moq" Version="4.18.4" />
+    <PackageVersion Include="NUnit" Version="3.13.3" />
+    <PackageVersion Include="NUnit3TestAdapter" Version="4.2.1" />
+    <PackageVersion Include="NUnit.Analyzers" Version="3.3.0" />
+    <PackageVersion Include="YamlDotNet" Version="13.2.0" />
+  </ItemGroup>
 </Project>

GofConsoleApp/Examples/Behavioral/ObserverPattern/Components/EnumTopic.cs

@@ -0,0 +1,11 @@
+namespace GofConsoleApp.Examples.Behavioral.ObserverPattern.Components;
+
+internal enum EnumTopic
+{
+    Sports,
+    Politics,
+    Weather,
+    Holidays,
+    Invalid,
+    Quit
+}

GofConsoleApp/Examples/Behavioral/ObserverPattern/Components/PersonAndrewSmith.cs

@@ -0,0 +1,19 @@
+using Core.Console.Interfaces;
+using GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+namespace GofConsoleApp.Examples.Behavioral.ObserverPattern.Components;
+
+internal class PersonAndrewSmith : ISubscriber<string>
+{
+    private readonly IConsoleLogger logger;
+
+    public PersonAndrewSmith(IConsoleLogger logger)
+    {
+        this.logger = logger;
+    }
+
+    public void Update(string input)
+    {
+        logger.Log($"Andrew Smith received: {input}");
+    }
+}

GofConsoleApp/Examples/Behavioral/ObserverPattern/Components/PersonJohnDoe.cs

@@ -0,0 +1,19 @@
+using Core.Console.Interfaces;
+using GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+namespace GofConsoleApp.Examples.Behavioral.ObserverPattern.Components;
+
+internal class PersonJohnDoe : ISubscriber<string>
+{
+    private readonly IConsoleLogger logger;
+
+    public PersonJohnDoe(IConsoleLogger logger)
+    {
+        this.logger = logger;
+    }
+
+    public void Update(string input)
+    {
+        logger.Log($"John Doe received: {input}");
+    }
+}

GofConsoleApp/Examples/Behavioral/ObserverPattern/ObserverPatternExample.cs

@@ -0,0 +1,34 @@
+using Core.Extensions;
+using GofConsoleApp.Examples.Behavioral.ObserverPattern.Components;
+using GofPatterns.Behavioral.ObserverPattern;
+using GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+namespace GofConsoleApp.Examples.Behavioral.ObserverPattern;
+
+internal class ObserverPatternExample : BaseExample
+{
+    private readonly IPublisher<string> newsPublisher = new Publisher<string>();
+
+    protected override bool Execute()
+    {
+        var johnDoe = new PersonJohnDoe(Logger);
+        var andrewSmith = new PersonAndrewSmith(Logger);
+
+        newsPublisher.AddSubscriber(johnDoe);
+        newsPublisher.AddSubscriber(andrewSmith);
+
+        while (true)
+        {
+            Logger.LogInfoQuit();
+
+            var newsUpdate = AcceptInputString("news update");
+
+            if (newsUpdate.Trim().ToLower().Equals("quit"))
+                break;
+
+            newsPublisher.NotifySubscribers(newsUpdate);
+        }
+
+        return true;
+    }
+}

GofConsoleApp/Examples/Behavioral/ObserverPattern/ObserverPatternExampleWithCategory.cs

@@ -0,0 +1,38 @@
+using Core.Extensions;
+using GofConsoleApp.Examples.Behavioral.ObserverPattern.Components;
+using GofPatterns.Behavioral.ObserverPattern;
+using GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+namespace GofConsoleApp.Examples.Behavioral.ObserverPattern;
+
+internal class ObserverPatternExampleWithCategory : BaseExample
+{
+    private readonly IPublisher<string, EnumTopic> newsPublisher = new Publisher<string, EnumTopic>();
+
+    protected override bool Execute()
+    {
+        var johnDoe = new PersonJohnDoe(Logger);
+        var andrewSmith = new PersonAndrewSmith(Logger);
+
+        newsPublisher.AddSubscriber(johnDoe, EnumTopic.Sports);
+        newsPublisher.AddSubscriber(andrewSmith, EnumTopic.Sports);
+        newsPublisher.AddSubscriber(johnDoe, EnumTopic.Politics);
+        newsPublisher.AddSubscriber(andrewSmith, EnumTopic.Weather);
+        newsPublisher.AddSubscriber(johnDoe, EnumTopic.Holidays);
+
+        do
+        {
+            Logger.LogInfoQuit();
+
+            var topic = AcceptInputEnum(EnumTopic.Invalid, nameof(EnumTopic), EnumTopic.Invalid);
+
+            if (IsInvalidOrQuit(topic, EnumTopic.Invalid, EnumTopic.Quit, out _))
+                return true;
+
+            var newsUpdate = AcceptInputString($"{topic} news update");
+
+            newsPublisher.NotifySubscribers(newsUpdate, topic);
+
+        } while (true);
+    }
+}

GofConsoleApp/Examples/Behavioral/StatePattern/StatePatternBulbExample.cs

@@ -18,18 +18,18 @@ protected override bool Execute()
 
         do
         {
-            var inputOption = AcceptInputEnum(Invalid, "state", Invalid);
+            var state = AcceptInputEnum(Invalid, "state", Invalid);
 
-            if (IsInvalidOrQuit(inputOption, Invalid, Quit, out var output))
+            if (IsInvalidOrQuit(state, Invalid, Quit, out var output))
                 return output;
 
-            if (bulb.State.Name.Equals(inputOption.ToString()))
+            if (bulb.State.Name.Equals(state.ToString()))
             {
                 Logger.Log($"Bulb already in {bulb.State.Name} state.");
                 continue;
             }
 
-            switch (inputOption)
+            switch (state)
             {
                 case On:
                     bulb.SetState(on);

GofConsoleApp/Examples/ExecutionHelpers/PatternOptions.cs

@@ -1,6 +1,7 @@
 using GofConsoleApp.Examples.Behavioral.CommandPattern;
 using GofConsoleApp.Examples.Behavioral.CorPattern;
 using GofConsoleApp.Examples.Behavioral.MediatorPattern;
+using GofConsoleApp.Examples.Behavioral.ObserverPattern;
 using GofConsoleApp.Examples.Behavioral.StatePattern;
 using GofConsoleApp.Examples.Behavioral.StrategyPattern;
 using GofConsoleApp.Examples.Creational.AbstractFactoryPattern;
@@ -24,6 +25,9 @@ internal static class PatternOptions
     internal const string AdapterPatternOption = "13";
     internal const string FlyweightPatternOption = "14";
     internal const string MediatorPatternOption = "15";
+    internal const string ObserverPatternOption = "16.1";
+    internal const string ObserverPatternOptionWithType = "16.2";
+
     internal const string ChainOfResponsibilityPatternOption = "21";
     internal const string ChainOfResponsibilityPatternOption2 = "21.2";
     internal const string ChainOfResponsibilityPatternOption3 = "21.3";
@@ -33,6 +37,7 @@ internal static class PatternOptions
     internal const string StatePatternOptionDriveExample = "23.2";
     internal const string StrategyPatternOptionSender = "24";
     internal const string StrategyPatternOptionPayment = "24.2";
+
     internal const string FactoryOption = "31";
     internal const string AbstractFactoryOption = "32";
     internal const string BuilderPatternOption = "33";
@@ -73,6 +78,14 @@ internal static class PatternOptions
             MediatorPatternOption,
             new PatternExampleMap("Flyweight Pattern >> Drawing shapes", new MediatorPatternExample())
         },
+        {
+            ObserverPatternOption,
+            new PatternExampleMap("Observer Pattern >> News Publisher", new ObserverPatternExample())
+        },
+        {
+            ObserverPatternOptionWithType,
+            new PatternExampleMap("Observer Pattern >> News Publisher with type", new ObserverPatternExampleWithCategory())
+        },
 
         // Behavioral Patterns
         {

GofPatterns/Behavioral/ObserverPattern/Exceptions/NoSubscriptionFoundException.cs

@@ -0,0 +1,6 @@
+namespace GofPatterns.Behavioral.ObserverPattern.Exceptions;
+
+public class NoSubscriptionFoundException : Exception
+{
+    public NoSubscriptionFoundException(string message) : base(message) { }
+}

GofPatterns/Behavioral/ObserverPattern/Interfaces/IPublisher.cs

@@ -0,0 +1,31 @@
+namespace GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+/// <summary>
+/// Publisher (or Broadcaster) interface.
+/// Publishers are responsible for managing subscribers and notifying them of events.
+/// </summary>
+/// <typeparam name="TInput"></typeparam>
+public interface IPublisher<TInput>
+{
+    public void AddSubscriber(ISubscriber<TInput> subscriber);
+
+    public void RemoveSubscribers();
+
+    public void NotifySubscribers(TInput input);
+}
+
+/// <summary>
+/// Publisher (or Broadcaster) interface.
+/// Publishers are responsible for managing subscribers and notifying them of events.
+/// Multiple subscribers can be subscribed to a category, and there can be multiple categories.
+/// </summary>
+/// <typeparam name="TInput"></typeparam>
+/// <typeparam name="TCategory"></typeparam>
+public interface IPublisher<TInput, in TCategory> where TCategory : notnull
+{
+    public void AddSubscriber(ISubscriber<TInput> subscriber, TCategory category);
+
+    public void RemoveSubscribers(TCategory category);
+
+    public void NotifySubscribers(TInput input, TCategory category);
+}

GofPatterns/Behavioral/ObserverPattern/Interfaces/ISubscriber.cs

@@ -0,0 +1,11 @@
+namespace GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+/// <summary>
+/// Subscriber (or Listener) interface.
+/// Subscribers are interested in certain events and implement the Update method to handle them.
+/// </summary>
+/// <typeparam name="TInput"></typeparam>
+public interface ISubscriber<in TInput>
+{
+    void Update(TInput input);
+}

GofPatterns/Behavioral/ObserverPattern/Publisher.cs

@@ -0,0 +1,68 @@
+using GofPatterns.Behavioral.ObserverPattern.Exceptions;
+using GofPatterns.Behavioral.ObserverPattern.Interfaces;
+
+namespace GofPatterns.Behavioral.ObserverPattern;
+
+/// <summary>
+/// Implementation of the Publisher (or Broadcaster) interface.
+/// </summary>
+/// <typeparam name="TInput"></typeparam>
+public class Publisher<TInput> : IPublisher<TInput>
+{
+    private readonly List<ISubscriber<TInput>> subscribers = new();
+
+    public void AddSubscriber(ISubscriber<TInput> subscriber)
+    {
+        subscribers.Add(subscriber);
+    }
+
+    public void RemoveSubscribers()
+    {
+        subscribers.Clear();
+    }
+
+    public void NotifySubscribers(TInput input)
+    {
+        subscribers.ForEach(x => x.Update(input));
+    }
+}
+
+/// <summary>
+/// Implementation of the Publisher (or Broadcaster) interface.
+/// </summary>
+/// <typeparam name="TInput"></typeparam>
+/// <typeparam name="TCategory"></typeparam>
+public class Publisher<TInput, TCategory> : IPublisher<TInput, TCategory> where TCategory : notnull
+{
+    private readonly Dictionary<TCategory, IPublisher<TInput>> publishers = new();
+
+    public void AddSubscriber(ISubscriber<TInput> subscriber, TCategory category)
+    {
+        IPublisher<TInput> publisher;
+
+        if (publishers.TryGetValue(category, out var outputPublisher))
+            publisher = outputPublisher;
+        else
+            publishers[category] = publisher = new Publisher<TInput>();
+
+        publisher.AddSubscriber(subscriber);
+    }
+
+    public void RemoveSubscribers(TCategory category)
+    {
+        VerifySubscription(category);
+        publishers.Remove(category);
+    }
+
+    public void NotifySubscribers(TInput input, TCategory category)
+    {
+        VerifySubscription(category);
+        publishers[category].NotifySubscribers(input);
+    }
+
+    private void VerifySubscription(TCategory type)
+    {
+        if (!publishers.ContainsKey(type))
+            throw new NoSubscriptionFoundException($"No subscription found for category: {type}");
+    }
+}