Added background service

.github/workflows/build-test-backgroundservice.yml

@@ -0,0 +1,19 @@
+name: .NET Build and Test for DfE.CoreLibs.BackgroundService
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'src/DfE.CoreLibs.BackgroundService/**'
+
+jobs:
+  build-and-test:
+    uses: ./.github/workflows/build-test-template.yml
+    with:
+      project_name: DfE.CoreLibs.BackgroundService
+      project_path: src/DfE.CoreLibs.BackgroundService
+      sonar_project_key: DFE-Digital_corelibs-backgroundService
+    secrets:
+      GITHUB__TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      SONAR__TOKEN: ${{ secrets.SONAR_TOKEN }}

.github/workflows/pack-backgroundservice.yml

@@ -0,0 +1,15 @@
+name: Build and Push NuGet Package for DfE.CoreLibs.BackgroundService
+
+on:
+  workflow_run:
+    workflows: [".NET Build and Test for DfE.CoreLibs.BackgroundService"]
+    types:
+      - completed
+
+jobs:
+  build-and-package:
+    uses: ./.github/workflows/nuget-package-template.yml
+    with:
+      project_name: DfE.CoreLibs.BackgroundService
+      project_path: src/DfE.CoreLibs.BackgroundService
+      nuget_package_name: DfE.CoreLibs.BackgroundService

DfE.CoreLibs.sln

@@ -5,6 +5,8 @@ VisualStudioVersion = 17.10.35122.118
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "DfE.CoreLibs.Caching", "src\DfE.CoreLibs.Caching\DfE.CoreLibs.Caching.csproj", "{D88D58F0-18C4-4C3B-805B-8A483500E73E}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DfE.CoreLibs.BackgroundService", "src\DfE.CoreLibs.BackgroundService\DfE.CoreLibs.BackgroundService.csproj", "{C7194A27-7254-49A3-8D0E-9B67708D3D43}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +17,10 @@ Global
 		{D88D58F0-18C4-4C3B-805B-8A483500E73E}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{D88D58F0-18C4-4C3B-805B-8A483500E73E}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{D88D58F0-18C4-4C3B-805B-8A483500E73E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{C7194A27-7254-49A3-8D0E-9B67708D3D43}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C7194A27-7254-49A3-8D0E-9B67708D3D43}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C7194A27-7254-49A3-8D0E-9B67708D3D43}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C7194A27-7254-49A3-8D0E-9B67708D3D43}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/DfE.CoreLibs.BackgroundService/DfE.CoreLibs.BackgroundService.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MediatR" Version="12.4.1" />
+    <PackageReference Include="MediatR.Contracts" Version="2.0.1" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="8.0.0" />
+  </ItemGroup>
+
+</Project>

src/DfE.CoreLibs.BackgroundService/Interfaces/IBackgroundServiceEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace DfE.CoreLibs.BackgroundService.Interfaces
+{
+    public interface IBackgroundServiceEvent : INotification
+    {
+    }
+}

src/DfE.CoreLibs.BackgroundService/Interfaces/IBackgroundServiceEventHandler.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace DfE.CoreLibs.BackgroundService.Interfaces
+{
+    public interface IBackgroundServiceEventHandler<in TEvent> : INotificationHandler<TEvent> where TEvent : IBackgroundServiceEvent
+    {
+    }
+}

src/DfE.CoreLibs.BackgroundService/Interfaces/IBackgroundServiceFactory.cs

@@ -0,0 +1,8 @@
+namespace DfE.CoreLibs.BackgroundService.Interfaces
+{
+    public interface IBackgroundServiceFactory
+    {
+        void EnqueueTask<TResult, TEvent>(Func<Task<TResult>> taskFunc, Func<TResult, TEvent>? eventFactory = null)
+            where TEvent : IBackgroundServiceEvent;
+    }
+}

src/DfE.CoreLibs.BackgroundService/ServiceCollectionExtensions.cs

@@ -0,0 +1,16 @@
+using DfE.CoreLibs.BackgroundService.Interfaces;
+using DfE.CoreLibs.BackgroundService.Services;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    public static class ServiceCollectionExtensions
+    {
+        public static IServiceCollection AddBackgroundService(this IServiceCollection services)
+        {
+            services.AddSingleton<IBackgroundServiceFactory, BackgroundServiceFactory>();
+            services.AddHostedService<BackgroundServiceFactory>();
+
+            return services;
+        }
+    }
+}

src/DfE.CoreLibs.BackgroundService/Services/BackgroundServiceFactory.cs

@@ -0,0 +1,61 @@
+using System.Collections.Concurrent;
+using DfE.CoreLibs.BackgroundService.Interfaces;
+using MediatR;
+
+namespace DfE.CoreLibs.BackgroundService.Services
+{
+    public class BackgroundServiceFactory(IMediator mediator) : Microsoft.Extensions.Hosting.BackgroundService, IBackgroundServiceFactory
+    {
+        private readonly ConcurrentDictionary<Type, ConcurrentQueue<Func<Task>>> _taskQueues = new();
+        private readonly ConcurrentDictionary<Type, SemaphoreSlim> _semaphores = new();
+
+        public void EnqueueTask<TResult, TEvent>(Func<Task<TResult>> taskFunc, Func<TResult, TEvent>? eventFactory = null)
+            where TEvent : IBackgroundServiceEvent
+        {
+            var taskType = taskFunc.GetType();
+            var queue = _taskQueues.GetOrAdd(taskType, new ConcurrentQueue<Func<Task>>());
+            _semaphores.GetOrAdd(taskType, new SemaphoreSlim(1, 1));
+
+            queue.Enqueue(async () =>
+            {
+                var result = await taskFunc();
+
+                if (eventFactory != null)
+                {
+                    var taskCompletedEvent = eventFactory.Invoke(result);
+                    await mediator.Publish(taskCompletedEvent);
+                }
+            });
+
+            _ = StartProcessingQueue(taskType);
+        }
+
+        private async Task StartProcessingQueue(Type taskType)
+        {
+            var queue = _taskQueues[taskType];
+            var semaphore = _semaphores[taskType];
+
+            await semaphore.WaitAsync();
+
+            try
+            {
+                while (queue.TryDequeue(out var taskToProcess))
+                {
+                    await taskToProcess();
+                }
+            }
+            finally
+            {
+                semaphore.Release();
+            }
+        }
+
+        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                await Task.Delay(1000, stoppingToken);
+            }
+        }
+    }
+}