Code(API::GetChatSession): Implement GetChatSession feature

src/Server/StellarChat.Server.Api/DAL/Mongo/Exceptions/Chat/ChatSessionNotFoundException.cs

@@ -0,0 +1,21 @@
+using StellarChat.Shared.Abstractions.Exceptions;
+
+namespace StellarChat.Server.Api.DAL.Mongo.Exceptions.Chat;
+
+internal sealed class ChatSessionNotFoundException : StellarChatException
+{
+    public Guid Id { get; }
+    public string? Title { get; }
+
+    public ChatSessionNotFoundException(Guid id) 
+        : base(
+            message: $"Chat session with ID: {id} not found.",
+            userMessage: $"The requested chat session could not be found.")
+        => Id = id;
+
+    public ChatSessionNotFoundException(string title)
+        : base(
+            message: $"Chat session with title: {title} not found.",
+            userMessage: $"The chat session with the title '{title}' could not be found.")
+        => Title = title;
+}

src/Server/StellarChat.Server.Api/Domain/Chat/Repositories/IChatSessionRepository.cs

@@ -2,7 +2,7 @@
 
 namespace StellarChat.Server.Api.Domain.Chat.Repositories;
 
-internal interface IChatSessionRepository
+public interface IChatSessionRepository
 {
     ValueTask<ChatSession?> GetAsync(Guid id);
     ValueTask<ChatSession?> GetByTitleAsync(string title);

src/Server/StellarChat.Server.Api/Extensions.cs

@@ -21,6 +21,11 @@ public static void AddInfrastructure(this WebApplicationBuilder builder)
             .AddScoped<IChatSessionRepository, ChatSessionRepository>()
             .AddMongoRepository<ChatMessageDocument, Guid>("messages")
             .AddMongoRepository<ChatSessionDocument, Guid>("chat-sessions");
+
+        builder.Services.AddMediator(options =>
+        {
+            options.ServiceLifetime = ServiceLifetime.Scoped;
+        });
     }
 
     public static WebApplication UseInfrastructure(this WebApplication app)

src/Server/StellarChat.Server.Api/Features/Chat/GetChatSession/GetChatSession.cs

@@ -0,0 +1,9 @@
+using Mediator;
+using StellarChat.Shared.Abstractions.Contracts.Chat;
+
+namespace StellarChat.Server.Api.Features.Chat.GetChatSession;
+
+internal sealed record GetChatSession : IQuery<ChatSessionResponse>
+{
+    public Guid Id { get; set; }
+}

src/Server/StellarChat.Server.Api/Features/Chat/GetChatSession/GetChatSessionEndpoint.cs

@@ -0,0 +1,26 @@
+using Mediator;
+using StellarChat.Shared.Abstractions.API.Endpoints;
+using StellarChat.Shared.Abstractions.Contracts.Chat;
+
+namespace StellarChat.Server.Api.Features.Chat.GetChatSession;
+
+internal sealed class GetChatSessionEndpoint : IEndpoint
+{
+    public void Expose(IEndpointRouteBuilder endpoints)
+    {
+        var chatHistory = endpoints.MapGroup("/chat-history").WithTags("Chat history");
+
+        chatHistory.MapGet("/sessions/{chatId:guid}", async (Guid chatId, IMediator mediator) => IEndpoint.Select(await mediator.Send(new GetChatSession { Id = chatId })))
+            .Produces<ChatSessionResponse>(StatusCodes.Status200OK)
+            .Produces(StatusCodes.Status404NotFound)
+            .WithName("GetChatSession")
+            .WithOpenApi(operation => new(operation)
+            {
+                Summary = "Retrieves a single chat session by 'chatId'."
+            });
+    }
+
+    public void Register(IServiceCollection services, IConfiguration configuration) { }
+
+    public void Use(IApplicationBuilder app) { }
+}

src/Server/StellarChat.Server.Api/Features/Chat/GetChatSession/GetChatSessionHandler.cs

@@ -0,0 +1,19 @@
+using Mapster;
+using Mediator;
+using StellarChat.Server.Api.DAL.Mongo.Exceptions.Chat;
+using StellarChat.Server.Api.Domain.Chat.Repositories;
+using StellarChat.Shared.Abstractions.Contracts.Chat;
+
+namespace StellarChat.Server.Api.Features.Chat.GetChatSession;
+
+internal sealed class GetChatSessionHandler : IQueryHandler<GetChatSession, ChatSessionResponse>
+{
+    private readonly IChatSessionRepository _chatSessionRepository;
+
+    public GetChatSessionHandler(IChatSessionRepository chatSessionRepository) 
+        => _chatSessionRepository = chatSessionRepository;
+
+    public async ValueTask<ChatSessionResponse> Handle(GetChatSession query, CancellationToken cancellationToken)
+        => (await _chatSessionRepository.GetAsync(query.Id))
+            .Adapt<ChatSessionResponse>() ?? throw new ChatSessionNotFoundException(query.Id);
+}

src/Server/StellarChat.Server.Api/StellarChat.Server.Api.csproj

@@ -11,6 +11,11 @@
   <ItemGroup>
     <PackageReference Include="Mapster" Version="7.4.1-pre01" />
     <PackageReference Include="Mapster.DependencyInjection" Version="1.0.2-pre01" />
+	<PackageReference Include="Mediator.Abstractions" Version="3.0.0-preview.24" />
+	<PackageReference Include="Mediator.SourceGenerator" Version="3.0.0-preview.24">
+		<PrivateAssets>all</PrivateAssets>
+		<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+	</PackageReference>
     <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="8.0.0" />
   </ItemGroup>
 

src/Shared/StellarChat.Shared.Abstractions/Contracts/Chat/ChatSessionResponse.cs

@@ -0,0 +1,3 @@
+namespace StellarChat.Shared.Abstractions.Contracts.Chat;
+
+public record ChatSessionResponse(Guid Id, string Title, string Metaprompt, HashSet<string> ActivePlugins, DateTimeOffset CreatedAt, DateTimeOffset UpdatedAt);

src/Shared/StellarChat.Shared.Infrastructure/Extensions.cs

@@ -31,8 +31,7 @@ public static WebApplicationBuilder AddSharedInfrastructure(this WebApplicationB
                 .AddCorsPolicy(builder.Configuration)
                 .AddMongo(builder.Configuration)
                 .RegisterEndpoints(builder.Configuration)
-                .AddSemanticKernel(builder.Configuration)
-                .AddMediator();
+                .AddSemanticKernel(builder.Configuration);
 
         return builder;
     }
@@ -62,7 +61,7 @@ public static string ToSnakeCase(this string input)
             Regex.Replace(
                 Regex.Replace(input, @"([\p{Lu}]+)([\p{Lu}][\p{Ll}])", "$1_$2"), @"([\p{Ll}\d])([\p{Lu}])", "$1_$2"), @"[-\s]", "_").ToLower();
 
-    public static bool IsEmpty(this string value) 
+    public static bool IsEmpty(this string value)
         => string.IsNullOrWhiteSpace(value);
 
     public static bool IsNotEmpty(this string value)
@@ -99,7 +98,7 @@ public static string GetUserIpAddress(this HttpContext context)
         if (context.Request.Headers.TryGetValue("x-forwarded-for", out var forwardedFor))
         {
             var ipAddresses = forwardedFor.ToString().Split(",", StringSplitOptions.RemoveEmptyEntries);
-            
+
             if (ipAddresses.Any())
             {
                 ipAddress = ipAddresses[0];

src/Shared/StellarChat.Shared.Infrastructure/StellarChat.Shared.Infrastructure.csproj

@@ -11,11 +11,6 @@
   </ItemGroup>  
 
   <ItemGroup>
-	  <PackageReference Include="Mediator.Abstractions" Version="3.0.0-preview.24" />
-	  <PackageReference Include="Mediator.SourceGenerator" Version="3.0.0-preview.24">
-	    <PrivateAssets>all</PrivateAssets>
-	    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-	  </PackageReference>
 	  <PackageReference Include="Microsoft.SemanticKernel" Version="1.6.3" />
 	  <PackageReference Include="MongoDB.Driver" Version="2.24.0" />
 	  <PackageReference Include="Serilog" Version="4.0.0-dev-02113" />