Code(API::CreatetChatSession): Implement Create chat session feature

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

@@ -0,0 +1,14 @@
+using StellarChat.Shared.Abstractions.Exceptions;
+
+namespace StellarChat.Server.Api.DAL.Mongo.Exceptions.Chat;
+
+public class ChatSessionAlreadyExistsException : StellarChatException
+{
+    public Guid Id { get; }
+
+    public ChatSessionAlreadyExistsException(Guid id)
+        : base(
+            message: $"Chat session with Id: '{id}' already exists.",
+            userMessage: $"A chat session with the same details already exists.")
+        => Id = id;
+}

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

@@ -6,6 +6,7 @@
 using StellarChat.Server.Api.DAL.Mongo.Documents.Chat;
 using StellarChat.Server.Api.DAL.Mongo.Repositories.Chat;
 using StellarChat.Server.Api.Domain.Chat.Repositories;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 
 namespace StellarChat.Server.Api;
 
@@ -15,6 +16,7 @@ public static void AddInfrastructure(this WebApplicationBuilder builder)
     {
         builder.AddSharedInfrastructure();
 
+        builder.Services.TryAddSingleton(TimeProvider.System);
         builder.Services.AddMappings();
         builder.Services
             .AddScoped<IChatMessageRepository, ChatMessageRepository>()

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

@@ -0,0 +1,6 @@
+using Mediator;
+using System.ComponentModel.DataAnnotations;
+
+namespace StellarChat.Server.Api.Features.Chat.CreateChatSession;
+
+internal sealed record CreateChatSession([Required] Guid ChatId, string Title) : ICommand;

src/Server/StellarChat.Server.Api/Features/Chat/CreateChatSession/CreateChatSessionEndpoint.cs

@@ -0,0 +1,35 @@
+using Mapster;
+using Mediator;
+using Microsoft.AspNetCore.Mvc;
+using StellarChat.Shared.Abstractions.API.Endpoints;
+using StellarChat.Shared.Abstractions.Contracts.Chat;
+
+namespace StellarChat.Server.Api.Features.Chat.CreateChatSession;
+
+internal sealed class CreateChatSessionEndpoint : IEndpoint
+{
+    public void Expose(IEndpointRouteBuilder endpoints)
+    {
+        var chatHistory = endpoints.MapGroup("/chat-history").WithTags("Chat history");
+
+        chatHistory.MapPost("/sessions", async ([FromBody] CreateChatSessionRequest request, IMediator mediator) =>
+        {
+            var chatId = Guid.NewGuid();
+            var command = request.Adapt<CreateChatSession>();
+
+            command = command with { ChatId = chatId };
+            await mediator.Send(command);
+
+            return Results.CreatedAtRoute("GetChatSession", new { ChatId = chatId }, chatId);
+        })
+         .Produces(StatusCodes.Status201Created)
+         .WithOpenApi(operation => new(operation)
+         {
+             Summary = "Creates a new chat session."
+         });
+    }
+
+    public void Register(IServiceCollection services, IConfiguration configuration) { }
+
+    public void Use(IApplicationBuilder app) { }
+}

src/Server/StellarChat.Server.Api/Features/Chat/CreateChatSession/CreateChatSessionHandler.cs

@@ -0,0 +1,42 @@
+using Mediator;
+using StellarChat.Server.Api.DAL.Mongo.Exceptions.Chat;
+using StellarChat.Server.Api.Domain.Chat.Models;
+using StellarChat.Server.Api.Domain.Chat.Repositories;
+
+namespace StellarChat.Server.Api.Features.Chat.CreateChatSession;
+
+internal class CreateChatSessionHandler : ICommandHandler<CreateChatSession>
+{
+    private readonly IChatSessionRepository _chatSessionRepository;
+    private readonly TimeProvider _clock;
+    private readonly ILogger<CreateChatSessionHandler> _logger;
+
+    public CreateChatSessionHandler(IChatSessionRepository chatSessionRepository, TimeProvider clock, ILogger<CreateChatSessionHandler> logger)
+    {
+        _chatSessionRepository = chatSessionRepository;
+        _clock = clock;
+        _logger = logger;
+    }
+
+    public async ValueTask<Unit> Handle(CreateChatSession command, CancellationToken cancellationToken)
+    {
+        if (await _chatSessionRepository.ExistsAsync(command.ChatId))
+        {
+            throw new ChatSessionAlreadyExistsException(command.ChatId);
+        }
+
+        var now = _clock.GetUtcNow();
+
+        // TODO: Retrieve activePlugins and metaprompt from settings
+        var activePlugins = new HashSet<string>();
+
+        var chatSession = ChatSession.Create(command.ChatId, command.Title, metaprompt: "", activePlugins, createdAt: now, updatedAt: now);
+
+        await _chatSessionRepository.AddAsync(chatSession);
+        _logger.LogInformation($"Chat session with ID: '{chatSession.Id}' has been created.");
+
+        // TODO: Create initial bot message 
+
+        return Unit.Value;
+    }
+}

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

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk.Web">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>

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

@@ -0,0 +1,5 @@
+using System.Text.Json.Serialization;
+
+namespace StellarChat.Shared.Abstractions.Contracts.Chat;
+
+public record CreateChatSessionRequest([property: JsonIgnore] Guid? ChatId, string Title);