Spec-driven Booking API with tests

Booking/Booking.Api/Booking.Api.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.2" />
+    <PackageReference Include="Swashbuckle.AspNetCore" Version="10.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Booking.Core\Booking.Core.csproj" />
+    <ProjectReference Include="..\Booking.Infrastructure\Booking.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

Booking/Booking.Api/Contracts/CreateAppointmentRequest.cs

@@ -0,0 +1,7 @@
+namespace Booking.Api.Contracts;
+
+public sealed record CreateAppointmentRequest(
+    DateTime StartUtc,
+    DateTime EndUtc,
+    string Customer
+);

Booking/Booking.Api/Program.cs

@@ -0,0 +1,69 @@
+using Booking.Api.Contracts;
+using Booking.Core;
+using Booking.Infrastructure;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// OpenAPI + Swagger UI
+builder.Services.AddOpenApi();
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+
+// DI
+builder.Services.AddSingleton<IAppointmentRepository, InMemoryAppointmentRepository>();
+builder.Services.AddSingleton<ITimeProvider, SystemTimeProvider>();
+builder.Services.AddSingleton<BookingService>();
+
+var app = builder.Build();
+
+// Swagger UI in Development
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseHttpsRedirection();
+
+// -------------------------
+// Endpoints (per spec)
+// -------------------------
+
+app.MapPost("/appointments", async (
+    CreateAppointmentRequest req,
+    BookingService service,
+    CancellationToken ct) =>
+{
+    try
+    {
+        var created = await service.CreateAsync(
+            startUtc: req.StartUtc,
+            endUtc: req.EndUtc,
+            customer: req.Customer,
+            ct: ct);
+
+        return Results.Ok(created);
+    }
+    catch (ArgumentException ex)
+    {
+        return Results.BadRequest(new { error = ex.Message });
+    }
+    catch (InvalidOperationException ex) when (ex.Message == BookingErrors.Conflict)
+    {
+        return Results.Conflict(new { error = ex.Message });
+    }
+})
+.WithName("CreateAppointment")
+.WithOpenApi();
+
+app.MapGet("/appointments", async (
+    IAppointmentRepository repo,
+    CancellationToken ct) =>
+{
+    var items = await repo.GetAllAsync(ct);
+    return Results.Ok(items);
+})
+.WithName("GetAppointments")
+.WithOpenApi();
+
+app.Run();

Booking/Booking.Core/Appointment.cs

@@ -0,0 +1,8 @@
+namespace Booking.Core;
+
+public sealed record Appointment(
+    Guid Id,
+    DateTime StartUtc,
+    DateTime EndUtc,
+    string Customer
+);

Booking/Booking.Core/Booking.Core.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Booking/Booking.Core/BookingErrors.cs

@@ -0,0 +1,10 @@
+namespace Booking.Core;
+
+public static class BookingErrors
+{
+    public const string CustomerRequired = "Customer is required.";
+    public const string InvalidRange = "EndUtc must be after StartUtc.";
+    public const string TooShort = "Minimum duration is 15 minutes.";
+    public const string InPast = "Cannot book an appointment in the past.";
+    public const string Conflict = "Appointment time conflicts with an existing booking.";
+}

Booking/Booking.Core/BookingService.cs

@@ -0,0 +1,50 @@
+namespace Booking.Core;
+
+public sealed class BookingService
+{
+    private readonly IAppointmentRepository _repo;
+    private readonly ITimeProvider _time;
+
+    public BookingService(IAppointmentRepository repo, ITimeProvider time)
+    {
+        _repo = repo;
+        _time = time;
+    }
+
+    public async Task<Appointment> CreateAsync(
+        DateTime startUtc,
+        DateTime endUtc,
+        string customer,
+        CancellationToken ct = default)
+    {
+        if (string.IsNullOrWhiteSpace(customer))
+            throw new ArgumentException(BookingErrors.CustomerRequired);
+
+        // (Spec) End must be after Start
+        if (endUtc <= startUtc)
+            throw new ArgumentException(BookingErrors.InvalidRange);
+
+        // (Spec) Min duration 15 minutes
+        if (endUtc - startUtc < TimeSpan.FromMinutes(15))
+            throw new ArgumentException(BookingErrors.TooShort);
+
+        // (Spec) Cannot book in the past
+        if (startUtc < _time.UtcNow)
+            throw new ArgumentException(BookingErrors.InPast);
+
+        // (Spec) No overlap allowed
+        var conflict = await _repo.ExistsOverlapAsync(startUtc, endUtc, ct);
+        if (conflict)
+            throw new InvalidOperationException(BookingErrors.Conflict);
+
+        var appointment = new Appointment(
+            Id: Guid.NewGuid(),
+            StartUtc: startUtc,
+            EndUtc: endUtc,
+            Customer: customer.Trim()
+        );
+
+        await _repo.AddAsync(appointment, ct);
+        return appointment;
+    }
+}

Booking/Booking.Core/IAppointmentRepository.cs

@@ -0,0 +1,8 @@
+namespace Booking.Core;
+
+public interface IAppointmentRepository
+{
+    Task AddAsync(Appointment appointment, CancellationToken ct = default);
+    Task<IReadOnlyList<Appointment>> GetAllAsync(CancellationToken ct = default);
+    Task<bool> ExistsOverlapAsync(DateTime startUtc, DateTime endUtc, CancellationToken ct = default);
+}

Booking/Booking.Core/TimeProvider.cs

@@ -0,0 +1,11 @@
+namespace Booking.Core;
+
+public interface ITimeProvider
+{
+    DateTime UtcNow { get; }
+}
+
+public sealed class SystemTimeProvider : ITimeProvider
+{
+    public DateTime UtcNow => DateTime.UtcNow;
+}

Booking/Booking.Infrastructure/Booking.Infrastructure.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Booking.Core\Booking.Core.csproj" />
+  </ItemGroup>
+
+</Project>

Booking/Booking.Infrastructure/InMemoryAppointmentRepository.cs

@@ -0,0 +1,37 @@
+using Booking.Core;
+
+namespace Booking.Infrastructure;
+
+public sealed class InMemoryAppointmentRepository : IAppointmentRepository
+{
+    private readonly List<Appointment> _items = new();
+    private readonly object _lock = new();
+
+    public Task AddAsync(Appointment appointment, CancellationToken ct = default)
+    {
+        lock (_lock)
+        {
+            _items.Add(appointment);
+        }
+        return Task.CompletedTask;
+    }
+
+    public Task<IReadOnlyList<Appointment>> GetAllAsync(CancellationToken ct = default)
+    {
+        lock (_lock)
+        {
+            return Task.FromResult((IReadOnlyList<Appointment>)_items.ToList());
+        }
+    }
+
+    public Task<bool> ExistsOverlapAsync(DateTime startUtc, DateTime endUtc, CancellationToken ct = default)
+    {
+        lock (_lock)
+        {
+            // Spec overlap rule:
+            // overlap when newStart < existingEnd AND newEnd > existingStart
+            var exists = _items.Any(a => startUtc < a.EndUtc && endUtc > a.StartUtc);
+            return Task.FromResult(exists);
+        }
+    }
+}

Booking/Booking.Tests/Booking.Tests.csproj

@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="FluentAssertions" Version="8.8.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Booking.Core\Booking.Core.csproj" />
+    <ProjectReference Include="..\Booking.Infrastructure\Booking.Infrastructure.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+</Project>