fleshout backend

backend/Data/IUserRepository.cs

@@ -1,5 +1,22 @@
 namespace Backend.Data;
 
+/// <summary>
+/// Storage-agnostic access to <see cref="User"/>. Implementations are selected by the
+/// <c>Persistence:Provider</c> setting; see <see cref="PersistenceServiceCollectionExtensions"/>.
+/// </summary>
 public interface IUserRepository
 {
+    Task<IReadOnlyList<User>> GetAllAsync(CancellationToken cancellationToken = default);
+
+    Task<User?> GetByIdAsync(Guid id, CancellationToken cancellationToken = default);
+
+    Task<User?> GetByEmailAsync(string email, CancellationToken cancellationToken = default);
+
+    Task<User> AddAsync(User user, CancellationToken cancellationToken = default);
+
+    /// <returns>The updated user, or <c>null</c> when no user has the given id.</returns>
+    Task<User?> UpdateAsync(User user, CancellationToken cancellationToken = default);
+
+    /// <returns><c>true</c> when a user was removed.</returns>
+    Task<bool> DeleteAsync(Guid id, CancellationToken cancellationToken = default);
 }

backend/Data/InMemory/InMemoryUserRepository.cs

@@ -0,0 +1,58 @@
+using System.Collections.Concurrent;
+
+namespace Backend.Data.InMemory;
+
+/// <summary>
+/// Default implementation so the skeleton runs with no database. State is per-process
+/// and lost on restart.
+/// </summary>
+public sealed class InMemoryUserRepository : IUserRepository
+{
+    private readonly ConcurrentDictionary<Guid, User> _users = new();
+
+    public Task<IReadOnlyList<User>> GetAllAsync(CancellationToken cancellationToken = default)
+    {
+        IReadOnlyList<User> users = _users.Values
+            .OrderBy(user => user.CreatedAt)
+            .ToList();
+
+        return Task.FromResult(users);
+    }
+
+    public Task<User?> GetByIdAsync(Guid id, CancellationToken cancellationToken = default)
+    {
+        _users.TryGetValue(id, out var user);
+
+        return Task.FromResult(user);
+    }
+
+    public Task<User?> GetByEmailAsync(string email, CancellationToken cancellationToken = default)
+    {
+        var user = _users.Values
+            .FirstOrDefault(candidate => string.Equals(candidate.Email, email, StringComparison.OrdinalIgnoreCase));
+
+        return Task.FromResult(user);
+    }
+
+    public Task<User> AddAsync(User user, CancellationToken cancellationToken = default)
+    {
+        _users[user.Id] = user;
+
+        return Task.FromResult(user);
+    }
+
+    public Task<User?> UpdateAsync(User user, CancellationToken cancellationToken = default)
+    {
+        if (!_users.ContainsKey(user.Id))
+        {
+            return Task.FromResult<User?>(null);
+        }
+
+        _users[user.Id] = user;
+
+        return Task.FromResult<User?>(user);
+    }
+
+    public Task<bool> DeleteAsync(Guid id, CancellationToken cancellationToken = default)
+        => Task.FromResult(_users.TryRemove(id, out _));
+}

backend/Data/PersistenceOptions.cs

@@ -0,0 +1,13 @@
+namespace Backend.Data;
+
+public sealed class PersistenceOptions
+{
+    public const string SectionName = "Persistence";
+
+    public string Provider { get; set; } = PersistenceProviders.InMemory;
+}
+
+public static class PersistenceProviders
+{
+    public const string InMemory = "InMemory";
+}

backend/Data/PersistenceServiceCollectionExtensions.cs

@@ -0,0 +1,37 @@
+using Backend.Data.InMemory;
+
+namespace Backend.Data;
+
+/// <summary>
+/// Single place where a storage backend is chosen. To add a real database, implement
+/// <see cref="IUserRepository"/> and register it under a new provider name here;
+/// controllers stay untouched.
+/// </summary>
+public static class PersistenceServiceCollectionExtensions
+{
+    public static IServiceCollection AddPersistence(
+        this IServiceCollection services,
+        IConfiguration configuration)
+    {
+        services.Configure<PersistenceOptions>(configuration.GetSection(PersistenceOptions.SectionName));
+
+        var provider = configuration.GetSection(PersistenceOptions.SectionName).Get<PersistenceOptions>()?.Provider
+            ?? PersistenceProviders.InMemory;
+
+        switch (provider)
+        {
+            case PersistenceProviders.InMemory:
+                // Singleton because the store itself holds the data.
+                services.AddSingleton<IUserRepository, InMemoryUserRepository>();
+                break;
+
+            default:
+                throw new InvalidOperationException(
+                    $"Unknown persistence provider '{provider}'. Supported providers: " +
+                    $"'{PersistenceProviders.InMemory}'. Register additional providers in " +
+                    $"{nameof(PersistenceServiceCollectionExtensions)}.");
+        }
+
+        return services;
+    }
+}

backend/Data/User.cs

@@ -0,0 +1,15 @@
+namespace Backend.Data;
+
+/// <summary>
+/// Placeholder domain entity. Replace with the real model once the project has one.
+/// </summary>
+public sealed class User
+{
+    public Guid Id { get; init; } = Guid.NewGuid();
+
+    public required string Email { get; set; }
+
+    public required string DisplayName { get; set; }
+
+    public DateTime CreatedAt { get; init; } = DateTime.UtcNow;
+}