jobtrackingapp/JobTrackerApi.Tests/ConcurrentInitializationTests.cs

using JobTrackerApi.Controllers;
using JobTrackerApi.Data;
using JobTrackerApi.Models;
using JobTrackerApi.Services;
using Microsoft.Data.Sqlite;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;
using Moq;
using Xunit;

namespace JobTrackerApi.Tests;

public sealed class ConcurrentInitializationTests
{
    [Fact]
    public async Task Concurrent_rule_reads_share_the_single_created_settings_row()
    {
        await using var database = await Database.CreateAsync();
        await using var first = database.CreateContext(new SaveGate(delay: false));
        await using var second = database.CreateContext(new SaveGate(delay: true));

        var results = await Task.WhenAll(
            new RulesController(first).Get(default),
            new RulesController(second).Get(default));

        Assert.All(results, result => Assert.NotNull(result.Result));
        await using var verify = database.CreateContext();
        Assert.Single(await verify.UserRuleSettings.ToListAsync());
    }

    [Fact]
    public async Task Concurrent_checklist_reads_share_the_single_default_item_set()
    {
        await using var database = await Database.CreateAsync();
        int jobId;
        await using (var setup = database.CreateContext())
        {
            var company = new Company { OwnerUserId = Database.Owner, Name = "Acme" };
            setup.Companies.Add(company);
            await setup.SaveChangesAsync();
            var job = new JobApplication
            {
                OwnerUserId = Database.Owner,
                CompanyId = company.Id,
                JobTitle = "Backend Developer",
                Status = "Applied",
                Description = "Needs .NET and SQL.",
            };
            setup.JobApplications.Add(job);
            await setup.SaveChangesAsync();
            jobId = job.Id;
        }

        await using var first = database.CreateContext(new SaveGate(delay: false));
        await using var second = database.CreateContext(new SaveGate(delay: true));
        var results = await Task.WhenAll(
            new ApplicationChecklistService(first).GetAsync(Database.Owner, jobId, default),
            new ApplicationChecklistService(second).GetAsync(Database.Owner, jobId, default));

        var expectedCount = results[0]!.Items.Count;
        Assert.Equal(expectedCount, results[1]!.Items.Count);
        await using var verify = database.CreateContext();
        Assert.Equal(expectedCount, await verify.ApplicationChecklistItems.CountAsync());
    }

    private sealed class SaveGate(bool delay) : SaveChangesInterceptor
    {
        private static readonly object Sync = new();
        private static TaskCompletionSource<bool> _bothArrived = NewSignal();
        private static int _arrivals;
        private int _used;

        public override async ValueTask<InterceptionResult<int>> SavingChangesAsync(
            DbContextEventData eventData,
            InterceptionResult<int> result,
            CancellationToken cancellationToken = default)
        {
            if (Interlocked.Exchange(ref _used, 1) != 0) return result;

            Task wait;
            lock (Sync)
            {
                if (_arrivals == 0 && _bothArrived.Task.IsCompleted) _bothArrived = NewSignal();
                _arrivals++;
                if (_arrivals == 2)
                {
                    _arrivals = 0;
                    _bothArrived.TrySetResult(true);
                }
                wait = _bothArrived.Task;
            }

            await wait.WaitAsync(cancellationToken);
            if (delay) await Task.Delay(100, cancellationToken);
            return result;
        }

        private static TaskCompletionSource<bool> NewSignal() =>
            new(TaskCreationOptions.RunContinuationsAsynchronously);
    }

    private sealed class Database : IAsyncDisposable
    {
        public const string Owner = "user-1";
        private readonly string _path;
        private readonly DbContextOptions<JobTrackerContext> _setupOptions;
        private readonly ICurrentUserService _currentUser;

        private Database(string path)
        {
            _path = path;
            _setupOptions = new DbContextOptionsBuilder<JobTrackerContext>()
                .UseSqlite($"Data Source={path}")
                .Options;
            var currentUser = new Mock<ICurrentUserService>();
            currentUser.SetupGet(service => service.UserId).Returns(Owner);
            _currentUser = currentUser.Object;
        }

        public static async Task<Database> CreateAsync()
        {
            var database = new Database(Path.Combine(Path.GetTempPath(), $"jobtracker-concurrent-{Guid.NewGuid():N}.db"));
            await using var db = new JobTrackerContext(database._setupOptions, database._currentUser);
            await db.Database.EnsureCreatedAsync();
            return database;
        }

        public JobTrackerContext CreateContext(SaveChangesInterceptor? interceptor = null)
        {
            var builder = new DbContextOptionsBuilder<JobTrackerContext>().UseSqlite($"Data Source={_path}");
            if (interceptor is not null) builder.AddInterceptors(interceptor);
            return new JobTrackerContext(builder.Options, _currentUser);
        }

        public ValueTask DisposeAsync()
        {
            SqliteConnection.ClearAllPools();
            File.Delete(_path);
            return ValueTask.CompletedTask;
        }
    }
}