EnvelopeGenerator/EnvelopeGenerator.Tests/Application/MediatorExtensionsTests.cs

using DigitalData.Core.Exceptions;
using EnvelopeGenerator.Application.Common.Extensions;
using MediatR;

namespace EnvelopeGenerator.Tests.Application;

[TestFixture]
public class MediatorExtensionsTests
{
    #region Stub infrastructure

    private sealed class StubRequest<TResponse> : IRequest<TResponse?> { }

    /// <summary>
    /// Minimal <see cref="ISender"/> stub that returns a pre-configured response for any <see cref="ISender.Send{TResponse}"/> call.
    /// </summary>
    private sealed class StubSender : ISender
    {
        private readonly object? _response;

        public StubSender(object? response) => _response = response;

        public Task<TResponse> Send<TResponse>(IRequest<TResponse> request, CancellationToken cancellationToken = default)
        {
            cancellationToken.ThrowIfCancellationRequested();
            return Task.FromResult((TResponse)_response!);
        }

        public Task Send<TRequest>(TRequest request, CancellationToken cancellationToken = default) where TRequest : IRequest
        {
            cancellationToken.ThrowIfCancellationRequested();
            return Task.CompletedTask;
        }

        public Task<object?> Send(object request, CancellationToken cancellationToken = default)
        {
            cancellationToken.ThrowIfCancellationRequested();
            return Task.FromResult(_response);
        }

        public IAsyncEnumerable<TResponse> CreateStream<TResponse>(IStreamRequest<TResponse> request, CancellationToken cancellationToken = default)
            => throw new NotImplementedException();

        public IAsyncEnumerable<object?> CreateStream(object request, CancellationToken cancellationToken = default)
            => throw new NotImplementedException();
    }

    private static ISender CreateSender<T>(T? response) => new StubSender(response);

    #endregion

    #region Throw — non-null scalar

    [Test]
    public async Task Throw_WithNonNullResponse_ReturnsResponse()
    {
        var sender = CreateSender<string>("hello");
        var request = new StubRequest<string?>();

        var result = await sender.GetOr(request).Throw(() => new InvalidOperationException());

        Assert.That(result, Is.EqualTo("hello"));
    }

    #endregion

    #region Throw — null response

    [Test]
    public void Throw_WithNullResponse_ThrowsCustomException()
    {
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        var ex = Assert.ThrowsAsync<InvalidOperationException>(
            () => sender.GetOr(request).Throw(() => new InvalidOperationException("custom")));

        Assert.That(ex!.Message, Is.EqualTo("custom"));
    }

    #endregion

    #region Throw — empty collection

    [Test]
    public void Throw_WithEmptyList_ThrowsCustomException()
    {
        var sender = CreateSender<List<string>>(new List<string>());
        var request = new StubRequest<List<string>?>();

        Assert.ThrowsAsync<ArgumentException>(
            () => sender.GetOr(request).Throw(() => new ArgumentException("empty")));
    }

    #endregion

    #region Throw — non-empty collection

    [Test]
    public async Task Throw_WithNonEmptyList_ReturnsResponse()
    {
        var expected = new List<int> { 1, 2 };
        var sender = CreateSender<List<int>>(expected);
        var request = new StubRequest<List<int>?>();

        var result = await sender.GetOr(request).Throw(() => new InvalidOperationException());

        Assert.That(result, Is.EqualTo(expected));
    }

    #endregion

    #region Throw — string edge case (string implements IEnumerable)

    [Test]
    public async Task Throw_WithEmptyString_ReturnsEmptyString()
    {
        var sender = CreateSender<string>("");
        var request = new StubRequest<string?>();

        var result = await sender.GetOr(request).Throw(() => new InvalidOperationException("should not throw"));

        Assert.That(result, Is.EqualTo(""));
    }

    #endregion

    #region ThrowNotFound — non-null scalar

    [Test]
    public async Task ThrowNotFound_WithNonNullResponse_ReturnsResponse()
    {
        var sender = CreateSender<string>("hello");
        var request = new StubRequest<string?>();

        var result = await sender.GetOr(request).ThrowNotFound();

        Assert.That(result, Is.EqualTo("hello"));
    }

    [Test]
    public async Task ThrowNotFound_WithExceptionMessage_AndNonNullResponse_ReturnsResponse()
    {
        var sender = CreateSender<int>(42);
        var request = new StubRequest<int?>();

        var result = await sender.GetOr(request).ThrowNotFound("not found");

        Assert.That(result, Is.EqualTo(42));
    }

    #endregion

    #region ThrowNotFound — null response

    [Test]
    public void ThrowNotFound_WithNullResponse_ThrowsNotFoundException()
    {
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        Assert.ThrowsAsync<NotFoundException>(() => sender.GetOr(request).ThrowNotFound());
    }

    [Test]
    public void ThrowNotFound_WithNullResponse_AndCustomMessage_ContainsMessage()
    {
        const string message = "Entity not found";
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        var ex = Assert.ThrowsAsync<NotFoundException>(
            () => sender.GetOr(request).ThrowNotFound(message));

        Assert.That(ex!.Message, Does.Contain(message));
    }

    [Test]
    public void ThrowNotFound_WithNullResponse_HasDefaultMessageWithTypeName()
    {
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        var ex = Assert.ThrowsAsync<NotFoundException>(() => sender.GetOr(request).ThrowNotFound());

        Assert.That(ex!.Message, Does.Contain(nameof(String)));
    }

    #endregion

    #region ThrowNotFound — empty collection

    [Test]
    public void ThrowNotFound_WithEmptyList_ThrowsNotFoundException()
    {
        var sender = CreateSender<List<string>>(new List<string>());
        var request = new StubRequest<List<string>?>();

        Assert.ThrowsAsync<NotFoundException>(() => sender.GetOr(request).ThrowNotFound());
    }

    [Test]
    public void ThrowNotFound_WithEmptyArray_ThrowsNotFoundException()
    {
        var sender = CreateSender<int[]>(Array.Empty<int>());
        var request = new StubRequest<int[]?>();

        Assert.ThrowsAsync<NotFoundException>(() => sender.GetOr(request).ThrowNotFound());
    }

    [Test]
    public void ThrowNotFound_WithEmptyCollection_AndCustomMessage_ContainsMessage()
    {
        const string message = "No items found";
        var sender = CreateSender<List<int>>(new List<int>());
        var request = new StubRequest<List<int>?>();

        var ex = Assert.ThrowsAsync<NotFoundException>(
            () => sender.GetOr(request).ThrowNotFound(message));

        Assert.That(ex!.Message, Does.Contain(message));
    }

    #endregion

    #region ThrowNotFound — non-empty collection

    [Test]
    public async Task ThrowNotFound_WithNonEmptyList_ReturnsResponse()
    {
        var expected = new List<string> { "a", "b" };
        var sender = CreateSender<List<string>>(expected);
        var request = new StubRequest<List<string>?>();

        var result = await sender.GetOr(request).ThrowNotFound();

        Assert.That(result, Is.EqualTo(expected));
    }

    [Test]
    public async Task ThrowNotFound_WithNonEmptyArray_ReturnsResponse()
    {
        var expected = new[] { 1, 2, 3 };
        var sender = CreateSender<int[]>(expected);
        var request = new StubRequest<int[]?>();

        var result = await sender.GetOr(request).ThrowNotFound();

        Assert.That(result, Is.EqualTo(expected));
    }

    #endregion

    #region ThrowInvalidOperation — null response

    [Test]
    public void ThrowInvalidOperation_WithNullResponse_ThrowsInvalidOperationException()
    {
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        Assert.ThrowsAsync<InvalidOperationException>(
            () => sender.GetOr(request).ThrowInvalidOperation());
    }

    [Test]
    public void ThrowInvalidOperation_WithNullResponse_AndCustomMessage_ContainsMessage()
    {
        const string message = "Something went wrong";
        var sender = CreateSender<string>(null);
        var request = new StubRequest<string?>();

        var ex = Assert.ThrowsAsync<InvalidOperationException>(
            () => sender.GetOr(request).ThrowInvalidOperation(message));

        Assert.That(ex!.Message, Does.Contain(message));
    }

    #endregion

    #region CancellationToken

    [Test]
    public void Throw_WithCancelledToken_ThrowsOperationCanceledException()
    {
        var sender = CreateSender<string>("value");
        var request = new StubRequest<string?>();
        var cts = new CancellationTokenSource();
        cts.Cancel();

        Assert.ThrowsAsync<OperationCanceledException>(
            () => sender.GetOr(request, cts.Token).Throw(() => new InvalidOperationException()));
    }

    [Test]
    public void ThrowNotFound_WithCancelledToken_ThrowsOperationCanceledException()
    {
        var sender = CreateSender<string>("value");
        var request = new StubRequest<string?>();
        var cts = new CancellationTokenSource();
        cts.Cancel();

        Assert.ThrowsAsync<OperationCanceledException>(
            () => sender.GetOr(request, cts.Token).ThrowNotFound());
    }

    #endregion
}