using AvParser.UI.Navigation;
using AvParser.UI.Tests.Fakes;
using AvParser.UI.ViewModels;

namespace AvParser.UI.Tests;

public class NavigationServiceTests
{
    private static (NavigationService Service, FakePage First, FakePage Second, OtherFakePage Third) Build()
    {
        var first = new FakePage("First");
        var second = new FakePage("Second");
        var third = new OtherFakePage();
        return (new NavigationService([first, second, third]), first, second, third);
    }

    [Fact]
    public void Starts_on_the_first_registered_page()
    {
        var (service, first, _, _) = Build();

        service.Current.ShouldBeSameAs(first);
    }

    [Fact]
    public void Rejects_an_empty_page_set() =>
        Should.Throw<ArgumentException>(() => new NavigationService(Array.Empty<PageViewModel>()));

    [Fact]
    public void Navigating_pushes_the_previous_page()
    {
        var (service, first, second, _) = Build();

        service.NavigateTo(second);

        service.Current.ShouldBeSameAs(second);
        service.GoBack();
        service.Current.ShouldBeSameAs(first);
    }

    [Fact]
    public void Navigating_to_the_current_page_is_a_no_op()
    {
        var (service, first, _, _) = Build();

        service.NavigateTo(first);
        service.GoBack();

        // Nothing was pushed, so GoBack had nothing to pop.
        service.Current.ShouldBeSameAs(first);
    }

    [Fact]
    public void GoBack_on_an_empty_stack_does_nothing()
    {
        var (service, first, _, _) = Build();

        service.GoBack();

        service.Current.ShouldBeSameAs(first);
    }

    [Fact]
    public void CanGoBack_tracks_the_stack()
    {
        var (service, _, second, _) = Build();
        var observed = new List<bool>();
        using var subscription = service.CanGoBack.Subscribe(observed.Add);

        service.NavigateTo(second);
        service.GoBack();

        observed.ShouldBe([false, true, false]);
    }

    [Fact]
    public void Navigates_by_type()
    {
        var (service, _, _, third) = Build();

        service.NavigateTo<OtherFakePage>();

        service.Current.ShouldBeSameAs(third);
    }

    [Fact]
    public void Throws_when_navigating_to_an_unregistered_type()
    {
        var service = new NavigationService([new FakePage("Only")]);

        Should
            .Throw<InvalidOperationException>(service.NavigateTo<OtherFakePage>)
            .Message.ShouldContain("OtherFakePage");
    }

    [Fact]
    public void CurrentChanges_replays_the_present_value()
    {
        var (service, first, second, _) = Build();
        service.NavigateTo(second);

        PageViewModel? seen = null;
        using var subscription = service.CurrentChanges.Subscribe(page =>
        {
            seen ??= page;
        });

        seen.ShouldBeSameAs(second);
        seen.ShouldNotBeSameAs(first);
    }
}