using Elternbeirat.Web.Shared;

namespace Elternbeirat.Web.Tests;

/// <summary>
/// Unit tests for the health cache behind the maintenance gate. The probe is a fake
/// that counts its calls, so no PocketBase is needed.
/// </summary>
public class PocketBaseHealthCacheTests
{
    private readonly SteppingClock _clock = new(new DateTimeOffset(2026, 10, 1, 10, 0, 0, TimeSpan.Zero));
    private int _probes;

    private Func<CancellationToken, Task<bool>> Probe(bool healthy) =>
        _ =>
        {
            _probes++;
            return Task.FromResult(healthy);
        };

    [Fact]
    public async Task Result_is_reused_within_the_lifetime()
    {
        var cache = new PocketBaseHealthCache(_clock);

        await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);
        _clock.Now += PocketBaseHealthCache.Lifetime - TimeSpan.FromSeconds(1);
        var healthy = await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);

        healthy.ShouldBeTrue();
        _probes.ShouldBe(1);
    }

    [Fact]
    public async Task Stale_result_is_probed_again()
    {
        // The way back after an outage: once the lifetime is over, the new answer
        // replaces the old one.
        var cache = new PocketBaseHealthCache(_clock);

        await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);
        _clock.Now += PocketBaseHealthCache.Lifetime;
        var healthy = await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);

        healthy.ShouldBeTrue();
        _probes.ShouldBe(2);
    }

    [Fact]
    public async Task Unhealthy_result_is_cached_too()
    {
        // While PocketBase is down, not every request should wait for a failing probe.
        var cache = new PocketBaseHealthCache(_clock);

        await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);
        var healthy = await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);

        healthy.ShouldBeFalse();
        _probes.ShouldBe(1);
    }

    /// <summary>
    /// A clock the test moves forward by hand, to step past the cache lifetime without
    /// waiting.
    /// </summary>
    /// <param name="start">The moment the clock shows at first.</param>
    private sealed class SteppingClock(DateTimeOffset start) : TimeProvider
    {
        public DateTimeOffset Now { get; set; } = start;

        public override DateTimeOffset GetUtcNow() => Now;
    }
}