using ZB.MOM.WW.ScadaBridge.Commons.Entities.ExternalSystems;

namespace ZB.MOM.WW.ScadaBridge.ExternalSystemGateway.Tests;

/// <summary>Tests for <see cref="ExternalDefinitionLookupCache"/> (review 2026-10-21 05/P2).</summary>
public class ExternalDefinitionLookupCacheTests
{
    private static ExternalSystemDefinition Sys() => new("S", "https://x", "none") { Id = 1 };

    /// <summary>Verifies hits within the TTL skip the repository and expiry refetches.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Hit_WithinTtl_SkipsFetch_AndExpiryRefetches()
    {
        var time = new FakeTimeProvider(DateTimeOffset.UtcNow);
        var cache = new ExternalDefinitionLookupCache(TimeSpan.FromSeconds(5), time);
        var fetches = 0;
        Task<ExternalSystemDefinition?> Fetch() { fetches++; return Task.FromResult<ExternalSystemDefinition?>(Sys()); }

        await cache.GetSystemAsync("S", Fetch);
        await cache.GetSystemAsync("S", Fetch);
        Assert.Equal(1, fetches);

        time.Advance(TimeSpan.FromSeconds(6));
        await cache.GetSystemAsync("S", Fetch);
        Assert.Equal(2, fetches);
    }

    /// <summary>Verifies misses are not cached and a zero TTL disables caching.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task NotFound_IsNotCached_AndZeroTtlDisables()
    {
        var cache = new ExternalDefinitionLookupCache(TimeSpan.FromSeconds(5));
        var fetches = 0;
        Task<ExternalSystemDefinition?> Miss() { fetches++; return Task.FromResult<ExternalSystemDefinition?>(null); }
        await cache.GetSystemAsync("S", Miss);
        await cache.GetSystemAsync("S", Miss);
        Assert.Equal(2, fetches);

        var off = new ExternalDefinitionLookupCache(TimeSpan.Zero);
        fetches = 0;
        Task<ExternalSystemDefinition?> Hit() { fetches++; return Task.FromResult<ExternalSystemDefinition?>(Sys()); }
        await off.GetSystemAsync("S", Hit);
        await off.GetSystemAsync("S", Hit);
        Assert.Equal(2, fetches);
    }

    private sealed class FakeTimeProvider(DateTimeOffset start) : TimeProvider
    {
        private DateTimeOffset _now = start;
        public override DateTimeOffset GetUtcNow() => _now;
        public void Advance(TimeSpan by) => _now += by;
    }
}