using Microsoft.Extensions.Logging.Abstractions;
using Xunit;
using ZB.MOM.WW.HistorianGateway.Contracts.Grpc;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests;

public sealed class GatewayHealthSnapshotTests
{
    [Fact]
    public async Task Counters_track_success_and_failure()
    {
        var fake = new FakeHistorianGatewayClient { RawSamples = Array.Empty<HistorianSample>() };
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);
        await ds.ReadRawAsync("T", default, default, 1, TestContext.Current.CancellationToken);
        fake.ThrowOnRead = new InvalidOperationException("boom");
        await Assert.ThrowsAnyAsync<Exception>(() => ds.ReadRawAsync("T", default, default, 1, TestContext.Current.CancellationToken));
        var h = ds.GetHealthSnapshot();
        Assert.Equal(2, h.TotalQueries);
        Assert.Equal(1, h.TotalSuccesses);
        Assert.Equal(1, h.TotalFailures);
        Assert.Equal(1, h.ConsecutiveFailures);
        Assert.Equal(h.TotalQueries, h.TotalSuccesses + h.TotalFailures); // invariant
    }

    [Fact]
    public async Task GetHealthSnapshot_does_no_io_and_starts_with_connections_closed()
    {
        var fake = new FakeHistorianGatewayClient();
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);
        var h = ds.GetHealthSnapshot();
        Assert.Equal(0, fake.GetConnectionStatusCallCount); // pure observation — never queries the gateway
        Assert.False(h.ProcessConnectionOpen);
        Assert.False(h.EventConnectionOpen);
        await ValueTask.CompletedTask;
    }

    [Fact]
    public async Task Connection_flags_are_derived_from_observed_reads()
    {
        var fake = new FakeHistorianGatewayClient { RawSamples = Array.Empty<HistorianSample>() };
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);
        await ds.ReadRawAsync("T", default, default, 1, TestContext.Current.CancellationToken);
        Assert.True(ds.GetHealthSnapshot().ProcessConnectionOpen);
        fake.ThrowOnRead = new InvalidOperationException("boom");
        await Assert.ThrowsAnyAsync<Exception>(() => ds.ReadRawAsync("T", default, default, 1, TestContext.Current.CancellationToken));
        var h = ds.GetHealthSnapshot();
        Assert.False(h.ProcessConnectionOpen);
        Assert.False(h.EventConnectionOpen);
        Assert.Equal(0, fake.GetConnectionStatusCallCount); // never probes the gateway
    }
}