using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests;

/// <summary>
///     Review 2026-10-21 R06:T-4 and T-2 on the read path.
///     <list type="bullet">
///         <item>T-4 — every <c>ReadAsync</c> batch fetched + parsed the whole device <c>/current</c> even while the
///         <c>/sample</c> pump held a live, healthy index. A read now answers from that index (READ only — the pump
///         stays its single writer) while the pump is live and not degraded, and keeps <c>/current</c> as the
///         fallback.</item>
///         <item>T-2 — Agent-restart detection lived only on the pump, and the read path discarded the
///         <c>/current</c> answer's <c>instanceId</c>: a browse-only driver kept a cached <c>/probe</c> model across an
///         Agent restart and never raised rediscovery. The fallback read now checks it.</item>
///     </list>
/// </summary>
public sealed class MTConnectReadPathTests
{
    private const long RestartedInstance = 1655000777L;
    private static readonly TimeSpan Watchdog = TimeSpan.FromSeconds(30);

    private static CancellationToken Ct => TestContext.Current.CancellationToken;

    private static MTConnectDriverOptions Opts() => new()
    {
        AgentUri = "http://fixture-agent:5000",
        RequestTimeoutMs = 5000,
        Tags = [new MTConnectTagDefinition("dev1_pos", DriverDataType.Float64)],
    };

    /// <summary>T-4: with a live, healthy pump the read is answered from its index — no /current round trip.</summary>
    [Fact]
    public async Task A_read_with_a_live_pump_answers_from_the_index_without_a_current_call()
    {
        var client = CannedAgentClient.FromFixtures();
        var driver = new MTConnectDriver(Opts(), "mt-t4", _ => client);
        await driver.InitializeAsync("{}", Ct);
        try
        {
            await driver.SubscribeAsync(["dev1_pos"], TimeSpan.FromMilliseconds(50), Ct);
            await client.PumpAsync(MTConnectPumpGenerationChunks.Pos(108, 113, "7.25")).WaitAsync(Watchdog, Ct);
            var currentCalls = client.CurrentCallCount;

            var result = (await driver.ReadAsync(["dev1_pos"], Ct)).Single();

            result.Value.ShouldBe(7.25d, "the read must serve the pump's newest value");
            client.CurrentCallCount.ShouldBe(currentCalls, "no /current while the pump's index is live");
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>Positive control for T-4: with no pump the read still issues exactly one /current.</summary>
    [Fact]
    public async Task A_read_with_no_pump_falls_back_to_one_current_call()
    {
        var client = CannedAgentClient.FromFixtures();
        var driver = new MTConnectDriver(Opts(), "mt-t4-fallback", _ => client);
        await driver.InitializeAsync("{}", Ct);
        try
        {
            var currentCalls = client.CurrentCallCount;

            await driver.ReadAsync(["dev1_pos"], Ct);

            client.CurrentCallCount.ShouldBe(currentCalls + 1);
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>T-4: a pump whose stream is failing does not serve reads — they fall back to /current.</summary>
    [Fact]
    public async Task A_read_with_a_degraded_pump_falls_back_to_current()
    {
        var client = CannedAgentClient.FromFixtures();
        // Every /sample fails: the pump stays alive (reconnecting under backoff) but its stream is degraded.
        client.SampleFailure = new IOException("connection refused");
        var options = new MTConnectDriverOptions
        {
            AgentUri = "http://fixture-agent:5000",
            RequestTimeoutMs = 5000,
            Tags = [new MTConnectTagDefinition("dev1_pos", DriverDataType.Float64)],
            Reconnect = new MTConnectReconnectOptions { MinBackoffMs = 1000, MaxBackoffMs = 1000 },
        };
        var driver = new MTConnectDriver(options, "mt-t4-degraded", _ => client);
        await driver.InitializeAsync("{}", Ct);
        try
        {
            await driver.SubscribeAsync(["dev1_pos"], TimeSpan.FromMilliseconds(50), Ct);
            await client.WaitForSampleCallsAsync(1).WaitAsync(Watchdog, Ct);
            var deadline = DateTime.UtcNow + Watchdog;
            while (driver.GetHealth().State != DriverState.Degraded && DateTime.UtcNow < deadline)
                await Task.Delay(20, Ct);
            driver.GetHealth().State.ShouldBe(DriverState.Degraded);
            var currentCalls = client.CurrentCallCount;

            await driver.ReadAsync(["dev1_pos"], Ct);

            client.CurrentCallCount.ShouldBe(currentCalls + 1, "a degraded stream's index is not trusted for reads");
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>T-2: a browse-only driver's read sees the Agent restart — once — and drops the stale model.</summary>
    [Fact]
    public async Task A_read_that_sees_a_new_instance_id_raises_rediscovery_once_and_drops_the_probe_model()
    {
        var client = CannedAgentClient.FromFixtures();
        var driver = new MTConnectDriver(Opts(), "mt-t2", _ => client);
        await driver.InitializeAsync("{}", Ct);
        var raised = 0;
        driver.OnRediscoveryNeeded += (_, _) => Interlocked.Increment(ref raised);
        try
        {
            driver.CachedProbeModel.ShouldNotBeNull("positive control: initialize cached the model");
            client.Current = new MTConnectStreamsResult(RestartedInstance, 5, 1, client.Current.Observations);

            await driver.ReadAsync(["dev1_pos"], Ct);
            await driver.ReadAsync(["dev1_pos"], Ct);

            raised.ShouldBe(1, "once per distinct instanceId, not once per read");
            driver.CachedProbeModel.ShouldBeNull("the model describes a process that no longer exists");
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>T-2 control: reads against the same Agent process never raise rediscovery.</summary>
    [Fact]
    public async Task Reads_against_the_same_instance_raise_nothing()
    {
        var client = CannedAgentClient.FromFixtures();
        var driver = new MTConnectDriver(Opts(), "mt-t2-same", _ => client);
        await driver.InitializeAsync("{}", Ct);
        var raised = 0;
        driver.OnRediscoveryNeeded += (_, _) => Interlocked.Increment(ref raised);
        try
        {
            await driver.ReadAsync(["dev1_pos"], Ct);
            await driver.ReadAsync(["dev1_pos"], Ct);

            raised.ShouldBe(0);
            driver.CachedProbeModel.ShouldNotBeNull();
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }
}