using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using NSubstitute;
using ZB.MOM.WW.ScadaBridge.CentralUI.Services;
using ZB.MOM.WW.ScadaBridge.DeploymentManager;
using ZB.MOM.WW.ScadaBridge.DeploymentManager.PendingUpdates;

namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Services;

/// <summary>
/// Unit tests for <see cref="PendingUpdatesCache"/> — the same single-flight TTL contract as
/// <see cref="SingleFlightMemoTests"/> proves for the primitive, exercised here through the
/// full DI-scope-per-flight shape: N concurrent callers before the evaluator resolves must
/// share ONE fleet flatten, a value produced inside the TTL is served without re-evaluating,
/// <c>forceRefresh</c> bypasses a fresh value but still joins an in-flight round, and a
/// faulted evaluation is never memoized.
/// </summary>
public class PendingUpdatesCacheTests : IDisposable
{
    private static readonly DateTimeOffset T0 = new(2026, 9, 14, 9, 0, 0, TimeSpan.Zero);

    private readonly IPendingUpdatesEvaluator _evaluator = Substitute.For<IPendingUpdatesEvaluator>();
    private readonly ServiceProvider _provider;

    /// <summary>Initializes a service provider that resolves the substitute pending-updates evaluator.</summary>
    public PendingUpdatesCacheTests()
    {
        var services = new ServiceCollection();
        services.AddScoped(_ => _evaluator);
        _provider = services.BuildServiceProvider();
    }

    // A generous TTL (1h) so every test's timing is driven by task completion, not the clock.
    private static IOptions<DeploymentManagerOptions> Options(TimeSpan? ttl = null) =>
        Microsoft.Extensions.Options.Options.Create(
            new DeploymentManagerOptions { PendingUpdatesCacheTtl = ttl ?? TimeSpan.FromHours(1) });

    private PendingUpdatesCache CreateSut(TimeSpan? ttl = null) =>
        new(_provider.GetRequiredService<IServiceScopeFactory>(), Options(ttl));

    private static PendingUpdatesSnapshot Snapshot() =>
        new(T0, Array.Empty<SitePendingUpdates>());

    /// <summary>Verifies that concurrent callers share a single evaluation.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task ConcurrentCallers_ShareOneEvaluation()
    {
        var released = new TaskCompletionSource<PendingUpdatesSnapshot>(
            TaskCreationOptions.RunContinuationsAsynchronously);
        _evaluator.EvaluateAsync(Arg.Any<CancellationToken>()).Returns(released.Task);
        var sut = CreateSut();

        var waiters = Enumerable.Range(0, 10).Select(_ => sut.GetAsync()).ToArray();
        released.SetResult(Snapshot());
        var results = await Task.WhenAll(waiters);

        await _evaluator.Received(1).EvaluateAsync(Arg.Any<CancellationToken>());
        Assert.All(results, r => Assert.Same(results[0], r));
    }

    /// <summary>Verifies that a call within the TTL serves the memoized value without re-evaluating.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task WithinTtl_ServesTheMemoizedValue_WithoutReEvaluating()
    {
        _evaluator.EvaluateAsync(Arg.Any<CancellationToken>()).Returns(Snapshot());
        var sut = CreateSut();

        var first = await sut.GetAsync();
        var second = await sut.GetAsync();

        await _evaluator.Received(1).EvaluateAsync(Arg.Any<CancellationToken>());
        Assert.Same(first, second);
    }

    /// <summary>Verifies that a forced refresh bypasses a still-fresh cached value.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task ForceRefresh_BypassesAFreshValue()
    {
        var snapshotA = Snapshot();
        var snapshotB = new PendingUpdatesSnapshot(T0.AddMinutes(1), Array.Empty<SitePendingUpdates>());
        _evaluator.EvaluateAsync(Arg.Any<CancellationToken>()).Returns(snapshotA, snapshotB);
        var sut = CreateSut();

        var first = await sut.GetAsync();
        var forced = await sut.GetAsync(forceRefresh: true);

        await _evaluator.Received(2).EvaluateAsync(Arg.Any<CancellationToken>());
        Assert.Same(snapshotA, first);
        Assert.Same(snapshotB, forced);
    }

    /// <summary>Verifies that a forced refresh still joins an evaluation that is already in flight.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task ForceRefresh_StillJoinsAnInFlightRound()
    {
        var released = new TaskCompletionSource<PendingUpdatesSnapshot>(
            TaskCreationOptions.RunContinuationsAsynchronously);
        _evaluator.EvaluateAsync(Arg.Any<CancellationToken>()).Returns(released.Task);
        var sut = CreateSut();

        var first = sut.GetAsync();
        var forcedA = sut.GetAsync(forceRefresh: true);
        var forcedB = sut.GetAsync(forceRefresh: true);

        var snapshot = Snapshot();
        released.SetResult(snapshot);

        Assert.Same(snapshot, await first);
        Assert.Same(snapshot, await forcedA);
        Assert.Same(snapshot, await forcedB);
        await _evaluator.Received(1).EvaluateAsync(Arg.Any<CancellationToken>());
    }

    /// <summary>Verifies that a failed evaluation surfaces to the caller and is not memoized.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task FailedEvaluation_SurfacesToTheCaller_AndIsNotMemoized()
    {
        _evaluator.EvaluateAsync(Arg.Any<CancellationToken>())
            .Returns(
                Task.FromException<PendingUpdatesSnapshot>(new InvalidOperationException("flatten failed")),
                Task.FromResult(Snapshot()));
        var sut = CreateSut();

        await Assert.ThrowsAsync<InvalidOperationException>(() => sut.GetAsync());

        // Same instant, well inside the TTL — a cached fault would starve every dashboard
        // for the rest of the window, so the next caller must start a new evaluation.
        var recovered = await sut.GetAsync();

        Assert.NotNull(recovered);
        await _evaluator.Received(2).EvaluateAsync(Arg.Any<CancellationToken>());
    }

    /// <summary>Releases the resources held by the test fixture.</summary>
    public void Dispose() => _provider.Dispose();
}