using Microsoft.Extensions.DependencyInjection;
using ZB.MOM.WW.ScadaBridge.AuditLog.Central;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Types;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;

namespace ZB.MOM.WW.ScadaBridge.SiteCallAudit.Tests.TestSupport;

/// <summary>
/// Deferred-work register row 61 — the replacement for <c>SiteCallAuditActor</c>'s deleted
/// repository-taking "test-mode" constructors.
///
/// <para>
/// Those constructors cached a scoped repository on an actor field for the actor's whole
/// lifetime. Nothing in production selected them, but the shape was one call site away from
/// re-introducing a captive-dependency bug, so it had to be allowlisted in the Host tests'
/// <c>CaptiveDependencyGuard</c>. The actor now has a single <see cref="IServiceProvider"/>
/// constructor; a fixture that wants a concrete repository builds one of these instead.
/// </para>
///
/// <para>
/// The actor's contract is unchanged and unweakened — it still resolves per scope and holds
/// nothing. Handing the SAME instance out of every scope is now the FIXTURE's explicit
/// choice, which is also why the serializing decorator below lives here rather than in
/// product code: it exists solely to compensate for that choice.
/// </para>
/// </summary>
internal static class StubRepositoryProvider
{
    /// <summary>
    /// Builds a provider whose every scope yields the same repository instance, wrapped in
    /// <see cref="SerializingSiteCallAuditRepository"/>, plus any collaborators supplied.
    /// </summary>
    /// <param name="repository">Repository instance shared by every scope.</param>
    /// <param name="siteEnumerator">Optional site enumerator; omit to leave the reconciliation tick disarmed.</param>
    /// <param name="pullClient">Optional pull client; omit to leave the reconciliation tick disarmed.</param>
    /// <param name="auditWriter">Optional central direct-write audit sink for relay actions.</param>
    /// <param name="serialize">
    /// False registers the repository unwrapped — for fixtures asserting on call ordering or
    /// identity where the decorator would get in the way.
    /// </param>
    public static ServiceProvider Build(
        ISiteCallAuditRepository repository,
        ISiteEnumerator? siteEnumerator = null,
        IPullSiteCallsClient? pullClient = null,
        ICentralAuditWriter? auditWriter = null,
        bool serialize = true)
    {
        ArgumentNullException.ThrowIfNull(repository);

        var shared = serialize ? new SerializingSiteCallAuditRepository(repository) : repository;

        var services = new ServiceCollection();
        services.AddScoped(_ => shared);

        if (siteEnumerator is not null)
        {
            services.AddSingleton(siteEnumerator);
        }

        if (pullClient is not null)
        {
            services.AddSingleton(pullClient);
        }

        if (auditWriter is not null)
        {
            services.AddSingleton(auditWriter);
        }

        return services.BuildServiceProvider();
    }
}

/// <summary>
/// Serializing wrapper for a repository instance shared across every DI scope in a test.
/// One call at a time, in arrival order.
/// </summary>
/// <remarks>
/// <para>
/// In production every consumer of <c>SiteCallAuditActor</c>'s repository gets its OWN DI
/// scope — one per message, one per background pass — so the off-mailbox reconciliation and
/// purge passes can safely run alongside mailbox handlers: separate scopes mean separate
/// <c>DbContext</c>s. A fixture that hands ONE instance (typically wrapping one
/// <c>DbContext</c>) to every scope breaks that assumption, and <c>DbContext</c> forbids
/// concurrent operations — "A second operation was started on this context instance" is a
/// hard fault, and the interleaving is nondeterministic, so it surfaces as a flaky test
/// rather than a reliable one.
/// </para>
/// <para>
/// Serializing at the CALL, not around the whole pass, is deliberate: it removes the
/// concurrency hazard while preserving the property the off-mailbox passes exist for — a long
/// drain (blocked in a network pull, holding no repository call) still lets ingest, query and
/// KPI messages be answered. Suspending the mailbox for the duration of a pass would have
/// been simpler and would have invalidated exactly those regression tests.
/// </para>
/// <para>
/// This type used to live inside the product actor, reachable only from its test
/// constructors. It moved here with register row 61: production never constructed it, and the
/// hazard it guards is created by the fixture, not by the actor.
/// </para>
/// </remarks>
internal sealed class SerializingSiteCallAuditRepository : ISiteCallAuditRepository
{
    private readonly ISiteCallAuditRepository _inner;
    private readonly SemaphoreSlim _gate = new(1, 1);

    public SerializingSiteCallAuditRepository(ISiteCallAuditRepository inner) => _inner = inner;

    public Task UpsertAsync(SiteCall siteCall, CancellationToken ct = default) =>
        RunAsync(() => _inner.UpsertAsync(siteCall, ct));

    public Task<SiteCall?> GetAsync(TrackedOperationId id, CancellationToken ct = default) =>
        RunAsync(() => _inner.GetAsync(id, ct));

    public Task<IReadOnlyList<SiteCall>> QueryAsync(
        SiteCallQueryFilter filter, SiteCallPaging paging, CancellationToken ct = default) =>
        RunAsync(() => _inner.QueryAsync(filter, paging, ct));

    public Task<int> PurgeTerminalAsync(DateTime olderThanUtc, CancellationToken ct = default) =>
        RunAsync(() => _inner.PurgeTerminalAsync(olderThanUtc, ct));

    public Task<SiteCallKpiSnapshot> ComputeKpisAsync(
        DateTime stuckCutoffUtc, DateTime deliveredSinceUtc, CancellationToken ct = default) =>
        RunAsync(() => _inner.ComputeKpisAsync(stuckCutoffUtc, deliveredSinceUtc, ct));

    public Task<IReadOnlyList<SiteCallSiteKpiSnapshot>> ComputePerSiteKpisAsync(
        DateTime stuckCutoffUtc, DateTime deliveredSinceUtc, CancellationToken ct = default) =>
        RunAsync(() => _inner.ComputePerSiteKpisAsync(stuckCutoffUtc, deliveredSinceUtc, ct));

    public Task<IReadOnlyList<SiteCallNodeKpiSnapshot>> ComputePerNodeKpisAsync(
        DateTime stuckCutoffUtc, DateTime deliveredSinceUtc, CancellationToken ct = default) =>
        RunAsync(() => _inner.ComputePerNodeKpisAsync(stuckCutoffUtc, deliveredSinceUtc, ct));

    private async Task RunAsync(Func<Task> call)
    {
        await _gate.WaitAsync().ConfigureAwait(false);
        try
        {
            await call().ConfigureAwait(false);
        }
        finally
        {
            _gate.Release();
        }
    }

    private async Task<T> RunAsync<T>(Func<Task<T>> call)
    {
        await _gate.WaitAsync().ConfigureAwait(false);
        try
        {
            return await call().ConfigureAwait(false);
        }
        finally
        {
            _gate.Release();
        }
    }
}