using Microsoft.Extensions.DependencyInjection;
using ScadaLink.Commons.Entities.Audit;
using ScadaLink.Commons.Interfaces.Repositories;
using ScadaLink.Commons.Types;
using ScadaLink.Commons.Types.Audit;
using ScadaLink.HealthMonitoring;

namespace ScadaLink.CentralUI.Services;

/// <summary>
/// Default <see cref="IAuditLogQueryService"/> implementation — a thin pass-through
/// to <see cref="IAuditLogRepository.QueryAsync"/>. Default page size is 100 (the
/// AuditResultsGrid default for #23 M7).
/// </summary>
/// <remarks>
/// <para>
/// #23 M7 (Bundle H follow-up): each query opens its OWN DI scope and resolves a
/// fresh <see cref="IAuditLogRepository"/> — and therefore a fresh
/// <c>ScadaLinkDbContext</c> — rather than sharing the scoped Blazor-circuit
/// context. Without this, the Audit Log page's query-string auto-load
/// (<c>/audit/log?correlationId=…</c>) races <c>AuditFilterBar.GetAllSitesAsync()</c>
/// on the single circuit-scoped <c>ScadaLinkDbContext</c>, producing EF Core's
/// "A second operation was started on this context instance" error. Scope-per-query
/// removes the shared state so the two initial loads can run concurrently. This
/// mirrors the scope-per-message pattern used by <c>AuditLogIngestActor</c>.
/// </para>
/// <para>
/// A second constructor takes an <see cref="IAuditLogRepository"/> directly — a
/// test seam (mirroring <c>AuditLogIngestActor</c>'s dual ctor) so unit tests can
/// substitute a stub without standing up a DI container.
/// </para>
/// </remarks>
public sealed class AuditLogQueryService : IAuditLogQueryService
{
    // M7 Bundle E (T13): trailing window for the Health dashboard's Audit KPI tiles.
    // Hard-coded here rather than configurable because the requirement
    // (Component-AuditLog.md §"Health & KPIs") fixes "rows/min over the last hour"
    // and "% errors over the last hour" as the KPI definition.
    private static readonly TimeSpan KpiWindow = TimeSpan.FromHours(1);

    // Production path: open a fresh scope per operation. Null in the test-seam ctor.
    private readonly IServiceScopeFactory? _scopeFactory;

    // Test seam: a directly-injected repository whose lifetime the test owns.
    // Null in the production ctor.
    private readonly IAuditLogRepository? _injectedRepository;

    private readonly ICentralHealthAggregator _healthAggregator;

    /// <summary>
    /// Production constructor — resolves <see cref="IAuditLogRepository"/> from a
    /// fresh DI scope on every call so each query gets its own
    /// <c>ScadaLinkDbContext</c> and never contends with the circuit-scoped
    /// context the filter bar uses.
    /// </summary>
    public AuditLogQueryService(
        IServiceScopeFactory scopeFactory,
        ICentralHealthAggregator healthAggregator)
    {
        _scopeFactory = scopeFactory ?? throw new ArgumentNullException(nameof(scopeFactory));
        _healthAggregator = healthAggregator ?? throw new ArgumentNullException(nameof(healthAggregator));
    }

    /// <summary>
    /// Test-seam constructor — injects a repository instance whose lifetime the
    /// caller owns. Used by unit tests that substitute a stub repository.
    /// </summary>
    public AuditLogQueryService(
        IAuditLogRepository repository,
        ICentralHealthAggregator healthAggregator)
    {
        _injectedRepository = repository ?? throw new ArgumentNullException(nameof(repository));
        _healthAggregator = healthAggregator ?? throw new ArgumentNullException(nameof(healthAggregator));
    }

    public int DefaultPageSize => 100;

    public async Task<IReadOnlyList<AuditEvent>> QueryAsync(
        AuditLogQueryFilter filter,
        AuditLogPaging? paging = null,
        CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(filter);
        var effective = paging ?? new AuditLogPaging(DefaultPageSize);

        // Test-seam ctor: use the injected repository directly.
        if (_injectedRepository is not null)
        {
            return await _injectedRepository.QueryAsync(filter, effective, ct);
        }

        // Production: a fresh scope (and thus a fresh DbContext) per query so the
        // page's auto-load never shares the circuit-scoped context.
        await using var scope = _scopeFactory!.CreateAsyncScope();
        var repository = scope.ServiceProvider.GetRequiredService<IAuditLogRepository>();
        return await repository.QueryAsync(filter, effective, ct);
    }

    /// <inheritdoc/>
    public async Task<AuditLogKpiSnapshot> GetKpiSnapshotAsync(CancellationToken ct = default)
    {
        // 1. Volume + error counts: aggregate over the trailing 1h window.
        //    BacklogTotal is left at 0 by the repository — we fill it from the
        //    in-memory health aggregator below. Resolved via a per-call scope on
        //    the production path for the same context-isolation reason as
        //    QueryAsync; the test-seam ctor uses the injected repository.
        AuditLogKpiSnapshot repoSnapshot;
        if (_injectedRepository is not null)
        {
            repoSnapshot = await _injectedRepository.GetKpiSnapshotAsync(KpiWindow, nowUtc: null, ct);
        }
        else
        {
            await using var scope = _scopeFactory!.CreateAsyncScope();
            var repository = scope.ServiceProvider.GetRequiredService<IAuditLogRepository>();
            repoSnapshot = await repository.GetKpiSnapshotAsync(KpiWindow, nowUtc: null, ct);
        }

        // 2. Backlog: sum PendingCount across every site's latest report.
        //    Sites that have not yet reported or whose reporter is disabled
        //    leave SiteAuditBacklog null — those contribute zero (a Missing
        //    snapshot is "unknown", not "zero", but the tile is best-effort).
        long backlog = 0;
        foreach (var state in _healthAggregator.GetAllSiteStates().Values)
        {
            var pending = state.LatestReport?.SiteAuditBacklog?.PendingCount;
            if (pending is > 0)
            {
                backlog += pending.Value;
            }
        }

        return repoSnapshot with { BacklogTotal = backlog };
    }

    /// <inheritdoc/>
    public async Task<IReadOnlyList<ExecutionTreeNode>> GetExecutionTreeAsync(
        Guid executionId,
        CancellationToken ct = default)
    {
        // Test-seam ctor: use the injected repository directly.
        if (_injectedRepository is not null)
        {
            return await _injectedRepository.GetExecutionTreeAsync(executionId, ct);
        }

        // Production: a fresh scope (and thus a fresh DbContext) per call — the
        // same context-isolation contract QueryAsync upholds, so the tree
        // page's auto-load never shares the circuit-scoped context.
        await using var scope = _scopeFactory!.CreateAsyncScope();
        var repository = scope.ServiceProvider.GetRequiredService<IAuditLogRepository>();
        return await repository.GetExecutionTreeAsync(executionId, ct);
    }
}