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>
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);

    private readonly IAuditLogRepository _repository;
    private readonly ICentralHealthAggregator _healthAggregator;

    public AuditLogQueryService(
        IAuditLogRepository repository,
        ICentralHealthAggregator healthAggregator)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _healthAggregator = healthAggregator ?? throw new ArgumentNullException(nameof(healthAggregator));
    }

    public int DefaultPageSize => 100;

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