using System;
using System.Threading;
using System.Threading.Tasks;

namespace StellaOps.AirGap.Time.Services;

public sealed partial class TimeAnchorPolicyService
{
    public async Task<TimeAnchorDriftResult> CalculateDriftAsync(
        string tenantId,
        DateTimeOffset targetTime,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);

        var now = _timeProvider.GetUtcNow();
        var status = await _statusService.GetStatusAsync(tenantId, now, cancellationToken).ConfigureAwait(false);

        if (!status.HasAnchor)
        {
            return new TimeAnchorDriftResult(
                HasAnchor: false,
                Drift: TimeSpan.Zero,
                DriftExceedsThreshold: false,
                AnchorTime: null);
        }

        var drift = targetTime - status.Anchor!.AnchorTime;
        var absDriftSeconds = Math.Abs(drift.TotalSeconds);
        var exceedsThreshold = absDriftSeconds > _options.MaxDriftSeconds;

        return new TimeAnchorDriftResult(
            HasAnchor: true,
            Drift: drift,
            DriftExceedsThreshold: exceedsThreshold,
            AnchorTime: status.Anchor.AnchorTime);
    }
}