namespace ZB.MOM.WW.OtOpcUa.Runtime.Historian;

/// <summary>Rows removed from one historian table by a single purge pass.</summary>
/// <param name="Table">Unqualified table name (the <c>table</c> tag on the retention counter).</param>
/// <param name="Rows">Rows deleted.</param>
public sealed record RetentionPurgeResult(string Table, long Rows);

/// <summary>
///     Backend-side retention purge: deletes history older than the backend's configured retention window.
///     Created by <see cref="IHistorianBackendProvider.CreateRetention"/> and driven on a timer by
///     <see cref="HistorianRetentionService"/>, which owns scheduling and the Primary gate.
/// </summary>
public interface IHistorianRetention
{
    /// <summary>How often <see cref="HistorianRetentionService"/> should run a pass.</summary>
    TimeSpan Interval { get; }

    /// <summary>
    ///     Runs one purge pass. Returns an empty list when the pass was skipped (another process holds the
    ///     purge lock). Implementations honour cancellation between batches.
    /// </summary>
    /// <param name="ct">Cancellation.</param>
    /// <returns>Per-table deleted-row counts.</returns>
    Task<IReadOnlyList<RetentionPurgeResult>> PurgeAsync(CancellationToken ct);
}