using SQLInsight.Core.Data;

namespace SQLInsight.Collectors.Performance;

public sealed class WaitStatsCollector : Collector<CumulativeSample<WaitStatsSnapshot, WaitStatsDelta>>
{
    internal const string Sql2005 = """
        SELECT wait_type, waiting_tasks_count, wait_time_ms, signal_wait_time_ms
        FROM sys.dm_os_wait_stats
        WHERE wait_time_ms > 0
        """;

    // SQL Server 2000: Wait Type, Requests, Wait Time, Signal Wait Time. Needs elevated rights; see docs/legacy-versions.md.
    internal const string Sql2000 = "DBCC SQLPERF(WAITSTATS) WITH NO_INFOMSGS";

    public override string Name => "wait-stats";
    public override TimeSpan DefaultInterval => TimeSpan.FromMinutes(5);

    protected override async Task<CumulativeSample<WaitStatsSnapshot, WaitStatsDelta>> CollectAsync(
        CollectorContext context, CumulativeSample<WaitStatsSnapshot, WaitStatsDelta>? previous)
    {
        var version = context.Instance.Version;
        var ct = context.CancellationToken;
        var startTime = await Db.StartTimeAsync(context.Connection, version, ct).ConfigureAwait(false);
        var waits = await Db.QueryAsync(
            context.Connection,
            version.Major >= 9 ? Sql2005 : Sql2000,
            r => new WaitStat(r.String(0), r.Long(1), r.Long(2), r.Long(3)),
            ct).ConfigureAwait(false);

        var snapshot = new WaitStatsSnapshot { CapturedAt = context.Now, SqlServerStartTime = startTime, Waits = waits };
        return new(snapshot, WaitStatsDelta.Compute(previous?.Snapshot, snapshot));
    }
}