using SQLInsight.Core.Data;

namespace SQLInsight.Core.Tests;

public class IndexUsageTests
{
    private static readonly DateTime Start = new(2026, 9, 1, 6, 0, 0, DateTimeKind.Utc);

    private static IndexSnapshot Snapshot(DateTime start, DateTimeOffset at, long reads, long writes) => new()
    {
        CapturedAt = at,
        SqlServerStartTime = start,
        Databases = [new IndexDatabase { Name = "AX", Indexes = [new IndexInfo { Schema = "dbo", Table = "INVENTTRANS", IndexId = 5, Name = "I_177ITEMIDX", Type = "NONCLUSTERED", UserSeeks = reads, UserUpdates = writes }] }],
    };

    [Fact]
    public void Usage_is_summed_across_restarts_and_tracked_from_the_first_restart_seen()
    {
        var first = IndexUsageTracking.Advance(null, Snapshot(Start, new DateTimeOffset(Start.AddDays(1)), 10, 100));
        var second = IndexUsageTracking.Advance(first, Snapshot(Start, new DateTimeOffset(Start.AddDays(2)), 15, 300));
        var restart = Start.AddDays(3);
        var afterRestart = IndexUsageTracking.Advance(second, Snapshot(restart, new DateTimeOffset(restart.AddHours(6)), 2, 50));

        var index = afterRestart.Databases[0].Indexes[0];
        Assert.Equal((17L, 350L), (index.TrackedReads, index.TrackedWrites));
        Assert.Equal(new DateTimeOffset(Start), index.TrackedSince);
        Assert.Equal(TimeSpan.FromDays(3.25), afterRestart.TrackedFor(index));
        Assert.Equal(TimeSpan.FromHours(6), afterRestart.Uptime);
        var delta = Assert.Single(second.UsageDeltas);
        Assert.Equal((5L, 200L), (delta.Reads, delta.Writes));
        Assert.Equal((2L, 50L), (afterRestart.UsageDeltas[0].Reads, afterRestart.UsageDeltas[0].Writes)); // counters started over
    }

    [Fact]
    public void A_counter_reset_without_a_restart_counts_what_the_counter_holds_now()
    {
        // The database was taken offline (or closed by AUTO_CLOSE) between the collections: same start time, lower counters.
        var first = IndexUsageTracking.Advance(null, Snapshot(Start, new DateTimeOffset(Start.AddDays(1)), 100, 1000));
        var second = IndexUsageTracking.Advance(first, Snapshot(Start, new DateTimeOffset(Start.AddDays(2)), 7, 40));

        var delta = Assert.Single(second.UsageDeltas);
        Assert.Equal((7L, 40L), (delta.Reads, delta.Writes));
        Assert.Equal((107L, 1040L), (second.Databases[0].Indexes[0].TrackedReads, second.Databases[0].Indexes[0].TrackedWrites));
    }
}