using Hutopy.Modules.Creators.Data;

namespace Hutopy.Modules.Creators.Services;

public class SlugPurger(CreatorsDbContext context)
{
    private static readonly SemaphoreSlim Semaphore = new(1, 1);
    private static DateTimeOffset s_lastPurgeTime = DateTimeOffset.MinValue;
    private static readonly TimeSpan MinTimeBetweenPurges = TimeSpan.FromSeconds(10);

    public async Task PurgeExpiredSlugsAsync(CancellationToken ct)
    {
        // Try to acquire the semaphore
        if (!await Semaphore.WaitAsync(0, ct))
        {
            // Another purge operation is in progress, skip this one
            return;
        }

        try
        {
            DateTimeOffset now = DateTimeOffset.UtcNow;
            if (now - s_lastPurgeTime < MinTimeBetweenPurges)
            {
                // Not enough time has passed since the last purge
                return;
            }

            // Delete expired slugs that are not in use
            await context
                .Slugs
                .Where(s => s.ReservedUntil < now && s.UsedBy == null)
                .ExecuteDeleteAsync(ct);

            // Update the last purge time regardless of whether we found expired slugs or not
            s_lastPurgeTime = now;
        }
        finally
        {
            Semaphore.Release();
        }
    }
}