using TarninaHub.Application.Matchmaking;

namespace TarninaHub.Infrastructure.Llm;

/// <summary>
/// In-memory sliding-window request limiter (per instance) for LLM cost control.
/// </summary>
public sealed class InMemoryLlmRequestLimiter : ILlmRequestLimiter
{
    private readonly int _maxPerWindow;
    private readonly TimeSpan _window;
    private readonly Queue<DateTimeOffset> _timestamps = new();
    private readonly Lock _gate = new();

    public InMemoryLlmRequestLimiter(int maxRequestsPerMinute, TimeSpan? window = null)
    {
        _maxPerWindow = Math.Max(1, maxRequestsPerMinute);
        _window = window ?? TimeSpan.FromMinutes(1);
    }

    public bool TryAcquire()
    {
        var now = DateTimeOffset.UtcNow;

        lock (_gate)
        {
            while (_timestamps.Count > 0 && now - _timestamps.Peek() > _window)
            {
                _timestamps.Dequeue();
            }

            if (_timestamps.Count >= _maxPerWindow)
            {
                return false;
            }

            _timestamps.Enqueue(now);

            return true;
        }
    }
}