using System;
using System.Threading;

namespace PerfectNumbers.Core.Gpu;

public static class GpuPrimeWorkLimiter
{
    private static SemaphoreSlim _semaphore = new(1, int.MaxValue);
    private static int _currentLimit = 1;

    public static Lease Acquire()
    {
        // TODO: Inline the pooled limiter guard from the GpuLimiterThroughputBenchmarks so prime-sieve
        // GPU jobs stop allocating Lease instances on every acquisition.
        var sem = _semaphore;
        sem.Wait();
        return new Lease(sem);
    }

    public static void SetLimit(int value)
    {
        if (value <= 0)
        {
            value = 1;
        }

        if (value == _currentLimit)
        {
            return;
        }

        // TODO: Switch to a shared limiter implementation with GpuWorkLimiter so we can coordinate CPU/GPU prime work using
        // the same semaphore pool without reallocating per adjustment.
        var previous = _semaphore;
        _semaphore = new SemaphoreSlim(value, value);
        _currentLimit = value;
        previous.Dispose();
    }

    public sealed class Lease : IDisposable
    {
        private readonly SemaphoreSlim _sem;

        internal Lease(SemaphoreSlim sem)
        {
            _sem = sem;
        }

        public void Dispose()
        {
            _sem.Release();
        }
    }
}