// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Buffers;

namespace Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv
{
  /// <summary>
  /// Provides programmatic configuration of Libuv transport features.
  /// </summary>
  public class LibuvTransportOptions
  {
    /// <summary>
    /// The number of libuv I/O threads used to process requests.
    /// </summary>
    /// <remarks>
    /// Defaults to half of <see cref="Environment.ProcessorCount" /> rounded down and clamped between 1 and 16.
    /// </remarks>
    public int ThreadCount { get; set; } = ProcessorThreadCount;

    /// <summary>
    /// Set to false to enable Nagle's algorithm for all connections.
    /// </summary>
    /// <remarks>
    /// Defaults to true.
    /// </remarks>
    public bool NoDelay { get; set; } = true;

    /// <summary>
    /// The maximum length of the pending connection queue.
    /// </summary>
    /// <remarks>
    /// Defaults to 128.
    /// </remarks>
    public int Backlog { get; set; } = 128;

    public long? MaxReadBufferSize { get; set; } = 1024 * 1024;

    public long? MaxWriteBufferSize { get; set; } = 64 * 1024;

    internal Func<MemoryPool<byte>> MemoryPoolFactory { get; set; } = SlabMemoryPoolFactory.Create;

    private static int ProcessorThreadCount
    {
      get
      {
        // Actual core count would be a better number
        // rather than logical cores which includes hyper-threaded cores.
        // Divide by 2 for hyper-threading, and good defaults (still need threads to do webserving).
        var threadCount = Environment.ProcessorCount >> 1;

        if (threadCount < 1)
          // Ensure shifted value is at least one
          return 1;

        if (threadCount > 16)
          // Receive Side Scaling RSS Processor count currently maxes out at 16
          // would be better to check the NIC's current hardware queues; but xplat...
          return 16;

        return threadCount;
      }
    }
  }
}