// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.ClientModel.Primitives;
using System.Collections.Generic;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
 
#pragma warning disable CA1307 // Specify StringComparison
 
namespace Microsoft.Extensions.AI;
 
/// <summary>Provides utility methods for creating <see cref="RequestOptions"/>.</summary>
internal static class RequestOptionsExtensions
{
    /// <summary>Creates a <see cref="RequestOptions"/> configured for use with OpenAI.</summary>
    public static RequestOptions ToRequestOptions(this CancellationToken cancellationToken, bool streaming)
    {
        RequestOptions requestOptions = new()
        {
            CancellationToken = cancellationToken,
            BufferResponse = !streaming
        };
 
        requestOptions.AddPolicy(MeaiUserAgentPolicy.Instance, PipelinePosition.PerCall);
 
        return requestOptions;
    }
 
    /// <summary>Provides a pipeline policy that adds a "MEAI/x.y.z" user-agent header.</summary>
    private sealed class MeaiUserAgentPolicy : PipelinePolicy
    {
        public static MeaiUserAgentPolicy Instance { get; } = new MeaiUserAgentPolicy();
 
        private static readonly string _userAgentValue = CreateUserAgentValue();
 
        public override void Process(PipelineMessage message, IReadOnlyList<PipelinePolicy> pipeline, int currentIndex)
        {
            AddUserAgentHeader(message);
            ProcessNext(message, pipeline, currentIndex);
        }
 
        public override ValueTask ProcessAsync(PipelineMessage message, IReadOnlyList<PipelinePolicy> pipeline, int currentIndex)
        {
            AddUserAgentHeader(message);
            return ProcessNextAsync(message, pipeline, currentIndex);
        }
 
        private static void AddUserAgentHeader(PipelineMessage message) =>
            message.Request.Headers.Add("User-Agent", _userAgentValue);
 
        private static string CreateUserAgentValue()
        {
            const string Name = "MEAI";
 
            if (typeof(MeaiUserAgentPolicy).Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion is string version)
            {
                int pos = version.IndexOf('+');
                if (pos >= 0)
                {
                    version = version.Substring(0, pos);
                }
 
                if (version.Length > 0)
                {
                    return $"{Name}/{version}";
                }
            }
 
            return Name;
        }
    }
}