// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Linq;
using System.Reflection;
using Microsoft.Extensions.DependencyInjection;
 
namespace Microsoft.AspNetCore.Hosting;
 
internal sealed class ConfigureServicesBuilder
{
    public ConfigureServicesBuilder(MethodInfo? configureServices)
    {
        MethodInfo = configureServices;
    }
 
    public MethodInfo? MethodInfo { get; }
 
    public Func<Func<IServiceCollection, IServiceProvider?>, Func<IServiceCollection, IServiceProvider?>> StartupServiceFilters { get; set; } = f => f;
 
    public Func<IServiceCollection, IServiceProvider?> Build(object instance) => services => Invoke(instance, services);
 
    private IServiceProvider? Invoke(object instance, IServiceCollection services)
    {
        return StartupServiceFilters(Startup)(services);
 
        IServiceProvider? Startup(IServiceCollection serviceCollection) => InvokeCore(instance, serviceCollection);
    }
 
    private IServiceProvider? InvokeCore(object instance, IServiceCollection services)
    {
        if (MethodInfo == null)
        {
            return null;
        }
 
        // Only support IServiceCollection parameters
        var parameters = MethodInfo.GetParameters();
        if (parameters.Length > 1 ||
            parameters.Any(p => p.ParameterType != typeof(IServiceCollection)))
        {
            throw new InvalidOperationException("The ConfigureServices method must either be parameterless or take only one parameter of type IServiceCollection.");
        }
 
        var arguments = new object[MethodInfo.GetParameters().Length];
 
        if (parameters.Length > 0)
        {
            arguments[0] = services;
        }
 
        return MethodInfo.InvokeWithoutWrappingExceptions(instance, arguments) as IServiceProvider;
    }
}