// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
#nullable enable
 
using System.Reflection;
 
namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders;
 
/// <summary>
/// An <see cref="IModelBinderProvider"/> for binding from the <see cref="IServiceProvider"/>.
/// </summary>
public class ServicesModelBinderProvider : IModelBinderProvider
{
    private readonly ServicesModelBinder _optionalServicesBinder = new() { IsOptional = true };
    private readonly ServicesModelBinder _servicesBinder = new();
 
    /// <inheritdoc />
    public IModelBinder? GetBinder(ModelBinderProviderContext context)
    {
        ArgumentNullException.ThrowIfNull(context);
 
        if (context.BindingInfo.BindingSource != null &&
            context.BindingInfo.BindingSource.CanAcceptDataFrom(BindingSource.Services))
        {
            // IsRequired will be false for a Reference Type
            // without a default value in a oblivious nullability context
            // however, for services we should treat them as required
            var isRequired = context.Metadata.IsRequired ||
                    (context.Metadata.Identity.ParameterInfo?.HasDefaultValue != true &&
                        !context.Metadata.ModelType.IsValueType &&
                        context.Metadata.NullabilityState == NullabilityState.Unknown);
 
            if (context.BindingInfo.ServiceKey != null)
            {
                return new KeyedServicesModelBinder(context.BindingInfo.ServiceKey, !isRequired);
            }
 
            return isRequired ? _servicesBinder : _optionalServicesBinder;
        }
 
        return null;
    }
}