// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Options;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Simplification;
 
namespace Microsoft.CodeAnalysis.CSharp.Simplification
{
    internal sealed partial class CSharpNullableAnnotationReducer : AbstractCSharpReducer
    {
        private static readonly ObjectPool<IReductionRewriter> s_pool = new(
            () => new Rewriter(s_pool));
 
        private static readonly Func<NullableTypeSyntax, SemanticModel, SimplifierOptions, CancellationToken, SyntaxNode> s_simplifyNullableType = SimplifyNullableType;
 
        public CSharpNullableAnnotationReducer() : base(s_pool)
        {
        }
 
        protected override bool IsApplicable(CSharpSimplifierOptions options)
           => true;
 
        private static SyntaxNode SimplifyNullableType(
            NullableTypeSyntax node,
            SemanticModel semanticModel,
            SimplifierOptions options,
            CancellationToken cancellationToken)
        {
            // If annotations are enabled, there's no further simplification to do
            var context = semanticModel.GetNullableContext(node.Span.End);
 
            // Work around https://github.com/dotnet/roslyn/issues/37809
            if (semanticModel.IsSpeculativeSemanticModel && context.AnnotationsInherited())
            {
                // Work around bug where GetNullableContext() on a speculative model doesn't inherit automatically
                context = semanticModel.ParentModel.GetNullableContext(semanticModel.OriginalPositionForSpeculation);
            }
 
            if (context.AnnotationsEnabled())
            {
                return node;
            }
 
            // If it's not a reference type, also leave the ?
            var type = semanticModel.GetTypeInfo(node, cancellationToken).Type;
            if (type == null || !type.IsReferenceType)
            {
                return node;
            }
 
            // Drop the ?
            return node.ElementType.WithAppendedTrailingTrivia(node.QuestionToken.GetAllTrivia());
        }
    }
}