// 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.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());
    }
}