// 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.Collections.Generic;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using System.Collections.Immutable;
using Microsoft.CodeAnalysis.CSharp.Symbols;

namespace Microsoft.CodeAnalysis.CSharp
{
    /// <summary>
    /// This binder is for binding the argument to typeof.  It traverses
    /// the syntax marking each open type ("unbound generic type" in the
    /// C# spec) as either allowed or not allowed, so that BindType can 
    /// appropriately return either the corresponding type symbol or an 
    /// error type.  It also indicates whether the argument as a whole 
    /// should be considered open so that the flag can be set 
    /// appropriately in BoundTypeOfOperator.
    /// </summary>
    internal sealed class TypeofBinder : Binder
    {
        private readonly Dictionary<GenericNameSyntax, bool> _allowedMap;

        internal TypeofBinder(ExpressionSyntax typeExpression, Binder next)
            // Unsafe types are not unsafe in typeof, so it is effectively an unsafe region.
            : base(next, next.Flags | BinderFlags.UnsafeRegion)
        {
            OpenTypeVisitor.Visit(typeExpression, out _allowedMap);
        }

        protected override bool IsUnboundTypeAllowed(GenericNameSyntax syntax)
        {
            bool allowed;
            return _allowedMap != null && _allowedMap.TryGetValue(syntax, out allowed) && allowed;
        }
    }
}