// 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.
 
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
 
namespace Microsoft.CodeAnalysis.Shared.Extensions
{
    internal partial class ISymbolExtensions
    {
        /// <summary>
        /// Visits types or members that have signatures (i.e. methods, fields, etc.) and determines
        /// if any of them reference a pointer type and should thus have the <see
        /// langword="unsafe"/> modifier on them.
        /// </summary>
        private class RequiresUnsafeModifierVisitor : SymbolVisitor<bool>
        {
            private readonly HashSet<ISymbol> _visited = new();
 
            public override bool DefaultVisit(ISymbol node)
            {
                Debug.Fail("Unhandled symbol kind in RequiresUnsafeModifierVisitor: " + node.Kind);
                return false;
            }
 
            public override bool VisitArrayType(IArrayTypeSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.ElementType.Accept(this);
            }
 
            public override bool VisitDynamicType(IDynamicTypeSymbol symbol)
            {
                // The dynamic type is never unsafe (well....you know what I mean)
                return false;
            }
 
            public override bool VisitField(IFieldSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.Type.Accept(this);
            }
 
            public override bool VisitNamedType(INamedTypeSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.GetAllTypeArguments().Any(ts => ts.Accept(this));
            }
 
            public override bool VisitPointerType(IPointerTypeSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return true;
            }
 
            public override bool VisitFunctionPointerType(IFunctionPointerTypeSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return true;
            }
 
            public override bool VisitProperty(IPropertySymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return
                    symbol.Type.Accept(this) ||
                    symbol.Parameters.Any(static (p, self) => p.Accept(self), this);
            }
 
            public override bool VisitTypeParameter(ITypeParameterSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.ConstraintTypes.Any(static (ts, self) => ts.Accept(self), this);
            }
 
            public override bool VisitMethod(IMethodSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return
                    symbol.ReturnType.Accept(this) ||
                    symbol.Parameters.Any(static (p, self) => p.Accept(self), this) ||
                    symbol.TypeParameters.Any(static (tp, self) => tp.Accept(self), this);
            }
 
            public override bool VisitParameter(IParameterSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.Type.Accept(this);
            }
 
            public override bool VisitEvent(IEventSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.Type.Accept(this);
            }
 
            public override bool VisitAlias(IAliasSymbol symbol)
            {
                if (!_visited.Add(symbol))
                {
                    return false;
                }
 
                return symbol.Target.Accept(this);
            }
        }
    }
}