// Copyright (c) .NET Foundation and contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

using System.Linq;
using ILLink.Shared.DataFlow;
using ILLink.Shared.TrimAnalysis;
using ILLink.Shared.TypeSystemProxy;
using Microsoft.CodeAnalysis;

namespace ILLink.RoslynAnalyzer.TrimAnalysis
{
    public static class SingleValueExtensions
    {
        public static SingleValue? FromTypeSymbol(ITypeSymbol type)
        {
            if (type.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T)
            {
                var underlyingType = (type as INamedTypeSymbol)?.TypeArguments.FirstOrDefault();
                return underlyingType?.TypeKind switch
                {
                    TypeKind.TypeParameter =>
                        new NullableValueWithDynamicallyAccessedMembers(new TypeProxy(type),
                            new GenericParameterValue((ITypeParameterSymbol)underlyingType)),
                    // typeof(Nullable<>)
                    TypeKind.Error => new SystemTypeValue(new TypeProxy(type)),
                    TypeKind.Class or TypeKind.Enum or TypeKind.Interface or TypeKind.Struct =>
                        new NullableSystemTypeValue(new TypeProxy(type), new SystemTypeValue(new TypeProxy(underlyingType))),
                    _ => UnknownValue.Instance
                };
            }
            return type.Kind switch
            {
                SymbolKind.TypeParameter => new GenericParameterValue((ITypeParameterSymbol)type),
                SymbolKind.NamedType => new SystemTypeValue(new TypeProxy(type)),
                // If the symbol is an Array type, the BaseType is System.Array
                SymbolKind.ArrayType => new SystemTypeValue(new TypeProxy(type.BaseType!)),
                SymbolKind.FunctionPointerType => new SystemTypeValue(new TypeProxy(type)),
                SymbolKind.ErrorType => UnknownValue.Instance,
                _ => null
            };

        }
    }
}