// 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.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.LanguageService;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.ExtractMethod;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.ExtractMethod;

internal sealed partial class CSharpExtractMethodService
{
    internal abstract partial class CSharpSelectionResult
    {
        /// <summary>
        /// Used when selecting just an expression to extract.
        /// </summary>
        private sealed class ExpressionResult(
            SemanticDocument document,
            SelectionType selectionType,
            TextSpan finalSpan)
            : CSharpSelectionResult(document, selectionType, finalSpan)
        {
            public override bool ContainingScopeHasAsyncKeyword()
                => false;

            public override SyntaxNode GetContainingScope()
            {
                Contract.ThrowIfNull(SemanticDocument);
                Contract.ThrowIfFalse(IsExtractMethodOnExpression);

                var firstToken = GetFirstTokenInSelection();
                var lastToken = GetLastTokenInSelection();

                var scope = firstToken.GetCommonRoot(lastToken).GetAncestorOrThis<ExpressionSyntax>();
                Contract.ThrowIfNull(scope);

                return CSharpSyntaxFacts.Instance.GetRootStandaloneExpression(scope);
            }

            protected override (ITypeSymbol? returnType, bool returnsByRef) GetReturnTypeInfoWorker(CancellationToken cancellationToken)
            {
                if (GetContainingScope() is not ExpressionSyntax node)
                {
                    throw ExceptionUtilities.Unreachable();
                }

                var model = SemanticDocument.SemanticModel;

                // special case for array initializer and explicit cast
                if (node.IsArrayInitializer())
                {
                    var variableDeclExpression = node.GetAncestorOrThis<VariableDeclarationSyntax>();
                    if (variableDeclExpression != null)
                        return (model.GetTypeInfo(variableDeclExpression.Type, cancellationToken).Type, returnsByRef: false);
                }

                if (node.IsExpressionInCast())
                {
                    // bug # 12774 and # 4780
                    // if the expression is under cast, we use the heuristic below
                    // 1. if regular binding returns a meaningful type, we use it as it is
                    // 2. if it doesn't, even if the cast itself wasn't included in the selection, we will treat it 
                    //    as it was in the selection
                    var (regularType, returnsByRef) = GetRegularExpressionType(model, node, cancellationToken);
                    if (regularType != null)
                        return (regularType, returnsByRef);

                    if (node.Parent is CastExpressionSyntax castExpression)
                        return (model.GetTypeInfo(castExpression, cancellationToken).Type, returnsByRef: false);
                }

                return GetRegularExpressionType(model, node, cancellationToken);
            }

            private static (ITypeSymbol? typeSymbol, bool returnsByRef) GetRegularExpressionType(
                SemanticModel semanticModel, ExpressionSyntax node, CancellationToken cancellationToken)
            {
                // regular case. always use ConvertedType to get implicit conversion right.
                var expression = node.WalkDownParentheses();
                var returnsByRef = false;
                if (expression is RefExpressionSyntax refExpression)
                {
                    expression = refExpression.Expression;
                    returnsByRef = true;
                }

                var typeSymbol = GetRegularExpressionTypeWorker();
                return (typeSymbol, returnsByRef);

                ITypeSymbol? GetRegularExpressionTypeWorker()
                {
                    var info = semanticModel.GetTypeInfo(expression, cancellationToken);
                    var conv = semanticModel.GetConversion(expression, cancellationToken);

                    if (info.ConvertedType == null || info.ConvertedType.IsErrorType())
                    {
                        // there is no implicit conversion involved. no need to go further
                        return info.GetTypeWithAnnotatedNullability();
                    }

                    // always use converted type if method group
                    if ((!node.IsKind(SyntaxKind.ObjectCreationExpression) && semanticModel.GetMemberGroup(expression, cancellationToken).Length > 0) ||
                        IsCoClassImplicitConversion(info, conv, semanticModel.Compilation.CoClassType()))
                    {
                        return info.GetConvertedTypeWithAnnotatedNullability();
                    }

                    // check implicit conversion
                    if (conv.IsImplicit && (conv.IsConstantExpression || conv.IsEnumeration))
                    {
                        return info.GetConvertedTypeWithAnnotatedNullability();
                    }

                    // use FormattableString if conversion between String and FormattableString
                    if (info.Type?.SpecialType == SpecialType.System_String &&
                        info.ConvertedType?.IsFormattableStringOrIFormattable() == true)
                    {
                        return info.GetConvertedTypeWithAnnotatedNullability();
                    }

                    // always try to use type that is more specific than object type if possible.
                    return !info.Type.IsObjectType() ? info.GetTypeWithAnnotatedNullability() : info.GetConvertedTypeWithAnnotatedNullability();
                }
            }

            private static bool IsCoClassImplicitConversion(TypeInfo info, Conversion conversion, INamedTypeSymbol? coclassSymbol)
            {
                if (!conversion.IsImplicit ||
                     info.ConvertedType == null ||
                     info.ConvertedType.TypeKind != TypeKind.Interface)
                {
                    return false;
                }

                // let's see whether this interface has coclass attribute
                return info.ConvertedType.HasAttribute(coclassSymbol);
            }

            public override SyntaxNode GetOutermostCallSiteContainerToProcess(CancellationToken cancellationToken)
            {
                var container = this.GetInnermostStatementContainer();

                Contract.ThrowIfNull(container);
                Contract.ThrowIfFalse(
                    container.IsStatementContainerNode() ||
                    container is BaseListSyntax or TypeDeclarationSyntax or ConstructorDeclarationSyntax or CompilationUnitSyntax);

                return container;
            }
        }
    }
}