// 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;
using System.Collections.Immutable;
using System.Threading;
using Microsoft.CodeAnalysis.Classification;
using Microsoft.CodeAnalysis.Classification.Classifiers;
using Microsoft.CodeAnalysis.Collections;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CSharp.Classification;

internal sealed class OperatorOverloadSyntaxClassifier : AbstractSyntaxClassifier
{
    public override ImmutableArray<Type> SyntaxNodeTypes { get; } =
    [
        typeof(AssignmentExpressionSyntax),
        typeof(BinaryExpressionSyntax),
        typeof(PrefixUnaryExpressionSyntax),
        typeof(PostfixUnaryExpressionSyntax),
    ];

    public override void AddClassifications(
        SyntaxNode syntax,
        TextSpan textSpan,
        SemanticModel semanticModel,
        ClassificationOptions options,
        SegmentedList<ClassifiedSpan> result,
        CancellationToken cancellationToken)
    {
        // Short-circuit simple assignments to prevent calculation of symbol info as it can be expensive.
        if (syntax.IsKind(SyntaxKind.SimpleAssignmentExpression))
        {
            return;
        }

        // Short-circuit operators whose span doesn't intersect the requested span.
        var operatorSpan = GetOperatorTokenSpan(syntax);
        if (operatorSpan.IsEmpty || !operatorSpan.IntersectsWith(textSpan))
        {
            return;
        }

        var symbolInfo = semanticModel.GetSymbolInfo(syntax, cancellationToken);
        if (symbolInfo.Symbol is IMethodSymbol { MethodKind: MethodKind.UserDefinedOperator })
        {
            result.Add(new ClassifiedSpan(operatorSpan, ClassificationTypeNames.OperatorOverloaded));
        }
    }

    private static TextSpan GetOperatorTokenSpan(SyntaxNode syntax)
        => syntax switch
        {
            AssignmentExpressionSyntax assignmentExpression => assignmentExpression.OperatorToken.Span,
            BinaryExpressionSyntax binaryExpression => binaryExpression.OperatorToken.Span,
            PrefixUnaryExpressionSyntax prefixUnaryExpression => prefixUnaryExpression.OperatorToken.Span,
            PostfixUnaryExpressionSyntax postfixUnaryExpression => postfixUnaryExpression.OperatorToken.Span,
            _ => default,
        };
}