// 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.Classifiers;

internal sealed class DiscardSyntaxClassifier : AbstractSyntaxClassifier
{
    public override ImmutableArray<Type> SyntaxNodeTypes { get; } = [typeof(DiscardDesignationSyntax), typeof(DiscardPatternSyntax), typeof(ParameterSyntax), typeof(IdentifierNameSyntax)];

    public override void AddClassifications(
       SyntaxNode syntax,
       TextSpan textSpan,
       SemanticModel semanticModel,
       ClassificationOptions options,
       SegmentedList<ClassifiedSpan> result,
       CancellationToken cancellationToken)
    {
        if (syntax.Kind() is SyntaxKind.DiscardDesignation or SyntaxKind.DiscardPattern)
        {
            result.Add(new ClassifiedSpan(syntax.Span, ClassificationTypeNames.Keyword));
            return;
        }

        switch (syntax)
        {
            case ParameterSyntax parameter when parameter.Identifier.Text == "_":
                var symbol = semanticModel.GetDeclaredSymbol(parameter, cancellationToken);

                if (symbol?.IsDiscard == true)
                {
                    result.Add(new ClassifiedSpan(parameter.Identifier.Span, ClassificationTypeNames.Keyword));
                }

                break;

            case IdentifierNameSyntax identifierName when identifierName.Identifier.Text == "_":
                var symbolInfo = semanticModel.GetSymbolInfo(identifierName, cancellationToken);

                if (symbolInfo.Symbol?.Kind == SymbolKind.Discard)
                {
                    result.Add(new ClassifiedSpan(syntax.Span, ClassificationTypeNames.Keyword));
                }

                break;
        }
    }
}