// 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.

#nullable disable

using System.Collections.Generic;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.DocumentationComments;
using Microsoft.CodeAnalysis.MetadataAsSource;
using Microsoft.CodeAnalysis.Shared.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.DocumentationComments;

internal sealed class DocCommentConverter : CSharpSyntaxRewriter
{
    private readonly IDocumentationCommentFormattingService _formattingService;
    private readonly CancellationToken _cancellationToken;

    public static SyntaxNode ConvertToRegularComments(SyntaxNode node, IDocumentationCommentFormattingService formattingService, CancellationToken cancellationToken)
    {
        var converter = new DocCommentConverter(formattingService, cancellationToken);

        return converter.Visit(node);
    }

    private DocCommentConverter(IDocumentationCommentFormattingService formattingService, CancellationToken cancellationToken)
        : base(visitIntoStructuredTrivia: false)
    {
        _formattingService = formattingService;
        _cancellationToken = cancellationToken;
    }

    public override SyntaxNode Visit(SyntaxNode node)
    {
        _cancellationToken.ThrowIfCancellationRequested();

        if (node == null)
        {
            return node;
        }

        // Process children first
        node = base.Visit(node);

        // Check the leading trivia for doc comments.
        if (node.GetLeadingTrivia().Any(SyntaxKind.SingleLineDocumentationCommentTrivia))
        {
            var newLeadingTrivia = new List<SyntaxTrivia>();

            foreach (var trivia in node.GetLeadingTrivia())
            {
                if (trivia.Kind() == SyntaxKind.SingleLineDocumentationCommentTrivia)
                {
                    var structuredTrivia = (DocumentationCommentTriviaSyntax)trivia.GetStructure();
                    var commentLines = ConvertDocCommentToRegularComment(structuredTrivia).ToSyntaxTriviaList();

                    if (commentLines.Count > 0)
                    {
                        newLeadingTrivia.Add(SyntaxFactory.Comment("//"));
                        newLeadingTrivia.Add(SyntaxFactory.ElasticCarriageReturnLineFeed);

                        newLeadingTrivia.AddRange(commentLines);
                    }
                }
                else
                {
                    newLeadingTrivia.Add(trivia);
                }
            }

            node = node.WithLeadingTrivia(newLeadingTrivia);
        }

        return node;
    }

    private IEnumerable<SyntaxTrivia> ConvertDocCommentToRegularComment(DocumentationCommentTriviaSyntax structuredTrivia)
    {
        var xmlFragment = DocumentationCommentUtilities.ExtractXMLFragment(structuredTrivia.ToFullString(), "///");

        var docComment = DocumentationComment.FromXmlFragment(xmlFragment);

        var commentLines = AbstractMetadataAsSourceService.DocCommentFormatter.Format(_formattingService, docComment);

        foreach (var line in commentLines)
        {
            if (!string.IsNullOrWhiteSpace(line))
            {
                yield return SyntaxFactory.Comment("// " + line);
            }
            else
            {
                yield return SyntaxFactory.Comment("//");
            }

            yield return SyntaxFactory.ElasticCarriageReturnLineFeed;
        }
    }
}
