Creating a Sales Copilot - Working with PDF files

internal sealed class PdfPigReader : IngestionDocumentReader
{
    public override Task<IngestionDocument> ReadAsync(Stream source, string identifier, 
        string mediaType, CancellationToken cancellationToken = default)
    {
        using var pdf = PdfDocument.Open(source);
        var document = new IngestionDocument(identifier);
        foreach (var page in pdf.GetPages())
        {
            document.Sections.Add(GetPageSection(page));
        }
        return Task.FromResult(document);
    }

    private static IngestionDocumentSection GetPageSection(Page pdfPage)
    {
        var section = new IngestionDocumentSection
        {
            PageNumber = pdfPage.Number,
        };

        var letters = pdfPage.Letters;
        var words = NearestNeighbourWordExtractor.Instance.GetWords(letters);

        foreach (var textBlock in DocstrumBoundingBoxes.Instance.GetBlocks(words))
        {
            section.Elements.Add(new IngestionDocumentParagraph(textBlock.Text)
            {
                Text = textBlock.Text
            });
        }

        return section;
    }
}

internal sealed class DocumentReader(DirectoryInfo rootDirectory) : IngestionDocumentReader
{
    private readonly MarkdownReader _markdownReader = new();
    private readonly PdfPigReader _pdfReader = new();
    private readonly WordReader _wordReader = new();
    private readonly PowerPointReader _powerPointReader = new();
    public override Task<IngestionDocument> ReadAsync(Stream source, string identifier,
        string mediaType, CancellationToken cancellationToken = default)
    => mediaType switch
    {
        "application/pdf" => _pdfReader.ReadAsync(source, identifier, mediaType, cancellationToken),
        "text/markdown" => _markdownReader.ReadAsync(source, identifier, mediaType, cancellationToken),
        "application/vnd.openxmlformats-officedocument.wordprocessingml.document" =>
            _wordReader.ReadAsync(source, identifier, mediaType, cancellationToken),
        "application/vnd.openxmlformats-officedocument.presentationml.presentation" =>
            _powerPointReader.ReadAsync(source, identifier, mediaType, cancellationToken),
        _ => throw new InvalidOperationException($"Unsupported media type '{mediaType}'"),
    };
    public override Task<IngestionDocument> ReadAsync(FileInfo source, string identifier, string? mediaType = null, CancellationToken cancellationToken = default)
    {
        if (Path.IsPathFullyQualified(identifier))
        {
            // Normalize the identifier to its relative path
            identifier = Path.GetRelativePath(rootDirectory.FullName, identifier);
        }

        mediaType = GetCustomMediaType(source) ?? mediaType;
        return base.ReadAsync(source, identifier, mediaType, cancellationToken);
    }

    private static string? GetCustomMediaType(FileInfo source)
        => source.Extension switch
        {
            ".md" => "text/markdown",
            _ => null
        };
}