using System.IO;
using iText.Kernel.Pdf;
using iText.Kernel.Utils;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using static EnvelopeGenerator.Jobs.FinalizeDocument.FinalizeDocumentExceptions;

namespace EnvelopeGenerator.Jobs.FinalizeDocument;

public class PDFMerger
{
    private readonly ILogger<PDFMerger> _logger;

    public PDFMerger() : this(NullLogger<PDFMerger>.Instance)
    {
    }

    public PDFMerger(ILogger<PDFMerger> logger)
    {
        _logger = logger;
    }

    public byte[] MergeDocuments(byte[] document, byte[] report)
    {
        try
        {
            using var finalStream = new MemoryStream();
            using var documentReader = new PdfReader(new MemoryStream(document));
            using var reportReader = new PdfReader(new MemoryStream(report));
            using var writer = new PdfWriter(finalStream);
            using var targetDoc = new PdfDocument(documentReader, writer);
            using var reportDoc = new PdfDocument(reportReader);

            var merger = new PdfMerger(targetDoc);
            merger.Merge(reportDoc, 1, reportDoc.GetNumberOfPages());

            targetDoc.Close();
            return finalStream.ToArray();
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to merge PDF documents");
            throw new MergeDocumentException("Documents could not be merged", ex);
        }
    }
}