using DevExpress.Pdf;
using DevExpress.Office.DigitalSignatures;
using DevExpress.Office.Tsp;

async Task<PdfSignatureAppearance> BuildSignatureAppearance(PdfSignatureAppearanceType signatureAppearanceType, string dateTimeFormat,
    bool rightToLeftTextDirection, bool showDate, bool showDistinguishedName, bool showLabels, bool showLocation, bool showName,
    bool showReason, Stream signatureBackgroundImageStream = null, Stream signatureImageStream = null) {
    var appearance = new PdfSignatureAppearance() {
        AppearanceType = signatureAppearanceType,
        ApplicationVersion = "v1.0",
        DateTimeFormat = dateTimeFormat,
        RightToLeftTextDirection = rightToLeftTextDirection,
        ShowDate = showDate,
        ShowDistinguishedName = showDistinguishedName,
        ShowLabels = showLabels,
        ShowLocation = showLocation,
        ShowName = showName,
        ShowReason = showReason,
        SignatureDetailsFont = new PdfSignatureFontSettings("Calibri"),
        SignatureNameFont = new PdfSignatureFontSettings("Calibri")
    };

    if(signatureBackgroundImageStream != null)
        appearance.SetBackgroundImageData(signatureBackgroundImageStream);
    if(signatureAppearanceType == PdfSignatureAppearanceType.Image && signatureImageStream != null)
        appearance.SetImageData(signatureImageStream);

    return appearance;
}

async Task<PdfSignatureFieldInfo> CreateSignatureField(PdfDocumentProcessor processor) {
    var page = processor.Document.Pages.Last();

    var cropBox = page.CropBox;
    var signatureFieldBounds = new PdfRectangle(
        cropBox.Width / 3,
        cropBox.Height / 10,
        cropBox.Width / 3 * 2,
        cropBox.Height / 10 * 2);

    var signatureFieldInfo = new PdfSignatureFieldInfo(processor.Document.Pages.Count);
    signatureFieldInfo.Name = "SignatureField";
    signatureFieldInfo.SignatureBounds = signatureFieldBounds;

    return signatureFieldInfo;
}

async Task<MemoryStream> Sign(Stream documentStream, Stream certificateStream, Stream signatureImageStream,
    HashAlgorithmType certificateHashAlgorithm, HashAlgorithmType tsaHashAlgorithm, PdfSignatureAppearance signatureAppearance = null) {
    using var processor = new PdfDocumentProcessor();

    processor.LoadDocument(documentStream);
    var signatureFieldInfo = await CreateSignatureField(processor);

    using var documentSigner = new PdfDocumentSigner(documentStream);

    var tsaClient = new TsaClient(
        new Uri("https://www.freetsa.org/tsr", UriKind.Absolute),
        tsaHashAlgorithm);
    var pkcs7Signer = new Pkcs7Signer(certificateStream, "dxdemo", certificateHashAlgorithm, tsaClient);

    var signatureBuilder = new PdfSignatureBuilder(pkcs7Signer, signatureFieldInfo) {
        ApplicationName = "DevExpress Office File API Demo",
        CertificationLevel = PdfCertificationLevel.NoCertification,
        ContactInfo = "support@devexpress.com",
        Location = "Area 51",
        Name = "John Doe",
        Reason = "Demo",
        SigningTime = DateTime.UtcNow
    };

    if(signatureAppearance != null)
        signatureBuilder.SetSignatureAppearance(signatureAppearance);
    else if(signatureImageStream != null)
        signatureBuilder.SetImageData(signatureImageStream);

    var outputStream = new MemoryStream();
    documentSigner.SaveDocument(outputStream, signatureBuilder);
    outputStream.Position = 0;

    return outputStream;
}