using System.Text;
using DevExpress.Pdf;

Stream ValidateSignatures(Stream documentStream, bool validateClrOcsp, bool validateLtv) {
    var outputStream = new MemoryStream();
    var streamWriter = new StreamWriter(outputStream);

    using var documentSigner = new PdfDocumentSigner(documentStream);

    var signatureInfo = documentSigner.GetSignatureInfo();

    streamWriter.WriteLine($"Found {signatureInfo.Count} signatures");
    streamWriter.WriteLine();

    foreach(var signature in signatureInfo)
        ValidateSignature(documentSigner, signature, signatureInfo.IndexOf(signature), validateClrOcsp, streamWriter);

    if(validateLtv)
        ValidateLtv(documentSigner, streamWriter);

    streamWriter.Flush();
    outputStream.Position = 0;
    return outputStream;
}

void ValidateSignature(PdfDocumentSigner documentSigner, PdfSignatureInfo signature, int signatureIndex, bool validateClrOcsp, StreamWriter streamWriter) {
    streamWriter.WriteLine($"Signature #{signatureIndex}");
    streamWriter.WriteLine($"===");
    streamWriter.WriteLine($"Field Name : {signature.FieldName}");
    streamWriter.WriteLine($"Signer name : {signature.SignerName}");

    var pkcs7 = documentSigner.GetPdfPkcs7Signature(signature.FieldName);
    streamWriter.WriteLine($"Valid : {pkcs7.VerifySignature()}");

    var certificate = pkcs7.GetSignatureCertificate();
    streamWriter.WriteLine($"Certificate Issuer : {certificate.IssuerName.Name}");
    streamWriter.WriteLine($"Certificate Valid : {certificate.Verify()}");

    var timestampDate = pkcs7.GetTimeStampDate();
    streamWriter.WriteLine($"Has Timestamp : {timestampDate.HasValue}");
    if(timestampDate.HasValue) {
        streamWriter.WriteLine($"Timestamp : {timestampDate}");
        streamWriter.WriteLine($"Timestamp Valid : {pkcs7.VerifyTimeStamp()}");
        streamWriter.WriteLine($"Document Timestamp : {pkcs7.IsDocumentTimeStamp}");
    }

    if(validateClrOcsp)
        ValidateClrOscp(pkcs7, streamWriter);

    streamWriter.WriteLine();
}

void ValidateClrOscp(PdfPkcs7Signature pkcs7, StreamWriter streamWriter) {
    streamWriter.WriteLine();
    streamWriter.WriteLine($"CRL/OCSP Information");
    streamWriter.WriteLine($"CRL Embedded : {pkcs7.CrlList != null}");
    streamWriter.WriteLine($"OCSP Embedded : {pkcs7.OcspList != null}");

    var crlOcspOptions = new PdfRevocationVerificationOptions() {
        TryFetchCrlOnline = pkcs7.CrlList == null,
        TryFetchOcspOnline = pkcs7.OcspList == null,
    };

    var crlOcspResult = pkcs7.CheckCertificateRevocation(DateTime.UtcNow, crlOcspOptions);

    streamWriter.WriteLine($"Certificate Revoked : {crlOcspResult.IsCrlRevoked}");
    if(crlOcspResult.IsCrlRevoked)
        streamWriter.WriteLine($"CRL Found Online : {crlOcspResult.IsCrlFoundOnline}");
    streamWriter.WriteLine($"OCSP Response Status : {crlOcspResult.OcspRevocationStatus}");
    if(crlOcspResult.OcspRevocationStatus != PdfOcspRevocationStatus.None)
        streamWriter.WriteLine($"OCSP found online : {crlOcspResult.IsOcspFoundOnline}");
}

void ValidateLtv(PdfDocumentSigner documentSigner, StreamWriter streamWriter) {
    streamWriter.WriteLine($"===");
    streamWriter.WriteLine($"LTV Information");
    streamWriter.WriteLine($"===");
    streamWriter.WriteLine();

    var ltvOptions = new PdfLtvOptions() {
        TryFetchCrlOnline = true,
        TryFetchOcspOnline = true,
        VerifyEntireCertificateChain = true,
    };

    var ltvResult = documentSigner.VerifyLtv(ltvOptions);
    foreach(var entry in ltvResult) {
        streamWriter.WriteLine($"Signature Name : {entry.SignatureFieldName}");
        streamWriter.WriteLine($"Certificates In Chain : {entry.CertificateRevocationResults.Count}");

        foreach(var revocation in entry.CertificateRevocationResults) {
            streamWriter.WriteLine($"Certificate {revocation.Key.Subject}");
            streamWriter.WriteLine($"Certificate revoked : {revocation.Value.IsCrlRevoked}");
            if(revocation.Value.IsCrlRevoked)
                streamWriter.WriteLine($"CRL found online : {revocation.Value.IsCrlFoundOnline}");
            streamWriter.WriteLine($"OCSP Response Status : {revocation.Value.OcspRevocationStatus}");
            if(revocation.Value.OcspRevocationStatus != PdfOcspRevocationStatus.None)
                streamWriter.WriteLine($"OCSP found online : {revocation.Value.IsOcspFoundOnline}");
            streamWriter.WriteLine();
        }
    }

    streamWriter.WriteLine();
}