using System;
using System.Collections.Generic;
using System.Text;


using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.X509;
using System.Collections;
using Org.BouncyCastle.Pkcs;
using iTextSharp.text.pdf;
using System.IO;
using iTextSharp.text.xml.xmp;
using Org.BouncyCastle.Security;
using System.Security.Cryptography.X509Certificates;

namespace Sleis.Pdf
{
    public class PdfSignatureMaker
    {
        public SimpleCert Cert { get; set; }

        public void Init()
        {
            if (Cert == null)
            {
                throw new ArgumentNullException("cert");
            }
        }

        public string Sign(string input, PdfSignatureArgs args)
        {
            if (String.IsNullOrEmpty(input) || !File.Exists(input))
            {
                throw new FileNotFoundException("Input does not exist");
            }

            string output = Path.Combine(Path.GetDirectoryName(input),
                                         String.Format("{0}-Signed.pdf", 
                                         Path.GetFileNameWithoutExtension(input)));

            PdfReader reader = new PdfReader(input);
            FileStream fs = new FileStream(output, FileMode.Create, FileAccess.Write);
            PdfStamper st = PdfStamper.CreateSignature(reader, fs, '\0', null, true);

            st.MoreInfo = args.GetAllArgs();
            st.XmpMetadata = args.GetStreamedArgs();

            PdfSignatureAppearance sap = st.SignatureAppearance;
            sap.SetCrypto(null, Cert.Chain, null, PdfSignatureAppearance.WINCER_SIGNED);
            sap.Reason = args.Reason;
            sap.Contact = args.Contact;
            sap.Location = args.Locality;
            sap.CertificationLevel = PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED;
            sap.Acro6Layers = true;
            sap.Layer2Text = String.Format(
                "SLEIS signed on: {0}. See document signature for details.", 
                DateTime.Now.ToString());

            iTextSharp.text.Rectangle rect = st.Reader.GetPageSize(1);
            sap.Image = iTextSharp.text.Image.GetInstance(args.Display.Background.File.FullName);
            sap.SignDate = DateTime.Now;

            sap.SetVisibleSignature(new iTextSharp.text.Rectangle(args.Display.Location.X,
                                                                  args.Display.Location.Y,
                                                                  args.Display.Location.X + args.Display.Size.Width,
                                                                  args.Display.Location.Y + args.Display.Size.Height), 1, null);


            PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, new PdfName("adbe.pkcs7.detached"));
            dic.Reason = sap.Reason;
            dic.Location = sap.Location;
            dic.Contact = sap.Contact;
            dic.Date = new PdfDate(sap.SignDate);
            sap.CryptoDictionary = dic;

            int contentEstimated = 15000;
            // Preallocate excluded byte-range for the signature content (hex encoded)
            Dictionary<PdfName, int> exc = new Dictionary<PdfName, int>();
            exc[PdfName.CONTENTS] = contentEstimated * 2 + 2;
            sap.PreClose(exc);

            PdfPKCS7 sgn = new PdfPKCS7(Cert.Akp, Cert.Chain, null, "SHA1", false);
            IDigest messageDigest = DigestUtilities.GetDigest("SHA1");
            Stream data = sap.RangeStream;
            byte[] buf = new byte[8192];
            int n;
            while ((n = data.Read(buf, 0, buf.Length)) > 0)
            {
                messageDigest.BlockUpdate(buf, 0, n);
            }
            byte[] hash = new byte[messageDigest.GetDigestSize()];
            messageDigest.DoFinal(hash, 0);
            DateTime cal = DateTime.Now;
            byte[] ocsp = null;
            if (Cert.Chain.Length >= 2)
            {
                String url = PdfPKCS7.GetOCSPURL(Cert.Chain[0]);
                if (url != null && url.Length > 0)
                {
                    ocsp = new OcspClientBouncyCastle(Cert.Chain[0], Cert.Chain[1], url).GetEncoded();
                }
            }
            byte[] sh = sgn.GetAuthenticatedAttributeBytes(hash, cal, ocsp);
            sgn.Update(sh, 0, sh.Length);

            byte[] paddedSig = new byte[contentEstimated];
            byte[] encodedSig = sgn.GetEncodedPKCS7(hash, cal);
            System.Array.Copy(encodedSig, 0, paddedSig, 0, encodedSig.Length);
            if (contentEstimated + 2 < encodedSig.Length)
            {
                throw new Exception("Not enough space for signature");
            }

            PdfDictionary dic2 = new PdfDictionary();
            dic2.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));
            sap.Close(dic2);

            return output;
        }

    }
}