package eu.siacs.conversations.crypto.sasl;

import android.util.Base64;

import java.math.BigInteger;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import eu.siacs.conversations.entities.Account;
import eu.siacs.conversations.utils.CryptoHelper;
import eu.siacs.conversations.xml.TagWriter;

public class DigestMd5 extends SaslMechanism {
    public DigestMd5(final TagWriter tagWriter, final Account account, final SecureRandom rng) {
        super(tagWriter, account, rng);
    }

    @Override
    public String getMechanism() {
        return "DIGEST-MD5";
    }

    @Override
    public String getResponse(final String challenge) {
        final String encodedResponse;
        try {
            final String[] challengeParts = new String(Base64.decode(challenge,
                    Base64.DEFAULT)).split(",");
            String nonce = "";
            for (int i = 0; i < challengeParts.length; ++i) {
                String[] parts = challengeParts[i].split("=");
                if (parts[0].equals("nonce")) {
                    nonce = parts[1].replace("\"", "");
                } else if (parts[0].equals("rspauth")) {
                    return "";
                }
            }
            final String digestUri = "xmpp/" + account.getServer();
            final String nonceCount = "00000001";
            final String x = account.getUsername() + ":" + account.getServer() + ":"
                    + account.getPassword();
            final MessageDigest md = MessageDigest.getInstance("MD5");
            final byte[] y = md.digest(x.getBytes(Charset.defaultCharset()));
            final String cNonce = new BigInteger(100, rng).toString(32);
            final byte[] a1 = CryptoHelper.concatenateByteArrays(y,
                    (":" + nonce + ":" + cNonce).getBytes(Charset
                            .defaultCharset()));
            final String a2 = "AUTHENTICATE:" + digestUri;
            final String ha1 = CryptoHelper.bytesToHex(md.digest(a1));
            final String ha2 = CryptoHelper.bytesToHex(md.digest(a2.getBytes(Charset
                    .defaultCharset())));
            final String kd = ha1 + ":" + nonce + ":" + nonceCount + ":" + cNonce
                    + ":auth:" + ha2;
            final String response = CryptoHelper.bytesToHex(md.digest(kd.getBytes(Charset
                    .defaultCharset())));
            final String saslString = "username=\"" + account.getUsername()
                    + "\",realm=\"" + account.getServer() + "\",nonce=\""
                    + nonce + "\",cnonce=\"" + cNonce + "\",nc=" + nonceCount
                    + ",qop=auth,digest-uri=\"" + digestUri + "\",response="
                    + response + ",charset=utf-8";
            encodedResponse = Base64.encodeToString(
                    saslString.getBytes(Charset.defaultCharset()),
                    Base64.NO_WRAP);
        } catch (final NoSuchAlgorithmException e) {
            return "";
        }

        return encodedResponse;
    }
}