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 int getPriority() {
		return 10;
	}

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

	private State state = State.INITIAL;

	@Override
	public String getResponse(final String challenge) throws AuthenticationException {
		switch (state) {
			case INITIAL:
				state = State.RESPONSE_SENT;
				final String encodedResponse;
				try {
					final Tokenizer tokenizer = new Tokenizer(Base64.decode(challenge, Base64.DEFAULT));
					String nonce = "";
					for (final String token : tokenizer) {
						final String[] parts = token.split("=", 2);
						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) {
					throw new AuthenticationException(e);
				}

				return encodedResponse;
			case RESPONSE_SENT:
				state = State.VALID_SERVER_RESPONSE;
				break;
			case VALID_SERVER_RESPONSE:
				if (challenge==null) {
					return null; //everything is fine
				}
			default:
				throw new InvalidStateException(state);
		}
		return null;
	}
}