/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 */

package org.apache.ahc.auth;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.StringTokenizer;
import java.util.ArrayList;
import java.util.List;

import org.apache.ahc.util.EncodingUtil;
import org.apache.ahc.util.AsyncHttpClientException;
import org.apache.ahc.util.NameValuePair;
import org.apache.ahc.util.ParameterFormatter;
import org.apache.ahc.codec.HttpRequestMessage;
import org.slf4j.LoggerFactory;
import org.slf4j.Logger;

public class DigestScheme extends RFC2617Scheme {

    /** Log object for this class. */
    private static final Logger LOG = LoggerFactory.getLogger(DigestScheme.class);

    /**
     * Hexa values used when creating 32 character long digest in HTTP DigestScheme
     * in case of authentication.
     *
     * @see #encode(byte[])
     */
    private static final char[] HEXADECIMAL = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
        'e', 'f'
    };

    /** Whether the digest authentication process is complete */
    private boolean complete;

    //TODO: supply a real nonce-count, currently a server will interprete a repeated request as a replay
    private static final String NC = "00000001"; //nonce-count is always 1
    private static final int QOP_MISSING = 0;
    private static final int QOP_AUTH_INT = 1;
    private static final int QOP_AUTH = 2;

    private int qopVariant = QOP_MISSING;
    private String cnonce;

    private final ParameterFormatter formatter;
    /**
     * Default constructor for the digest authetication scheme.
     *
     * @since 3.0
     */
    public DigestScheme() {
        super();
        this.complete = false;
        this.formatter = new ParameterFormatter();
    }

    /**
     * Processes the Digest challenge.
     *
     * @param challenge the challenge string
     *
     * @throws MalformedChallengeException is thrown if the authentication challenge
     * is malformed
     *
     * @since 3.0
     */
    public void processChallenge(final String challenge)
      throws MalformedChallengeException {
        super.processChallenge(challenge);

        if (getParameter("realm") == null) {
            throw new MalformedChallengeException("missing realm in challange");
        }
        if (getParameter("nonce") == null) {
            throw new MalformedChallengeException("missing nonce in challange");
        }

        boolean unsupportedQop = false;
        // qop parsing
        String qop = getParameter("qop");
        if (qop != null) {
            StringTokenizer tok = new StringTokenizer(qop,",");
            while (tok.hasMoreTokens()) {
                String variant = tok.nextToken().trim();
                if (variant.equals("auth")) {
                    qopVariant = QOP_AUTH;
                    break; //that's our favourite, because auth-int is unsupported
                } else if (variant.equals("auth-int")) {
                    qopVariant = QOP_AUTH_INT;
                } else {
                    unsupportedQop = true;
                    LOG.warn("Unsupported qop detected: "+ variant);
                }
            }
        }

        if (unsupportedQop && (qopVariant == QOP_MISSING)) {
            throw new MalformedChallengeException("None of the qop methods is supported");
        }

        cnonce = createCnonce();
        this.complete = true;
    }

    /**
     * Tests if the Digest authentication process has been completed.
     *
     * @return <tt>true</tt> if Digest authorization has been processed,
     *   <tt>false</tt> otherwise.
     *
     * @since 3.0
     */
    public boolean isComplete() {
        String s = getParameter("stale");
        if ("true".equalsIgnoreCase(s)) {
            return false;
        } else {
            return this.complete;
        }
    }

    /**
     * Returns textual designation of the digest authentication scheme.
     *
     * @return <code>digest</code>
     */
    public String getSchemeName() {
        return "digest";
    }

    /**
     * Returns <tt>false</tt>. Digest authentication scheme is request based.
     *
     * @return <tt>false</tt>.
     *
     * @since 3.0
     */
    public boolean isConnectionBased() {
        return false;
    }

    /**
     * Produces a digest authorization string for the given set of
     * {@link Credentials}, method name and URI.
     *
     * @param credentials A set of credentials to be used for athentication
     * @param request The request being authenticated
     *
     * @throws InvalidCredentialsException if authentication credentials
     *         are not valid or not applicable for this authentication scheme
     * @throws AuthenticationException if authorization string cannot
     *   be generated due to an authentication failure
     *
     * @return a digest authorization string
     *
     */
    public String authenticate(Credentials credentials, HttpRequestMessage request)
    throws AuthenticationException {

        LOG.trace("enter DigestScheme.authenticate(Credentials, HttpMethod)");

        UsernamePasswordCredentials usernamepassword = null;
        try {
            usernamepassword = (UsernamePasswordCredentials) credentials;
        } catch (ClassCastException e) {
            throw new InvalidCredentialsException(
                    "Credentials cannot be used for digest authentication: "
                    + credentials.getClass().getName());
        }
        getParameters().put("methodname", request.getRequestMethod());
        StringBuffer buffer = new StringBuffer(request.getPath());
        String query = request.getUrl().getQuery();
        if (query != null) {
            if (query.indexOf("?") != 0) {
                buffer.append("?");
            }
            buffer.append(request.getQuery());
        }
        getParameters().put("uri", buffer.toString());
        String charset = getParameter("charset");
        if (charset == null) {
            getParameters().put("charset", request.getCredentialCharset());
        }
        String digest = createDigest(
            usernamepassword.getUserName(),
            usernamepassword.getPassword());
        return "Digest " + createDigestHeader(usernamepassword.getUserName(),
                digest);
    }

    /**
     * Creates an MD5 response digest.
     *
     * @param uname Username
     * @param pwd Password
     *
     * @return The created digest as string. This will be the response tag's
     *         value in the Authentication HTTP header.
     * @throws AuthenticationException when MD5 is an unsupported algorithm
     */
    private String createDigest(final String uname, final String pwd) throws AuthenticationException {

        LOG.trace("enter DigestScheme.createDigest(String, String, Map)");

        final String digAlg = "MD5";

        // Collecting required tokens
        String uri = getParameter("uri");
        String realm = getParameter("realm");
        String nonce = getParameter("nonce");
        String qop = getParameter("qop");
        String method = getParameter("methodname");
        String algorithm = getParameter("algorithm");
        // If an algorithm is not specified, default to MD5.
        if (algorithm == null) {
            algorithm = "MD5";
        }
        // If an charset is not specified, default to ISO-8859-1.
        String charset = getParameter("charset");
        if (charset == null) {
            charset = "ISO-8859-1";
        }

        if (qopVariant == QOP_AUTH_INT) {
            LOG.warn("qop=auth-int is not supported");
            throw new AuthenticationException(
                "Unsupported qop in HTTP Digest authentication");
        }

        MessageDigest md5Helper;

        try {
            md5Helper = MessageDigest.getInstance(digAlg);
        } catch (Exception e) {
            throw new AuthenticationException(
              "Unsupported algorithm in HTTP Digest authentication: "
               + digAlg);
        }

        // 3.2.2.2: Calculating digest
        StringBuffer tmp = new StringBuffer(uname.length() + realm.length() + pwd.length() + 2);
        tmp.append(uname);
        tmp.append(':');
        tmp.append(realm);
        tmp.append(':');
        tmp.append(pwd);
        // unq(username-value) ":" unq(realm-value) ":" passwd
        String a1 = tmp.toString();
        //a1 is suitable for MD5 algorithm
        if(algorithm.equals("MD5-sess")) {
            // H( unq(username-value) ":" unq(realm-value) ":" passwd )
            //      ":" unq(nonce-value)
            //      ":" unq(cnonce-value)

            String tmp2=encode(md5Helper.digest(EncodingUtil.getBytes(a1, charset)));
            StringBuffer tmp3 = new StringBuffer(tmp2.length() + nonce.length() + cnonce.length() + 2);
            tmp3.append(tmp2);
            tmp3.append(':');
            tmp3.append(nonce);
            tmp3.append(':');
            tmp3.append(cnonce);
            a1 = tmp3.toString();
        } else if(!algorithm.equals("MD5")) {
            LOG.warn("Unhandled algorithm " + algorithm + " requested");
        }
        String md5a1 = encode(md5Helper.digest(EncodingUtil.getBytes(a1, charset)));

        String a2 = null;
        if (qopVariant == QOP_AUTH_INT) {
            LOG.error("Unhandled qop auth-int");
            //we do not have access to the entity-body or its hash
            //TODO: add Method ":" digest-uri-value ":" H(entity-body)
        } else {
            a2 = method + ":" + uri;
        }
        String md5a2 = encode(md5Helper.digest(EncodingUtil.getAsciiBytes(a2)));

        // 3.2.2.1
        String serverDigestValue;
        if (qopVariant == QOP_MISSING) {
            LOG.debug("Using null qop method");
            StringBuffer tmp2 = new StringBuffer(md5a1.length() + nonce.length() + md5a2.length());
            tmp2.append(md5a1);
            tmp2.append(':');
            tmp2.append(nonce);
            tmp2.append(':');
            tmp2.append(md5a2);
            serverDigestValue = tmp2.toString();
        } else {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Using qop method " + qop);
            }
            String qopOption = getQopVariantString();
            StringBuffer tmp2 = new StringBuffer(md5a1.length() + nonce.length()
                + NC.length() + cnonce.length() + qopOption.length() + md5a2.length() + 5);
            tmp2.append(md5a1);
            tmp2.append(':');
            tmp2.append(nonce);
            tmp2.append(':');
            tmp2.append(NC);
            tmp2.append(':');
            tmp2.append(cnonce);
            tmp2.append(':');
            tmp2.append(qopOption);
            tmp2.append(':');
            tmp2.append(md5a2);
            serverDigestValue = tmp2.toString();
        }

        String serverDigest =
            encode(md5Helper.digest(EncodingUtil.getAsciiBytes(serverDigestValue)));

        return serverDigest;
    }

    /**
     * Creates digest-response header as defined in RFC2617.
     *
     * @param uname Username
     * @param digest The response tag's value as String.
     *
     * @return The digest-response as String.
     */
    private String createDigestHeader(final String uname, final String digest)
        throws AuthenticationException {

        LOG.trace("enter DigestScheme.createDigestHeader(String, Map, "
            + "String)");

        String uri = getParameter("uri");
        String realm = getParameter("realm");
        String nonce = getParameter("nonce");
        String opaque = getParameter("opaque");
        String response = digest;
        String algorithm = getParameter("algorithm");

        List params = new ArrayList(20);
        params.add(new NameValuePair("username", uname));
        params.add(new NameValuePair("realm", realm));
        params.add(new NameValuePair("nonce", nonce));
        params.add(new NameValuePair("uri", uri));
        params.add(new NameValuePair("response", response));

        if (qopVariant != QOP_MISSING) {
            params.add(new NameValuePair("qop", getQopVariantString()));
            params.add(new NameValuePair("nc", NC));
            params.add(new NameValuePair("cnonce", this.cnonce));
        }
        if (algorithm != null) {
            params.add(new NameValuePair("algorithm", algorithm));
        }
        if (opaque != null) {
            params.add(new NameValuePair("opaque", opaque));
        }

        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < params.size(); i++) {
            NameValuePair param = (NameValuePair) params.get(i);
            if (i > 0) {
                buffer.append(", ");
            }
            boolean noQuotes = "nc".equals(param.getName()) ||
                               "qop".equals(param.getName());
            this.formatter.setAlwaysUseQuotes(!noQuotes);
            this.formatter.format(buffer, param);
        }
        return buffer.toString();
    }

    private String getQopVariantString() {
        String qopOption;
        if (qopVariant == QOP_AUTH_INT) {
            qopOption = "auth-int";
        } else {
            qopOption = "auth";
        }
        return qopOption;
    }

    /**
     * Encodes the 128 bit (16 bytes) MD5 digest into a 32 characters long
     * <CODE>String</CODE> according to RFC 2617.
     *
     * @param binaryData array containing the digest
     * @return encoded MD5, or <CODE>null</CODE> if encoding failed
     */
    private static String encode(byte[] binaryData) {
        LOG.trace("enter DigestScheme.encode(byte[])");

        if (binaryData.length != 16) {
            return null;
        }

        char[] buffer = new char[32];
        for (int i = 0; i < 16; i++) {
            int low = (int) (binaryData[i] & 0x0f);
            int high = (int) ((binaryData[i] & 0xf0) >> 4);
            buffer[i * 2] = HEXADECIMAL[high];
            buffer[(i * 2) + 1] = HEXADECIMAL[low];
        }

        return new String(buffer);
    }


    /**
     * Creates a random cnonce value based on the current time.
     *
     * @return The cnonce value as String.
     * @throws AsyncHttpClientException if MD5 algorithm is not supported.
     */
    public static String createCnonce() {
        LOG.trace("enter DigestScheme.createCnonce()");

        String cnonce;
        final String digAlg = "MD5";
        MessageDigest md5Helper;

        try {
            md5Helper = MessageDigest.getInstance(digAlg);
        } catch (NoSuchAlgorithmException e) {
            throw new AsyncHttpClientException(
              "Unsupported algorithm in HTTP Digest authentication: "
               + digAlg);
        }

        cnonce = Long.toString(System.currentTimeMillis());
        cnonce = encode(md5Helper.digest(EncodingUtil.getAsciiBytes(cnonce)));

        return cnonce;
    }
}