/*
 *  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.
 */

/**
* @author Alexander Y. Kleymenov
* @version $Revision$
*/

package org.apache.harmony.security.provider.cert;

import java.io.IOException;
import java.io.InputStream;
import java.security.cert.CertPath;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

import org.apache.harmony.security.asn1.ASN1Any;
import org.apache.harmony.security.asn1.ASN1Explicit;
import org.apache.harmony.security.asn1.ASN1Implicit;
import org.apache.harmony.security.asn1.ASN1Oid;
import org.apache.harmony.security.asn1.ASN1Sequence;
import org.apache.harmony.security.asn1.ASN1SequenceOf;
import org.apache.harmony.security.asn1.ASN1Type;
import org.apache.harmony.security.asn1.BerInputStream;
import org.apache.harmony.security.pkcs7.ContentInfo;
import org.apache.harmony.security.pkcs7.SignedData;
import org.apache.harmony.security.x509.Certificate;

/**
 * This class is an implementation of X.509 CertPath. This implementation
 * provides ability to create the instance of X.509 Certification Path
 * by several means:<br>
 *
 * &nbsp;  1. It can be created over the list of X.509 certificates
 * (implementations of X509Certificate class) provided in constructor.<br>
 *
 * &nbsp;  2. It can be created by means of <code>getInstance</code> methods
 * on the base of the following ASN.1 DER encoded forms:<br>
 *
 * &nbsp;&nbsp;  - PkiPath as defined in
 * ITU-T Recommendation X.509(2000) Corrigendum 1(2001)
 * (can be seen at
 * ftp://ftp.bull.com/pub/OSIdirectory/DefectResolution/TechnicalCorrigenda/ApprovedTechnicalCorrigendaToX.509/8%7CX.509-TC1(4th).pdf)
 * <br>
 * &nbsp;&nbsp;  - PKCS #7 SignedData object provided in the form of
 * ContentInfo structure. CertPath object is generated on the base of
 * certificates presented in <code>certificates</code> field of the SignedData
 * object which in its turn is retrieved from ContentInfo structure.
 * (see http://www.ietf.org/rfc/rfc2315.txt
 * for more info on PKCS #7)
 * <br>
 * &nbsp;
 */
public class X509CertPathImpl extends CertPath {
    /**
     * @serial
     */
    private static final long serialVersionUID = 7989755106209515436L;

    /**
     * Supported encoding types for CerthPath. Used by the various APIs that
     * encode this into bytes such as {@link #getEncoded()}.
     */
    private enum Encoding {
        PKI_PATH("PkiPath"),
        PKCS7("PKCS7");

        private final String apiName;

        Encoding(String apiName) {
            this.apiName = apiName;
        }

        static Encoding findByApiName(String apiName) throws CertificateEncodingException {
            for (Encoding element : values()) {
                if (element.apiName.equals(apiName)) {
                    return element;
                }
            }

            return null;
        }
    }

    /** Unmodifiable list of encodings for the API. */
    static final List<String> encodings = Collections.unmodifiableList(Arrays.asList(new String[] {
            Encoding.PKI_PATH.apiName,
            Encoding.PKCS7.apiName,
    }));

    /** The list of certificates in the order of target toward trust anchor. */
    private final List<X509Certificate> certificates;

    /** PkiPath encoding of the certification path. */
    private byte[] pkiPathEncoding;

    /** PKCS7 encoding of the certification path. */
    private byte[] pkcs7Encoding;

    /**
     * Creates an instance of X.509 CertPath over the specified list of
     * certificates.
     *
     * @throws CertificateException if some of the object in the list is not an
     *             instance of subclass of X509Certificate.
     */
    public X509CertPathImpl(List<? extends java.security.cert.Certificate> certs)
            throws CertificateException {
        super("X.509");

        final int size = certs.size();
        certificates = new ArrayList<X509Certificate>(size);

        for (int i = 0; i < size; i++) {
            final java.security.cert.Certificate cert = certs.get(i);
            if (!(cert instanceof X509Certificate)) {
                throw new CertificateException("Certificate " + i + " is not an X.509 certificate");
            }

            certificates.add((X509Certificate) cert);
        }
    }

    /**
     * Creates an X.509 CertPath over the specified {@code certs}. The
     * {@code certs} should be sorted correctly when calling into the
     * constructor. Additionally, the {@code encodedPath} should match the
     * expected output for the {@code type} of encoding.
     */
    private X509CertPathImpl(List<X509Certificate> certs, Encoding type) {
        super("X.509");

        certificates = certs;
    }

    /**
     * Extract a CertPath from a PKCS#7 {@code contentInfo} object.
     */
    private static X509CertPathImpl getCertPathFromContentInfo(ContentInfo contentInfo)
            throws CertificateException {
        final SignedData sd = contentInfo.getSignedData();
        if (sd == null) {
            throw new CertificateException("Incorrect PKCS7 encoded form: missing signed data");
        }

        List<Certificate> certs = sd.getCertificates();
        if (certs == null) {
            certs = Collections.emptyList();
        }

        final List<X509Certificate> result = new ArrayList<X509Certificate>(certs.size());
        for (Certificate cert : certs) {
            result.add(new X509CertImpl(cert));
        }

        return new X509CertPathImpl(result, Encoding.PKCS7);
    }

    /**
     * Generates certification path object on the base of PkiPath encoded form
     * provided via input stream.
     *
     * @throws CertificateException if some problems occurred during the
     *         decoding.
     */
    public static X509CertPathImpl getInstance(InputStream in) throws CertificateException {
        try {
            return (X509CertPathImpl) ASN1.decode(in);
        } catch (IOException e) {
            throw new CertificateException("Failed to decode CertPath", e);
        }
    }

    /**
     * Generates certification path object on the basis of encoding provided via
     * input stream. The format of provided encoded form is specified by
     * parameter <code>encoding</code>.
     *
     * @throws CertificateException if specified encoding form is not supported,
     *         or some problems occurred during the decoding.
     */
    public static X509CertPathImpl getInstance(InputStream in, String encoding)
            throws CertificateException {
        try {
            final Encoding encType = Encoding.findByApiName(encoding);
            if (encType == null) {
                throw new CertificateException("Unsupported encoding: " + encoding);
            }

            switch (encType) {
                case PKI_PATH:
                    return (X509CertPathImpl) ASN1.decode(in);
                case PKCS7:
                    return getCertPathFromContentInfo((ContentInfo) ContentInfo.ASN1.decode(in));
                default:
                    throw new CertificateException("Unsupported encoding: " + encoding);
            }
        } catch (IOException e) {
            throw new CertificateException("Failed to decode CertPath", e);
        }
    }

    /**
     * Generates certification path object on the base of PkiPath
     * encoded form provided via array of bytes.
     * @throws CertificateException if some problems occurred during
     * the decoding.
     */
    public static X509CertPathImpl getInstance(byte[] in) throws CertificateException {
        try {
            return (X509CertPathImpl) ASN1.decode(in);
        } catch (IOException e) {
            throw new CertificateException("Failed to decode CertPath", e);
        }
    }

    /**
     * Generates certification path object on the base of encoding provided via
     * array of bytes. The format of provided encoded form is specified by
     * parameter {@code encoding}.
     *
     * @throws CertificateException if specified encoding form is not supported,
     *             or some problems occurred during the decoding.
     */
    public static X509CertPathImpl getInstance(byte[] in, String encoding)
            throws CertificateException {
        try {
            final Encoding encType = Encoding.findByApiName(encoding);
            if (encType == null) {
                throw new CertificateException("Unsupported encoding: " + encoding);
            }

            switch (encType) {
                case PKI_PATH:
                    return (X509CertPathImpl) ASN1.decode(in);
                case PKCS7:
                    return getCertPathFromContentInfo((ContentInfo) ContentInfo.ASN1.decode(in));
                default:
                    throw new CertificateException("Unsupported encoding: " + encoding);
            }
        } catch (IOException e) {
            throw new CertificateException("Failed to decode CertPath", e);
        }
    }

    // ---------------------------------------------------------------------
    // ---- java.security.cert.CertPath abstract method implementations ----
    // ---------------------------------------------------------------------

    /**
     * @see java.security.cert.CertPath#getCertificates()
     * method documentation for more info
     */
    @Override
    public List<X509Certificate> getCertificates() {
        return Collections.unmodifiableList(certificates);
    }

    /**
     * Returns in PkiPath format which is our default encoding.
     *
     * @see java.security.cert.CertPath#getEncoded()
     */
    @Override
    public byte[] getEncoded() throws CertificateEncodingException {
        return getEncoded(Encoding.PKI_PATH);
    }

    /**
     * @see #getEncoded(String)
     */
    private byte[] getEncoded(Encoding encoding) throws CertificateEncodingException {
        switch (encoding) {
            case PKI_PATH:
                if (pkiPathEncoding == null) {
                    pkiPathEncoding = ASN1.encode(this);
                }

                return pkiPathEncoding.clone();
            case PKCS7:
                if (pkcs7Encoding == null) {
                    pkcs7Encoding = PKCS7_SIGNED_DATA_OBJECT.encode(this);
                }

                return pkcs7Encoding.clone();
            default:
                throw new CertificateEncodingException("Unsupported encoding: " + encoding);
        }
    }

    /**
     * @see java.security.cert.CertPath#getEncoded(String)
     */
    @Override
    public byte[] getEncoded(String encoding) throws CertificateEncodingException {
        final Encoding encType = Encoding.findByApiName(encoding);
        if (encType == null) {
            throw new CertificateEncodingException("Unsupported encoding: " + encoding);
        }

        return getEncoded(encType);
    }

    /**
     * @see java.security.cert.CertPath#getEncodings()
     * method documentation for more info
     */
    @Override
    public Iterator<String> getEncodings() {
        return encodings.iterator();
    }

    /**
     * ASN.1 DER Encoder/Decoder for PkiPath structure.
     */
    public static final ASN1SequenceOf ASN1 = new ASN1SequenceOf(ASN1Any.getInstance()) {
        /**
         * Builds the instance of X509CertPathImpl on the base of the list of
         * ASN.1 encodings of X.509 certificates provided via PkiPath structure.
         * This method participates in decoding process.
         */
        public Object getDecodedObject(BerInputStream in) throws IOException {
            // retrieve the decoded content
            final List<byte[]> encodedCerts = (List<byte[]>) in.content;

            final int size = encodedCerts.size();
            final List<X509Certificate> certificates = new ArrayList<X509Certificate>(size);

            for (int i = size - 1; i >= 0; i--) {
                // create the X.509 certificate on the base of its encoded form
                // and add it to the list.
                certificates.add(new X509CertImpl((Certificate) Certificate.ASN1
                        .decode(encodedCerts.get(i))));
            }

            // create and return the resulting object
            return new X509CertPathImpl(certificates, Encoding.PKI_PATH);
        }

        /**
         * Returns the Collection of the encoded form of certificates contained
         * in the X509CertPathImpl object to be encoded.
         * This method participates in encoding process.
         */
        public Collection<byte[]> getValues(Object object) {
            // object to be encoded
            final X509CertPathImpl cp = (X509CertPathImpl) object;

            // if it has no certificates in it - create the sequence of size 0
            if (cp.certificates == null) {
                return Collections.emptyList();
            }

            final int size = cp.certificates.size();
            final List<byte[]> encodings = new ArrayList<byte[]>(size);

            try {
                for (int i = size - 1; i >= 0; i--) {
                    // get the encoded form of certificate and place it into the
                    // list to be encoded in PkiPath format
                    encodings.add(cp.certificates.get(i).getEncoded());
                }
            } catch (CertificateEncodingException e) {
                throw new IllegalArgumentException("Encoding error occurred", e);
            }

            return encodings;
        }
    };


    /**
     * Encoder for PKCS#7 SignedData. It is assumed that only certificate field
     * is important all other fields contain pre-calculated encodings.
     */
    private static final ASN1Sequence ASN1_SIGNED_DATA = new ASN1Sequence(
            new ASN1Type[] {
                    // version ,digestAlgorithms, content info
                    ASN1Any.getInstance(),
                    // certificates
                    new ASN1Implicit(0, ASN1),
                    // set of crls is optional and is missed here
                    ASN1Any.getInstance(),// signers info
            }) {

        // precalculated ASN.1 encodings for
        // version ,digestAlgorithms, content info field of SignedData
        private final byte[] PRECALCULATED_HEAD = new byte[] { 0x02, 0x01,
                0x01,// version (v1)
                0x31, 0x00,// empty set of DigestAlgorithms
                0x30, 0x03, 0x06, 0x01, 0x00 // empty ContentInfo with oid=0
        };

        // precalculated empty set of SignerInfos
        private final byte[] SIGNERS_INFO = new byte[] { 0x31, 0x00 };

        protected void getValues(Object object, Object[] values) {
            values[0] = PRECALCULATED_HEAD;
            values[1] = object; // pass X509CertPathImpl object
            values[2] = SIGNERS_INFO;
        }

        // stub to prevent using the instance as decoder
        public Object decode(BerInputStream in) throws IOException {
            throw new RuntimeException(
                    "Invalid use of encoder for PKCS#7 SignedData object");
        }
    };

    private static final ASN1Sequence PKCS7_SIGNED_DATA_OBJECT = new ASN1Sequence(
            new ASN1Type[] { ASN1Any.getInstance(), // contentType
                    new ASN1Explicit(0, ASN1_SIGNED_DATA) // SignedData
            }) {

        // precalculated ASN.1 encoding for SignedData object oid
        private final byte[] SIGNED_DATA_OID = ASN1Oid.getInstance().encode(
                ContentInfo.SIGNED_DATA);

        protected void getValues(Object object, Object[] values) {
            values[0] = SIGNED_DATA_OID;
            values[1] = object; // pass X509CertPathImpl object
        }

        // stub to prevent using the instance as decoder
        public Object decode(BerInputStream in) throws IOException {
            throw new RuntimeException(
                    "Invalid use of encoder for PKCS#7 SignedData object");
        }
    };
}