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/*
 * 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.sshd.common.kex;

import java.util.Collections;
import java.util.Comparator;
import java.util.EnumSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

import org.apache.sshd.common.util.GenericUtils;

/**
 * @author Apache MINA SSHD Project
 */
public enum KexProposalOption {
    ALGORITHMS(Constants.PROPOSAL_KEX_ALGS, "kex algorithms"),
    SERVERKEYS(Constants.PROPOSAL_SERVER_HOST_KEY_ALGS, "server host key algorithms"),
    C2SENC(Constants.PROPOSAL_ENC_ALGS_CTOS, "encryption algorithms (client to server)"),
    S2CENC(Constants.PROPOSAL_ENC_ALGS_STOC, "encryption algorithms (server to client)"),
    C2SMAC(Constants.PROPOSAL_MAC_ALGS_CTOS, "mac algorithms (client to server)"),
    S2CMAC(Constants.PROPOSAL_MAC_ALGS_STOC, "mac algorithms (server to client)"),
    C2SCOMP(Constants.PROPOSAL_COMP_ALGS_CTOS, "compression algorithms (client to server)"),
    S2CCOMP(Constants.PROPOSAL_COMP_ALGS_STOC, "compression algorithms (server to client)"),
    C2SLANG(Constants.PROPOSAL_LANG_CTOS, "languages (client to server)"),
    S2CLANG(Constants.PROPOSAL_LANG_STOC, "languages (server to client)");

    public static final Set CIPHER_PROPOSALS = Collections.unmodifiableSet(EnumSet.of(C2SENC, S2CENC));

    public static final Set MAC_PROPOSALS = Collections.unmodifiableSet(EnumSet.of(C2SMAC, S2CMAC));

    public static final Set COMPRESSION_PROPOSALS
            = Collections.unmodifiableSet(EnumSet.of(C2SCOMP, S2CCOMP));

    public static final Set LANGUAGE_PROPOSALS = Collections.unmodifiableSet(EnumSet.of(C2SLANG, S2CLANG));

    public static final Set FIRST_KEX_PACKET_GUESS_MATCHES
            = Collections.unmodifiableSet(EnumSet.of(ALGORITHMS, SERVERKEYS));

    /**
     * Compares values according to {@link KexProposalOption#getProposalIndex()}
     */
    public static final Comparator BY_PROPOSAL_INDEX
            = Comparator.comparingInt(KexProposalOption::getProposalIndex);

    /**
     * A {@link List} of all the options sorted according to {@link #getProposalIndex()}
     *
     * @see #BY_PROPOSAL_INDEX
     */
    public static final List VALUES = Collections.unmodifiableList(
            EnumSet.allOf(KexProposalOption.class)
                    .stream()
                    .sorted(BY_PROPOSAL_INDEX)
                    .collect(Collectors.toList()));

    public static final int PROPOSAL_MAX = VALUES.size();

    private final int proposalIndex;

    private final String description;

    KexProposalOption(int index, String desc) {
        proposalIndex = index;
        description = desc;
    }

    /**
     * @return The proposal option location in the KEX array
     */
    public final int getProposalIndex() {
        return proposalIndex;
    }

    /**
     * @return User-friendly name for the KEX negotiation item
     * @see    RFC-4253 - section 7.1
     */
    public final String getDescription() {
        return description;
    }

    /**
     * @param  n The option name - ignored if {@code null}/empty
     * @return   The matching {@link KexProposalOption#name()} - case insensitive or {@code null} if no match
     *           found
     */
    public static KexProposalOption fromName(String n) {
        if (GenericUtils.isEmpty(n)) {
            return null;
        }

        for (KexProposalOption o : VALUES) {
            if (n.equalsIgnoreCase(o.name())) {
                return o;
            }
        }

        return null;
    }

    public static KexProposalOption fromProposalIndex(int index) {
        if ((index < 0) || (index >= VALUES.size())) {
            return null;
        } else {
            return VALUES.get(index);
        }
    }

    public static final class Constants {
        public static final int PROPOSAL_KEX_ALGS = 0;
        public static final int PROPOSAL_SERVER_HOST_KEY_ALGS = 1;
        public static final int PROPOSAL_ENC_ALGS_CTOS = 2;
        public static final int PROPOSAL_ENC_ALGS_STOC = 3;
        public static final int PROPOSAL_MAC_ALGS_CTOS = 4;
        public static final int PROPOSAL_MAC_ALGS_STOC = 5;
        public static final int PROPOSAL_COMP_ALGS_CTOS = 6;
        public static final int PROPOSAL_COMP_ALGS_STOC = 7;
        public static final int PROPOSAL_LANG_CTOS = 8;
        public static final int PROPOSAL_LANG_STOC = 9;

        private Constants() {
            throw new UnsupportedOperationException("No instance allowed");
        }
    }
}