/*_############################################################################
  _## 
  _##  SNMP4J - SNMPv3SecurityModel.java  
  _## 
  _##  Copyright (C) 2003-2026  Frank Fock (SNMP4J.org)
  _##  
  _##  Licensed 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.snmp4j.security;

import org.snmp4j.asn1.BER;
import org.snmp4j.asn1.BERInputStream;
import org.snmp4j.event.CounterEvent;
import org.snmp4j.mp.CounterSupport;
import org.snmp4j.smi.Integer32;
import org.snmp4j.smi.OctetString;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

/**
 * The abstract class {@code SNMPv3SecurityModel} implements
 * common methods and fields for security models for the SNMPv3
 * message processing model.
 * @author Frank Fock
 * @version 2.0
 * @since 2.0
 */
public abstract class SNMPv3SecurityModel implements SecurityModel {

    protected OctetString localEngineID;
    protected CounterSupport counterSupport;

    public SNMPv3SecurityModel() {
        counterSupport = CounterSupport.getInstance();
    }

    /**
     * Returns the local engine ID.
     * @return
     *    the local engine ID.
     * @since 1.2
     */
    public OctetString getLocalEngineID() {
        return localEngineID;
    }

    protected static byte[] buildWholeMessage(Integer32 snmpVersion,
                                              byte[] scopedPdu,
                                              byte[] globalData,
                                              SecurityParameters securityParameters)
            throws IOException
    {
        int length =
                snmpVersion.getBERLength() +
                        globalData.length +
                        securityParameters.getBERLength() +
                        scopedPdu.length;
        int totalLength = BER.getBERLengthOfLength(length) + length + 1;

        ByteArrayOutputStream os = new ByteArrayOutputStream(totalLength);
        BER.encodeHeader(os, BER.SEQUENCE, length);
        snmpVersion.encodeBER(os);
        os.write(globalData);
        securityParameters.encodeBER(os);
        os.write(scopedPdu);
        int secParamsPos = 1 + snmpVersion.getBERLength() +
                BER.getBERLengthOfLength(length)  + globalData.length;
        securityParameters.setSecurityParametersPosition(secParamsPos);
        return os.toByteArray();
    }

    protected static byte[] buildMessageBuffer(BERInputStream scopedPDU)
            throws IOException
    {
        scopedPDU.mark(16);
        int readLengthBytes = (int)scopedPDU.getPosition();
        BER.MutableByte mutableByte = new BER.MutableByte();
        int length = BER.decodeHeader(scopedPDU, mutableByte);
        readLengthBytes = (int)scopedPDU.getPosition() - readLengthBytes;
        byte[] buf = new byte[length + readLengthBytes];
        scopedPDU.reset();

        int offset = 0;
        int avail = scopedPDU.available();
        while ((offset < buf.length) && (avail > 0)) {
            int read = scopedPDU.read(buf, offset, buf.length - offset);
            if (read < 0) {
                break;
            }
            offset += read;
        }
        return buf;
    }

    /**
     * Gets the counter support instance that can be used to register for
     * counter incrementation events.
     *
     * @return a {@code CounterSupport} instance that is used to fire
     * {@link CounterEvent}.
     */
    public CounterSupport getCounterSupport() {
        return counterSupport;
    }

    /**
     * Sets the counter support instance. By default, the singleton instance
     * provided by the {@link CounterSupport} instance is used.
     *
     * @param counterSupport
     *         a {@code CounterSupport} subclass instance.
     */
    public void setCounterSupport(CounterSupport counterSupport) {
        if (counterSupport == null) {
            throw new NullPointerException();
        }
        this.counterSupport = counterSupport;
    }
}
