/*
    * Copyright 2024–2026 Michael Osipov
    *
    * 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 net.sf.michaelo.tomcat.pac;
  
  import java.math.BigInteger;
  import java.nio.Buffer;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  /**
   * A thin wrapper around {@link ByteBuffer} to comply with the encoding rules defined by the <a href=
   * "https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-pac/6655b92f-ab06-490b-845d-037e6987275f">{@code PACTYPE}</a>
   * structure from MS-PAC.
   */
  public class PacDataBuffer {
  
  	private static final BigInteger TWO_COMPL_REF = BigInteger.ONE.shiftLeft(64);
  
  	private final ByteBuffer buf;
  
  	/**
  	 * Constructs a PAC data buffer from a byte array.
  	 *
  	 * @param pacDataBytes PAC data encoded as bytes
  	 */
  	public PacDataBuffer(byte[] pacDataBytes) {
  		buf = ByteBuffer.wrap(pacDataBytes);
  		buf.order(ByteOrder.LITTLE_ENDIAN);
  	}
  
  	public int position() {
  		return ((Buffer) buf).position();
  	}
  
  	public PacDataBuffer position(int newPosition) {
  		((Buffer) buf).position(newPosition);
  		return this;
  	}
  
  	public PacDataBuffer skip(int bytes) {
  		((Buffer) buf).position(buf.position() + bytes);
  		return this;
  	}
  
  	protected PacDataBuffer align(int bytes) {
  		int shift = ((Buffer) buf).position() & bytes - 1;
  		if (bytes != 0 && shift != 0) skip(bytes - shift);
  		return this;
  	}
  
  	public PacDataBuffer get(byte[] dst) {
  		buf.get(dst);
  		return this;
  	}
  
  	public int getInt() {
  		align(4);
  		return buf.getInt();
  	}
  
  	public int getUnsignedShort() {
  		align(2);
  		return buf.getShort() & 0xffff;
  	}
  
  	public long getUnsignedInt() {
  		align(4);
  		return buf.getInt() & 0xffffffffL;
  	}
  
  	public BigInteger getUnsignedLong() {
  		align(8);
  		long temp = buf.getLong();
  		BigInteger value = BigInteger.valueOf(temp);
  		if (value.compareTo(BigInteger.ZERO) < 0) value = value.add(TWO_COMPL_REF);
  		return value;
  	}
  }