/**
 * Copyright [2009-2010] [dennis zhuang(killme2008@gmail.com)] 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
 */
/**
 * Copyright [2009-2010] [dennis zhuang(killme2008@gmail.com)] 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 com.google.code.yanf4j.util;

import java.util.ArrayList;
import java.util.List;
import com.google.code.yanf4j.buffer.IoBuffer;

/**
 * ByteBuffer matcher based on shift-and algorithm
 * 
 * @author dennis
 * 
 */
public class ShiftAndByteBufferMatcher implements ByteBufferMatcher {

  private int[] b;
  private int mask;

  private int patternLimit;
  private int patternPos;
  private int patternLen;

  public ShiftAndByteBufferMatcher(IoBuffer pat) {
    if (pat == null || pat.remaining() == 0) {
      throw new IllegalArgumentException("blank buffer");
    }
    this.patternLimit = pat.limit();
    this.patternPos = pat.position();
    this.patternLen = pat.remaining();
    preprocess(pat);
    this.mask = 1 << (this.patternLen - 1);
  }

  /**
   * Ԥ����
   * 
   * @param pat
   */
  private void preprocess(IoBuffer pat) {
    this.b = new int[256];
    for (int i = this.patternPos; i < this.patternLimit; i++) {
      int p = ByteBufferUtils.uByte(pat.get(i));
      this.b[p] = this.b[p] | (1 << i);
    }
  }

  public final List<Integer> matchAll(IoBuffer buffer) {
    List<Integer> matches = new ArrayList<Integer>();
    int bufferLimit = buffer.limit();
    int d = 0;
    for (int pos = buffer.position(); pos < bufferLimit; pos++) {
      d <<= 1;
      d |= 1;
      d &= this.b[ByteBufferUtils.uByte(buffer.get(pos))];
      if ((d & this.mask) != 0) {
        matches.add(pos - this.patternLen + 1);
      }
    }
    return matches;
  }

  public final int matchFirst(IoBuffer buffer) {
    if (buffer == null) {
      return -1;
    }
    int bufferLimit = buffer.limit();
    int d = 0;
    for (int pos = buffer.position(); pos < bufferLimit; pos++) {
      d <<= 1;
      d |= 1;
      d &= this.b[buffer.get(pos) & 0XFF];
      if ((d & this.mask) != 0) {
        return pos - this.patternLen + 1;
      }
    }
    return -1;
  }

}