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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.lucene.analysis.morph;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.InputStreamDataInput;
import org.apache.lucene.util.IOSupplier;

/** n-gram connection cost data */
public abstract class ConnectionCosts {

  public static final String FILENAME_SUFFIX = ".dat";

  private final ByteBuffer buffer;
  private final int forwardSize;

  protected ConnectionCosts(
      IOSupplier connectionCostResource,
      String connectionCostsCodecHeader,
      int dictCodecVersion)
      throws IOException {
    try (InputStream is = new BufferedInputStream(connectionCostResource.get())) {
      final DataInput in = new InputStreamDataInput(is);
      CodecUtil.checkHeader(in, connectionCostsCodecHeader, dictCodecVersion, dictCodecVersion);
      forwardSize = in.readVInt();
      int backwardSize = in.readVInt();
      int size = forwardSize * backwardSize;

      // copy the matrix into a direct byte buffer
      final ByteBuffer tmpBuffer = ByteBuffer.allocateDirect(size * 2);
      int accum = 0;
      for (int j = 0; j < backwardSize; j++) {
        for (int i = 0; i < forwardSize; i++) {
          accum += in.readZInt();
          tmpBuffer.putShort((short) accum);
        }
      }
      buffer = tmpBuffer.asReadOnlyBuffer();
    }
  }

  public int get(int forwardId, int backwardId) {
    // map 2d matrix into a single dimension short array
    int offset = (backwardId * forwardSize + forwardId) * 2;
    return buffer.getShort(offset);
  }
}