/*
 * Ivory: A Hadoop toolkit for web-scale information retrieval
 *
 * 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 ivory.smrf.model.constrained;

import ivory.core.ConfigurationException;
import ivory.core.RetrievalEnvironment;
import ivory.smrf.model.MarkovRandomField;
import ivory.smrf.model.builder.MRFBuilder;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * @author Don Metzler
 * @author Lidan Wang
 */
public abstract class ConstrainedMRFBuilder extends MRFBuilder {
  private MRFBuilder builder;

  public ConstrainedMRFBuilder(RetrievalEnvironment env, Node model) throws ConfigurationException {
    super(env);

    NodeList children = model.getChildNodes();
    for (int i = 0; i < children.getLength(); i++) {
      Node child = children.item(i);

      // This is the model that is going to be constrained.
      if ("constrainedmodel".equals(child.getNodeName())) {
        builder = MRFBuilder.get(env, child);
      }
    }

    if (builder == null) {
      throw new ConfigurationException(
          "ConstrainedMRFBuilder is missing required constrainedModel node!");
    }
  }

  @Override
  public MarkovRandomField buildMRF(String[] queryTerms) throws ConfigurationException {
    // build unconstrained MRF model
    MarkovRandomField unconstrainedMRF = builder.buildMRF(queryTerms);

    // get constrained version of the model
    return buildConstrainedMRF(queryTerms, unconstrainedMRF);
  }

  protected abstract MarkovRandomField buildConstrainedMRF(String[] queryTerms,
      MarkovRandomField mrf);
}