content: package org.apache.lucene.search;
  
  /**
   * 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.
   */
  
  import java.io.Serializable;
  import java.util.ArrayList;
  
  /** Expert: Describes the score computation for document and query. */
  public class Explanation implements java.io.Serializable {
    private float value;                            // the value of this node
    private String description;                     // what it represents
    private ArrayList<Explanation> details;                      // sub-explanations
  
    public Explanation() {}
  
    public Explanation(float value, String description) {
      this.value = value;
      this.description = description;
    }
  
    /**
     * Indicates whether or not this Explanation models a good match.
     *
     * <p>
     * By default, an Explanation represents a "match" if the value is positive.
     * </p>
     * @see #getValue
     */
    public boolean isMatch() {
      return (0.0f < getValue());
    }
  
  
    
    /** The value assigned to this explanation node. */
    public float getValue() { return value; }
    /** Sets the value assigned to this explanation node. */
    public void setValue(float value) { this.value = value; }
  
    /** A description of this explanation node. */
    public String getDescription() { return description; }
    /** Sets the description of this explanation node. */
    public void setDescription(String description) {
      this.description = description;
    }
  
    /**
     * A short one line summary which should contain all high level
     * information about this Explanation, without the "Details"
     */
    protected String getSummary() {
      return getValue() + " = " + getDescription();
    }
    
    /** The sub-nodes of this explanation node. */
    public Explanation[] getDetails() {
      if (details == null)
        return null;
      return details.toArray(new Explanation[0]);
    }
  
    /** Adds a sub-node to this explanation node. */
    public void addDetail(Explanation detail) {
      if (details == null)
        details = new ArrayList<Explanation>();
      details.add(detail);
    }
  
    /** Render an explanation as text. */
    @Override
    public String toString() {
      return toString(0);
    }
    protected String toString(int depth) {
      StringBuilder buffer = new StringBuilder();
      for (int i = 0; i < depth; i++) {
        buffer.append("  ");
      }
      buffer.append(getSummary());
      buffer.append("\n");
  
      Explanation[] details = getDetails();
      if (details != null) {
        for (int i = 0 ; i < details.length; i++) {
          buffer.append(details[i].toString(depth+1));
        }
      }
  
      return buffer.toString();
    }
  
  
    /** Render an explanation as HTML. */
    public String toHtml() {
      StringBuilder buffer = new StringBuilder();
      buffer.append("<ul>\n");
  
      buffer.append("<li>");
      buffer.append(getSummary());
      buffer.append("<br />\n");
  
      Explanation[] details = getDetails();
      if (details != null) {
        for (int i = 0 ; i < details.length; i++) {
          buffer.append(details[i].toHtml());
        }
      }
  
      buffer.append("</li>\n");
      buffer.append("</ul>\n");
  
      return buffer.toString();
    }
    
    /**
     * Small Util class used to pass both an idf factor as well as an
     * explanation for that factor.
     * 
     * This class will likely be held on a {@link Weight}, so be aware 
     * before storing any large or un-serializable fields.
     *
     */
    public static abstract class IDFExplanation implements Serializable {
      /**
       * @return the idf factor
       */
      public abstract float getIdf();
      /**
       * This should be calculated lazily if possible.
       * 
       * @return the explanation for the idf factor.
       */
      public abstract String explain();
    }
  }
  