Answerer.java

package org.batfish.common;

import java.util.function.BiFunction;

import org.batfish.common.plugin.IBatfish;
import org.batfish.common.util.BatfishObjectMapper;
import org.batfish.common.util.JsonDiff;
import org.batfish.datamodel.answers.AnswerElement;
import org.batfish.datamodel.answers.JsonDiffAnswerElement;
import org.batfish.datamodel.questions.Question;
import org.codehaus.jettison.json.JSONException;
import org.codehaus.jettison.json.JSONObject;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public abstract class Answerer {

   public static Answerer create(Question question, IBatfish batfish) {
      String questionName = question.getName();
      BiFunction<Question, IBatfish, Answerer> answererCreator = batfish
            .getAnswererCreators().get(questionName);
      if (answererCreator == null) {
         throw new BatfishException(
               "Cannot create answerer for missing question with name: "
                     + questionName);
      }
      return answererCreator.apply(question, batfish);
   }

   protected final IBatfish _batfish;

   protected final BatfishLogger _logger;

   protected final Question _question;

   public Answerer(Question question, IBatfish batfish) {
      _batfish = batfish;
      _logger = batfish.getLogger();
      _question = question;
   }

   public abstract AnswerElement answer();

   // this is the default differential answerer
   // if you want a custom one for a subclass, override this function in the
   // subclass
   public AnswerElement answerDiff() {
      _batfish.pushBaseEnvironment();
      _batfish.checkEnvironmentExists();
      _batfish.popEnvironment();
      _batfish.pushDeltaEnvironment();
      _batfish.checkEnvironmentExists();
      _batfish.popEnvironment();
      _batfish.pushBaseEnvironment();
      AnswerElement before = create(_question, _batfish).answer();
      _batfish.popEnvironment();
      _batfish.pushDeltaEnvironment();
      AnswerElement after = create(_question, _batfish).answer();
      _batfish.popEnvironment();
      ObjectMapper mapper = new BatfishObjectMapper();
      try {
         String beforeJsonStr = mapper.writeValueAsString(before);
         String afterJsonStr = mapper.writeValueAsString(after);
         JSONObject beforeJson = new JSONObject(beforeJsonStr);
         JSONObject afterJson = new JSONObject(afterJsonStr);
         JsonDiff diff = new JsonDiff(beforeJson, afterJson);

         return new JsonDiffAnswerElement(diff);
      }
      catch (JsonProcessingException | JSONException e) {
         throw new BatfishException(
               "Could not convert diff element to json string", e);
      }
   }
}