content: /**
   * Copyright (c) 2017-2018, the Alpha Team.
   * All rights reserved.
   *
   * Additional changes made by Siemens.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1) Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   *
   * 2) Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package at.ac.tuwien.kr.alpha.core.programs.transformation;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  
  import at.ac.tuwien.kr.alpha.api.programs.ASPCore2Program;
  import at.ac.tuwien.kr.alpha.api.programs.Predicate;
  import at.ac.tuwien.kr.alpha.api.programs.atoms.Atom;
  import at.ac.tuwien.kr.alpha.api.programs.atoms.BasicAtom;
  import at.ac.tuwien.kr.alpha.api.programs.literals.Literal;
  import at.ac.tuwien.kr.alpha.api.programs.rules.Rule;
  import at.ac.tuwien.kr.alpha.api.programs.rules.heads.ChoiceHead;
  import at.ac.tuwien.kr.alpha.api.programs.rules.heads.ChoiceHead.ChoiceElement;
  import at.ac.tuwien.kr.alpha.api.programs.rules.heads.Head;
  import at.ac.tuwien.kr.alpha.api.programs.terms.Term;
  import at.ac.tuwien.kr.alpha.commons.Predicates;
  import at.ac.tuwien.kr.alpha.commons.programs.Programs;
  import at.ac.tuwien.kr.alpha.commons.programs.Programs.ASPCore2ProgramBuilder;
  import at.ac.tuwien.kr.alpha.commons.programs.atoms.Atoms;
  import at.ac.tuwien.kr.alpha.commons.programs.rules.Rules;
  import at.ac.tuwien.kr.alpha.commons.programs.rules.heads.Heads;
  import at.ac.tuwien.kr.alpha.commons.programs.terms.Terms;
  
  /**
   * Copyright (c) 2017-2021, the Alpha Team.
   */
  // TODO this could already give NormalProgram as result type
  public class ChoiceHeadToNormal extends ProgramTransformation<ASPCore2Program, ASPCore2Program> {
  	private final static String PREDICATE_NEGATION_PREFIX = "_n";
  
  	@Override
  	public ASPCore2Program apply(ASPCore2Program inputProgram) {
  		ASPCore2ProgramBuilder programBuilder = Programs.builder();
  		List<Rule<Head>> additionalRules = new ArrayList<>();
  
  		List<Rule<Head>> srcRules = new ArrayList<>(inputProgram.getRules());
  		Iterator<Rule<Head>> ruleIterator = srcRules.iterator();
  		while (ruleIterator.hasNext()) {
  			Rule<Head> rule = ruleIterator.next();
  
  			Head ruleHead = rule.getHead();
  			if (!(ruleHead instanceof ChoiceHead)) {
  				// Rule is constraint or without choice in the head. Leave as is.
  				continue;
  			}
  
  			// Remove this rule, as it will be transformed.
  			ruleIterator.remove();
  
  			ChoiceHead choiceHead = (ChoiceHead) ruleHead;
  			// Choice rules with boundaries are not yet supported.
  			if (choiceHead.getLowerBound() != null || choiceHead.getUpperBound() != null) {
  				throw new UnsupportedOperationException("Found choice rule with bounds, which are not yet supported. Rule is: " + rule);
  			}
  
  			// Only rewrite rules with a choice in their head.
  			for (ChoiceElement choiceElement : choiceHead.getChoiceElements()) {
  				// Create two guessing rules for each choiceElement.
  
  				// Construct common body to both rules.
  				BasicAtom head = choiceElement.getChoiceAtom();
  				List<Literal> ruleBody = new ArrayList<>(rule.getBody());
  				ruleBody.addAll(choiceElement.getConditionLiterals());
  
  				if (containsIntervalTerms(head)) {
  					throw new RuntimeException("Program contains a choice rule with interval terms in its head. This is not supported (yet).");
  				}
  
  				// Construct head atom for the choice.
  				Predicate headPredicate = head.getPredicate();
  
  				Predicate negPredicate = Predicates.getPredicate(PREDICATE_NEGATION_PREFIX + headPredicate.getName(), headPredicate.getArity() + 1, true);
  				List<Term> headTerms = new ArrayList<>(head.getTerms());
  				headTerms.add(0, Terms.newConstant("1")); // FIXME: when introducing classical negation, this is 1 for classical positive atoms and 0 for
  																	// classical negative atoms.
  				BasicAtom negHead = Atoms.newBasicAtom(negPredicate, headTerms);
  
  				// Construct two guessing rules.
  				List<Literal> guessingRuleBodyWithNegHead = new ArrayList<>(ruleBody);
  				guessingRuleBodyWithNegHead.add(Atoms.newBasicAtom(head.getPredicate(), head.getTerms()).toLiteral(false));
  				additionalRules.add(Rules.newRule(Heads.newNormalHead(negHead), guessingRuleBodyWithNegHead));
  
  				List<Literal> guessingRuleBodyWithHead = new ArrayList<>(ruleBody);
  				guessingRuleBodyWithHead.add(Atoms.newBasicAtom(negPredicate, headTerms).toLiteral(false));
  				additionalRules.add(Rules.newRule(Heads.newNormalHead(head), guessingRuleBodyWithHead));
  
  				// TODO: when cardinality constraints are possible, process the boundaries by adding a constraint with a cardinality check.
  			}
  		}
  		return programBuilder.addRules(srcRules).addRules(additionalRules).addFacts(inputProgram.getFacts())
  				.addInlineDirectives(inputProgram.getInlineDirectives()).build();
  	}
  
  	private static boolean containsIntervalTerms(Atom atom) {
  		for (Term term : atom.getTerms()) {
  			if (Terms.termContainsIntervalTerm(term)) {
  				return true;
  			}
  		}
  		return false;
  	}
  }
  