/*
    * #%L
    * prolobjectlink-jpi-jtrolog
    * %%
    * Copyright (C) 2012 - 2018 WorkLogic Project
    * %%
    * This program is free software: you can redistribute it and/or modify
    * it under the terms of the GNU Lesser General Public License as
    * published by the Free Software Foundation, either version 2.1 of the
   * License, or (at your option) any later version.
   * 
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Lesser Public License for more details.
   * 
   * You should have received a copy of the GNU General Lesser Public
   * License along with this program.  If not, see
   * <http://www.gnu.org/licenses/lgpl-2.1.html>.
   * #L%
   */
  package jTrolog.engine;
  
  import jTrolog.terms.Struct;
  import jTrolog.terms.Clause;
  import jTrolog.errors.PrologException;
  import jTrolog.parser.Parser;
  
  import java.util.List;
  
  /**
   * @author janerist@stud.ntnu.no
   * @author ivar.orstavik@hist.no
   */
  @SuppressWarnings({ "rawtypes" })
  class ChoicePoint {
  	// CP head
  	Struct head;
  	int headCtx = -1;
  	// CP body
  	private Struct[] body;
  	private int nextInBody = 0;
  	private int bodySize = 0;
  	int bodyCtx;
  
  	// CP parent and cutParent
  	ChoicePoint parent;
  	ChoicePoint cutParent;
  
  	// alternative rules
  	List alternatives;
  	int altPos;
  	int alternativeCount;
  
  	// or primitive
  	PrimitiveInfo prim;
  
  	/**
  	 * recycles previously used CP objects on the stack
  	 * 
  	 * @param s
  	 * @param ctx
  	 * @param parent
  	 */
  	final void set(final Struct s, final int ctx, final ChoicePoint parent) throws PrologException {
  		head = s;
  		headCtx = ctx;
  		this.parent = parent;
  		cutParent = Parser.isSemiAndNotIf(parent.head) ? parent.parent.cutParent : this;
  
  		altPos = 0;
  		this.alternatives = null;
  		this.alternativeCount = 0;
  
  		bodyCtx = -1;
  
  		nextInBody = 0;
  		bodySize = 0;
  	}
  
  	final void setRules(final List rules) throws PrologException {
  		altPos = 0;
  		alternatives = rules;
  		alternativeCount = alternatives.size();
  	}
  
  	final boolean hasAlternatives() {
  		return altPos < alternativeCount;
  	}
  
  	final Clause nextAlternative() {
  		return (Clause) alternatives.get(altPos++);
  	}
  
  	/**
  	 * removes any choice points (alternative rules) on the ChoicePoint.
  	 */
  	final void cutAlternatives() {
  		altPos = alternativeCount;
 	}
 
 	public String toString() {
 		if (prim != null)
 			return "!!" + head + "<" + headCtx + ">" + "!!";
 		String s2 = head == null ? "?-\n   " : head + "<" + headCtx + "> :-\n   ";
 		if (body != null) {
 			for (int i = 0; i < bodySize; i++) {
 				if (i != 0)
 					s2 += ",\n   ";
 				Object rule = body[i];
 				if (i == nextInBody)
 					s2 += "**" + rule + "**";
 				else
 					s2 += rule;
 			}
 		}
 		if (hasAlternatives()) {
 			s2 += "\n\n                                rules:\n";
 			for (int i = altPos; i < alternativeCount; i++)
 				s2 += "                              " + alternatives.get(i) + "\n";
 		}
 		return s2;
 	}
 
 	boolean hasTODO() {
 		return nextInBody < bodySize;
 	}
 
 	public void fail() {
 		bodySize = 0;
 		nextInBody = 0;
 		parent.nextInBody--;
 	}
 
 	Struct getTODO() {
 		return body[nextInBody++];
 	}
 
 	final void setBody(final Struct[] body, final int bodyCtx) {
 		this.bodyCtx = bodyCtx;
 		this.body = body;
 		nextInBody = 0;
 		bodySize = body.length;
 	}
 
 	public void reuse() {
 		this.head = body[0];
 		this.headCtx = bodyCtx;
 		this.nextInBody = 0;
 		this.altPos = 0;
 	}
 }