/** Our internal representation of a IfZero expr
 * in the V0 language.
 * See http://www.radford.edu/itec380/2019spring-ibarland/Project
 * 
 * @author Ian Barland
 * @version 2018.Nov.16
 */
public class IfZero extends Expr {
  static final String START_TOKEN = "?0";
  static final String STOP_TOKEN  = ":!";
  
  
  Expr test, zerAns, posAns;
  
  IfZero( Expr _test, Expr _zerAns, Expr _posAns) {
    this.test = _test;
    this.zerAns = _zerAns;
    this.posAns = _posAns;
    }
  
  public String toString() {
    return START_TOKEN
         + " "
         + this.test.toString()
         + " "
         + this.zerAns.toString()
         + " "
         + this.posAns.toString()
         + " "
         + STOP_TOKEN
         ;
    }

  public static IfZero parse( java.util.Scanner s, String punctuation ) {
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), START_TOKEN.substring(0,1)); // consume&verify the '?' of "?0"
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), START_TOKEN.substring(1)  ); // consume&verify the '0' of "?0"

      // NOTE: recur with `Expr.parse` -- not `parse` = `IfZero.parse` which is NOT what we want!
      Expr theTest       = Expr.parse(s,punctuation);
      Expr theZeroAnswer = Expr.parse(s,punctuation);
      Expr thePosAnswer  = Expr.parse(s,punctuation);
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), STOP_TOKEN.substring(0,1));         // consume&verify the ":" of ":!"
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), STOP_TOKEN.substring(1));           // consume&verify the "!" of ":!" 
      return new IfZero(theTest,theZeroAnswer,thePosAnswer);
      }
    
    
  static final double EPSILON = 1e-10;
  public Value eval() {
    if ( Math.abs((((Num)(this.test.eval())).doubleValue()) % 2) < EPSILON ) {
      return this.zerAns.eval();
      }
   else {
      return this.posAns.eval();
      }
    }
    
  @Override
  public boolean equals( /* IfZero this, */ Object that) {
    if (this==that) {
      return true;
      }
    else if (that==null) {
      return false;
      }
   else if (this.getClass() != that.getClass()) {
      return false;
      }
   else {
      IfZero thatt = (IfZero) that;
      return this.test.equals(thatt.test)
          && this.zerAns.equals(thatt.zerAns)
          && this.posAns.equals(thatt.posAns);
      }
    
    }
    
  @Override
  public int hashCode() {
    if (cachedHash == null) {
      int hashSoFar = 0;
      hashSoFar += this.test.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.zerAns.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.posAns.hashCode();
      cachedHash = hashSoFar;
      }
    return cachedHash;
    }
  private Integer cachedHash = null; 
  }