/** Our internal representation of a Parity expr
 * in the T0 language.
 * See http://www.radford.edu/itec380/2018fall-ibarland/Project
 * 
 * @author Ian Barland
 * @version 2018.Nov.16
 */
public class Parity extends Expr {
  static final String START_TOKEN = "even";
  static final String STOP_TOKEN  = "dawg";
  
  
  Expr test, evenAns, oddAns;
  
  Parity( Expr _test, Expr _evenAns, Expr _oddAns) {
    this.test = _test;
    this.evenAns = _evenAns;
    this.oddAns = _oddAns;
    }
  
  public String toString() {
    return START_TOKEN+"? "
         + this.test.toString()
         + " dope "
         + this.evenAns.toString()
         + " nope "
         + this.oddAns.toString()
         + " "
         + STOP_TOKEN
         ;
    }

  public static Parity parse( java.util.Scanner s, String punctuation ) {
      assert UtilIan.nextSplittingBy(s,punctuation).equals(START_TOKEN);  // consume&verify the "even"
      UtilIan.nextChar(s,'?');  // verify&consume the "?"
      // NOTE: recur with `Expr.parse` -- not `parse` = `Parity.parse` which is NOT what we want!
      Expr theTest = Expr.parse(s,punctuation);
      assert UtilIan.nextSplittingBy(s,punctuation).equals("dope");
      Expr theEvenAns = Expr.parse(s,punctuation);
      assert UtilIan.nextSplittingBy(s,punctuation).equals("nope");
      Expr theOddAns = Expr.parse(s,punctuation);
      assert UtilIan.nextSplittingBy(s,punctuation).equals(STOP_TOKEN);  // consume&verify the "dawg"
      return new Parity(theTest,theEvenAns,theOddAns);
      }
    
    
  static final double EPSILON = 1e-10;
  public Value eval() {
    if ( Math.abs((((Num)(this.test.eval())).doubleValue()) % 2) < EPSILON ) {
      return this.evenAns.eval();
      }
   else {
      return this.oddAns.eval();
      }
    }
    
  @Override
  public boolean equals( /* Parity this, */ Object that) {
    if (this==that) {
      return true;
      }
    else if (that==null) {
      return false;
      }
   else if (this.getClass() != that.getClass()) {
      return false;
      }
   else {
      Parity thatt = (Parity) that;
      return this.test.equals(thatt.test)
          && this.evenAns.equals(thatt.evenAns)
          && this.oddAns.equals(thatt.oddAns);
      }
    
    }
    
  @Override
  public int hashCode() {
    if (cachedHash == null) {
      int hashSoFar = (int)0x3141834e907b1159L; // fingerprint
      hashSoFar += this.test.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.evenAns.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.oddAns.hashCode();
      cachedHash = hashSoFar;
      }
    return cachedHash;
    }
  private Integer cachedHash = null; 
  }