/** Our internal representation of a BinOp
 * in the X0 language.
 * See http://www.radford.edu/itec380/2019spring-ibarland/Homeworks/Project/
 * 
 * @author Ian Barland
 * @version 2018.Nov.16
 */
import java.util.*;
public class BinOp extends Expr {

  Expr left, right;
  String op;
  
  static final String START_TOKEN = "~";
  static final String STOP_TOKEN  = "!";
  
  
  public static final List<String> OPS = Arrays.asList( "add", "sub", "mlt" );

  BinOp( Expr _left, String _op, Expr _right ) {
    this.op    = _op;
    this.left  = _left;
    this.right = _right;
    }
  
  @Override
  public String toString( /* BinOp this */) {
    return START_TOKEN
         + this.left.toString()
         + " "
         + this.op
         + " "
         + this.right.toString()
         + STOP_TOKEN
         ;
      }
  
  public static BinOp parse(java.util.Scanner s, String punctuation) {
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), START_TOKEN);  // Consume (&verify) opening punctuation.

      Expr lefty = Expr.parse(s,punctuation);
      // NOTE: recur with `Expr.parse` -- not `parse` = `BinOp.parse` which is NOT what we want!

      String op = UtilIan.nextSplittingBy(s,punctuation);
      if (!(OPS.contains(op))) throw new InputMismatchException(String.format("Unknown operator \"%s\".",op));

      Expr righty = Expr.parse(s,punctuation);
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), STOP_TOKEN);  // Consume (&verify) closing punctuation.

      return new BinOp(lefty, op, righty );  
      }
      
  public Value eval( /* BinOp this */) {
    String theOp    = this.op;
    double leftVal  = ((Num)(this.left .eval())).doubleValue();
    double rightVal = ((Num)(this.right.eval())).doubleValue();
    return evalOp( theOp, leftVal, rightVal );
    }
    
  /** Evaluate U's `op` w/ `l` and `r` */
  static Value evalOp( String op, double l, double r ) {
    if (op.equals("add")) {
      return new Num(l + r);
      }
    else if (op.equals("sub")) {
      return new Num(l - r);
      }
    else if (op.equals("mlt")) {
      return new Num(l * r);
      }
    else {
      throw new RuntimeException("BinOp.eval(): unknown binary operator `" + op + "`");
      }
    }
  
  @Override
  public boolean equals( /* BinOp this, */ Object that) {
    if (this==that) {
      return true;
      }
   else if (that==null) {
      return false;
      }
   else if (this.getClass() != that.getClass()) {
      return false;
      }
   else {
      BinOp thatt = (BinOp) that;
      return this.left.equals(thatt.left)
          && this.op.equals(thatt.op)
          && this.right.equals(thatt.right);
      }
    
    }
    
  @Override
  public int hashCode() {
    if (cachedHash == null) {
      int hashSoFar = 0;
      hashSoFar += this.left.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.op.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.right.hashCode();
      cachedHash = hashSoFar;
      }
    return cachedHash;
    }
  private Integer cachedHash = null;

  
  
  
  }