/** Our internal representation of a BinOp
 * in the Z0 language.
 * See http://www.radford.edu/itec380/2021spring-ibarland/Homeworks/Project/
 * 
 * @author Ian Barland
 * @version 2021.Apr.05
 */
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public record BinOp( String op, Expr left, Expr right) implements Expr {

  
  static final String START_TOKEN = "[";
  static final String STOP_TOKEN  = "]";
  
  public static final List<Pair<String,BinaryOperator<Double>>> 
    OP_FUNCS = List.of( new Pair<>( "add", Double::sum )
                      , new Pair<>( "sub", (a,b) -> a-b )
                      , new Pair<>( "mul", (a,b) -> a*b )
                      );

  
  public static final List<String> 
    OPS = OP_FUNCS.stream().map( Pair::first ).collect(Collectors.toList());
    //OPS = List.of( "add", "sub", "mul" );   // <-- Alternately just use this, if `OP_FUNCS` not declared.

    

  
  @Override
  public String toString( /* BinOp this */ ) {
    return START_TOKEN
         + this.op
         + " "
         + this.left.toString()
         + " "
         + 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.

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

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

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

      return new BinOp(op, lefty, 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 evalBinOp( theOp, leftVal, rightVal );
    }
    
  /** Evaluate Z's `op` w/ `l` and `r` */
  static Value evalBinOp( String op, double l, double r ) {
    Pair<String,BinaryOperator<Double>>  opFunc = OP_FUNCS.stream()   // didn't declare OP_FUNCS?  See comment below.
                                                          .filter(pr -> pr.first().equals(op) )
                                                          .findFirst()
                                                          .orElseThrow( () -> new InputMismatchException(String.format("Unknown op `%s`; must be one of %s.", op, OPS)) );
    return new Num( opFunc.second().apply(l,r) );

    /* If OP_FUNCS wasn't defined, delete the above two statments, and instead use the following:

    return switch(op) {
             case "add" -> new Num(l+r);
             case "sub" -> new Num(l-r);
             case "mul" -> new Num(l*r);
             default -> throw new RuntimeException(String.format("Unknown op `%s`; must be one of %s.", op, OPS));
             };
    */
    }
  
  
  }