/*
 * Name: Mike Cifelli
 * Course: CIS 443 - Programming Languages
 * Assignment: Lisp Interpreter 1
 */

package eval;

import parser.*;

/**
 * <code>EQUAL</code> represents the EQUAL function in Lisp.
 */
public class EQUAL extends LispFunction {

    // The number of arguments that EQUAL takes.
    private static final int NUM_ARGS = 2;

    public SExpression call(Cons argList) {
        // retrieve the number of arguments passed to EQUAL
        int argListLength = LENGTH.getLength(argList);

        // make sure we have received the proper number of arguments
        if (argListLength != NUM_ARGS) {
            Cons originalSExpr = new Cons(new Symbol("EQUAL"), argList);
            String errMsg = "too " +
                            ((argListLength > NUM_ARGS) ? "many" : "few") +
                            " arguments given to EQUAL: " + originalSExpr;

            throw new RuntimeException(errMsg);
        }

        SExpression argOne = argList.getCar();  // first argument
        Cons cdr = (Cons) argList.getCdr();
        SExpression argTwo = cdr.getCar();      // second argumnet

        if (argOne.consp() && argTwo.consp()) {
            Cons listOne = (Cons) argOne;
            Cons listTwo = (Cons) argTwo;
            SExpression listOneCar = listOne.getCar();
            SExpression listTwoCar = listTwo.getCar();
            SExpression listOneCdr = listOne.getCdr();
            SExpression listTwoCdr = listTwo.getCdr();

            SExpression carEqual =
                    call(new Cons(listOneCar, LIST.makeList(listTwoCar)));
            SExpression cdrEqual =
                    call(new Cons(listOneCdr, LIST.makeList(listTwoCdr)));

            return (((carEqual == Symbol.T) && (cdrEqual == Symbol.T))
                    ? Symbol.T : Nil.getUniqueInstance());
        }

        return ((argOne.toString().equals(argTwo.toString()))
                ? Symbol.T : Nil.getUniqueInstance());
    }

}