package function.builtin;

import function.ArgumentValidator;
import function.FunctionNames;
import function.LispFunction;
import sexpression.Cons;
import sexpression.SExpression;
import sexpression.Symbol;

import java.math.BigInteger;

@FunctionNames({ "GENSYM" })
public class GENSYM extends LispFunction {

    public static final String GENSYM_PREFIX = "#G";

    private static BigInteger counter = BigInteger.ZERO;

    private static Symbol generateSymbol() {
        incrementCounter();

        return new Symbol(GENSYM_PREFIX + counter);
    }

    private static void incrementCounter() {
        counter = counter.add(BigInteger.ONE);
    }

    private ArgumentValidator argumentValidator;

    public GENSYM(String name) {
        this.argumentValidator = new ArgumentValidator(name);
        this.argumentValidator.setMaximumNumberOfArguments(0);
    }

    @Override
    public SExpression call(Cons argumentList) {
        argumentValidator.validate(argumentList);

        return generateSymbol();
    }
}