package function.builtin;

import function.*;
import sexpression.*;

public class APPLY extends LispFunction {

    private static final int NUMBER_OF_ARGUMENTS = 2;
    private ArgumentValidator argumentValidator;

    public static SExpression apply(Cons argList) {
        return new APPLY().call(argList);
    }

    public APPLY() {
        this.argumentValidator = new ArgumentValidator("APPLY");
        this.argumentValidator.setExactNumberOfArguments(NUMBER_OF_ARGUMENTS);
    }

    public SExpression call(Cons argList) {
        argumentValidator.validate(argList);

        Cons cdr = (Cons) argList.getCdr();
        SExpression functionName = argList.getCar();
        SExpression argumentList = cdr.getCar();

        if (argumentList.listp()) {
            LispFunction function = EVAL.lookupFunction(functionName.toString());

            if (function == null) {
                if (functionName.functionp()) {
                    function = ((LambdaExpression) functionName).getFunction();
                } else if (LAMBDA.isLambdaExpression(functionName)) {
                    Cons lexpr = (Cons) functionName;

                    function = LAMBDA.createFunction(lexpr);
                } else {
                    throw new RuntimeException("undefined function " + functionName);
                }
            }

            return function.call((Cons) argumentList);
        }

        throw new RuntimeException("APPLY: " + argumentList + " is not a list");
    }

}