package serene.simple;

import java.util.function.Function;

public class FnSpecialForm extends SpecialForm {
    public FnSpecialForm(ListNode paramsAndBody) {
        super(paramsAndBody);
    }

    @Override
    public Object eval(final Scope parentScope) {
        final ListNode<Node> formalParams = (ListNode<Node>) this.node.rest().first();
        final ListNode<Node> body = this.node.rest().rest();

        return new Function<Object, Object>() {
            @Override
            public Object apply(Object arg) {
                Object args[] = {arg};
                return this.apply(args);
            }

            public Object apply(Object... args) {
                Scope scope = new Scope(parentScope);
                if (args.length != formalParams.length) {
                    throw new RuntimeException(String.format("Wrong number of arguments. Expected: %s, Got: %s.",
                                                             formalParams.length,
                                                             args.length));
                }
                // Map parameter values to formal parameter names
                int i = 0;
                for (Node param : formalParams) {
                    SymbolNode paramSymbol = (SymbolNode) param;
                    scope.insertSymbol(paramSymbol.name, args[i]);
                    i++;
                }

                // Evaluate body
                Object output = null;
                for (Node node : body) {
                    output = node.eval(scope);
                }
                return output;
            }
        };
    }
}