package serene.simple;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import static java.util.Arrays.asList;

public class ListNode<T extends Node> extends Node implements Iterable<T> {
    public static final ListNode<?> EMPTY = new ListNode<>();

    public final T first;
    public final ListNode<T> rest;
    public final int length;

    public ListNode() {
        this.first = null;
        this.rest = null;
        this.length = 0;
    }

    public ListNode(T f, ListNode<T> r) {
        this.first = f;
        this.rest = r;
        this.length = r.length + 1;
    }

    @SafeVarargs
    public static <T extends Node> ListNode<T> list(T... objs) {
        return list(asList(objs));
    }

    public static <T extends Node> ListNode<T> list(List<T> objs) {
        ListNode<T> l = (ListNode<T>) EMPTY;
        for (int i = objs.size() - 1; i >= 0; i--) {
            l = l.cons(objs.get(i));
        }
        return l;
    }

    public ListNode<T> cons(T node) {
        return new ListNode<T>(node, this);
    }

    @Override
    public Object eval(Scope scope) {
        Function f = (Function) this.first.eval(scope);
        List<Object> args = new ArrayList<Object>();

        for (T node : this.rest) {
            args.add(node.eval(scope));
        }
        return f.apply(args.toArray());
    }

        public T first() {
        if (this != EMPTY) {
            return this.first;
        }
        return null;
    }

    public ListNode<T> rest() {
        if (this != EMPTY) {
            return this.rest;
        }
        return (ListNode<T>) EMPTY;
    }


    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {
            private ListNode<T> l = ListNode.this;

            @Override
            public boolean hasNext() {
                return this.l != EMPTY;
            }

            @Override
            public T next() {
                if (this.l == EMPTY) {
                    return null;
                }
                T first = this.l.first;
                this.l = this.l.rest;
                return first;
            }

            @Override
            public void remove() {
                throw new SereneException("Iterator is immutable");
            }
        };
    }
}