var LabelDropdown = (function(){

    var treedata    = {};
    var currents    = {};
    var notselected = {};

    var fill = function(dd, list, first_id) {
        var count = 0;
        dd.options.length = 0;
        if (!first_id) first_id = '0';

        var ns = notselected[dd.id];
        dd.options[count++] = new Option(ns.name, first_id, false, false);
        list.each(function(elem) {
            dd.options[count++] = new Option(elem.name, elem.id, false, false);
        });
    };

    var init = function(dd, current) {
        // clear crumble. we're gonna update it anyhow
        $(dd.id + "_crumble").update('');

        if (current == '' || current == '0') {
            // take all the top levels. No crumble.
            fill(dd, treedata[dd.id], 0);
            select(dd,0);
            return;
        }

        // okay, there's something selected. First, make
        // the dropdown contain what's needed, select the actual
        // element, then fix up the crumble path.
        var active = find_in_tree(dd, current);
        var par = find_parent_of(dd, active.id);
		var crumbletarget = par;
        if (par) {
            // parent entry found. we're on some sub-level.
            // Fill with our siblings.

			if(active.children.length) {
				// we've got children. this means we go into the
				// crumble, and the children get listed. Select
				// the parent
				fill(dd, active.children, par.id);
				select(dd, par.id);
				crumbletarget = active;
			}
			else {
				// no children. we go into the list and should
				// get selected
				fill(dd, par.children, par.id);
				select(dd, active.id);
			}
        }
        else {
            // no parent entry found. we're selected on top level.
            fill(dd, treedata[dd.id], 0);

			if(active.children.length) {
				// we've got children. this means we go into the
				// crumble, and the children get listed. Select
				// the parent
				fill(dd, active.children, 0);
				crumbletarget = active;
			}
			else {
				// no children. we go into the list and should
				// get selected
				fill(dd, treedata[dd.id], 0);
				select(dd, active.id);
			}

        }

        // Now, fix the crumble tree.
        while (crumbletarget) {
            add_crumble(dd, crumbletarget);
            crumbletarget = find_parent_of(dd, crumbletarget.id);
        }

    };

    var find_parent_of = function(dd, elem_id) {
        var elem = find_in_tree(dd, elem_id);
        return find_in_tree(dd, elem.parentid);
    };

    var find_in_tree = function(dd, elem_id) {
        var td = treedata[dd.id];

        var found = null;

        var _set = function(elem) {
            found = elem;
        }

        // TODO: do this without ugly exception abuse
        var _find = function(elem) {
            if (elem.id == elem_id) {
                _set(elem);
                throw "e-found";
            }
            elem.children.each(_find);
        }
        // prototyp does the catching for us, but
        // it appears they could be changing this
        // in the future.
        try {
            td.each(_find);
        }
        catch (err) {
        }
        return found;
    };

    var crumble_id_gen = 0;
    var add_crumble = function(dd, elem, append) {
        var old_options = dd.options;

        var crumble_id = "dropdown_crumble_" + (crumble_id_gen++);
        var crumble_id_a = crumble_id + "_a";
        var crumble_html = '<span id="'+crumble_id+'"><a href="#" id="'+crumble_id+'_a">'+elem.name+'</a>: </span>';
        var crumble = $(dd.id + "_crumble");

        if (append) crumble.insert({'bottom': crumble_html});
        else        crumble.insert({'top':    crumble_html});

        var link_container = $(crumble_id);
        var link = $(crumble_id_a);

        link.observe('click', function() {
            // drop crumble and all right-hand siblings
            var right_siblings = link_container.nextSiblings();
            right_siblings.each(function(e){ e.remove(); });
            link_container.remove();


            // restore options
            var par = find_parent_of(dd, elem.id);
            if (!par) fill(dd, treedata[dd.id]);
            else      fill(dd, par.children, par.id);
            select(dd, elem.id);
        });
    };
    var select = function(dd, elem_id) {
        for (var i = 0; i < dd.options.length; i++) {
            if (dd.options[i].value == elem_id) {
                dd.selectedIndex =i;
                return;
            }
        }
    };

    var currently_selected_elem = function(dd) {
        var elem_id = dd.options[dd.selectedIndex].value;
        return find_in_tree(dd, elem_id);
    };

    var push_current = function(dd) {
        var curr = currently_selected_elem(dd);
        if (curr.children.size() > 0) {
            fill(dd, curr.children, curr.id);
            add_crumble(dd, curr, true);
        }
    }

    var changed = function(dd) {
        var elem_id = dd.options[dd.selectedIndex].value;
        //init(dd, elem_id);
        push_current(dd);
    };


    var register = function(id, current, tree) {
        treedata[id]    = tree.slice(1,tree.length);
        currents[id]    = current;
        notselected[id] = tree[0];
        var dd = $(id);
        init(dd, current);
        dd.observe('change', function() {
            changed(dd);
        });
    };


    return {
        'register': register
    }

})();