template "widget[@type='ForEach']", mode="widget_defs" {
    param "hmi_element";

    if "count(path) != 1" error > ForEach widget «$hmi_element/@id» must have one HMI path given.
    if "count(arg) != 1" error > ForEach widget «$hmi_element/@id» must have one argument given : a class name.

    const "class","arg[1]/@value";

    const "base_path","path/@value";
    const "hmi_index_base", "$indexed_hmitree/*[@hmipath = $base_path]";
    const "hmi_tree_base", "$hmitree/descendant-or-self::*[@path = $hmi_index_base/@path]";
    const "hmi_tree_items", "$hmi_tree_base/*[@class = $class]";
    const "hmi_index_items", "$indexed_hmitree/*[@path = $hmi_tree_items/@path]"; 
    const "items_paths", "$hmi_index_items/@hmipath"; 
    |     index_pool: [
    foreach "$hmi_index_items" {
    |       «@index»`if "position()!=last()" > ,`
    }
    |     ],
    |     init: function() {
    const "prefix","concat($class,':')";
    const "buttons_regex","concat('^',$prefix,'[+\-][0-9]+')";
    const "buttons", "$hmi_element/*[regexp:test(@inkscape:label, $buttons_regex)]"; 
    foreach "$buttons" {
        const "op","substring-after(@inkscape:label, $prefix)";
    |         id("«@id»").setAttribute("onclick", "hmi_widgets['«$hmi_element/@id»'].on_click('«$op»', evt)");
    }
    |
    |         this.items = [
    const "items_regex","concat('^',$prefix,'[0-9]+')";
    const "unordered_items","$hmi_element//*[regexp:test(@inkscape:label, $items_regex)]";
    foreach "$unordered_items" {
        const "elt_label","concat($prefix, string(position()))"; 
        const "elt","$unordered_items[@inkscape:label = $elt_label]";
        const "pos","position()";
        const "item_path", "$items_paths[$pos]";
    |           [ /* item="«$elt_label»" path="«$item_path»" */
        if "count($elt)=0" error > Missing item labeled «$elt_label» in ForEach widget «$hmi_element/@id»
        foreach "func:refered_elements($elt)[@id = $hmi_elements/@id][not(@id = $elt/@id)]" {
            if "not(func:is_descendant_path(func:widget(@id)/path/@value, $item_path))"
                error > Widget id="«@id»" label="«@inkscape:label»" is having wrong path. Accroding to ForEach widget ancestor id="«$hmi_element/@id»", path should be descendant of "«$item_path»".
    |             hmi_widgets["«@id»"]`if "position()!=last()" > ,`
        }
    |           ]`if "position()!=last()" > ,`
    }
    |         ]
    |     },
    |     item_offset: 0,
}

template "widget[@type='ForEach']", mode="widget_class"
||
class ForEachWidget extends Widget{

    unsub_items(){
        for(let item of this.items){
            for(let widget of item) {
                widget.unsub();
            }
        }
    }

    unsub(){
        this.unsub_items();
        this.offset = 0;
        this.relativeness = undefined;
    }

    sub_items(){
        for(let i = 0; i < this.items.length; i++) {
            let item = this.items[i];
            let orig_item_index = this.index_pool[i];
            let item_index = this.index_pool[i+this.item_offset];
            let item_index_offset = item_index - orig_item_index;
            if(this.relativeness[0])
                item_index_offset += this.offset;
            for(let widget of item) {
                /* all variables of all widgets in a ForEach are all relative. 
                   Really.

                   TODO: allow absolute variables in ForEach widgets
                */
                widget.sub(item_index_offset, widget.indexes.map(_=>true));
            }
        }
    }

    sub(new_offset=0, relativeness=[]){
        this.offset = new_offset;
        this.relativeness = relativeness;
        this.sub_items();
    }

    apply_cache() {
        this.items.forEach(item=>item.forEach(widget=>widget.apply_cache()));
    }

    on_click(opstr, evt) {
        let new_item_offset = eval(String(this.item_offset)+opstr);
        if(new_item_offset + this.items.length > this.index_pool.length) {
            if(this.item_offset + this.items.length == this.index_pool.length)
                new_item_offset = 0;
            else
                new_item_offset = this.index_pool.length - this.items.length;
        } else if(new_item_offset < 0) {
            if(this.item_offset == 0)
                new_item_offset = this.index_pool.length - this.items.length;
            else
                new_item_offset = 0;
        }
        this.item_offset = new_item_offset;
        this.unsub_items();
        this.sub_items();
        update_subscriptions();
        need_cache_apply.push(this);
        jumps_need_update = true;
        requestHMIAnimation();
    }
}
||