(function(F/*the fossil object*/){
  "use strict";
  /* JS code for /forumpage and friends. Requires fossil.dom. */
  const P = fossil.page, D = fossil.dom;

  F.onPageLoad(function(){
    const scrollbarIsVisible = (e)=>e.scrollHeight > e.clientHeight;
    /* Returns an event handler which implements the post expand/collapse toggle
       on contentElem when the given widget is activated. */
    const getWidgetHandler = function(widget, contentElem){
      return function(ev){
        if(ev) ev.preventDefault();
        const wasExpanded = widget.classList.contains('expanded');
        widget.classList.toggle('expanded');
        contentElem.classList.toggle('expanded');
        if(wasExpanded){
          contentElem.classList.add('shrunken');
          contentElem.parentElement.scrollIntoView({
            /* This is non-standard, but !(MSIE, Safari) supposedly support it:
               https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView#Browser_compatibility
            */ behavior: 'smooth'
          });
        }else{
          contentElem.classList.remove('shrunken');
        }
        return false;
      };
    };

    /* Adds an Expand/Collapse toggle to all div.forumPostBody
       elements which are deemed "too large" (those for which
       scrolling is currently activated because they are taller than
       their max-height). */
    document.querySelectorAll(
      'div.forumHier, div.forumTime, div.forumHierRoot'
    ).forEach(function f(forumPostWrapper){
      const content = forumPostWrapper.querySelector('div.forumPostBody');
      if(!content || !scrollbarIsVisible(content)) return;
      const parent = content.parentElement,
            widget =  D.addClass(
              D.div(),
              'forum-post-collapser','bottom'
            ),
            rightTapZone = D.addClass(
              D.div(),
              'forum-post-collapser','right'
            );
      /* Repopulates the rightTapZone with arrow indicators. Because
         of the wildly varying height of these elements, This has to
         be done dynamically at init time and upon collapse/expand. Will not
         work until the rightTapZone has been added to the DOM. */
      const refillTapZone = function f(){
        if(!f.baseTapIndicatorHeight){
          /* To figure out how often to place an arrow in the rightTapZone,
             we simply grab the first header element from the page and use
             its hight as our basis for calculation. */
          const h1 = document.querySelector('h1, h2');
          f.baseTapIndicatorHeight = h1.getBoundingClientRect().height;
        }
        D.clearElement(rightTapZone);
        var rtzHeight = parseInt(window.getComputedStyle(rightTapZone).height);
        do {
          D.append(rightTapZone, D.span());
          rtzHeight -= f.baseTapIndicatorHeight * 8;
        }while(rtzHeight>0);
      };
      const handlerStep1 = getWidgetHandler(widget, content);
      const widgetEventHandler = ()=>{ handlerStep1(); refillTapZone(); };
      content.classList.add('with-expander');
      widget.addEventListener('click', widgetEventHandler, false);
      /** Append 3 children, which CSS will evenly space across the
          widget. This improves visibility over having the label
          in only the left, right, or center. */
      var i = 0;
      for( ; i < 3; ++i ) D.append(widget, D.span());
      if(content.nextSibling){
        forumPostWrapper.insertBefore(widget, content.nextSibling);
      }else{
        forumPostWrapper.appendChild(widget);
      }
      content.appendChild(rightTapZone);
      rightTapZone.addEventListener('click', widgetEventHandler, false);
      refillTapZone();
    });
  })/*onload callback*/;
  
})(window.fossil);
