/**
   This file contains the client-side implementation of fossil's /chat
   application. 
*/
(function(){
  const F = window.fossil, D = F.dom;
  const E1 = function(selector){
    const e = document.querySelector(selector);
    if(!e) throw new Error("missing required DOM element: "+selector);
    return e;
  };
  /**
     Returns true if e is entirely within the bounds of the window's viewport.
  */
  const isEntirelyInViewport = function(e) {
    const rect = e.getBoundingClientRect();
    return (
      rect.top >= 0 &&
      rect.left >= 0 &&
      rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
      rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );
  };

  /**
     Returns true if e's on-screen position vertically overlaps that
     of element v's. Horizontal overlap is ignored (we don't need it
     for our case).
  */
  const overlapsElemView = function(e,v) {
    const r1 = e.getBoundingClientRect(),
          r2 = v.getBoundingClientRect();
    if(r1.top<=r2.bottom && r1.top>=r2.top) return true;
    else if(r1.bottom<=r2.bottom && r1.bottom>=r2.top) return true;
    return false;
  };

  (function(){
    let dbg = document.querySelector('#debugMsg');
    if(dbg){
      /* This can inadvertently influence our flexbox layouts, so move
         it out of the way. */
      D.append(document.body,dbg);

          if(fe) mip.parentNode.insertBefore(e, fe);
          else D.append(mip.parentNode, e);
        }else{
          D.append(holder,e);
          this.e.newestMessage = e;
        }
        if(!atEnd && !this.isBatchLoading
           && e.dataset.xfrom!==this.me
           && (prevMessage
               ? !overlapsElemView(prevMessage, this.e.messagesWrapper)
               : false)){
          /* If a new non-history message arrives while the user is
             scrolled elsewhere, do not scroll to the latest
             message, but gently alert the user that a new message
             has arrived. */
          F.toast.message("New message has arrived.");
        }else if(!this.isBatchLoading && e.dataset.xfrom===Chat.me){
          this.scheduleScrollOfMsg(e);

             yet have enough information to know how far to scroll!
             For such cases we have to delay the scroll until the
             image loads (and we hope it does so before another
             message arrives).
          */
          if(1===+e.dataset.hasImage){
            e.querySelector('img').addEventListener('load',()=>e.scrollIntoView());
          }else if(!prevMessage || (prevMessage && isEntirelyInViewport(prevMessage))){
            e.scrollIntoView(false);
          }
        }
      },
      /** Returns true if chat-only mode is enabled. */
      isChatOnlyMode: ()=>document.body.classList.contains('chat-only-mode'),
      /**