/*
** Copyright © 2018 Warren Young
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the Simplified BSD License (also
** known as the "2-Clause License" or "FreeBSD License".)
**
** This program is distributed in the hope that it will be useful,
** but without any warranty; without even the implied warranty of
** merchantability or fitness for a particular purpose.
**
** Contact: wyoung on the Fossil forum, https://fossil-scm.org/forum/
**
*******************************************************************************
**
** This file contains the JS code specific to the Fossil default skin.
** Currently, the only thing this does is handle clicks on its hamburger
** menu button.
*/
(function() {
  var panel = document.getElementById("hbdrop");
  if (!panel) return;   // site admin might've nuked it
  if (!panel.style) return;  // shouldn't happen, but be sure
  var panelBorder = panel.style.border;

  // Disable animation if this browser doesn't support CSS transitions.
  //
  // We need this ugly calling form for old browsers that don't allow
  // panel.style.hasOwnProperty('transition'); catering to old browsers
  // is the whole point here.
  var animate = panel.style.transition !== null && (typeof(panel.style.transition) == "string");
  var animMS = 400;

  // Calculate panel height despite its being hidden at call time.
  // Based on https://stackoverflow.com/a/29047447/142454
  var panelHeight;  // computed on sitemap load
  function calculatePanelHeight() {
    // Get initial panel styles so we can restore them below.
    var es   = window.getComputedStyle(panel),
        edis = es.display,
        epos = es.position,
        evis = es.visibility;

    // Restyle the panel so we can measure its height while invisible.
    panel.style.visibility = 'hidden';
    panel.style.position   = 'absolute';
    panel.style.display    = 'block';
    panelHeight = panel.offsetHeight + 'px';

    // Revert styles now that job is done.
    panel.style.display    = edis;
    panel.style.position   = epos;
    panel.style.visibility = evis;
  }

  // Show the panel by changing the panel height, which kicks off the
  // slide-open/closed transition set up in the XHR onload handler.
  //
  // Schedule the change for a near-future time in case this is the
  // first call, where the div was initially invisible.  If we were
  // to change the panel's visibility and height at the same time
  // instead, that would prevent the browser from seeing the height
  // change as a state transition, so it'd skip the CSS transition:
  //
  // https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Transitions/Using_CSS_transitions#JavaScript_examples
  function showPanel() {
    if (animate) {
      setTimeout(function() {
        panel.style.maxHeight = panelHeight;
        panel.style.border    = panelBorder;
      }, 40);   // 25ms is insufficient with Firefox 62
    }
    else {
      panel.style.display = 'block';
    }
  }

  // Return true if the panel is showing.
  function panelShowing() {
    if (animate) {
      return panel.style.maxHeight == panelHeight;
    }
    else {
      return panel.style.display == 'block';
    }
  }

  // Click handler for the hamburger button.
  var needSitemapHTML = true;
  document.querySelector("div.mainmenu > a").onclick = function() {
    if (panelShowing()) {
      // Transition back to hidden state.
      if (animate) {
        panel.style.maxHeight = '0';
        setTimeout(function() {
          // Browsers show a 1px high border line when maxHeight == 0,
          // our "hidden" state, so hide the borders in that state, too.
          panel.style.border = 'none';
        }, animMS);
      }
      else {
        panel.style.display = 'none';
      }
    }
    else if (needSitemapHTML) {
      // Only get it once per page load: it isn't likely to
      // change on us.
      var xhr = new XMLHttpRequest();
      xhr.onload = function() {
        var doc = xhr.responseXML;
        if (doc) {
          var sm = doc.querySelector("ul#sitemap");
          if (sm && xhr.status == 200) {
            // Got sitemap.  Insert it into the drop-down panel.
            needSitemapHTML = false;
            panel.innerHTML = sm.outerHTML;

            // Display the panel
            if (animate) {
              // Set up a CSS transition to animate the panel open and
              // closed.  Only needs to be done once per page load.
              // Based on https://stackoverflow.com/a/29047447/142454
              calculatePanelHeight();
              panel.style.transition = 'max-height ' + animMS +
                  'ms ease-in-out';
              panel.style.overflowY  = 'hidden';
              panel.style.maxHeight  = '0';
              showPanel();
            }
            panel.style.display = 'block';
          }
        }
        // else, can't parse response as HTML or XML
      }
      xhr.open("GET", "$home/sitemap?popup");   // note the TH1 substitution!
      xhr.responseType = "document";
      xhr.send();
    }
    else {
      showPanel();   // just show what we built above
    }
    return false;  // prevent browser from acting on <a> click
  }
})();
