/* expandable sections */
(function () {
  function toggle (button, target) {
    var expanded = button.getAttribute('aria-expanded') === 'true';
    button.setAttribute('aria-expanded', !expanded);
    target.hidden = !target.hidden;
  }

  var expanders = document.querySelectorAll('[data-expands]');

  Array.prototype.forEach.call(expanders, function (expander) {
    var target = document.getElementById(expander.getAttribute('data-expands'));

    expander.addEventListener('click', function () {
      toggle(expander, target);
    })
  })
}());

/* menu button */
(function () {
  var button = document.getElementById('menu-button');
  if (button) {
    var menu = document.getElementById('patterns-list');
    button.addEventListener('click', function() {
      var expanded = this.getAttribute('aria-expanded') === 'true';
      this.setAttribute('aria-expanded', !expanded);
    })
  }
}());

/* persist navigation scroll point */
(function () {
  window.onbeforeunload = function () {
    var patternsNav = document.getElementById('patterns-nav');
    if (patternsNav) {
      var scrollPoint = patternsNav.scrollTop;
      localStorage.setItem('scrollPoint', scrollPoint);
    }
  }

  window.addEventListener('DOMContentLoaded', function () {
    if (document.getElementById('patterns-nav')) {
      if (window.location.href.indexOf('patterns/') !== -1) {
        document.getElementById('patterns-nav').scrollTop = parseInt(localStorage.getItem('scrollPoint'));
      } else {
        document.getElementById('patterns-nav').scrollTop = 0;
      }
    }
  })
}());

/* Add "link here" links to <h2> headings */
(function () {
  var headings = document.querySelectorAll('main > h2');

  Array.prototype.forEach.call(headings, function (heading) {
    var id = heading.getAttribute('id');

    if (id) {
      var newHeading = heading.cloneNode(true);
      newHeading.setAttribute('tabindex', '-1');

      var container = document.createElement('div');
      container.setAttribute('class', 'h2-container');
      container.appendChild(newHeading);

      heading.parentNode.insertBefore(container, heading);

      var link = document.createElement('a');
      link.setAttribute('href', '#' + id);
      var headingText = heading.textContent;
      link.setAttribute('aria-label', 'This ' + headingText + ' section');
      link.innerHTML = '<svg aria-hidden="true" class="link-icon" viewBox="0 0 50 50" focusable="false"> <use xlink:href="#link"></use> </svg>';

      container.appendChild(link);

      heading.parentNode.removeChild(heading);
    }
  })
}());

/* Enable scrolling by keyboard of code samples */
(function () {
  var codeBlocks = document.querySelectorAll('pre');

  Array.prototype.forEach.call(codeBlocks, function (block) {
    if (block.querySelector('code')) {
      block.setAttribute('role', 'region');
      block.setAttribute('aria-label', 'code sample');
      if (block.scrollWidth > block.clientWidth) {
        block.setAttribute('tabindex', '0');
      }
    }
  });
}());

/* Switch and persist theme */
(function () {
  function CSSSupported (property, value) {
    var prop = property + ':',
        el = document.createElement('test'),
        mStyle = el.style;
    el.style.cssText = prop + value;
    return mStyle[property];
  }

  var checkbox = document.getElementById('themer');
  var inverter = document.getElementById('inverter');

  if (!CSSSupported('filter', 'invert(100%)')) {
    checkbox.parentNode.hidden = true;
    return;
  }

  function darkTheme(media) {
    inverter.setAttribute('media', media);
    inverter.textContent = inverter.textContent.trim();
    localStorage.setItem('darkTheme', media);
  }

  checkbox.addEventListener('change', function () {
    darkTheme(this.checked ? 'screen' : 'none');
  });

  window.addEventListener('DOMContentLoaded', function () {
    if ('filter' in document.body.style) {
      if (localStorage.getItem('darkTheme') === 'screen') {
        checkbox.click();
      }
    }
  });
}());