const triggers = document.querySelectorAll('.accordion__trigger');

triggers.forEach(
  function(item, index) {
    
    //
    // Add click handler
    //
    item.addEventListener(
      'click', 
      function() {
        return accordion_toggle(item);
      }
    );
    
    //
    // Add keyboard handlers
    // Borrowed from https://www.w3.org/TR/wai-aria-practices/examples/accordion/accordion.html
    //
    item.addEventListener(
      'keydown', 
      function(event) {
        
        let trigger_arr = Array.prototype.slice.call( triggers );
        let target = event.target;
        let key = event.which.toString();
        let ctrl_modifier = (event.ctrlKey && key.match(/33|34/));

        if (key.match(/38|40/) || ctrl_modifier) {
          let index = trigger_arr.indexOf(target);
          let direction = (key.match(/34|40/)) ? 1 : -1;
          let length = triggers.length;
          let newIndex = (index + length + direction) % length;

          trigger_arr[newIndex].focus();

          event.preventDefault();
        }
        else if (key.match(/35|36/)) {
          // 35 = End, 36 = Home keyboard operations
          switch (key) {
            // Go to first accordion
            case '36':
              trigger_arr[0].focus();
              break;
              // Go to last accordion
            case '35':
              trigger_arr[trigger_arr.length - 1].focus();
              break;
          }
          event.preventDefault();
        }
      }
    );
    
  }
);

function accordion_toggle(trigger_item) {
  let content_element = document.getElementById( trigger_item.getAttribute('aria-controls') );
  
  if ( content_element ) {
    if ( content_element.classList.contains('accordion__content--expanded') ) {
      trigger_item.setAttribute('aria-expanded', false);
      accordion_content_collapse(content_element);
    } 
    else {
      trigger_item.setAttribute('aria-expanded', true);
      accordion_content_expand(content_element);
    }
  }
}

function accordion_content_collapse(content_element) {
  
  if ( content_element ) {
    content_element.classList.remove('accordion__content--expanded');
  }
}

function accordion_content_expand(content_element) {

  if ( content_element ) {
    content_element.classList.add('accordion__content--expanded');
  }
}