(function(){
  if (window.location.host != 'forum.omsk.com')
    return;

  let blacklist = [
    "OmskLis",
  ];

  window.addEventListener('DOMContentLoaded', (event) => {
    // get a message DOM element
    const getMessage = (el) => el.querySelector('.messageContent');

    // set text for a button and style for a message
    const initMessage = (message, button, hide) => {
      message.style.display = hide ? 'none' : 'block';
      button.textContent = hide ? 'Show' : 'Hide';
    };

    // add a button for each message
    for (let el of document.querySelectorAll('li.message')) {
      const blacklisted = blacklist.includes(el.attributes['data-author'].value);
      let button = document.createElement('button');
      button.addEventListener('click', (event) => {
        let button = event.target;
        let message = getMessage(button.parentNode);
        initMessage(message, button, message.style.display !== 'none');
      });

      let message = getMessage(el);
      initMessage(message, button, blacklisted);
      message.parentNode.insertBefore(button, message);
    }
  });
})();