function intersect(a, b) {
  if (b.length > a.length) { [a, b] = [b, a]; } // loop over shorter array
  return a.filter(item => (b.indexOf(item) !== -1));
}

function insertAfter(newNode, referenceNode) {
    referenceNode.parentNode.insertBefore(newNode, referenceNode.nextSibling);
}

function moveAll(fromNode, toNode) {
  for (let c; (c = fromNode.firstChild) != null; ) { toNode.appendChild(c); }
}

function removeAllFrom(fromNode) {
  for (let c; (c = fromNode.lastChild) != null; ) { fromNode.removeChild(c); }
}

function turnIntoCts(node, makeNodeCallback) {
  node.onclick = function(e){
    e.preventDefault();
    let newNode = makeNodeCallback();
    if(newNode !== node) {
      removeAllFrom(node);
      moveAll(newNode, node);
      node.className = newNode.className;
    } else {
      node.onclick = '';
      node.classList.remove('cts');
    }
  };
}

function makeCts(makeNodeCallback, title) {
  let ctsNode = document.createElement('div');
  let placeholder = document.createElement('div');
  placeholder.className = 'placeholder';
  placeholder.innerHTML = title;
  ctsNode.className = 'cts';
  ctsNode.appendChild(placeholder);
  turnIntoCts(ctsNode, makeNodeCallback);
  return ctsNode;
}

function naiveEllipsis(str, len, ellStr='...') {
  let ellLen = ellStr.length;
  if (str.length <= len) { return str; }
  let half = Math.floor((len - ellLen) / 2);
  let left = str.substring(0, half);
  let right = str.substring(str.length - (len - half - ellLen));
  return '' + left + ellStr + right;
}

function wrapIntoTag(node, tagName, className) {
  let tag = document.createElement(tagName);
  if (className !== undefined) { tag.className = className; }
  tag.appendChild(node);
  return tag;
}

function getEmbedableLinkTypes() {
  return [
    {
      name: 'Jpeg and png images',
      id: 'embed_jpeg_and_png_images',
      ctsDefault: false,
      re: /\.(jpeg|jpg|png|svg)(:[a-zA-Z]+)?(?:\?[\w&;\?=]*)?$/i,
      makeNode: function(aNode) {
        let aNode2 = document.createElement('a');
        let imgNode = document.createElement('img');
        imgNode.src = aNode.href;
        aNode2.href = aNode.href;
        aNode2.appendChild(imgNode);
        return wrapIntoTag(aNode2, 'div');
      }
    },
    {
      name: 'Gif images',
      id: 'embed_gif_images',
      ctsDefault: true,
      re: /\.gif(:[a-zA-Z]+)?(?:\?[\w&;\?=]*)?$/i,
      makeNode: function(aNode) {
        let aNode2 = document.createElement('a');
        let imgNode = document.createElement('img');
        imgNode.src = aNode.href;
        aNode2.href = aNode.href;
        aNode2.appendChild(imgNode);
        return wrapIntoTag(aNode2, 'div');
      }
    }
  ]
}

function embedLink(aNode, linkTypes, container, alwaysCts, afterNode) {
  let anyEmbed = false;
  let linkId = (aNode.href.replace(/^https?:/i, '').replace(/\'/i,''));
  let sameEmbed = container.querySelector('*[data-linkid=\'' + linkId + '\']'); // do not embed the same thing twice
  if (sameEmbed === null) {
    anyEmbed = [].some.call(linkTypes, function(linkType) {
      /* if (GM_getValue(linkType.id, true)) { TODO user embed particular link type setting */
        let reResult = linkType.re.exec(aNode.href);
        if (reResult !== null) {
          if ((linkType.match !== undefined) && (linkType.match(aNode, reResult) === false)) { return false; }
          let newNode;
          let isCts = alwaysCts /* || TODO user click-to-show setting */;
          if (isCts) {
            let linkTitle = (linkType.makeTitle !== undefined) ? linkType.makeTitle(aNode, reResult) : naiveEllipsis(aNode.href, 55);
            newNode = makeCts(() => linkType.makeNode(aNode, reResult, newNode), 'Click to show: ' + linkTitle);
          } else {
            newNode = linkType.makeNode(aNode, reResult);
          }
          if (!newNode) { return false; }
          aNode.classList.add('embedLink');
          /*
          if (GM_getValue('enable_link_text_update', true) && (linkType.linkTextUpdate !== undefined)) {
            linkType.linkTextUpdate(aNode, reResult);
          }
          */
          newNode.setAttribute('data-linkid', linkId);
          if (afterNode !== undefined) {
            insertAfter(newNode, afterNode);
          } else {
            container.appendChild(newNode);
          }
          //setHighlightOnHover(aNode, newNode);
          return true;
        }
      /* } */
    });
  }
  return anyEmbed;
}

function embedLinks(aNodes, container, alwaysCts, afterNode) {
  let anyEmbed = false;
  let embedableLinkTypes = getEmbedableLinkTypes();
  Array.from(aNodes).forEach(aNode => {
    let isEmbedded = embedLink(aNode, embedableLinkTypes, container, alwaysCts, afterNode);
    anyEmbed = anyEmbed || isEmbedded;
  });
  return anyEmbed;
}

function articleInfo(article) {
  let userId = article.querySelector('div.msg-avatar > a > img').alt;
  let tagNodes = article.querySelectorAll('.msg-tags > *');
  let tags = Array.from(tagNodes).map(d => d.textContent.toLowerCase());
  return { userId: userId, tags: tags };
}

function isFilteredX(x, filteredUsers, filteredTags) {
  let {userId, tags} = articleInfo(x);
  return (filteredUsers !== undefined && filteredUsers.indexOf(userId.toLowerCase()) !== -1)
         || (intersect(tags, filteredTags).length > 0);
}

function embedLinksToX(x, beforeNodeSelector, allLinksSelector, ctsUsers, ctsTags) {
  let isCtsPost = isFilteredX(x, ctsUsers, ctsTags);
  let allLinks = x.querySelectorAll(allLinksSelector);
  let embedContainer = document.createElement('div');
  embedContainer.className = 'embedContainer';
  let anyEmbed = embedLinks(allLinks, embedContainer, isCtsPost);
  if (anyEmbed) {
    let beforeNode = x.querySelector(beforeNodeSelector);
    x.insertBefore(embedContainer, beforeNode);
  }
}

function embedLinksToArticles() {
  let ctsUsers = [], ctsTags = [] // TODO click-to-show users and tags
  let beforeNodeSelector = 'nav.l';
  let allLinksSelector = 'p:not(.ir) a, pre a';
  Array.from(document.querySelectorAll('#content > article')).forEach(article => {
    embedLinksToX(article, beforeNodeSelector, allLinksSelector, ctsUsers, ctsTags);
  });
}

function embedLinksToPost() {
  let ctsUsers = [], ctsTags = [] // TODO click-to-show users and tags
  let beforeNodeSelector = '.msg-txt + *';
  let allLinksSelector = '.msg-txt a';
  Array.from(document.querySelectorAll('#content .msg-cont')).forEach(msg => {
    embedLinksToX(msg, beforeNodeSelector, allLinksSelector, ctsUsers, ctsTags);
  });
}

exports.embed = function() {
	if (document.querySelectorAll('#content > article').length) {
		embedLinksToArticles();
	} else {
		embedLinksToPost();
	}
}