tinymce.PluginManager.add('mathjax', function(editor, url) {

  // plugin configuration options
  let mathjaxClassName = editor.settings.mathjax.className || "math-tex";
  let mathjaxTempClassName = mathjaxClassName + '-original';
  let mathjaxSymbols = editor.settings.mathjax.symbols || {start: '\\(', end: '\\)'};
  let mathjaxUrl = editor.settings.mathjax.lib || null;
  let mathjaxConfigUrl = (editor.settings.mathjax.configUrl || url + '/config.js') + '?class=' + mathjaxTempClassName;
  let mathjaxScripts = [mathjaxConfigUrl];
  if (mathjaxUrl) {
    mathjaxScripts.push(mathjaxUrl);
  }

  // load mathjax and its config on editor init
  editor.on('init', function () {
    let scripts = editor.getDoc().getElementsByTagName('script');
    for (let i = 0; i < mathjaxScripts.length; i++) {
      // check if script have already loaded
      let id = editor.dom.uniqueId();
      let script = editor.dom.create('script', {id: id, type: 'text/javascript', src: mathjaxScripts[i]});
      let found = false;
      for (let j = 0; j < scripts.length; j++) {
        if (scripts[j].src == script.src) {
          found = true;
          break;
        }
      }
      // load script
      if (!found) {
        editor.getDoc().getElementsByTagName('head')[0].appendChild(script);
      }
    }
  });

  // remove extra tags on get content
  editor.on('GetContent', function (e) {
    let div = editor.dom.create('div');
    div.innerHTML = e.content;
    let elements = div.querySelectorAll('.' + mathjaxClassName);
    for (let i = 0; i < elements.length; i++) {
      let children = elements[i].querySelectorAll('span');
      for (let j = 0; j < children.length; j++) {
        children[j].remove();
      }
      let latex = elements[i].getAttribute('data-latex');
      elements[i].removeAttribute('contenteditable');
      elements[i].removeAttribute('style');
      elements[i].removeAttribute('data-latex');
      elements[i].innerHTML = latex;
    }
    e.content = div.innerHTML;
  });

  let checkElement = function(element) {
    if (element.childNodes.length != 2) {
      element.setAttribute('contenteditable', false);
      element.style.cursor = 'pointer';
      let latex = element.getAttribute('data-latex') || element.innerHTML;
      element.setAttribute('data-latex', latex);
      element.innerHTML = '';

      let math = editor.dom.create('span');
      math.innerHTML = latex;
      math.classList.add(mathjaxTempClassName);
      element.appendChild(math);

      let dummy = editor.dom.create('span');
      dummy.classList.add('dummy');
      dummy.innerHTML = 'dummy';
      dummy.setAttribute('hidden', 'hidden');
      element.appendChild(dummy);
    }
  };

  // add dummy tag on set content
  editor.on('BeforeSetContent', function (e) {
    let div = editor.dom.create('div');
    div.innerHTML = e.content;
    let elements = div.querySelectorAll('.' + mathjaxClassName);
    for (let i = 0 ; i < elements.length; i++) {
      checkElement(elements[i]);
    }
    e.content = div.innerHTML;
  });

  // refresh mathjax on set content
  editor.on('SetContent', function(e) {
    if (editor.getDoc().defaultView.MathJax) {
      editor.getDoc().defaultView.MathJax.startup.getComponents();
      editor.getDoc().defaultView.MathJax.typeset();
    }
  });

  // refresh mathjax on any content change
  editor.on('Change', function(data) {
    elements = editor.dom.getRoot().querySelectorAll('.' + mathjaxClassName);
    if (elements.length) {
      for (let i = 0 ; i < elements.length; i++) {
        checkElement(elements[i]);
      }
      if (editor.getDoc().defaultView.MathJax) {
        editor.getDoc().defaultView.MathJax.startup.getComponents();
        editor.getDoc().defaultView.MathJax.typeset();
      }
    }
  });

  // add button to tinimce
  editor.ui.registry.addToggleButton('mathjax', {
    text: 'Σ',
    tooltip: 'Mathjax',
    onAction: function() {
      let selected = editor.selection.getNode();
      let target = undefined;
      if (selected.classList.contains(mathjaxClassName)) {
        target = selected;
      }
      openMathjaxEditor(target);
    },
    onSetup: function (buttonApi) {
      return editor.selection.selectorChangedWithUnbind('.' + mathjaxClassName, buttonApi.setActive).unbind;
    }
  });

  // handle click on existing
  editor.on("click", function (e) {
    let closest = e.target.closest('.' + mathjaxClassName);
    if (closest) {
      openMathjaxEditor(closest);
    }
  });

  // open window with editor
  let openMathjaxEditor = function(target) {

    let mathjaxId = editor.id + '_' + editor.dom.uniqueId();

    let latex = '';
    if (target) {
      latex_attribute = target.getAttribute('data-latex');
      if (latex_attribute.length >= (mathjaxSymbols.start + mathjaxSymbols.end).length) {
        latex = latex_attribute.substr(mathjaxSymbols.start.length, latex_attribute.length - (mathjaxSymbols.start + mathjaxSymbols.end).length);
      }
    }

    // show new window
    editor.windowManager.open({
      title: 'Mathjax',
      width: 600,
      height: 300,
      body: {
        type: 'panel',
        items: [{
            type: 'textarea',
            name: 'title',
            label: 'LaTex'
          }, {
            type: 'htmlpanel',
            html: '<div style="text-align:right"><a href="https://wikibooks.org/wiki/LaTeX/Mathematics" target="_blank" style="font-size:small">LaTex</a></div>'
          }, {
            type: 'htmlpanel',
            html: '<iframe id="' + mathjaxId + '" style="width: 100%; min-height: 50px;"></iframe>'
        }]
      },
      buttons: [{type: 'submit', text: 'OK'}],
      onSubmit: function onsubmit(api) {
        let value = api.getData().title.trim();
        if (target) {
          target.innerHTML = '';
          target.setAttribute('data-latex', getMathText(value));
          checkElement(target);
        } else {
          let newElement = editor.getDoc().createElement('span');
          newElement.innerHTML = getMathText(value);
          newElement.classList.add(mathjaxClassName);
          checkElement(newElement);
          editor.insertContent(newElement.outerHTML);
        }
        editor.getDoc().defaultView.MathJax.startup.getComponents();
        editor.getDoc().defaultView.MathJax.typeset();
        api.close();
      },
      onChange: function(api) {
        var value = api.getData().title.trim();
        if (value != latex) {
          refreshDialogMathjax(value, document.getElementById(mathjaxId));
          latex = value;
        }
      },
      initialData: {title: latex}
    });

    // add scripts to iframe
    let iframe = document.getElementById(mathjaxId);
    let iframeWindow = iframe.contentWindow || iframe.contentDocument.document || iframe.contentDocument;
    let iframeDocument = iframeWindow.document;
    let iframeHead = iframeDocument.getElementsByTagName('head')[0];
    let iframeBody = iframeDocument.getElementsByTagName('body')[0];
  
    // get latex for mathjax from simple text
    let getMathText = function (value, symbols) {
      if (!symbols) {
        symbols = mathjaxSymbols;
      }
      return symbols.start + ' ' + value + ' ' + symbols.end;
    };

    // refresh latex in mathjax iframe
    let refreshDialogMathjax = function(latex) {
      let MathJax = iframeWindow.MathJax;
      let div = iframeBody.querySelector('div');
      if (!div) {
        div = iframeDocument.createElement('div');
        div.classList.add(mathjaxTempClassName);
        iframeBody.appendChild(div);
      }
      div.innerHTML = getMathText(latex, {start: '$$', end: '$$'});
      if (MathJax && MathJax.startup) {
        MathJax.startup.getComponents();
        MathJax.typeset();
      }
    };
    refreshDialogMathjax(latex);

    // add scripts for dialog iframe
    for (let i = 0; i < mathjaxScripts.length; i++) {
      let node = iframeWindow.document.createElement('script');
      node.src = mathjaxScripts[i];
      node.type = 'text/javascript';
      node.async = false;
      node.charset = 'utf-8';
      iframeHead.appendChild(node);
    }

  };
});