(function () {
  // Minimal event-handling wrapper.
  function stopEvent() {
    if (this.preventDefault) {this.preventDefault(); this.stopPropagation();}
    else {this.returnValue = false; this.cancelBubble = true;}
  }
  function addStop(event) {
    if (!event.stop) event.stop = stopEvent;
    return event;
  }
  function connect(node, type, handler) {
    function wrapHandler(event) {handler(addStop(event || window.event));}
    if (typeof node.addEventListener == "function")
      node.addEventListener(type, wrapHandler, false);
    else
      node.attachEvent("on" + type, wrapHandler);
  }

  function forEach(arr, f) {
    for (var i = 0, e = arr.length; i < e; ++i) f(arr[i]);
  }

  var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
    lineNumbers: true,
    onKeyEvent: function(i, e) {
      // Hook into ctrl-space
      if (e.keyCode == 32 && (e.ctrlKey || e.metaKey) && !e.altKey) {
        e.stop();
        return startComplete();
      }
    }
  });

  function startComplete() {
    // We want a single cursor position.
    if (editor.somethingSelected()) return;
    // Find the token at the cursor
    var cur = editor.getCursor(false), token = editor.getTokenAt(cur), tprop = token;
    // If it's not a 'word-style' token, ignore the token.
    if (!/^[\w$_]*$/.test(token.string)) {
      token = tprop = {start: cur.ch, end: cur.ch, string: "", state: token.state,
                       className: token.string == "." ? "js-property" : null};
    }
    // If it is a property, find out what it is a property of.
    while (tprop.className == "js-property") {
      tprop = editor.getTokenAt({line: cur.line, ch: tprop.start});
      if (tprop.string != ".") return;
      tprop = editor.getTokenAt({line: cur.line, ch: tprop.start});
      if (!context) var context = [];
      context.push(tprop);
    }
    var completions = getCompletions(token, context);
    if (!completions.length) return;
    function insert(str) {
      editor.replaceRange(str, {line: cur.line, ch: token.start}, {line: cur.line, ch: token.end});
    }
    // When there is only one completion, use it directly.
    if (completions.length == 1) {insert(completions[0]); return true;}

    // Build the select widget
    var complete = document.createElement("div");
    complete.className = "completions";
    var sel = complete.appendChild(document.createElement("select"));
    sel.multiple = true;
    for (var i = 0; i < completions.length; ++i) {
      var opt = sel.appendChild(document.createElement("option"));
      opt.appendChild(document.createTextNode(completions[i]));
    }
    sel.firstChild.selected = true;
    sel.size = Math.min(10, completions.length);
    var pos = editor.cursorCoords();
    complete.style.left = pos.x + "px";
    complete.style.top = pos.yBot + "px";
    document.body.appendChild(complete);
    // Hack to hide the scrollbar.
    if (completions.length <= 10)
      complete.style.width = (sel.clientWidth - 1) + "px";

    var done = false;
    function close() {
      if (done) return;
      done = true;
      complete.parentNode.removeChild(complete);
    }
    function pick() {
      insert(sel.options[sel.selectedIndex].value);
      close();
      setTimeout(function(){editor.focus();}, 50);
    }
    connect(sel, "blur", close);
    connect(sel, "keydown", function(event) {
      var code = event.keyCode;
      // Enter and space
      if (code == 13 || code == 32) {event.stop(); pick();}
      // Escape
      else if (code == 27) {event.stop(); close(); editor.focus();}
      else if (code != 38 && code != 40) {close(); editor.focus(); setTimeout(startComplete, 50);}
    });
    connect(sel, "dblclick", pick);

    sel.focus();
    // Opera sometimes ignores focusing a freshly created node
    if (window.opera) setTimeout(function(){if (!done) sel.focus();}, 100);
    return true;
  }

  var stringProps = ("charAt charCodeAt indexOf lastIndexOf substring substr slice trim trimLeft trimRight " +
                     "toUpperCase toLowerCase split concat match replace search").split(" ");
  var arrayProps = ("length concat join splice push pop shift unshift slice reverse sort indexOf " +
                    "lastIndexOf every some filter forEach map reduce reduceRight ").split(" ");
  var funcProps = "prototype apply call bind".split(" ");
  var keywords = ("break case catch continue debugger default delete do else false finally for function " +
                  "if in instanceof new null return switch throw true try typeof var void while with").split(" ");

  function getCompletions(token, context) {
    var found = [], start = token.string;
    function maybeAdd(str) {
      if (str.indexOf(start) == 0) found.push(str);
    }
    function gatherCompletions(obj) {
      if (typeof obj == "string") forEach(stringProps, maybeAdd);
      else if (obj instanceof Array) forEach(arrayProps, maybeAdd);
      else if (obj instanceof Function) forEach(funcProps, maybeAdd);
      for (var name in obj) maybeAdd(name);
    }

    if (context) {
      // If this is a property, see if it belongs to some object we can
      // find in the current environment.
      var obj = context.pop(), base;
      if (obj.className == "js-variable")
        base = window[obj.string];
      else if (obj.className == "js-string")
        base = "";
      else if (obj.className == "js-atom")
        base = 1;
      while (base != null && context.length)
        base = base[context.pop().string];
      if (base != null) gatherCompletions(base);
    }
    else {
      // If not, just look in the window object and any local scope
      // (reading into JS mode internals to get at the local variables)
      for (var v = token.state.localVars; v; v = v.next) maybeAdd(v.name);
      gatherCompletions(window);
      forEach(keywords, maybeAdd);
    }
    return found;
  }
})();
