(function() {
  "use strict";

  CodeMirror.defineOption("foldGutter", false, function(cm, val, old) {
    if (old && old != CodeMirror.Init) {
      cm.clearGutter(cm.state.foldGutter.options.gutter);
      cm.state.foldGutter = null;
      cm.off("gutterClick", onGutterClick);
      cm.off("change", onChange);
      cm.off("viewportChange", onViewportChange);
      cm.off("fold", onFold);
      cm.off("unfold", onFold);
    }
    if (val) {
      cm.state.foldGutter = new State(parseOptions(val));
      updateInViewport(cm);
      cm.on("gutterClick", onGutterClick);
      cm.on("change", onChange);
      cm.on("viewportChange", onViewportChange);
      cm.on("fold", onFold);
      cm.on("unfold", onFold);
    }
  });

  var Pos = CodeMirror.Pos;

  function State(options) {
    this.options = options;
    this.from = this.to = 0;
  }

  function parseOptions(opts) {
    if (opts === true) opts = {};
    if (opts.gutter == null) opts.gutter = "CodeMirror-foldgutter";
    if (opts.indicatorOpen == null) opts.indicatorOpen = "CodeMirror-foldgutter-open";
    if (opts.indicatorFolded == null) opts.indicatorFolded = "CodeMirror-foldgutter-folded";
    return opts;
  }

  function isFolded(cm, line) {
    var marks = cm.findMarksAt(Pos(line));
    for (var i = 0; i < marks.length; ++i)
      if (marks[i].__isFold && marks[i].find().from.line == line) return true;
  }

  function marker(spec) {
    if (typeof spec == "string") {
      var elt = document.createElement("div");
      elt.className = spec;
      return elt;
    } else {
      return spec.cloneNode(true);
    }
  }

  function updateFoldInfo(cm, from, to) {
    var opts = cm.state.foldGutter.options, cur = from;
    cm.eachLine(from, to, function(line) {
      var mark = null;
      if (isFolded(cm, cur)) {
        mark = marker(opts.indicatorFolded);
      } else {
        var pos = Pos(cur, 0), func = opts.rangeFinder || cm.getHelper(pos, "fold");
        var range = func && func(cm, pos);
        if (range && range.from.line + 1 < range.to.line)
          mark = marker(opts.indicatorOpen);
      }
      cm.setGutterMarker(line, opts.gutter, mark);
      ++cur;
    });
  }

  function updateInViewport(cm) {
    var vp = cm.getViewport(), state = cm.state.foldGutter;
    if (!state) return;
    cm.operation(function() {
      updateFoldInfo(cm, vp.from, vp.to);
    });
    state.from = vp.from; state.to = vp.to;
  }

  function onGutterClick(cm, line, gutter) {
    var opts = cm.state.foldGutter.options;
    if (gutter != opts.gutter) return;
    cm.foldCode(Pos(line, 0), opts.rangeFinder);
  }

  function onChange(cm) {
    var state = cm.state.foldGutter;
    state.from = state.to = 0;
    clearTimeout(state.changeUpdate);
    state.changeUpdate = setTimeout(function() { updateInViewport(cm); }, 600);
  }

  function onViewportChange(cm) {
    var state = cm.state.foldGutter;
    clearTimeout(state.changeUpdate);
    state.changeUpdate = setTimeout(function() {
      var vp = cm.getViewport();
      if (state.from == state.to || vp.from - state.to > 20 || state.from - vp.to > 20) {
        updateInViewport(cm);
      } else {
        cm.operation(function() {
          if (vp.from < state.from) {
            updateFoldInfo(cm, vp.from, state.from);
            state.from = vp.from;
          }
          if (vp.to > state.to) {
            updateFoldInfo(cm, state.to, vp.to);
            state.to = vp.to;
          }
        });
      }
    }, 400);
  }

  function onFold(cm, from) {
    var state = cm.state.foldGutter, line = from.line;
    if (line >= state.from && line < state.to)
      updateFoldInfo(cm, line, line + 1);
  }
})();