HackMD/lib/ot/selection.js

if (typeof ot === 'undefined') {
  // Export for browsers
  var ot = {};
}

ot.Selection = (function (global) {
  'use strict';

  var TextOperation = global.ot ? global.ot.TextOperation : require('./text-operation');

  // Range has `anchor` and `head` properties, which are zero-based indices into
  // the document. The `anchor` is the side of the selection that stays fixed,
  // `head` is the side of the selection where the cursor is. When both are
  // equal, the range represents a cursor.
  function Range (anchor, head) {
    this.anchor = anchor;
    this.head = head;
  }

  Range.fromJSON = function (obj) {
    return new Range(obj.anchor, obj.head);
  };

  Range.prototype.equals = function (other) {
    return this.anchor === other.anchor && this.head === other.head;
  };

  Range.prototype.isEmpty = function () {
    return this.anchor === this.head;
  };

  Range.prototype.transform = function (other) {
    function transformIndex (index) {
      var newIndex = index;
      var ops = other.ops;
      for (var i = 0, l = other.ops.length; i < l; i++) {
        if (TextOperation.isRetain(ops[i])) {
          index -= ops[i];
        } else if (TextOperation.isInsert(ops[i])) {
          newIndex += ops[i].length;
        } else {
          newIndex -= Math.min(index, -ops[i]);
          index += ops[i];
        }
        if (index < 0) { break; }
      }
      return newIndex;
    }

    var newAnchor = transformIndex(this.anchor);
    if (this.anchor === this.head) {
      return new Range(newAnchor, newAnchor);
    }
    return new Range(newAnchor, transformIndex(this.head));
  };

  // A selection is basically an array of ranges. Every range represents a real
  // selection or a cursor in the document (when the start position equals the
  // end position of the range). The array must not be empty.
  function Selection (ranges) {
    this.ranges = ranges || [];
  }

  Selection.Range = Range;

  // Convenience method for creating selections only containing a single cursor
  // and no real selection range.
  Selection.createCursor = function (position) {
    return new Selection([new Range(position, position)]);
  };

  Selection.fromJSON = function (obj) {
    var objRanges = obj.ranges || obj;
    for (var i = 0, ranges = []; i < objRanges.length; i++) {
      ranges[i] = Range.fromJSON(objRanges[i]);
    }
    return new Selection(ranges);
  };

  Selection.prototype.equals = function (other) {
    if (this.position !== other.position) { return false; }
    if (this.ranges.length !== other.ranges.length) { return false; }
    // FIXME: Sort ranges before comparing them?
    for (var i = 0; i < this.ranges.length; i++) {
      if (!this.ranges[i].equals(other.ranges[i])) { return false; }
    }
    return true;
  };

  Selection.prototype.somethingSelected = function () {
    for (var i = 0; i < this.ranges.length; i++) {
      if (!this.ranges[i].isEmpty()) { return true; }
    }
    return false;
  };

  // Return the more current selection information.
  Selection.prototype.compose = function (other) {
    return other;
  };

  // Update the selection with respect to an operation.
  Selection.prototype.transform = function (other) {
    for (var i = 0, newRanges = []; i < this.ranges.length; i++) {
      newRanges[i] = this.ranges[i].transform(other);
    }
    return new Selection(newRanges);
  };

  return Selection;

}(this));

// Export for CommonJS
if (typeof module === 'object') {
  module.exports = ot.Selection;
}