textDiffCodeMirrorBinding.js

// This file began as a copy of https://github.com/share/text-diff-binding/blob/master/index.js
// Draws also from https://github.com/ejones/sharedb-codemirror/blob/master/sharedb-codemirror.js
module.exports = TextDiffBinding;

// Accepts an instance of CodeMirror.
function TextDiffBinding(codeMirror) {
  this.codeMirror = codeMirror;
}

TextDiffBinding.prototype._get =
TextDiffBinding.prototype._insert =
TextDiffBinding.prototype._remove = function() {
  throw new Error('`_get()`, `_insert(index, length)`, and `_remove(index, length)` prototype methods must be defined.');
};

TextDiffBinding.prototype._getElementValue = function() {
  var value = this.codeMirror.getValue();
  // IE and Opera replace \n with \r\n. Always store strings as \n
  return value.replace(/\r\n/g, '\n');
};

TextDiffBinding.prototype._getInputEnd = function(previous, value) {
  if (!this.codeMirror.hasFocus()) return null;
  var selectionStartPos = this.codeMirror.getCursor("from");
  var selectionStart = this.codeMirror.indexFromPos(selectionStartPos);
  var end = value.length - selectionStart;
  if (end === 0) return end;
  if (previous.slice(previous.length - end) !== value.slice(value.length - end)) return null;
  return end;
};

TextDiffBinding.prototype.onInput = function() {
  var previous = this._get();
  var value = this._getElementValue();
  if (previous === value) return;

  var start = 0;
  // Attempt to use the DOM cursor position to find the end
  var end = this._getInputEnd(previous, value);
  if (end === null) {
    // If we failed to find the end based on the cursor, do a diff. When
    // ambiguous, prefer to locate ops at the end of the string, since users
    // more frequently add or remove from the end of a text input
    while (previous.charAt(start) === value.charAt(start)) {
      start++;
    }
    end = 0;
    while (
      previous.charAt(previous.length - 1 - end) === value.charAt(value.length - 1 - end) &&
      end + start < previous.length &&
      end + start < value.length
    ) {
      end++;
    }
  } else {
    while (
      previous.charAt(start) === value.charAt(start) &&
      start + end < previous.length &&
      start + end < value.length
    ) {
      start++;
    }
  }

  if (previous.length !== start + end) {
    var removed = previous.slice(start, previous.length - end);
    this._remove(start, removed);
  }
  if (value.length !== start + end) {
    var inserted = value.slice(start, value.length - end);
    this._insert(start, inserted);
  }
};

TextDiffBinding.prototype.onInsert = function(index, length) {
  this._transformSelectionAndUpdate(index, length, insertCursorTransform);
};
function insertCursorTransform(index, length, cursor) {
  return (index < cursor) ? cursor + length : cursor;
}

TextDiffBinding.prototype.onRemove = function(index, length) {
  this._transformSelectionAndUpdate(index, length, removeCursorTransform);
};
function removeCursorTransform(index, length, cursor) {
  return (index < cursor) ? cursor - Math.min(length, cursor - index) : cursor;
}

TextDiffBinding.prototype._transformSelectionAndUpdate = function(index, length, transformCursor) {
  if (this.codeMirror.hasFocus()) {
    var rawSelectionStartPos = this.codeMirror.getCursor("from");
    var rawSelectionStart = this.codeMirror.indexFromPos(rawSelectionStartPos);
    var selectionStart = transformCursor(index, length, rawSelectionStart);

    var rawSelectionEndPos = this.codeMirror.getCursor("to");
    var rawSelectionEnd = this.codeMirror.indexFromPos(rawSelectionEndPos);
    var selectionEnd = transformCursor(index, length, rawSelectionEnd);

    this.update();

    var selectionStartPos = this.codeMirror.posFromIndex(selectionStart);
    var selectionEndPos = this.codeMirror.posFromIndex(selectionEnd);

    this.codeMirror.setSelection(selectionStartPos, selectionEndPos, { scroll: false });
  } else {
    this.update();
  }
};

TextDiffBinding.prototype.update = function() {
  var value = this._get();
  if (this._getElementValue() === value) return;

  // Set the value, but do not scroll to the top.
  var scrollInfo = this.codeMirror.getScrollInfo();
  this.codeMirror.setValue(value);
  this.codeMirror.scrollTo(scrollInfo.left, scrollInfo.top);
};