flutter-go/zefyr/lib/util.dart

// Copyright (c) 2018, the Zefyr project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// Utility functions for Zefyr.
library zefyr.util;

import 'dart:math' as math;

import 'package:quill_delta/quill_delta.dart';

export 'src/fast_diff.dart';

int getPositionDelta(Delta user, Delta actual) {
  final userIter = new DeltaIterator(user);
  final actualIter = new DeltaIterator(actual);
  int diff = 0;
  while (userIter.hasNext || actualIter.hasNext) {
    num length = math.min(userIter.peekLength(), actualIter.peekLength());
    final userOp = userIter.next(length);
    final actualOp = actualIter.next(length);
    assert(userOp.length == actualOp.length);
    if (userOp.key == actualOp.key) continue;
    if (userOp.isInsert && actualOp.isRetain) {
      diff -= userOp.length;
    } else if (userOp.isDelete && actualOp.isRetain) {
      diff += userOp.length;
    } else if (userOp.isRetain && actualOp.isInsert) {
      if (actualOp.data.startsWith('\n') ) {
        // At this point user input reached its end (retain). If a heuristic
        // rule inserts a new line we should keep cursor on it's original position.
        continue;
      }
      diff += actualOp.length;
    } else {
      // TODO: this likely needs to cover more edge cases.
    }
  }
  return diff;
}