Function patchString

packages/nbdime/src/patch/stringified.ts:135–192

(
  base: string,
  diff: IDiffArrayEntry[] | null,
  level: number,
  stringifyPatch?: boolean,
)

 * Patch a string according to a line based diff
 */
export function patchString(
  base: string,
  diff: IDiffArrayEntry[] | null,
  level: number,
  stringifyPatch?: boolean,
): StringifiedPatchResult {
  let additions: DiffRangeRaw[] = [];
  let deletions: DiffRangeRaw[] = [];
  let baseIndex = 0;

  // Short-circuit if diff is empty
  if (diff === null) {
    return {
      remote: stringifyPatch ? stringify(base, level) : base,
      additions: additions,
      deletions: deletions,
    };
  }
  // Diffs are line-based, so flatten to character based:
  diff = flattenStringDiff(base, diff);

  // Index into obj, the next item to take unless diff says otherwise
  let take = 0;
  let skip = 0;
  let remote = '';
  for (let e of diff) {
    let index = e.key;

    // Take values from obj not mentioned in diff, up to not including index
    let unchanged = base.slice(take, index);
    remote += unchanged;
    baseIndex += unchanged.length;

    if (e.op === 'addrange') {
      let added = e.valuelist;
      additions.push(new DiffRangeRaw(remote.length, added.length, e.source));
      remote += added;
      skip = 0;
    } else if (e.op === 'removerange') {
      // Delete a number of values by skipping
      skip = e.length;
      deletions.push(new DiffRangeRaw(baseIndex, skip, e.source));
      baseIndex += skip;
    }
    take = Math.max(take, index + skip);
  }
  remote += base.slice(take, base.length);
  if (stringifyPatch) {
    // The remote string should be stringified
    remote = stringify(remote, level);
    // Shift all indices by indentation + one to account for opening quote
    _offsetRanges(level * JSON_INDENT.length + 1, additions, deletions);
    // Offset ranges by JSON escaping
    _adjustRangesByJSONEscapes(remote, additions);
    _adjustRangesByJSONEscapes(stringify(base, level), deletions);
  }
  return { remote: remote, additions: additions, deletions: deletions };
}