patch_addPadding method

String patch_addPadding(List<Patch> patches)

Add some padding on text start and end so that edges can match something. Intended to be called only from within patch_apply. patches is a List of Patch objects. Returns the padding string added to each side.

Implementation

String patch_addPadding(List<Patch> patches) {
  final paddingLength = Patch_Margin;
  final paddingCodes = <int>[];
  for (int x = 1; x <= paddingLength; x++) {
    paddingCodes.add(x);
  }
  String nullPadding = String.fromCharCodes(paddingCodes);

  // Bump all the patches forward.
  for (final aPatch in patches) {
    aPatch.start1 += paddingLength;
    aPatch.start2 += paddingLength;
  }

  // Add some padding on start of first diff.
  var patch = patches[0],
    diffs = patch.diffs;
  if (diffs.isEmpty || diffs[0].operation != Operation.equal) {
    // Add nullPadding equality.
    diffs.insert(0, Diff(Operation.equal, nullPadding));
    patch.start1 -= paddingLength; // Should be 0.
    patch.start2 -= paddingLength; // Should be 0.
    patch.length1 += paddingLength;
    patch.length2 += paddingLength;
  } else if (paddingLength > diffs[0].text.length) {
    // Grow first equality.
    Diff firstDiff = diffs[0];
    int extraLength = paddingLength - firstDiff.text.length;
    firstDiff.text =
        nullPadding.substring(firstDiff.text.length) + firstDiff.text;
    patch.start1 -= extraLength;
    patch.start2 -= extraLength;
    patch.length1 += extraLength;
    patch.length2 += extraLength;
  }

  // Add some padding on end of last diff.
  patch = patches.last;
  diffs = patch.diffs;
  if (diffs.isEmpty || diffs.last.operation != Operation.equal) {
    // Add nullPadding equality.
    diffs.add(Diff(Operation.equal, nullPadding));
    patch.length1 += paddingLength;
    patch.length2 += paddingLength;
  } else if (paddingLength > diffs.last.text.length) {
    // Grow last equality.
    final lastDiff = diffs.last;
    final extraLength = paddingLength - lastDiff.text.length;
    lastDiff.text = lastDiff.text + nullPadding.substring(0, extraLength);
    patch.length1 += extraLength;
    patch.length2 += extraLength;
  }

  return nullPadding;
}