diff_match_patch.prototype.diff_cleanupSemantic = function()

in pontoon/base/static/js/lib/diff.js [729:835]

• 105 lines of code
• 18 McCabe index (conditional complexity)

diff_match_patch.prototype.diff_cleanupSemantic = function(diffs) {
  var changes = false;
  var equalities = [];  // Stack of indices where equalities are found.
  var equalitiesLength = 0;  // Keeping our own length var is faster in JS.
  /** @type {?string} */
  var lastequality = null;
  // Always equal to diffs[equalities[equalitiesLength - 1]][1]
  var pointer = 0;  // Index of current position.
  // Number of characters that changed prior to the equality.
  var length_insertions1 = 0;
  var length_deletions1 = 0;
  // Number of characters that changed after the equality.
  var length_insertions2 = 0;
  var length_deletions2 = 0;
  while (pointer < diffs.length) {
    if (diffs[pointer][0] == DIFF_EQUAL) {  // Equality found.
      equalities[equalitiesLength++] = pointer;
      length_insertions1 = length_insertions2;
      length_deletions1 = length_deletions2;
      length_insertions2 = 0;
      length_deletions2 = 0;
      lastequality = diffs[pointer][1];
    } else {  // An insertion or deletion.
      if (diffs[pointer][0] == DIFF_INSERT) {
        length_insertions2 += diffs[pointer][1].length;
      } else {
        length_deletions2 += diffs[pointer][1].length;
      }
      // Eliminate an equality that is smaller or equal to the edits on both
      // sides of it.
      if (lastequality && (lastequality.length <=
          Math.max(length_insertions1, length_deletions1)) &&
          (lastequality.length <= Math.max(length_insertions2,
                                           length_deletions2))) {
        // Duplicate record.
        diffs.splice(equalities[equalitiesLength - 1], 0,
                     [DIFF_DELETE, lastequality]);
        // Change second copy to insert.
        diffs[equalities[equalitiesLength - 1] + 1][0] = DIFF_INSERT;
        // Throw away the equality we just deleted.
        equalitiesLength--;
        // Throw away the previous equality (it needs to be reevaluated).
        equalitiesLength--;
        pointer = equalitiesLength > 0 ? equalities[equalitiesLength - 1] : -1;
        length_insertions1 = 0;  // Reset the counters.
        length_deletions1 = 0;
        length_insertions2 = 0;
        length_deletions2 = 0;
        lastequality = null;
        changes = true;
      }
    }
    pointer++;
  }

  // Normalize the diff.
  if (changes) {
    this.diff_cleanupMerge(diffs);
  }
  this.diff_cleanupSemanticLossless(diffs);

  // Find any overlaps between deletions and insertions.
  // e.g: <del>abcxxx</del><ins>xxxdef</ins>
  //   -> <del>abc</del>xxx<ins>def</ins>
  // e.g: <del>xxxabc</del><ins>defxxx</ins>
  //   -> <ins>def</ins>xxx<del>abc</del>
  // Only extract an overlap if it is as big as the edit ahead or behind it.
  pointer = 1;
  while (pointer < diffs.length) {
    if (diffs[pointer - 1][0] == DIFF_DELETE &&
        diffs[pointer][0] == DIFF_INSERT) {
      var deletion = diffs[pointer - 1][1];
      var insertion = diffs[pointer][1];
      var overlap_length1 = this.diff_commonOverlap_(deletion, insertion);
      var overlap_length2 = this.diff_commonOverlap_(insertion, deletion);
      if (overlap_length1 >= overlap_length2) {
        if (overlap_length1 >= deletion.length / 2 ||
            overlap_length1 >= insertion.length / 2) {
          // Overlap found.  Insert an equality and trim the surrounding edits.
          diffs.splice(pointer, 0,
              [DIFF_EQUAL, insertion.substring(0, overlap_length1)]);
          diffs[pointer - 1][1] =
              deletion.substring(0, deletion.length - overlap_length1);
          diffs[pointer + 1][1] = insertion.substring(overlap_length1);
          pointer++;
        }
      } else {
        if (overlap_length2 >= deletion.length / 2 ||
            overlap_length2 >= insertion.length / 2) {
          // Reverse overlap found.
          // Insert an equality and swap and trim the surrounding edits.
          diffs.splice(pointer, 0,
              [DIFF_EQUAL, deletion.substring(0, overlap_length2)]);
          diffs[pointer - 1][0] = DIFF_INSERT;
          diffs[pointer - 1][1] =
              insertion.substring(0, insertion.length - overlap_length2);
          diffs[pointer + 1][0] = DIFF_DELETE;
          diffs[pointer + 1][1] =
              deletion.substring(overlap_length2);
          pointer++;
        }
      }
      pointer++;
    }
    pointer++;
  }
};