export default function diffSequence()

in packages/diff-sequences/src/index.ts [782:872]

• 65 lines of code
• 7 McCabe index (conditional complexity)

export default function diffSequence(
  aLength: number,
  bLength: number,
  isCommon: IsCommon,
  foundSubsequence: FoundSubsequence,
): void {
  validateLength('aLength', aLength);
  validateLength('bLength', bLength);
  validateCallback('isCommon', isCommon);
  validateCallback('foundSubsequence', foundSubsequence);

  // Count common items from the start in the forward direction.
  const nCommonF = countCommonItemsF(0, aLength, 0, bLength, isCommon);

  if (nCommonF !== 0) {
    foundSubsequence(nCommonF, 0, 0);
  }

  // Unless both sequences consist of common items only,
  // find common items in the half-trimmed index intervals.
  if (aLength !== nCommonF || bLength !== nCommonF) {
    // Invariant: intervals do not have common items at the start.
    // The start of an index interval is closed like array slice method.
    const aStart = nCommonF;
    const bStart = nCommonF;

    // Count common items from the end in the reverse direction.
    const nCommonR = countCommonItemsR(
      aStart,
      aLength - 1,
      bStart,
      bLength - 1,
      isCommon,
    );

    // Invariant: intervals do not have common items at the end.
    // The end of an index interval is open like array slice method.
    const aEnd = aLength - nCommonR;
    const bEnd = bLength - nCommonR;

    // Unless one sequence consists of common items only,
    // therefore the other trimmed index interval consists of changes only,
    // find common items in the trimmed index intervals.
    const nCommonFR = nCommonF + nCommonR;
    if (aLength !== nCommonFR && bLength !== nCommonFR) {
      const nChange = 0; // number of change items is not yet known
      const transposed = false; // call the original unwrapped functions
      const callbacks = [{foundSubsequence, isCommon}];

      // Indexes in sequence a of last points in furthest reaching paths
      // from outside the start at top left in the forward direction:
      const aIndexesF = [NOT_YET_SET];
      // from the end at bottom right in the reverse direction:
      const aIndexesR = [NOT_YET_SET];

      // Initialize one object as output of all calls to divide function.
      const division = {
        aCommonFollowing: NOT_YET_SET,
        aCommonPreceding: NOT_YET_SET,
        aEndPreceding: NOT_YET_SET,
        aStartFollowing: NOT_YET_SET,
        bCommonFollowing: NOT_YET_SET,
        bCommonPreceding: NOT_YET_SET,
        bEndPreceding: NOT_YET_SET,
        bStartFollowing: NOT_YET_SET,
        nChangeFollowing: NOT_YET_SET,
        nChangePreceding: NOT_YET_SET,
        nCommonFollowing: NOT_YET_SET,
        nCommonPreceding: NOT_YET_SET,
      };

      // Find and return common subsequences in the trimmed index intervals.
      findSubsequences(
        nChange,
        aStart,
        aEnd,
        bStart,
        bEnd,
        transposed,
        callbacks,
        aIndexesF,
        aIndexesR,
        division,
      );
    }

    if (nCommonR !== 0) {
      foundSubsequence(nCommonR, aEnd, bEnd);
    }
  }
}