Function findCommonItems

packages/diff-sequences/src/__tests__/index.test.ts:200–236

(
  a: Array<unknown> | string,
  b: Array<unknown> | string,
)

// Return array of items in a longest common subsequence of array-like objects.
const findCommonItems = (
  a: Array<unknown> | string,
  b: Array<unknown> | string,
): Array<unknown> => {
  const aLength = a.length;
  const bLength = b.length;
  const isCommon = (aIndex: number, bIndex: number) => {
    assertMin('input aIndex', aIndex, 0);
    assertEnd('input aIndex', aIndex, aLength);
    assertMin('input bIndex', bIndex, 0);
    assertEnd('input bIndex', bIndex, bLength);
    return a[aIndex] === b[bIndex];
  };

  const array: Array<unknown> = [];
  diff(
    aLength,
    bLength,
    isCommon,
    (nCommon: number, aCommon: number, bCommon: number) => {
      assertMin('output nCommon', nCommon, 1);
      assertMin('output aCommon', aCommon, 0);
      assertMax('output aCommon + nCommon', aCommon + nCommon, aLength);
      assertMin('output bCommon', bCommon, 0);
      assertMax('output bCommon + nCommon', bCommon + nCommon, bLength);
      assertCommonItems(a, b, nCommon, aCommon, bCommon);
      for (; nCommon !== 0; nCommon -= 1, aCommon += 1) {
        array.push(a[aCommon]);
      }
    },
  );

  const nDifferences = countDifferences(aLength, bLength, isCommon);
  expect(aLength + bLength - 2 * array.length).toBe(nDifferences);

  return array;
};

// Assert that array-like objects have the expected common items.
const expectCommonItems = (