Function diffLinesRaw

packages/utils/src/diff/diffLines.ts:178–233

(
  aLines: Array<string>,
  bLines: Array<string>,
  options?: DiffOptions,
)

// Compare two arrays of strings line-by-line.
export function diffLinesRaw(
  aLines: Array<string>,
  bLines: Array<string>,
  options?: DiffOptions,
): [Array<Diff>, boolean] {
  const truncate = options?.truncateThreshold ?? false
  const truncateThreshold = Math.max(
    Math.floor(options?.truncateThreshold ?? 0),
    0,
  )
  const aLength = truncate
    ? Math.min(aLines.length, truncateThreshold)
    : aLines.length
  const bLength = truncate
    ? Math.min(bLines.length, truncateThreshold)
    : bLines.length
  const truncated = aLength !== aLines.length || bLength !== bLines.length

  const isCommon = (aIndex: number, bIndex: number) =>
    aLines[aIndex] === bLines[bIndex]

  const diffs: Array<Diff> = []
  let aIndex = 0
  let bIndex = 0

  const foundSubsequence = (
    nCommon: number,
    aCommon: number,
    bCommon: number,
  ) => {
    for (; aIndex !== aCommon; aIndex += 1) {
      diffs.push(new Diff(DIFF_DELETE, aLines[aIndex]))
    }

    for (; bIndex !== bCommon; bIndex += 1) {
      diffs.push(new Diff(DIFF_INSERT, bLines[bIndex]))
    }

    for (; nCommon !== 0; nCommon -= 1, aIndex += 1, bIndex += 1) {
      diffs.push(new Diff(DIFF_EQUAL, bLines[bIndex]))
    }
  }

  diffSequences(aLength, bLength, isCommon, foundSubsequence)

  // After the last common subsequence, push remaining change items.
  for (; aIndex !== aLength; aIndex += 1) {
    diffs.push(new Diff(DIFF_DELETE, aLines[aIndex]))
  }

  for (; bIndex !== bLength; bIndex += 1) {
    diffs.push(new Diff(DIFF_INSERT, bLines[bIndex]))
  }

  return [diffs, truncated]
}