Function joinAlignedDiffsNoExpand

packages/utils/src/diff/joinAlignedDiffs.ts:115–293

(
  diffs: Array<Diff>,
  options: DiffOptionsNormalized,
)

// Given array of aligned strings with inverse highlight formatting,
// return joined lines with diff formatting (and patch marks, if needed).
export function joinAlignedDiffsNoExpand(
  diffs: Array<Diff>,
  options: DiffOptionsNormalized,
): string {
  const iLength = diffs.length
  const nContextLines = options.contextLines
  const nContextLines2 = nContextLines + nContextLines

  // First pass: count output lines and see if it has patches.
  let jLength = iLength
  let hasExcessAtStartOrEnd = false
  let nExcessesBetweenChanges = 0
  let i = 0
  while (i !== iLength) {
    const iStart = i
    while (i !== iLength && diffs[i][0] === DIFF_EQUAL) {
      i += 1
    }

    if (iStart !== i) {
      if (iStart === 0) {
        // at start
        if (i > nContextLines) {
          jLength -= i - nContextLines // subtract excess common lines
          hasExcessAtStartOrEnd = true
        }
      }
      else if (i === iLength) {
        // at end
        const n = i - iStart
        if (n > nContextLines) {
          jLength -= n - nContextLines // subtract excess common lines
          hasExcessAtStartOrEnd = true
        }
      }
      else {
        // between changes
        const n = i - iStart
        if (n > nContextLines2) {
          jLength -= n - nContextLines2 // subtract excess common lines
          nExcessesBetweenChanges += 1
        }
      }
    }

    while (i !== iLength && diffs[i][0] !== DIFF_EQUAL) {
      i += 1
    }
  }

  const hasPatch = nExcessesBetweenChanges !== 0 || hasExcessAtStartOrEnd
  if (nExcessesBetweenChanges !== 0) {
    jLength += nExcessesBetweenChanges + 1
  } // add patch lines
  else if (hasExcessAtStartOrEnd) {
    jLength += 1
  } // add patch line