Function lineDiff

src/context/approach-diff.ts:42–62

(a: string, b: string)

/** Classic LCS line diff → unified-style lines ('  ctx' / '- old' / '+ new'). PURE. */
export function lineDiff(a: string, b: string): string[] {
  const A = a.split('\n'), B = b.split('\n');
  const n = A.length, m = B.length;
  // LCS table (texts here are small — worklog entries, not files).
  const L: number[][] = Array.from({ length: n + 1 }, () => new Array(m + 1).fill(0));
  for (let i = n - 1; i >= 0; i--) {
    for (let j = m - 1; j >= 0; j--) {
      L[i]![j] = A[i] === B[j] ? L[i + 1]![j + 1]! + 1 : Math.max(L[i + 1]![j]!, L[i]![j + 1]!);
    }
  }
  const out: string[] = [];
  let i = 0, j = 0;
  while (i < n && j < m) {
    if (A[i] === B[j]) { out.push(`  ${A[i]}`); i++; j++; }
    else if (L[i + 1]![j]! >= L[i]![j + 1]!) { out.push(`- ${A[i]}`); i++; }
    else { out.push(`+ ${B[j]}`); j++; }
  }
  while (i < n) out.push(`- ${A[i++]}`);
  while (j < m) out.push(`+ ${B[j++]}`);
  return out;
}

/** Terms (surface forms) whose stem appears in EVERY text — the stable core of the approach. PURE. */
export function commonCore(texts: string[], cap = 8): string[] {