Function findMatch

src/tools/filesystem/fuzzy-match.ts:101–178

(
  content: string,
  search: string,
  opts: { fuzzyThreshold?: number; fuzzyMargin?: number; allowFuzzy?: boolean } = {},
)

 * Returns null if no confident match. The threshold/margin guard fuzzy tier.
 */
export function findMatch(
  content: string,
  search: string,
  opts: { fuzzyThreshold?: number; fuzzyMargin?: number; allowFuzzy?: boolean } = {},
): MatchResult | null {
  const fuzzyThreshold = opts.fuzzyThreshold ?? 0.85;
  const fuzzyMargin = opts.fuzzyMargin ?? 0.08;
  const allowFuzzy = opts.allowFuzzy ?? true;

  // ── Tier 0: exact ──
  {
    const first = content.indexOf(search);
    if (first !== -1) {
      const occurrences = content.split(search).length - 1;
      return { start: first, end: first + search.length, matched: search, tier: 'exact', occurrences };
    }
  }

  const contentLines = content.split('\n');
  const searchLines = search.split('\n');
  // Drop a trailing empty line from a search that ended in \n.
  if (searchLines.length > 1 && searchLines[searchLines.length - 1] === '') searchLines.pop();
  const nSearch = searchLines.length;
  const lineStarts = computeLineStarts(content);

  // ── Tier 1: line-trimmed exact ──
  {
    const normSearch = searchLines.map(normLine);
    const matches: number[] = [];
    for (let i = 0; i + nSearch <= contentLines.length; i++) {
      let ok = true;
      for (let j = 0; j < nSearch; j++) {
        if (normLine(contentLines[i + j]!) !== normSearch[j]) { ok = false; break; }
      }
      if (ok) matches.push(i);
    }
    if (matches.length >= 1) {
      const i = matches[0]!;
      const { start, end } = lineRangeToOffsets(lineStarts, content, i, i + nSearch);
      return {
        start, end,
        matched: content.slice(start, end),
        tier: 'whitespace',
        occurrences: matches.length,
      };
    }
  }

  // ── Tier 2: fuzzy anchor (only when the block is substantial) ──
  const nonBlank = searchLines.filter(l => normLine(l).length > 0).length;
  if (!allowFuzzy || nonBlank < 2) return null;

  let best = { score: -1, index: -1 };
  let second = { score: -1, index: -1 };
  for (let i = 0; i + nSearch <= contentLines.length; i++) {
    const window = contentLines.slice(i, i + nSearch);
    const score = blockSim(window, searchLines);
    if (score > best.score) {