/**
 * Shared Levenshtein edit-distance helper for CLI "did you mean …?"
 * suggestions. Lives in cli/lib so `dench crm`, `dench apps`, and any
 * other hand-rolled dispatcher can suggest the closest known verb
 * instead of dead-ending on `Unknown subcommand: entires`.
 */

export function levenshteinDistance(a: string, b: string): number {
  if (a === b) return 0;
  if (a.length === 0) return b.length;
  if (b.length === 0) return a.length;
  let prev = Array.from({ length: b.length + 1 }, (_, i) => i);
  let curr = new Array<number>(b.length + 1);
  for (let i = 1; i <= a.length; i += 1) {
    curr[0] = i;
    for (let j = 1; j <= b.length; j += 1) {
      const cost = a[i - 1] === b[j - 1] ? 0 : 1;
      curr[j] = Math.min(prev[j] + 1, curr[j - 1] + 1, prev[j - 1] + cost);
    }
    [prev, curr] = [curr, prev];
  }
  return prev[b.length];
}

/**
 * Return the candidate closest to `input` (case-insensitive), or null
 * when nothing is plausibly a typo. Exact case-insensitive matches win
 * outright; otherwise the best candidate must be within
 * max(2, floor(len/2)) edits — same threshold the CRM field
 * suggester has used in production.
 */
export function closestMatch(
  input: string,
  candidates: readonly string[],
): string | null {
  const lower = input.toLowerCase();
  const caseMatch = candidates.find(
    (candidate) => candidate.toLowerCase() === lower,
  );
  if (caseMatch) return caseMatch;
  let best: string | null = null;
  let bestDistance = Number.POSITIVE_INFINITY;
  for (const candidate of candidates) {
    const distance = levenshteinDistance(lower, candidate.toLowerCase());
    if (distance < bestDistance) {
      bestDistance = distance;
      best = candidate;
    }
  }
  const threshold = Math.max(2, Math.floor(input.length / 2));
  return best !== null && bestDistance <= threshold ? best : null;
}