/** Shared invite-field email check (create-flow Invite your members). */
export const INVITE_EMAIL_PATTERN = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

const COUNT_WORDS = [
  "zero",
  "one",
  "two",
  "three",
  "four",
  "five",
  "six",
  "seven",
  "eight",
  "nine",
  "ten",
] as const;

/** Lowercase count for paste-result copy (`five`, or digits past ten). */
export function formatInviteCountWord(n: number): string {
  if (Number.isInteger(n) && n >= 0 && n <= 10) {
    return COUNT_WORDS[n] ?? String(n);
  }
  return String(n);
}

export function splitInvitePasteTokens(raw: string): string[] {
  return raw
    .split(/[\s,;]+/)
    .map((token) => token.trim())
    .filter((token) => token.length > 0);
}

export type ParseInvitePasteResult = {
  added: string[];
  invalidRemainder: string;
  skippedDuplicate: number;
};

/**
 * Split a pasted list into valid new addresses and leftovers that stay in the
 * field. Tokens that are not emails, duplicates, or that would exceed `max`
 * remain in {@link ParseInvitePasteResult.invalidRemainder}.
 */
export function parseInvitePaste(
  raw: string,
  existing: readonly string[],
  max: number,
): ParseInvitePasteResult {
  const tokens = splitInvitePasteTokens(raw);
  const added: string[] = [];
  const invalid: string[] = [];
  const seen = new Set(
    existing
      .map((email) => email.trim().toLowerCase())
      .filter((email) => email.length > 0),
  );
  let skippedDuplicate = 0;

  for (const token of tokens) {
    const lower = token.toLowerCase();
    if (!INVITE_EMAIL_PATTERN.test(lower)) {
      invalid.push(token);
      continue;
    }
    if (seen.has(lower)) {
      skippedDuplicate += 1;
      continue;
    }
    if (existing.length + added.length >= max) {
      invalid.push(token);
      continue;
    }
    seen.add(lower);
    added.push(lower);
  }

  return {
    added,
    invalidRemainder: invalid.join(", "),
    skippedDuplicate,
  };
}