/**
 * Shape detection for Swedish personal identity numbers submitted where an
 * organisationsnummer belongs.
 *
 * A legal-entity organisationsnummer always carries 20 or higher in its
 * "month" position (SFS 1974:174 2 §), while a personnummer has a real
 * calendar month 01-12 (samordningsnummer offsets the day by 60 instead).
 * That makes the two distinguishable without a checksum: any 10- or
 * 12-digit value with a month of 01-12 and a plausible day is a personal
 * identity number, never a company.
 *
 * Used to stop a personnummer from being stored as a business org_number,
 * where nothing masks it: list responses only mask identifiers on
 * customer_type='individual' rows (GDPR art. 5.1 c data minimisation).
 *
 * Deliberately crypto-free so the client form, the Zod schemas and the
 * server routes can all share it, same as mask-personal-number.ts.
 */
export function looksLikeSwedishPersonalNumber(value: string): boolean {
  const digits = value.replace(/[\s+-]/g, '')
  if (!/^(\d{10}|\d{12})$/.test(digits)) return false

  if (digits.length === 12) {
    // 12-digit organisationsnummer are written with a '16' century prefix
    // (Skatteverket convention); personnummer centuries are 18/19/20.
    const century = digits.slice(0, 2)
    if (century !== '18' && century !== '19' && century !== '20') return false
  }

  const body = digits.length === 12 ? digits.slice(2) : digits
  const month = parseInt(body.slice(2, 4), 10)
  const day = parseInt(body.slice(4, 6), 10)

  if (month < 1 || month > 12) return false

  // Day 1-31 for a personnummer, 61-91 for a samordningsnummer (+60 offset).
  const birthDay = day > 60 ? day - 60 : day
  return birthDay >= 1 && birthDay <= 31
}

/**
 * True when a customer row's org_number is really its personnummer: the row
 * is an individual (privatperson) and the value has personnummer shape.
 *
 * Every write path treats that combination as "personnummer submitted in the
 * wrong field": the value is moved into personal_number (encrypted, masked on
 * read) and org_number is left empty. Nothing masks org_number, so leaving it
 * there is exactly the unmasked-identifier leak the business-type guard above
 * exists to prevent; and the MCP create tool had no personal_number input at
 * all until 2026-08-21, so agents had nowhere else to put it.
 */
export function orgNumberHoldsPersonalNumber(
  customerType: string | null | undefined,
  orgNumber: string | null | undefined,
): boolean {
  return (
    customerType === 'individual'
    && typeof orgNumber === 'string'
    && orgNumber.trim() !== ''
    && looksLikeSwedishPersonalNumber(orgNumber)
  )
}

/**
 * The personnummer as it should be stored once it has been lifted out of
 * org_number: separators are kept (the encrypt path accepts any of the four
 * input forms) but whitespace is dropped, because "19900101 1234" passes the
 * shape check yet fails PERSONAL_NUMBER_INPUT_RE and the legacy-plaintext
 * reveal regex.
 */
export function normalizeReroutedPersonalNumber(orgNumber: string): string {
  return orgNumber.replace(/\s+/g, '')
}

/** Digits only, for comparing a personnummer across its written forms. */
export function personalNumberDigits(value: string): string {
  return value.replace(/\D/g, '')
}