export const isValidPhone = (value: string) => /^[0-9]{10}$/.test(value.replace(/\D/g, ''));

export const isValidOtp = (value: string) => /^[0-9]{6}$/.test(value);

/**
 * Single source of truth for how many digits an MPIN has. The backend accepts
 * 4 or 6; this app standardises on 4, so the keypad, the validators and the
 * stored-profile handling all read from here rather than each hard-coding it.
 */
export const MPIN_LENGTH = 4;

/**
 * The backend refuses an all-same-digit MPIN. That rule is checked after
 * decryption server-side, so it comes back as a `VALIDATION_ERROR` with a
 * message rather than a field map — cheaper and clearer to catch it here
 * before spending a round trip.
 */
export const isValidMpin = (value: string) =>
  new RegExp(`^[0-9]{${MPIN_LENGTH}}$`).test(value) && !isRepeatedDigits(value);

export const isRepeatedDigits = (value: string) =>
  value.length > 0 && /^(\d)\1*$/.test(value);

/**
 * A straight run up or down — 1234, 6789, 4321. The backend refuses these
 * when an MPIN is SET, in the same message-only way as repeated digits.
 */
export const isSequentialDigits = (value: string) => {
  if (value.length < 2 || !/^[0-9]+$/.test(value)) {
    return false;
  }

  const step = Number(value[1]) - Number(value[0]);

  if (step !== 1 && step !== -1) {
    return false;
  }

  for (let index = 1; index < value.length; index += 1) {
    if (Number(value[index]) - Number(value[index - 1]) !== step) {
      return false;
    }
  }

  return true;
};

/**
 * The stricter check for CHOOSING an MPIN — creation and reset.
 *
 * Deliberately separate from `isValidMpin`, which sign-in also uses: an MPIN
 * like 1234 set before the backend began refusing runs still has to be
 * enterable at sign-in, or its owner is locked out of their own profile.
 */
export const isAcceptableNewMpin = (value: string) =>
  isValidMpin(value) && !isSequentialDigits(value);

/** Constraints as the API documents them, not as any one bank formats them. */
export const isValidAccountNumber = (value: string) => /^[0-9]{5,20}$/.test(value);

/**
 * An IFSC is always 11 characters. Every IFSC input caps at this and the
 * validator requires exactly this many, so the two cannot drift apart.
 */
export const IFSC_LENGTH = 11;

export const isValidIfsc = (value: string) =>
  new RegExp(`^[A-Za-z0-9]{${IFSC_LENGTH}}$`).test(value);

export const isValidMmid = (value: string) => /^[0-9]{7}$/.test(value);

export const isValidNickname = (value: string) => value.length <= 60;

export const isValidAmount = (value: string) => {
  const amount = Number(value);
  return Number.isFinite(amount) && amount > 0;
};