import { useMemo, useState } from 'react';

import { useAccountSelection } from '../../home/hooks/useAccounts';

/**
 * The half of a transfer form that is the same whichever way the money is
 * addressed: which account it leaves, how much, and the note against it.
 *
 * The account list is read from `GET /accounts` on every mount — never from
 * Redux, and never carried in from the previous screen.
 *
 * There is no balance check here, and that is not an omission. No endpoint in
 * the CBS API returns a balance, so the app has nothing to compare an amount
 * against; inventing a limit would be worse than having none, because a
 * customer refused by the app has no way to find out they were refused
 * wrongly. The bank rejects an overdrawn transfer on submission, and that
 * refusal is the authoritative one.
 */
export const useTransferForm = () => {
  const { accounts, selectedAccountNumber, setSelectedAccountNumber, selectedAccount, isLoading, refetch } =
    useAccountSelection();

  const [amount, setAmount] = useState('');
  const [remarks, setRemarks] = useState('');

  /** Grouping separators are allowed in, but never reach the parsed value. */
  const parsedAmount = useMemo(() => Number.parseFloat(amount.replace(/,/g, '')), [amount]);

  const amountError = useMemo(() => {
    if (amount.length === 0) {
      return undefined;
    }

    if (Number.isNaN(parsedAmount) || parsedAmount <= 0) {
      return 'Enter a valid amount';
    }

    return undefined;
  }, [amount, parsedAmount]);

  const amountValid = !amountError && parsedAmount > 0;

  const handleAmountChange = (value: string) => {
    // One decimal point, digits either side, at most two paise. Filtering on
    // the way in beats validating after the fact: the field cannot hold
    // something the parser would then have to reject.
    const cleaned = value.replace(/[^0-9.]/g, '');
    const [rupees = '', ...rest] = cleaned.split('.');
    const paise = rest.join('').slice(0, 2);

    setAmount(rest.length ? `${rupees}.${paise}` : rupees);
  };

  return {
    accounts,
    selectedAccount,
    sourceAccountNumber: selectedAccountNumber,
    setSourceAccountNumber: setSelectedAccountNumber,
    accountsLoading: isLoading,
    refetchAccounts: refetch,
    amount,
    handleAmountChange,
    parsedAmount,
    amountError,
    amountValid,
    remarks,
    setRemarks,
  };
};