import type { LookupDto } from '@impuestos/contracts';
import {
  computeRucDv,
  deadlineDay,
  deadlineDigit,
  dueDateFor,
  formatIsoDate,
  fromDate,
  nextDeadline,
  addMonths,
} from '@impuestos/rules';

const RUC_WITH_DV = /^(\d{1,8})-(\d)$/;
const BARE_DIGITS = /^\d{1,8}$/;

/**
 * The landing hook: type a RUC or a CI and see your own filing dates before creating an
 * account. Public, so it reveals only what the number itself already encodes: the check
 * digit and the calendario perpetuo day. It never touches the database.
 *
 * An unparseable number is a valid response with `valid: false`, not an error, so the
 * landing can correct the user inline instead of dead ending (CONTRACTS.md section 3).
 */
export function lookupNumber(raw: string, now: Date): LookupDto {
  const cleaned = raw.trim().replace(/[.\s]/g, '');

  const withDv = RUC_WITH_DV.exec(cleaned);
  if (withDv) {
    const base = withDv[1] as string;
    const dv = Number(withDv[2]);
    return build({ base, dv, docType: 'ruc', valid: computeRucDv(base) === dv, now });
  }

  if (BARE_DIGITS.test(cleaned)) {
    // A bare number is read as a CI. Individuals whose RUC is their CI plus a check digit
    // can type either, and the filing day is the same for both.
    return build({ base: cleaned, dv: null, docType: 'ci', valid: true, now });
  }

  return invalid();
}

function build(args: {
  base: string;
  dv: number | null;
  docType: 'ruc' | 'ci';
  valid: boolean;
  now: Date;
}): LookupDto {
  if (!args.valid) return { ...invalid(), docType: args.docType, base: args.base, dv: args.dv };

  const digit = deadlineDigit(args.base);
  return {
    valid: true,
    docType: args.docType,
    base: args.base,
    dv: args.dv,
    deadlineDigit: digit,
    deadlineDay: deadlineDay(digit),
    nextDeadlines: nextThreeIvaDeadlines(digit, args.now),
  };
}

/** The next three monthly IVA due dates, which is what the landing card shows. */
function nextThreeIvaDeadlines(digit: number, now: Date): string[] {
  const first = nextDeadline({ digit, obligation: 'iva_120', from: now });
  return [0, 1, 2].map((offset) =>
    formatIsoDate(
      offset === 0
        ? fromDate(first.dueDate)
        : dueDateFor('iva_120', addMonths(first.period, offset), digit),
    ),
  );
}

function invalid(): LookupDto {
  return {
    valid: false,
    docType: 'ruc',
    base: '',
    dv: null,
    deadlineDigit: 0,
    deadlineDay: deadlineDay(0),
    nextDeadlines: ['', '', ''],
  };
}