import type { FunnelUserAnswers } from '@funnelsgrove/runtime';

const asTrimmedStringOrNull = (value: unknown): string | null => {
  if (typeof value !== 'string') {
    return null;
  }

  const trimmed = value.trim();
  return trimmed || null;
};

const readBrowserLocale = (): string | null => {
  if (typeof navigator === 'undefined') {
    return null;
  }

  return asTrimmedStringOrNull(navigator.language);
};

const normalizeCountryCode = (countryCode: string | null): string | null => {
  if (!countryCode) {
    return null;
  }

  if (/^[a-z]{2}$/i.test(countryCode)) {
    return countryCode.toUpperCase();
  }

  return countryCode;
};

const getCountryFromLocale = (locale: string | null): string | null => {
  if (!locale) {
    return null;
  }

  const region = locale
    .split('-')[1]
    ?.trim()
    .toUpperCase();

  return region && /^[A-Z]{2}$/.test(region) ? region : null;
};

export function getStepContentLocale(
  attributes: FunnelUserAnswers,
  browserLocale: string | null = readBrowserLocale(),
): string | null {
  return (
    asTrimmedStringOrNull(attributes.browserLanguage) ||
    asTrimmedStringOrNull(attributes.language) ||
    asTrimmedStringOrNull(attributes.locale) ||
    asTrimmedStringOrNull(browserLocale)
  );
}

export function getStepCountryCode(
  attributes: FunnelUserAnswers,
  locale: string | null = getStepContentLocale(attributes),
): string | null {
  const explicitCountry =
    asTrimmedStringOrNull(attributes.countryCode) || asTrimmedStringOrNull(attributes.country);

  return normalizeCountryCode(explicitCountry) || getCountryFromLocale(locale);
}