src/locationLabels.js

export function uniqueLocationParts(parts) {
  const seen = new Set();
  return parts.map((part) => String(part || "").trim()).filter((part) => {
    if (!part) return false;
    const key = normalizeLocationName(part);
    if (seen.has(key)) return false;
    seen.add(key);
    return true;
  });
}

export function locationHeading(city, lang) {
  const country = lang === "zh" ? city?.countryZh : city?.countryEn;
  const place = lang === "zh" ? city?.cityZh : city?.cityEn;
  return uniqueLocationParts([country, place]).join(" · ");
}

export function combinedLocationHeading(city) {
  if (hasCountryCityEcho(city)) {
    return uniqueLocationParts([
      city?.countryZh || city?.cityZh,
      city?.countryEn || city?.cityEn,
    ]).join(" | ");
  }

  return uniqueLocationParts([
    locationHeading(city, "zh"),
    locationHeading(city, "en"),
  ]).join(" | ");
}

export function bookshelfLocationLabel(city) {
  return uniqueLocationParts([
    city?.countryEn || city?.countryZh,
    city?.cityEn || city?.cityZh,
  ]).join(" · ");
}

function hasCountryCityEcho(city) {
  return sameLocationName(city?.countryZh, city?.cityZh)
    || sameLocationName(city?.countryEn, city?.cityEn)
    || cityNameExtendsCountry(city?.countryZh, city?.cityZh);
}

function sameLocationName(left, right) {
  const normalizedLeft = normalizeLocationName(left);
  const normalizedRight = normalizeLocationName(right);
  return Boolean(normalizedLeft && normalizedRight && normalizedLeft === normalizedRight);
}

function normalizeLocationName(value) {
  return String(value || "")
    .trim()
    .toLocaleLowerCase()
    .replace(/\s+/g, " ");
}

function cityNameExtendsCountry(country, city) {
  const normalizedCountry = normalizeLocationName(country);
  const normalizedCity = normalizeLocationName(city);
  return Boolean(normalizedCountry && normalizedCity && normalizedCity === `${normalizedCountry}城`);
}