const MAX_REGION_LENGTH = 3;

function sanitizeSegment(value) {
  if (typeof value !== "string") {
    return "";
  }
  const trimmed = value.trim();
  if (!trimmed || trimmed === "全部") {
    return "";
  }
  return trimmed;
}

function normalizeRegionArray(region) {
  if (!Array.isArray(region)) {
    return [];
  }
  const sanitized = region.map(sanitizeSegment);
  const hasValue = sanitized.some(Boolean);
  if (!hasValue) {
    return [];
  }
  const normalized = sanitized.slice(0, MAX_REGION_LENGTH);
  while (normalized.length < MAX_REGION_LENGTH) {
    normalized.push("");
  }
  return normalized;
}

function deriveRegionFromParts(parts = {}) {
  const segments = [];
  if (parts.province) {
    segments.push(parts.province);
  }
  if (parts.city) {
    segments.push(parts.city);
  }
  if (parts.district && parts.district !== parts.city) {
    segments.push(parts.district);
  }
  if (!segments.length && parts.city) {
    segments.push(parts.city);
  }
  return normalizeRegionArray(segments);
}

function getRegionParts(region, fallback = {}) {
  const normalized = normalizeRegionArray(region);
  if (!normalized.length) {
    return {
      province: sanitizeSegment(fallback.province),
      city: sanitizeSegment(fallback.city),
      district: sanitizeSegment(fallback.district)
    };
  }
  const [province = "", city = "", district = ""] = normalized;
  return {
    province: province || sanitizeSegment(fallback.province),
    city: city || province || sanitizeSegment(fallback.city),
    district: district || sanitizeSegment(fallback.district)
  };
}

function formatRegionDisplay(region, fallbackList = []) {
  const normalized = normalizeRegionArray(region);
  const source = normalized.length ? normalized : fallbackList;
  if (!source || !source.length) {
    return "";
  }
  return source
    .filter(sanitizeSegment)
    .filter((item, index, arr) => arr.indexOf(item) === index)
    .join(" · ");
}

module.exports = {
  normalizeRegionArray,
  deriveRegionFromParts,
  getRegionParts,
  formatRegionDisplay
};