export function validatePayload(payload, type, rootKey, requiredIdKeyByType) {
  if (typeof payload !== "object" || payload === null || Array.isArray(payload)) {
    return "Payload must be an object";
  }
  if (typeof payload.schemaVersion !== "number") {
    return "schemaVersion must be a number";
  }
  const allowedTopLevel = new Set(["schemaVersion", rootKey]);
  const unknownTopLevel = Object.keys(payload).filter((key) => !allowedTopLevel.has(key));
  if (unknownTopLevel.length > 0) {
    return `Unsupported top-level keys for ${type}: ${unknownTopLevel.join(", ")}`;
  }
  if (!Array.isArray(payload[rootKey])) {
    return `Missing array root: ${rootKey}`;
  }

  const idKey = requiredIdKeyByType[type];
  if (!idKey) {
    return null;
  }

  const list = payload[rootKey];
  for (let index = 0; index < list.length; index += 1) {
    const entry = list[index];
    if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
      return `${rootKey}[${index}] must be an object`;
    }
    const idValue = String(entry[idKey] ?? "").trim();
    if (!idValue) {
      return `${rootKey}[${index}] is missing required key: ${idKey}`;
    }
  }

  return null;
}

export function validateCatalogMetaPayload(payload, frozenCatalogKeys) {
  if (typeof payload !== "object" || payload === null || Array.isArray(payload)) {
    return "Catalog payload must be an object";
  }
  if (typeof payload.schemaVersion !== "number") {
    return "schemaVersion must be a number";
  }
  const allowedTopLevel = new Set(["schemaVersion", ...frozenCatalogKeys]);
  const unknownTopLevel = Object.keys(payload).filter((key) => !allowedTopLevel.has(key));
  if (unknownTopLevel.length > 0) {
    return `Unsupported catalog keys: ${unknownTopLevel.join(", ")}`;
  }
  for (const key of frozenCatalogKeys) {
    if (!Array.isArray(payload[key])) {
      return `${key} must be an array`;
    }
  }
  return null;
}