/**
 * Converts a camelCase string to snake_case.
 */
export function camelToSnake(str: string): string {
  // Skip all-uppercase keys (e.g. OR, AND, NOT — logical operators)
  if (str === str.toUpperCase()) return str;
  return str.replace(/[A-Z]/g, (letter) => `_${letter.toLowerCase()}`);
}

/**
 * Converts a snake_case string to camelCase.
 */
function snakeToCamel(str: string): string {
  return str.replace(/_([a-z])/g, (_, letter) => letter.toUpperCase());
}

/**
 * Keys whose values are user-controlled, opaque blobs. Their nested keys must
 * be passed through verbatim — converting them would silently rewrite the
 * user's own keys and break round-trips (see issue #5055).
 *
 * The check runs against the source key, so a multi-word key must be listed in
 * both casings to be covered in both directions: the camelCase form for the
 * outbound `camelToSnakeKeys` path and the snake_case form for the inbound
 * `snakeToCamelKeys` path. `metadata` is spelled identically in both, so one
 * entry suffices; `structuredDataSchema` needs both.
 */
const OPAQUE_VALUE_KEYS = new Set([
  "metadata",
  "structuredDataSchema",
  "structured_data_schema",
  // Custom-category names are user-controlled keys (`[{ "<name>": "<desc>" }]`).
  // Listed in both casings so they round-trip verbatim in both directions
  // (see issue #5738; same class as `metadata`/`structuredDataSchema`).
  "customCategories",
  "custom_categories",
]);

/**
 * Recursively converts all keys of an object from camelCase to snake_case.
 * Used for converting user-facing camelCase params to API snake_case payloads.
 * Values under {@link OPAQUE_VALUE_KEYS} (e.g. `metadata`) are left untouched.
 */
export function camelToSnakeKeys(obj: any): any {
  if (obj === null || obj === undefined || typeof obj !== "object") return obj;
  if (Array.isArray(obj)) return obj.map(camelToSnakeKeys);
  if (obj instanceof Date) return obj;

  return Object.fromEntries(
    Object.entries(obj).map(([key, value]) => [
      camelToSnake(key),
      OPAQUE_VALUE_KEYS.has(key) ? value : camelToSnakeKeys(value),
    ]),
  );
}

/**
 * Recursively converts all keys of an object from snake_case to camelCase.
 * Used for converting API snake_case responses to user-facing camelCase.
 * Values under {@link OPAQUE_VALUE_KEYS} (e.g. `metadata`) are left untouched.
 */
export function snakeToCamelKeys(obj: any): any {
  if (obj === null || obj === undefined || typeof obj !== "object") return obj;
  if (Array.isArray(obj)) return obj.map(snakeToCamelKeys);
  if (obj instanceof Date) return obj;

  return Object.fromEntries(
    Object.entries(obj).map(([key, value]) => [
      snakeToCamel(key),
      OPAQUE_VALUE_KEYS.has(key) ? value : snakeToCamelKeys(value),
    ]),
  );
}