/**
 * Helpers for finding an {@link XOTemplate} export in a loaded ES module.
 */

/**
 * Returns true when `value` looks like an XOTemplate object (pre-schema check).
 * Used only to pick the correct export before {@link parseTemplate} validates fully.
 */
export function isTemplateLike(
  value: unknown,
): value is Record<string, unknown> {
  if (value === null || typeof value !== "object" || Array.isArray(value)) {
    return false;
  }

  const candidate = value as Record<string, unknown>;
  return (
    typeof candidate.$schema === "string" &&
    typeof candidate.name === "string" &&
    typeof candidate.roles === "object" &&
    candidate.roles !== null
  );
}

/**
 * Picks the single XOTemplate export from a dynamically loaded module.
 *
 * Resolution order:
 * 1. `default` export, when template-like
 * 2. Exactly one named template-like export
 *
 * @throws When no template export exists or multiple template exports are found.
 */
export function pickTemplateExport(
  moduleExports: Record<string, unknown>,
): Record<string, unknown> {
  const defaultExport = moduleExports.default;
  if (isTemplateLike(defaultExport)) {
    return defaultExport;
  }

  const namedTemplateExports = Object.entries(moduleExports).filter(
    ([exportName, exportValue]) =>
      exportName !== "default" && isTemplateLike(exportValue),
  );

  if (namedTemplateExports.length === 1) {
    const [, exportValue] = namedTemplateExports[0]!;
    if (!isTemplateLike(exportValue)) {
      throw new Error("No XOTemplate export found.");
    }
    return exportValue;
  }

  if (namedTemplateExports.length > 1) {
    const exportNames = namedTemplateExports.map(([name]) => name).join(", ");
    throw new Error(
      `Multiple template exports found (${exportNames}). ` +
        "Use a single named export or a default export.",
    );
  }

  throw new Error(
    "No XOTemplate export found. Export a template object as `default` or a named export.",
  );
}