/**
 * chatCore executor client-header normalizer (Quality Gate v2 / Fase 9 — chatCore god-file
 * decomposition, #3501).
 *
 * Pure helper extracted from chatCore: normalizes a Headers instance or a plain header object into a
 * lowercased-tolerant Record<string,string>, and backfills the client User-Agent (both casings) when
 * one is supplied and not already present. Returns null when nothing was collected. Side-effect-free;
 * behaviour is byte-identical to the previous module-level function.
 */

export function buildExecutorClientHeaders(
  headers: Headers | Record<string, unknown> | null | undefined,
  userAgent?: string | null
) {
  const normalized: Record<string, string> = {};

  if (headers instanceof Headers) {
    headers.forEach((value, key) => {
      normalized[key] = value;
    });
  } else if (headers && typeof headers === "object") {
    for (const [key, value] of Object.entries(headers)) {
      if (typeof value === "string") {
        normalized[key] = value;
      }
    }
  }

  const normalizedUserAgent = typeof userAgent === "string" ? userAgent.trim() : "";
  if (normalizedUserAgent && !normalized["user-agent"] && !normalized["User-Agent"]) {
    normalized["user-agent"] = normalizedUserAgent;
    normalized["User-Agent"] = normalizedUserAgent;
  }

  return Object.keys(normalized).length > 0 ? normalized : null;
}