import { randomUUID } from "crypto";
import { setUserAgentHeader } from "../executors/base.ts";

/**
 * Header keys that are forwarded from the client to the upstream provider.
 * Used by both OpencodeExecutor and DefaultExecutor.
 */
const OPENCODE_HEADER_KEYS = [
  "x-opencode-session",
  "x-opencode-request",
  "x-opencode-project",
  "x-opencode-client",
] as const;

/**
 * Case-insensitive lookup for a header in a headers record.
 */
function findHeader(headers: Record<string, string>, name: string): string | undefined {
  return Object.entries(headers).find(([key]) => key.toLowerCase() === name.toLowerCase())?.[1];
}

/**
 * Forward OpenCode client request metadata headers to the upstream provider.
 *
 * Shared logic used by OpencodeExecutor and DefaultExecutor:
 * 1. Forwards User-Agent from clientHeaders via `setUserAgentHeader()`
 * 2. Forwards x-opencode-session, x-opencode-request, x-opencode-project,
 *    x-opencode-client headers (case-insensitive match)
 *
 * @param headers - The outbound headers record to mutate
 * @param clientHeaders - The client-provided headers to forward from
 * @param options.synthesizeRequestId - When true (OpencodeExecutor only), maps
 *   x-session-affinity / x-session-id to x-opencode-session when the latter is
 *   missing, and synthesizes a UUID for x-opencode-request if also missing.
 */
export function forwardOpencodeClientHeaders(
  headers: Record<string, string>,
  clientHeaders: Record<string, string>,
  options?: { synthesizeRequestId?: boolean }
): void {
  // 1. Forward User-Agent
  const clientUA = clientHeaders["User-Agent"] || clientHeaders["user-agent"];
  if (clientUA) {
    setUserAgentHeader(headers, clientUA);
  }

  // 2. Forward x-opencode-* metadata headers
  for (const headerName of OPENCODE_HEADER_KEYS) {
    const value = findHeader(clientHeaders, headerName);
    if (value) {
      headers[headerName] = value;
    }
  }

  // 3. OpencodeExecutor-only: synthesize session/request id from fallback headers
  if (options?.synthesizeRequestId && !headers["x-opencode-session"]) {
    const sessionAffinity =
      findHeader(clientHeaders, "x-session-affinity") || findHeader(clientHeaders, "x-session-id");
    if (sessionAffinity) {
      headers["x-opencode-session"] = sessionAffinity;

      if (!headers["x-opencode-request"]) {
        headers["x-opencode-request"] = randomUUID();
      }
    }
  }
}