import { EventMessage } from "fastify";

export async function* transformAsyncIterable(
  source: AsyncIterable<EventMessage>
): AsyncIterable<string> {
  for await (const message of source) {
    yield serializeSSEEvent(message);
  }
  yield serializeSSEEvent({ event: "end", data: "Stream closed" });
}

export function serializeSSEEvent(chunk: EventMessage): string {
  let payload = "";
  if (chunk.id) {
    payload += `id: ${chunk.id}\n`;
  }
  if (chunk.event) {
    payload += `event: ${chunk.event}\n`;
  }
  if (chunk.data) {
    payload += `data: ${chunk.data}\n`;
  }
  if (chunk.retry) {
    payload += `retry: ${chunk.retry}\n`;
  }
  if (!payload) {
    return "";
  }
  payload += "\n";
  return payload;
}