/**
 * Shared SSE parsing for the AI service streams.
 *
 * Normalizes CRLF (sse-starlette's wire terminator is \r\n) to LF, then
 * splits frames on blank lines. Multiple `data:` lines within one frame
 * are joined with \n per the SSE spec. Frames with no data lines
 * (keep-alive `: ping` comments) are ignored (G-1).
 */
export function parseSseEvents(buffer: string): { events: string[]; rest: string } {
  const normalized = buffer.replace(/\r\n/g, '\n');
  const events: string[] = [];

  const separatorIndex = normalized.lastIndexOf('\n\n');
  if (separatorIndex === -1) return { events, rest: normalized };

  const complete = normalized.slice(0, separatorIndex);
  const rest = normalized.slice(separatorIndex + 2);

  for (const frame of complete.split('\n\n')) {
    const dataLines = frame
      .split('\n')
      .filter((line) => line.startsWith('data:'))
      .map((line) => line.slice(5).trimStart());
    if (dataLines.length === 0) continue; // ping/comment frame — ignore (G-1)
    events.push(dataLines.join('\n'));
  }
  return { events, rest };
}