/**
 * Per-request SSE helpers — single-request streaming pattern.
 * Used by chat streaming and model comparison endpoints where
 * one route handler streams SSE to one client.
 */

import type { FastifyReply } from 'fastify';

export function startSSE(reply: FastifyReply): void {
  reply.raw.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    Connection: 'keep-alive',
    'X-Accel-Buffering': 'no',
  });
  reply.hijack();
}

export function sendSSEEvent(reply: FastifyReply, event: string, data: unknown): void {
  const payload = typeof data === 'string' ? data : JSON.stringify(data);
  reply.raw.write(`event: ${event}\ndata: ${payload}\n\n`);
}

export function sendSSEData(reply: FastifyReply, data: unknown): void {
  const payload = typeof data === 'string' ? data : JSON.stringify(data);
  reply.raw.write(`data: ${payload}\n\n`);
}

export function endSSE(reply: FastifyReply): void {
  reply.raw.write('data: [DONE]\n\n');
  reply.raw.end();
}