/***********************************************************************************************************************************************************************
 * File Name: uploadProgress.service.js
 * Type of Program: Service
 * Description: In-memory SSE broadcaster for real upload progress on the
 *              Express -> S3 (Garage) leg of an asset upload. Keyed by a
 *              client-generated uploadId so the browser can open the stream
 *              before the upload request itself is even sent.
 *
 *              No Redis — single-process only, same tradeoff already made by
 *              mediaToken.service.js's in-memory token cache. Fine for one
 *              instance; a second app instance would just never see progress
 *              for uploads routed to the other process.
 *
 * Author: Kenneth Obsequio (@lash0000)
 ***********************************************************************************************************************************************************************/
"use strict";

const clients = new Map(); // uploadId -> Response

function subscribe(uploadId, res) {
  res.writeHead(200, {
    "Content-Type": "text/event-stream",
    "Cache-Control": "no-cache, no-transform",
    Connection: "keep-alive",
    "X-Accel-Buffering": "no", // disable proxy-side buffering (nginx-style intermediaries)
  });
  res.write(": connected\n\n");
  clients.set(uploadId, res);

  res.on("close", () => {
    if (clients.get(uploadId) === res) clients.delete(uploadId);
  });
}

// No-ops if nobody's subscribed (client never opened the stream, or already
// disconnected) — progress is a best-effort visual, never load-bearing for
// the actual upload.
function publish(uploadId, data) {
  const res = clients.get(uploadId);
  if (!res) return;
  res.write(`data: ${JSON.stringify(data)}\n\n`);
}

function complete(uploadId, data = {}) {
  const res = clients.get(uploadId);
  if (!res) return;
  res.write(`data: ${JSON.stringify({ ...data, done: true })}\n\n`);
  res.end();
  clients.delete(uploadId);
}

module.exports = { subscribe, publish, complete };