const windowMs = 30000;
const minimumSpanMs = 4000;
const samplesByJob = new Map();

export function updateSpeeds(jobs) {
  const now = performance.now();
  const seenIds = new Set();

  for (const job of jobs) {
    seenIds.add(job.id);
    let samples = samplesByJob.get(job.id) || [];
    const last = samples[samples.length - 1];
    const progressWentBack = last && job.bytesDone < last.bytes;
    const notTransferring = job.status !== "downloading" && job.status !== "extracting" && job.status !== "moving";
    if (progressWentBack || notTransferring || (last && last.status !== job.status)) {
      samples = [];
    }

    samples.push({ bytes: job.bytesDone, time: now, status: job.status });
    while (samples.length > 2 && now - samples[1].time >= windowMs) {
      samples.shift();
    }
    samplesByJob.set(job.id, samples);
  }

  for (const id of samplesByJob.keys()) {
    if (!seenIds.has(id)) samplesByJob.delete(id);
  }
}

export function speedOf(jobId) {
  const samples = samplesByJob.get(jobId);
  if (!samples || samples.length < 2) return 0;
  const first = samples[0];
  const last = samples[samples.length - 1];
  const spanMs = last.time - first.time;
  if (spanMs < minimumSpanMs) return 0;
  return ((last.bytes - first.bytes) * 1000) / spanMs;
}