Calculation Progress

const POLL_INTERVAL_MS  = 500;
const STALL_TIMEOUT_MS  = 60_000;
const LERP_SPEED        = 0.08; // fraction of remaining gap closed per frame (~60 fps)

// ── Shared animation state ────────────────────────────────────────────────
let targetPct    = 0;   // set by polling
let displayedPct = 0;   // driven by rAF loop
let animating    = false;

function startAnimationLoop() {
  if (animating) return;
  animating = true;

  function tick() {
    if (!animating) return;

    const gap = targetPct - displayedPct;
    if (Math.abs(gap) > 0.1) {
      displayedPct += gap * LERP_SPEED;
    } else {
      displayedPct = targetPct; // snap when close enough
    }

    renderProgressBar(displayedPct);
    requestAnimationFrame(tick);
  }

  requestAnimationFrame(tick);
}

function stopAnimationLoop(finalPct) {
  animating    = false;
  displayedPct = finalPct;
  targetPct    = finalPct;
  renderProgressBar(finalPct);
}

// ── Main entry ────────────────────────────────────────────────────────────
async function calculateTakeoffWithProgress(requestData, token) {
  // Submit the calculation (runs server-side; response arrives when done)
  const calculationPromise = fetch('/api', {
    method: 'POST',
    headers: {
      'Authorization': 'Bearer ' + token,
      'Content-Type': 'application/json',
      'X-API-Version': '1.3.6'
    },
    body: JSON.stringify({ query: 'takeoff', data: requestData })
  });

  startAnimationLoop();           // begin smooth bar before first poll arrives
  await pollProgress(token);      // update targetPct as responses arrive

  const response = await calculationPromise;
  return response.json();
}

// ── Polling loop ──────────────────────────────────────────────────────────
async function pollProgress(token) {
  while (true) {
    await sleep(POLL_INTERVAL_MS);

    const res = await fetch('/api', {
      method: 'POST',
      headers: {
        'Authorization': 'Bearer ' + token,
        'Content-Type': 'application/json',
        'X-API-Version': '1.3.6'
      },
      body: JSON.stringify({ query: 'progress' })
    });

    const progress = await res.json();

    if (progress === null) {
      // State file not written yet — calculation hasn't started, retry
      continue;
    }

    // ── Update shared target (animation loop reads this) ──────────────────
    targetPct = Math.min(100, Math.round(progress.progress / progress.total * 100));

    updateStatusTitle(progress.title);
    updateStatusMessage(progress.description);
    updateElapsedTime(progress.elapsed_ms);

    // ── Terminal states ───────────────────────────────────────────────────
    if (progress.status === 'completed') {
      stopAnimationLoop(100);
      break;
    }

    if (progress.status === 'error') {
      stopAnimationLoop(displayedPct);
      showError(progress.error_message);
      break;
    }

    // Stall guard — calculation taking unreasonably long
    if ((progress.elapsed_ms ?? 0) > STALL_TIMEOUT_MS) {
      stopAnimationLoop(displayedPct);
      showError('The calculation is taking too long. Please try again.');
      break;
    }
  }
}

// ── UI helpers (implement to match your framework) ────────────────────────
function renderProgressBar(pct) {
  document.getElementById('progress-bar').style.width = pct.toFixed(1) + '%';
}

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}