$w.onReady(function () {
  const toNum = (v) => Number(String(v ?? "").replace(",", "."));
  const r0 = (x) => Math.round(+x);             // bar interi
  const r2 = (x) => (Math.round((+x) * 100) / 100).toFixed(2); // 2 decimali (% precise)

  $w("#button1").onClick(() => {
    // --- Input ---
    const V       = toNum($w("#input6").value);
    const xEAN    = toNum($w("#input5").value) / 100;

    // Current mix
    const O2v = toNum($w("#input4").value) / 100;
    const Hev = toNum($w("#input7").value) / 100;
    const P0  = toNum($w("#input8").value);

    // Target mix
    const O2t = toNum($w("#input9").value) / 100;
    const Het = toNum($w("#input10").value) / 100;
    const Pt  = toNum($w("#input11").value);

    // --- Validations ---
    if ([xEAN,O2v,Hev,P0,O2t,Het,Pt].some(isNaN)) {
      $w("#text17").text = "Error: please fill all numeric fields.";
      return;
    }
    if (O2v + Hev > 1 || O2t + Het > 1) {
      $w("#text17").text = "Error: O2% + He% must be ≤ 100%.";
      return;
    }
    if (Pt <= P0) {
      $w("#text17").text = "Error: target pressure must be higher than current pressure.";
      return;
    }

    // --- Initial partial pressures ---
    const O2pp0 = P0 * O2v;
    const Hepp0 = P0 * Hev;
    const N2pp0 = P0 * (1 - O2v - Hev);

    // 1) Helium
    const He_pp_tar = Pt * Het;
    let addHe = He_pp_tar - Hepp0;
    if (addHe < -1e-9) {
      $w("#text17").text = "Impossible: current He already above target.";
      return;
    }
    addHe = Math.max(0, addHe);
    const P1 = P0 + addHe;

    // 2) Oxygen
    let addO2;
    if (Math.abs(1 - xEAN) < 1e-9) {
      addO2 = Pt * O2t - O2pp0;
    } else {
      addO2 = (Pt*O2t - O2pp0 - xEAN*Pt + xEAN*P1) / (1 - xEAN);
    }
    if (addO2 < -1e-9) addO2 = 0;
    const P2 = P1 + addO2;

    // 3) Air/EAN
    const addEAN = Pt - P2;
    if (addEAN < -1e-9) {
      $w("#text17").text = "Impossible: overshoot final pressure.";
      return;
    }

    // --- Final mix check ---
    const O2ppF = O2pp0 + addO2 + addEAN * xEAN;
    const HeppF = Hepp0 + addHe;
    const N2ppF = N2pp0 + addEAN * (1 - xEAN);
    const O2f = O2ppF / Pt;
    const Hef = HeppF / Pt;
    const N2f = 1 - O2f - Hef;

    // Rounded values for steps
    const heBars  = r0(addHe);
    const o2Bars  = r0(addO2);
    const eanBars = r0(addEAN);
    const pStart  = r0(P0);
    const pAfterHe= r0(P0 + addHe);
    const pAfterO2= r0(P1 + addO2);
    const pFinal  = r0(Pt);

    // Output
    const line1 = `STEP 1 — Helium (He): add ${heBars} bar → from ${pStart} to ${pAfterHe} bar \n`;
    const line2 = `STEP 2 — Oxygen (O₂): add ${o2Bars} bar → from ${pAfterHe} to ${pAfterO2} bar \n`;
    const line3 = `STEP 3 — Air/EAN (${(xEAN*100).toFixed(0)}% O₂): add ${eanBars} bar → from ${pAfterO2} to ${pFinal} bar \n`;

    $w("#text17").text =
      `${line1}\n${line2}\n${line3}\n\n` +
      `Final mix @ ${pFinal} bar:\n` +
      `• O₂ ≈ ${r2(O2f*100)}% | He ≈ ${r2(Hef*100)}% | N₂ ≈ ${r2(N2f*100)}%`;
  });
});