The model file and what it stores

toJSON() {
  const text = this.idsText();   // the file carries the IDS text itself; the snapshots only its { name, hash }
  const out = text ? { ...this.state, ids: { ...this.state.ids, text } } : { ...this.state };
  // the pictures carry their PNG in the file (0.8 D8.15); one whose PNG went missing is left out rather than saved blank
  if (this.state.pictures) out.pictures = this.state.pictures.filter((p) => this.pictureSrcs.has(p.hash)).map((p) => ({ ...p, src: this.pictureSrcs.get(p.hash) }));
  return JSON.stringify(out, null, 1);
}

function vec(p) {
  if (!Array.isArray(p) || p.length !== 3) throw new Error(t('model.err.point'));
  const v = p.map(Number);
  if (v.some((n) => !Number.isFinite(n) || Math.abs(n) > 1e7)) throw new Error(t('model.err.coords'));
  return v;
}

function checkMember(m, custom) {
  if (!getProfile(m.profile, custom)) throw new Error(t('model.err.profile-unknown', { name: m.profile }));
  if (!MATERIALS.includes(m.material) && !cleanText(m.material, 30)) throw new Error(t('model.err.material'));
  m.material = cleanText(m.material, 30);
  if (!['top', 'middle', 'bottom'].includes(m.position)) throw new Error(t('model.err.position'));
  if (!Number.isFinite(m.rotation)) throw new Error(t('model.err.rotation'));
  m.rotation = ((m.rotation % 360) + 360) % 360;
  const dx = m.end[0] - m.start[0], dy = m.end[1] - m.start[1], dz = m.end[2] - m.start[2];
  if (Math.hypot(dx, dy, dz) < 1) throw new Error(t('model.err.same-points'));
}

/** Grid lines from labels + spacings ("A B C", "6000 6000"). Returns { x, y } or throws a plain message. */
export function gridsFromSpacings(xLabels, xSpacings, yLabels, ySpacings) {
  const axis = (labels, spacings, which) => {
    const ls = String(labels).split(/[\s,]+/).filter(Boolean);
    const ss = String(spacings).split(/[\s,]+/).filter(Boolean).map(Number);
    if (ls.length > 60) throw new Error(t('model.err.grid-max', { max: 60 }));
    if (ls.length && ss.length !== ls.length - 1) throw new Error(t('model.err.grid-spacings', { which, n: Math.max(0, ls.length - 1) }));
    if (ss.some((v) => !Number.isFinite(v) || v <= 0 || v > 200000)) throw new Error(t('model.err.grid-positive', { which }));
    if (new Set(ls).size !== ls.length) throw new Error(t('model.err.grid-labels', { which }));
    let at = 0;
    return ls.map((label, i) => { if (i) at += ss[i - 1]; return { label: label.slice(0, 8), at }; });
  };
  return { x: axis(xLabels, xSpacings, t('model.grids.numbered')), y: axis(yLabels, ySpacings, t('model.grids.lettered')) };
}

export function spacingsOf(lines) {
  return lines.slice(1).map((g, i) => +(g.at - lines[i].at).toFixed(3)).join(' ');
}

/** A loose bolt (untrusted): d 3–100, length 5–5000 mm, head anywhere within 10 km, axis any non-zero direction. */
function cleanBolt(b) {
  if (!b || typeof b !== 'object') return null;
  const d = Number(b.d), L = Number(b.length);
  const head = Array.isArray(b.head) ? b.head.map(Number) : [], ax = Array.isArray(b.axis) ? b.axis.map(Number) : [];
  if (!(d >= 3 && d <= 100) || !(L >= 5 && L <= 5000) || head.length !== 3 || ax.length !== 3 || [...head, ...ax].some((v) => !Number.isFinite(v)) || head.some((v) => Math.abs(v) > 1e7)) return null;
  const n = Math.hypot(...ax);
  if (n < 1e-9) return null;
  const r = (v) => Math.round(v * 1000) / 1000;
  return { d: r(d), length: r(L), grade: cleanText(b.grade, 20), kind: b.kind === 'ANCHORBOLT' ? 'ANCHORBOLT' : 'BOLT', head: head.map(r), axis: ax.map((v) => Math.round(v / n * 1e6) / 1e6), phase: cleanPhase(b.phase) || 1 };
}