async function req(pfad, opts = {}) {
  const r = await fetch('/api' + pfad, {
    headers: { 'content-type': 'application/json' },
    ...opts,
    body: opts.body ? JSON.stringify(opts.body) : undefined,
  })
  if (!r.ok) {
    let detail = r.statusText
    try { detail = (await r.json()).detail || detail } catch { /* leer */ }
    throw new Error(detail)
  }
  const ct = r.headers.get('content-type') || ''
  return ct.includes('json') ? r.json() : r.text()
}

// Pfade: /api/themen/<slug>/v<N>/…  – die Version ist immer Teil der Adresse
const e = encodeURIComponent
const v = (slug, n) => `/themen/${e(slug)}/v${n}`
export const api = {
  themen: () => req('/themen'),
  anlegen: (name, hinweise = '', spezialisierung = '') => req('/themen', { method: 'POST', body: { name, hinweise, spezialisierung } }),
  loeschen: (slug) => req(`/themen/${e(slug)}`, { method: 'DELETE' }),
  versionAnlegen: (slug, eingaben) => req(`/themen/${e(slug)}/versionen`, { method: 'POST', body: eingaben }),
  versionLoeschen: (slug, n) => req(v(slug, n), { method: 'DELETE' }),
  state: (slug, n) => req(v(slug, n)),
  start: (slug, n) => req(v(slug, n) + '/start', { method: 'POST' }),
  pause: (slug, n) => req(v(slug, n) + '/pause', { method: 'POST' }),
  reset: (slug, n) => req(v(slug, n) + '/reset', { method: 'POST' }),
  buch: (slug, n) => req(v(slug, n) + '/buch'),
  position: (slug, n) => req(v(slug, n) + '/position'),
  positionSetzen: (slug, n, daten) => req(v(slug, n) + '/position', { method: 'PUT', body: daten }),
  buchMdUrl: (slug, n) => '/api' + v(slug, n) + '/buch.md',
  pdfUrl: (slug, n) => '/api' + v(slug, n) + '/buch.pdf',
  kernUrl: (slug, n) => '/api' + v(slug, n) + '/kern.md',
}