KantSites/public/assets/editor-model.js

export const labels = { section: 'Sektion', row: 'Zeile', column: 'Spalte', heading: 'Überschrift', text: 'Text', image: 'Bild', button: 'Button', gallery: 'Galerie', postlist: 'Beitragsliste', postnav: 'Beitragsnavigation', iconcard: 'Symbolkarte', stat: 'Kennzahl', quote: 'Kundenstimme', logos: 'Logoleiste', cta: 'Aufruf-Band', contact: 'Kontaktdaten', divider: 'Trennlinie', spacer: 'Abstand', accordion: 'Akkordeon', accordionitem: 'Akkordeon-Eintrag', tabs: 'Tabs', tabitem: 'Tab', form: 'Formular', breadcrumb: 'Brotkrumen', menu: 'Navigation', partialref: 'Verknüpfte Sektion', embed: 'Externer Inhalt', icon: 'Symbol', progress: 'Fortschritt', slider: 'Slider', legal: 'Rechtszeile', social: 'Soziale Profile' };
export const icons = { section: '▣', row: '☰', column: '▥', heading: 'H', text: 'T', image: '▧', button: '↗', gallery: '▦', postlist: '☷', postnav: '⇄', iconcard: '◈', stat: '№', quote: '❝', logos: '⬚', cta: '◉', contact: '✆', divider: '—', spacer: '⇳', accordion: '⌵', accordionitem: '·', tabs: '▭', tabitem: '▫', form: '✉', breadcrumb: '⟩', menu: '☰', partialref: '⧉', legal: '§', embed: '⬓', icon: '◆', progress: '▰', slider: '⇄', social: '⚭' };
// A namespaced type belongs to a plugin this installation may not have. Such blocks stay in the
// document, stay selectable and movable, but the editor never edits or fills them.
/**
 * The toolbox, grouped the way the page is actually built. A flat list of thirty-one types said
 * nothing about which of them belong together or where they may go; the first group is the
 * scaffolding, the rest is what goes inside it.
 */
export const CATEGORIES = [
  { name: 'Aufbau', hint: 'Sektion → Zeile → Spalte. Der Inhalt kommt in die Spalte.', types: ['section', 'row', 'column'] },
  { name: 'Inhalt', types: ['heading', 'text', 'image', 'button', 'icon', 'divider', 'spacer'] },
  { name: 'Bausteine', types: ['iconcard', 'stat', 'quote', 'cta', 'contact', 'social', 'logos', 'progress'] },
  { name: 'Gruppen', types: ['gallery', 'accordion', 'accordionitem', 'tabs', 'tabitem', 'slider'] },
  { name: 'Seite und Daten', types: ['postlist', 'postnav', 'breadcrumb', 'menu', 'form', 'legal', 'partialref', 'embed'] },
];

/** How many columns a row can be added with. */
export const ROW_COLUMNS = [2, 3, 4];

/**
 * Why a type cannot be added where the selection currently is. The toolbox says this instead of
 * simply greying a button out: a rule you are told is one you learn, a button that merely stops
 * working is one you keep pressing.
 */
export function whyNot(type) {
  if (REQUIRE[type]) return `${labels[type]}: gehört in ${REQUIRE[type].map(parent => labels[parent]).join(' oder ')}. Wähle dort zuerst ein Element aus.`;
  if (ROOT_NEEDS_CONTAINER.includes(type)) return `${labels[type]}: gehört in eine Sektion. Füge zuerst eine Sektion ein oder wähle eine aus.`;
  return `${labels[type]}: passt an dieser Stelle nicht. Wähle ein anderes Element aus.`;
}

export const PLUGIN_TYPE = /^[a-z][a-z0-9]{1,30}\.[a-z][a-z0-9-]{1,40}$/;
export const isPluginBlock = block => typeof block?.type === 'string' && PLUGIN_TYPE.test(block.type);
export const blockLabel = block => labels[block?.type] ?? (isPluginBlock(block) ? `Baustein ${block.type}` : 'Unbekannt');
export const blockIcon = block => icons[block?.type] ?? '❔';
export const isContainer = block => ['section', 'row', 'column', 'gallery', 'logos', 'accordion', 'accordionitem', 'tabs', 'tabitem', 'slider'].includes(block?.type);
// Nothing may be dropped into a plugin block: the core does not know its layout contract.
// Containers that accept only one kind of child, mirrored by the server side validator.
// ---------------------------------------------------------------------------------------------
// What may sit inside what.
//
// Three rules, the same three the Flatsome UX Builder uses, because they cover the cases and
// because they are the ones people already have in their hands:
//
//   ALLOW    a container that takes only these children and nothing else
//   REQUIRE  a block that exists only inside one of these parents
//   ROOT_NEEDS_CONTAINER
//            a block that may sit in any container but not loose at the top of a document
//
// Until now a row took anything - a heading could land directly in it, next to the columns -
// and a column could stand anywhere. That is why the toolbox offered rows and columns out of
// nowhere. The structure the editor has always described in its own hint text is
// section -> row -> column -> content, and these rules are that sentence made binding.
// ---------------------------------------------------------------------------------------------

/** Containers that take one kind of child and nothing else. */
export const ALLOW = { row: ['column'], gallery: ['image'], logos: ['image'], accordion: ['accordionitem'], tabs: ['tabitem'] };
/** Blocks that exist only inside one of these parents. */
export const REQUIRE = { column: ['row'], accordionitem: ['accordion'], tabitem: ['tabs'] };
/**
 * A row is not refused by any particular parent - a tab panel or an accordion entry may well
 * hold one - but it is not a thing a document starts with. At the top level a page begins with
 * a section, and that is where a row belongs.
 */
export const ROOT_NEEDS_CONTAINER = ['row'];

export const canContain = (parent, block) => isContainer(parent) && !isPluginBlock(parent)
  && (ALLOW[parent.type] === undefined || ALLOW[parent.type].includes(block?.type))
  && (block?.type === undefined || REQUIRE[block.type] === undefined || REQUIRE[block.type].includes(parent.type));
export const clone = value => structuredClone(value);

export function locate(blocks, id, parent = null) {
  for (let index = 0; index < blocks.length; index++) {
    const block = blocks[index];
    if (block.id === id) return { block, siblings: blocks, index, parent };
    const child = locate(block.children || [], id, block);
    if (child) return child;
  }
  return null;
}

export function createBlock(type) {
  if (!Object.hasOwn(labels, type)) throw new Error('Unbekannter Block.');
  const block = { id: `b_${crypto.randomUUID().replaceAll('-', '')}`, type };
  if (isContainer(block)) block.children = [];
  if (type === 'accordion') block.children = [createBlock('accordionitem')];
  // A single tab is not a tab group, and the script needs at least two to enhance anything.
  if (type === 'tabs') block.children = [createBlock('tabitem'), createBlock('tabitem')];
  if (type === 'heading') block.props = { text: 'Deine neue Überschrift', level: 2 };
  if (type === 'text') block.props = { text: 'Hier beginnt dein neuer Inhalt.' };
  if (type === 'button') block.props = { text: 'Mehr erfahren', href: '/' };
  if (type === 'postlist') block.props = { count: 3, category: '', tag: '', layout: 'karten' };
  if (type === 'postnav') block.props = { previousLabel: 'Vorheriger Beitrag', nextLabel: 'Nächster Beitrag' };
  if (type === 'legal') block.props = { label: 'Rechtliches' };
  if (type === 'iconcard') block.props = { icon: 'check', title: 'Deine Leistung', text: 'Beschreibe hier kurz, worum es geht.', href: '' };
  if (type === 'stat') block.props = { value: '15+', label: 'Jahre Erfahrung' };
  if (type === 'quote') block.props = { text: 'Ein Satz, den eine Kundin oder ein Kunde über dich gesagt hat.', author: 'Name', role: '', rating: 5 };
  if (type === 'cta') block.props = { title: 'Bereit für den nächsten Schritt?', text: '', buttonText: 'Jetzt anfragen', href: '/' };
  if (type === 'contact') block.props = { phone: '', email: '', address: '' };
  if (type === 'spacer') block.props = { size: 'medium' };
  if (type === 'accordionitem') block.props = { title: 'Eine Frage', open: false };
  if (type === 'tabitem') block.props = { title: 'Neuer Tab' };
  if (type === 'form') block.props = { form: '' };
  if (type === 'menu') block.props = { slot: 'header', layout: 'horizontal' };
  if (type === 'partialref') block.props = { partial: '' };
  // An embed starts empty and blocked: no address, so nothing loads before someone enters one.
  if (type === 'embed') block.props = { group: 'external', title: '', provider: '', url: '', hint: '', height: 400 };
  if (type === 'icon') block.props = { icon: 'star', size: 48, decorative: true, label: '', href: '' };
  if (type === 'progress') block.props = { label: 'Fortschritt', value: 70, showValue: true };
  // Welche Profile es gibt, steht in den Einstellungen; der Block bringt nur die Darstellung mit.
  if (type === 'social') block.props = { size: 24, shape: 'plain', layout: 'horizontal', labels: false, networks: [], newTab: true };
  if (type === 'slider') block.props = { desktopVisible: 3, tabletVisible: 2, mobileVisible: 1, snap: true, dots: true, autoplay: 0 };
  if (type === 'image') block.props = { src: '/assets/image-placeholder.svg', alt: 'Abstrakte Landschaft als Platzhalter', decorative: false, width: 1000, height: 600 };
  return block;
}

/** Raises the document schema to the version that knows this block type. */
export function upgradeForType(document, type) {
  if (type === 'gallery') upgradeDocument(document, 3);
  if (type === 'postlist') upgradeDocument(document, 5);
  if (type === 'postnav') upgradeDocument(document, 18);
  if (type === 'legal') upgradeDocument(document, 19);
  if (['iconcard', 'stat', 'quote', 'logos', 'cta', 'contact', 'divider', 'spacer', 'accordion', 'accordionitem'].includes(type)) upgradeDocument(document, 6);
  if (type === 'tabs' || type === 'tabitem') upgradeDocument(document, 7);
  if (type === 'form') upgradeDocument(document, 8);
  if (type === 'breadcrumb') upgradeDocument(document, 9);
  if (type === 'menu' || type === 'partialref') upgradeDocument(document, 11);
  if (type === 'embed') upgradeDocument(document, 14);
  if (['icon', 'progress', 'slider'].includes(type)) upgradeDocument(document, 15);
  if (type === 'social') upgradeDocument(document, 23);
}

/**
 * Where clicking a type in the toolbox would put it - without putting it anywhere.
 *
 * Asking and doing used to be the same step, so nothing could tell beforehand whether a type
 * fits at all. The toolbox needs exactly that answer to grey out what does not belong here, and
 * the answer has to be the one the click will actually follow, or the two drift apart.
 *
 * The search goes from the inside out: into the selection when it is a container that takes
 * this type, otherwise next to it, climbing until some ancestor accepts it, and finally the top
 * level. Returns null when the type cannot go anywhere from this selection.
 *
 * @return {{parentId: string|null, index: number}|null}
 */
export function insertionTarget(document, selected, type) {
  // A section starts a page area. Explicit insertion points and drag/drop can still nest it.
  if (type === 'section') {
    const top = blockPath(document.blocks, selected)[0];
    return { parentId: null, index: top ? document.blocks.findIndex(block => block.id === top.id) + 1 : document.blocks.length };
  }
  const probe = { type };
  let item = locate(document.blocks, selected);
  // Content belongs to a chosen entry. Do not silently place it outside the accordion.
  if (item?.block.type === 'accordion' && type !== 'accordionitem') return null;
  if (item && canContain(item.block, probe)) return { parentId: item.block.id, index: (item.block.children ?? []).length };
  while (item) {
    const parentId = item.parent?.id ?? null;
    if (dropList(document, parentId, probe)) return { parentId, index: item.index + 1 };
    item = item.parent ? locate(document.blocks, item.parent.id) : null;
  }
  return dropList(document, null, probe) ? { parentId: null, index: document.blocks.length } : null;
}

export function insertBlock(document, type, selected) {
  const target = insertionTarget(document, selected, type);
  if (!target) return null;
  return insertBlockAt(document, type, target.parentId, target.index);
}

export function duplicateBlock(document, selected) {
  const target = locate(document.blocks, selected);
  if (!target) return null;
  const copy = clone(target.block);
  const rekey = block => {
    block.id = `b_${crypto.randomUUID().replaceAll('-', '')}`;
    delete block.anchor;
    if (block.type === 'heading' && block.props.level === 1) block.props.level = 2;
    (block.children || []).forEach(rekey);
  };
  rekey(copy);
  target.siblings.splice(target.index + 1, 0, copy);
  return copy.id;
}

export function moveBlock(document, selected, targetId, inside = false) {
  const source = locate(document.blocks, selected);
  const target = locate(document.blocks, targetId);
  if (!source || !target || selected === targetId || locate(source.block.children || [], targetId)) return false;
  if (inside && !isContainer(target.block)) return false;
  if (inside && !canContain(target.block, source.block)) return false;
  if (!inside && target.parent && !canContain(target.parent, source.block)) return false;
  source.siblings.splice(source.index, 1);
  const destination = locate(document.blocks, targetId);
  if (inside) (destination.block.children ??= []).push(source.block);
  else destination.siblings.splice(destination.index, 0, source.block);
  return true;
}

/**
 * Where a block may land. `parentId` of null means the top level. Returns the list that would
 * hold the block, or null when the parent refuses this kind of child - a gallery takes images
 * and nothing else, an accordion takes entries.
 */
export function dropList(document, parentId, block) {
  if (parentId === null) {
    const type = block?.type;
    const loose = type !== undefined && (REQUIRE[type] !== undefined || ROOT_NEEDS_CONTAINER.includes(type));
    return loose ? null : document.blocks;
  }
  const parent = locate(document.blocks, parentId)?.block;
  return parent && canContain(parent, block) ? (parent.children ??= []) : null;
}

/** Puts an already built block at an exact position, or refuses when the parent will not take it. */
function place(document, block, parentId, index) {
  const list = dropList(document, parentId, block);
  if (!list) return null;
  list.splice(Math.max(0, Math.min(index, list.length)), 0, block);
  return block.id;
}

/** Inserts a new block at an exact position instead of behind the selection. */
export function insertBlockAt(document, type, parentId, index) {
  upgradeForType(document, type);
  return place(document, createBlock(type), parentId, index);
}

/**
 * Moves an existing block to an exact position. Unlike moveBlock this keeps the index, so a
 * block dragged between two others lands between them and not at the end of the container.
 */
export function moveBlockTo(document, selected, parentId, index) {
  const source = locate(document.blocks, selected);
  if (!source) return false;
  // Dropping a container into itself or into its own child would detach the branch.
  if (parentId === selected || (parentId !== null && locate(source.block.children || [], parentId))) return false;
  if (!dropList(document, parentId, source.block)) return false;
  const from = source.siblings, fromIndex = source.index;
  from.splice(fromIndex, 1);
  // Re-read: removing the block may have shifted the target list or emptied a parent.
  const list = dropList(document, parentId, source.block);
  if (!list) { from.splice(fromIndex, 0, source.block); return false; }
  // The index still counts in the list as it was before the block was taken out, so the shift
  // has to be settled first and only then clamped - the other way round an index pointing past
  // the end is clamped to the old length and then pulled one step too far forward.
  let at = index;
  if (list === from && fromIndex < index) at -= 1;
  at = Math.max(0, Math.min(at, list.length));
  list.splice(at, 0, source.block);
  return true;
}

export const devices = { desktop: 'Desktop', tablet: 'Tablet', mobile: 'Mobil' };

// Called only inside a history transaction: all other fields and IDs stay untouched.
// Die höchste Fassung, die dieser Editor kennt. Sie stand bisher als Liste an zwei Stellen und
// blieb bei 12 stehen, während Bausteine schon v13 bis v15 verlangten: in einem aktuellen Dokument
// liess sich dann gar nichts mehr einfügen, und ein Symbol, ein Slider oder ein externer Inhalt
// nirgends. Eine Zahl, an einer Stelle.
export const SCHEMA_VERSION = 23;

export const VISIBILITY = { all: 'Auf allen Geräten', desktop: 'Nur Desktop', tablet: 'Nur Tablet', mobile: 'Nur Mobil', 'hide-desktop': 'Auf Desktop ausblenden', 'hide-tablet': 'Auf Tablet ausblenden', 'hide-mobile': 'Auf Mobil ausblenden', hidden: 'Überall ausblenden' };

export function setVisibility(document, id, value) {
  if (!Object.hasOwn(VISIBILITY, value)) throw new Error('Unbekannte Sichtbarkeit.');
  const block = locate(document.blocks, id)?.block;
  if (!block) return;
  if (value === 'all') {
    if (block.layout) delete block.layout.visibility;
  } else {
    upgradeDocument(document, 22);
    (block.layout ??= {}).visibility = value;
  }
}
const known = version => Number.isInteger(version) && version >= 1 && version <= SCHEMA_VERSION;

export function upgradeDocument(document, version = 2) {
  if (!known(document.schemaVersion) || !known(version) || version < 2) throw new Error('Unbekanntes Dokumentschema.');
  document.schemaVersion = Math.max(document.schemaVersion, version);
  return document;
}

export function effectiveDesign(block, device, key) {
  let value, source;
  for (const name of Object.keys(devices)) {
    if (block.layout?.design?.[name]?.[key] !== undefined) {
      value = block.layout.design[name][key]; source = name;
    }
    if (name === device) break;
  }
  return { value, source };
}

export function setDesign(document, id, device, key, value) {
  if (!known(document.schemaVersion)) throw new Error('Unbekanntes Dokumentschema.');
  if (!Object.hasOwn(devices, device)) throw new Error('Unbekannte Vorschaugröße.');
  const block = locate(document.blocks, id)?.block;
  if (!block) return;
  if (value === '') {
    const design = block.layout?.design;
    if (!design?.[device] || !Object.hasOwn(design[device], key)) return;
    delete design[device][key];
    if (!Object.keys(design[device]).length) delete design[device];
    if (!Object.keys(design).length) delete block.layout.design;
  } else {
    upgradeDocument(document);
    ((block.layout ??= {}).design ??= {})[device] ??= {};
    block.layout.design[device][key] = value;
  }
}

export function blockPath(blocks, id) {
  const found = locate(blocks, id);
  return found ? [...(found.parent ? blockPath(blocks, found.parent.id) : []), found.block] : [];
}

export function setEffect(document, id, key, value) {
  const block = locate(document.blocks, id)?.block;
  if (!block) return;
  upgradeDocument(document, 3);
  ((block.layout ??= {}).effects ??= {})[key] = value;
}

export function mediaProps(media) {
  const largest = media.variants.at(-1);
  return { mediaId: media.id, src: largest.src, width: largest.width, height: largest.height, alt: media.decorative ? '' : media.alt, decorative: Boolean(media.decorative), caption: '', sources: media.variants.map(({ src, width }) => ({ src, width })) };
}

export function insertMedia(document, selected, items) {
  const target = locate(document.blocks, selected)?.block;
  upgradeDocument(document, 3);
  if (target?.type === 'image') { target.props = { ...target.props, ...mediaProps(items[0]), caption: target.props.caption || '' }; return target.id; }
  let parent = target;
  if (target?.type !== 'gallery') {
    const id = insertBlock(document, 'gallery', selected); parent = locate(document.blocks, id).block;
  }
  for (const item of items) { const image = createBlock('image'); image.props = mediaProps(item); (parent.children ??= []).push(image); }
  return parent.id;
}

/**
 * A row with a given number of columns, inserted where the selection is.
 *
 * A row on its own looks like nothing, which is why "add a row" was hard to find: what people
 * want is a row that already has columns in it.
 */
/**
 * A full screen hero: edge to edge, as tall as the screen, content centred, with room for a
 * background image and a dark overlay so text stays readable on any photo.
 *
 * The parts all exist on their own - width "full", min-height in dvh, display flex, overlay - but
 * finding that combination is a research project. This is the one click.
 */
export function insertHero(document, selected) {
  const section = createBlock('section');
  section.layout = { tone: 'ink', width: 'full' };
  section.style = {
    desktop: {
      // dvh, not vh: on a phone 100vh is taller than the screen.
      minHeight: '100dvh', display: 'flex', alignItems: 'center',
      backgroundSize: 'cover', backgroundPosition: 'center', backgroundRepeat: 'no-repeat',
      overlayColor: '#000000', overlayOpacity: 0.4,
      padding: { top: '80px', right: '32px', bottom: '80px', left: '32px' },
      textAlign: 'center',
    },
    mobile: { minHeight: '80dvh', padding: { top: '56px', right: '20px', bottom: '56px', left: '20px' } },
  };
  // A hero at the top of a page carries its main heading - but a page has exactly one, and
  // inserting a second would produce a document the editor refuses to save.
  const hasMainHeading = blocks => blocks.some(block =>
    (block.type === 'heading' && block.props?.level === 1) || hasMainHeading(block.children ?? []));
  const heading = createBlock('heading');
  heading.props = { text: 'Deine Botschaft, ganzflächig.', level: hasMainHeading(document.blocks) ? 2 : 1 };
  const paragraph = createBlock('text');
  paragraph.props = { text: 'Ein Satz, der sagt, worum es geht. Wähle im Designbereich unter Hintergrund ein Bild und stelle die Deckkraft der Überlagerung so ein, dass der Text lesbar bleibt.' };
  const button = createBlock('button');
  section.children = [heading, paragraph, button];
  upgradeDocument(document, 10);
  const top = blockPath(document.blocks, selected)[0];
  const index = top ? document.blocks.findIndex(block => block.id === top.id) + 1 : document.blocks.length;
  document.blocks.splice(index, 0, section);
  return section.id;
}

/** A row with its columns already in it. On its own an empty row is a box with nothing in it. */
function buildRow(columns) {
  const count = Math.max(1, Math.min(6, Number(columns) || 2));
  const names = { 1: 'one', 2: 'two', 3: 'three', 4: 'four' };
  const row = createBlock('row');
  row.layout = { design: { desktop: { columns: names[count] ?? 'auto', gap: 'medium' }, mobile: { columns: 'one' } } };
  row.children = Array.from({ length: count }, () => createBlock('column'));
  return row;
}

/** A row at an exact position, for a marked insertion point or a drop in the preview. */
export function insertRowAt(document, columns, parentId, index) {
  upgradeDocument(document);
  return place(document, buildRow(columns), parentId, index);
}

export function insertRow(document, columns, selected) {
  const row = buildRow(columns);
  upgradeDocument(document);
  // Same placement rule as a single element, so the row does not land somewhere else than the
  // toolbox promised.
  const target = insertionTarget(document, selected, 'row');
  return target ? place(document, row, target.parentId, target.index) : null;
}

export function insertPreset(document, name, selected) {
  if (name === 'hero') return insertHero(document, selected);
  if (!['intro', 'columns', 'cta'].includes(name)) throw new Error('Unbekannte Vorlage.');
  const section = createBlock('section');
  const heading = text => { const block = createBlock('heading'); block.props.text = text; return block; };
  const paragraph = text => { const block = createBlock('text'); block.props.text = text; return block; };
  section.layout = { tone: name === 'cta' ? 'ink' : 'paper', width: name === 'columns' ? 'normal' : 'narrow' };
  section.children = [heading(name === 'cta' ? 'Lass uns gemeinsam starten.' : name === 'columns' ? 'Was wir für dich tun.' : 'Raum für deine nächste Idee.'), paragraph('Erzähle hier, was dein Angebot besonders macht und welchen Nutzen deine Besucher davon haben.')];
  if (name === 'columns') {
    const row = createBlock('row');
    row.layout = { design: { desktop: { columns: 'two', gap: 'medium' }, mobile: { columns: 'one' } } };
    row.children = ['Persönlich beraten', 'Gemeinsam umsetzen'].map(text => {
      const column = createBlock('column');
      const title = heading(text); title.props.level = 3;
      column.children = [title, paragraph('Beschreibe dein Angebot in wenigen verständlichen Sätzen.')];
      return column;
    });
    section.children.push(row);
    upgradeDocument(document);
  } else section.children.push(createBlock('button'));
  const top = blockPath(document.blocks, selected)[0];
  const index = top ? document.blocks.findIndex(block => block.id === top.id) + 1 : document.blocks.length;
  document.blocks.splice(index, 0, section);
  return section.id;
}

export class EditorHistory {
  constructor(document) { this.reset(document); }
  reset(document) {
    this.document = clone(document);
    this.past = [];
    this.future = [];
    this.mergeKey = null;
    this.saved = JSON.stringify(document);
  }
  change(mutator, mergeKey = null) {
    const next = clone(this.document);
    const result = mutator(next);
    if (JSON.stringify(next) === JSON.stringify(this.document)) return result;
    if (!mergeKey || this.mergeKey !== mergeKey) this.past.push(this.document);
    if (this.past.length > 100) this.past.shift();
    this.document = next;
    this.future = [];
    this.mergeKey = mergeKey;
    return result;
  }
  undo() {
    if (!this.past.length) return;
    this.future.push(this.document);
    this.document = this.past.pop();
    this.mergeKey = null;
  }
  redo() {
    if (!this.future.length) return;
    this.past.push(this.document);
    this.document = this.future.pop();
    this.mergeKey = null;
  }
  markSaved(document) { this.saved = JSON.stringify(document); this.mergeKey = null; }
  get dirty() { return JSON.stringify(this.document) !== this.saved; }
}

// ---------------------------------------------------------------------------------------------
// Free block styles (document schema v10).
//
// A style is { device: { property: value, hover: { property: value } } }. Desktop is the base,
// tablet and mobile override it. Everything mirrors StyleSchema on the server: the editor can only
// offer what the server accepts, and a value the server would reject never reaches a document.
// ---------------------------------------------------------------------------------------------

/** The value that actually applies on a device, plus the device it was inherited from. */
export function effectiveStyle(block, device, key, side = null) {
  let value, source;
  for (const name of Object.keys(devices)) {
    const stored = block?.style?.[name]?.[key];
    const candidate = side === null ? stored : stored?.[side];
    if (candidate !== undefined) { value = candidate; source = name; }
    if (name === device) break;
  }
  return { value, source };
}

export function hoverStyle(block, device, key) {
  return block?.style?.[device]?.hover?.[key];
}

/** Removes empty objects so an untouched block never carries a style skeleton. */
function prune(block) {
  for (const device of Object.keys(block.style ?? {})) {
    const values = block.style[device];
    for (const key of Object.keys(values)) {
      if (values[key] && typeof values[key] === 'object' && Object.keys(values[key]).length === 0) delete values[key];
    }
    if (Object.keys(values).length === 0) delete block.style[device];
  }
  if (block.style && Object.keys(block.style).length === 0) delete block.style;
}

/**
 * Sets one style value. An empty value removes it, which makes the block fall back to the wider
 * device and finally to the theme. Called inside a history transaction like every other change.
 */
export function scrolledStyle(block, device, key) {
  return block?.style?.[device]?.scrolled?.[key];
}

export function setStyle(document, id, device, key, value, { side = null, hover = false, scrolled = false } = {}) {
  if (!Object.hasOwn(devices, device)) throw new Error('Unbekannte Vorschaugröße.');
  const block = locate(document.blocks, id)?.block;
  if (!block) return;
  const empty = value === '' || value === null || value === undefined;
  if (!empty) upgradeDocument(document, 10);
  if (key === 'backgroundImage' && value === 'none') upgradeDocument(document, 20);

  block.style ??= {};
  block.style[device] ??= {};
  let target = block.style[device];
  if (hover) { target.hover ??= {}; target = target.hover; }
  // The scrolled state of the header: same shape as hover, applied once the page has moved.
  if (scrolled) { target.scrolled ??= {}; target = target.scrolled; }

  if (side !== null) {
    if (empty) { if (target[key]) delete target[key][side]; }
    else { target[key] ??= {}; target[key][side] = value; }
  } else if (empty) {
    delete target[key];
  } else {
    target[key] = value;
  }
  prune(block);
}

/** Drops every style of one device, so it inherits again. */
export function resetStyleDevice(document, id, device) {
  const block = locate(document.blocks, id)?.block;
  if (!block?.style) return;
  delete block.style[device];
  prune(block);
}

/** Drops the whole styling of a block. */
export function clearStyle(document, id) {
  const block = locate(document.blocks, id)?.block;
  if (!block) return;
  delete block.style;
}

/** Copies the styling of one block onto another, with fresh objects. */
export function copyStyle(document, fromId, toId) {
  const source = locate(document.blocks, fromId)?.block;
  const target = locate(document.blocks, toId)?.block;
  if (!source || !target) return false;
  if (!source.style) { delete target.style; return true; }
  upgradeDocument(document, 10);
  target.style = structuredClone(source.style);
  return true;
}

/** UI relevance only. Existing values remain editable, including on older documents. */
export function relevantProperty(block, key, property) {
  if (Object.values(block.style ?? {}).some(values => values[key] !== undefined || values.hover?.[key] !== undefined || values.scrolled?.[key] !== undefined)) return true;
  const container = isContainer(block);
  if (property.group === 'slider') return block.type === 'slider';
  if (property.group === 'menu') return block.type === 'menu';
  if (property.group === 'image') return ['image', 'gallery', 'logos', 'postlist'].includes(block.type);
  if (property.group === 'text' || key === 'textShadow') return !['image', 'gallery', 'logos', 'spacer', 'divider', 'embed'].includes(block.type);
  if (['flexDirection', 'flexWrap', 'justifyContent', 'alignItems', 'gridColumns', 'gap', 'rowGap', 'columnGap'].includes(key)) return container || ['button', 'menu', 'form', 'postlist', 'contact', 'social'].includes(block.type);
  return true;
}