export const labels = { section: 'Sektion', row: 'Zeile', column: 'Spalte', heading: 'Überschrift', text: 'Text', image: 'Bild', button: 'Button', gallery: 'Galerie' };
export const icons = { section: '▣', row: '☰', column: '▥', heading: 'H', text: 'T', image: '▧', button: '↗', gallery: '▦' };
export const isContainer = block => ['section', 'row', 'column', 'gallery'].includes(block?.type);
export const canContain = (parent, block) => isContainer(parent) && (parent.type !== 'gallery' || block.type === 'image');
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 === '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 === 'image') block.props = { src: '/assets/image-placeholder.svg', alt: 'Abstrakte Landschaft als Platzhalter', decorative: false, width: 1000, height: 600 };
  return block;
}

export function insertBlock(document, type, selected) {
  const block = createBlock(type);
  if (type === 'gallery') upgradeDocument(document, 3);
  let target = locate(document.blocks, selected);
  if (target?.block.type === 'gallery' && type !== 'image') { target.siblings.splice(target.index + 1, 0, block); return block.id; }
  if (target?.parent?.type === 'gallery' && type !== 'image') target = locate(document.blocks, target.parent.id);
  if (!target) document.blocks.push(block);
  else if (canContain(target.block, block)) (target.block.children ??= []).push(block);
  else target.siblings.splice(target.index + 1, 0, block);
  return block.id;
}

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('-', '')}`;
    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;
}

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

// Called only inside a history transaction: all other fields and IDs stay untouched.
export function upgradeDocument(document, version = 2) {
  if (![1, 2, 3].includes(document.schemaVersion) || ![2, 3].includes(version)) 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 (![1, 2, 3].includes(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 = mediaProps(items[0]); 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;
}

export function insertPreset(document, name, 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; }
}