import type { RichTextNode, RichTextRoot } from '@unito/integration-api';

const SENTINEL_OPENER = '【';
const SENTINEL_CLOSER = '】';

export type CanRender = (node: RichTextNode, ancestors: ReadonlyArray<RichTextNode>) => boolean;

const BLOCK_PARENT_TYPES = new Set(['root', 'blockquote', 'listItem']);

// ---- Encoder ----

export function encodeSentinels(rootNode: RichTextRoot, canRender: CanRender): RichTextRoot {
  return {
    type: 'root',
    children: encodeChildren(rootNode.children, [rootNode], true, canRender),
  };
}

function encodeChildren(
  children: RichTextNode[],
  ancestors: ReadonlyArray<RichTextNode>,
  blockContext: boolean,
  canRender: CanRender,
): RichTextNode[] {
  const result: RichTextNode[] = [];

  for (const child of children) {
    if (child.type === 'text') {
      result.push(child);
      continue;
    }

    if (canRender(child, ancestors)) {
      if (child.children) {
        const childBlockContext = BLOCK_PARENT_TYPES.has(child.type);
        result.push({
          ...child,
          children: encodeChildren(child.children, [child, ...ancestors], childBlockContext, canRender),
        });
      } else {
        result.push(child);
      }
      continue;
    }

    const encode = ENCODERS[child.type];
    if (encode) {
      result.push(...encode(child, canRender, ancestors));
      continue;
    }

    result.push(...encodeAsSentinels(child, ancestors, blockContext, canRender));
  }

  return result;
}

function encodeAsSentinels(
  node: RichTextNode,
  ancestors: ReadonlyArray<RichTextNode>,
  blockContext: boolean,
  canRender: CanRender,
): RichTextNode[] {
  if (!node.children || node.children.length === 0) {
    const marker = selfCloseMarker(node);
    return [blockContext ? wrapBlock(marker) : { type: 'text', value: marker }];
  }
  const opener = openMarker(node);
  const closer = closeMarker(node);
  const inner = encodeChildren(node.children, [node, ...ancestors], blockContext, canRender);
  if (blockContext) return [wrapBlock(opener), ...inner, wrapBlock(closer)];
  return [{ type: 'text', value: opener }, ...inner, { type: 'text', value: closer }];
}

type NodeEncoder = (node: RichTextNode, canRender: CanRender, ancestors: ReadonlyArray<RichTextNode>) => RichTextNode[];

const ENCODERS: Record<string, NodeEncoder> = {
  table: encodeTableAsMarkdown,
};

function encodeTableAsMarkdown(
  node: RichTextNode,
  canRender: CanRender,
  ancestors: ReadonlyArray<RichTextNode>,
): RichTextNode[] {
  const [firstRow, ...bodyRows] = node.children ?? [];
  if (!firstRow) return [];

  const cellSep: RichTextNode = { type: 'text', value: ' | ' };
  const rowSep: RichTextNode = { type: 'break' };

  const encodeRow = (row: RichTextNode): RichTextNode[] => {
    const cells = (row.children ?? []).map(cell =>
      escapeCellTextNodes(encodeChildren(cell.children ?? [], [cell, row, node, ...ancestors], false, canRender)),
    );
    const inner = cells.flatMap((cell, i) => (i === 0 ? cell : [cellSep, ...cell]));
    return [{ type: 'text', value: '| ' }, ...inner, { type: 'text', value: ' |' }];
  };

  const separator: RichTextNode = {
    type: 'text',
    value: `| ${(firstRow.children ?? []).map(() => '---').join(' | ')} |`,
  };
  const rows = [encodeRow(firstRow), [separator], ...bodyRows.map(encodeRow)];
  const children = mergeAdjacentText(rows.flatMap((row, i) => (i === 0 ? row : [rowSep, ...row])));

  return [{ type: 'paragraph', children }];
}

function escapeCellTextNodes(nodes: RichTextNode[]): RichTextNode[] {
  return nodes.map(node => {
    if (node.type === 'text' && node.value !== undefined) {
      return { ...node, value: escapeMarkdownCell(node.value) };
    }
    if (node.children) {
      return { ...node, children: escapeCellTextNodes(node.children) };
    }
    return node;
  });
}

function mergeAdjacentText(nodes: RichTextNode[]): RichTextNode[] {
  const result: RichTextNode[] = [];
  for (const node of nodes) {
    const last = result[result.length - 1];
    if (last?.type === 'text' && node.type === 'text') {
      result[result.length - 1] = { type: 'text', value: (last.value ?? '') + (node.value ?? '') };
    } else {
      result.push(node);
    }
  }
  return result;
}

function escapeMarkdownCell(value: string): string {
  return value.replace(/\\/g, '\\\\').replace(/\|/g, '\\|').replace(/\r?\n/g, ' ');
}

function wrapBlock(value: string): RichTextNode {
  return { type: 'paragraph', children: [{ type: 'text', value }] };
}

function openMarker(node: RichTextNode): string {
  return `${SENTINEL_OPENER} ${node.type}${serializeAttrs(node.data)} ${SENTINEL_CLOSER}`;
}

function closeMarker(node: RichTextNode): string {
  return `${SENTINEL_OPENER} end ${node.type} ${SENTINEL_CLOSER}`;
}

function selfCloseMarker(node: RichTextNode): string {
  return `${SENTINEL_OPENER} ${node.type}${serializeAttrs(node.data)} / ${SENTINEL_CLOSER}`;
}

function serializeAttrs(data: Record<string, unknown> | undefined): string {
  if (!data) return '';
  const parts: string[] = [];
  for (const [key, value] of Object.entries(data)) {
    const serialized = serializeValue(value);
    if (serialized !== null) parts.push(`${key}=${serialized}`);
  }
  return parts.length === 0 ? '' : ' ' + parts.join(' ');
}

// Emits the value in JSON-literal form so the decoder can round-trip
// types: strings as `"foo"`, booleans/numbers/bigints as `true` / `42` /
// `9007199254740992`. Returns null when the value can't survive the wire
// format (non-primitive, or string content with `"` / `】` / control chars
// that would break the regex-based decoder). The encoder drops the entry
// and keeps going — the rest of the node still round-trips.
function serializeValue(value: unknown): string | null {
  if (typeof value === 'string') {
    if (value.includes('"') || value.includes(SENTINEL_CLOSER) || /[\n\r]/.test(value)) return null;
    return `"${value}"`;
  }
  if (typeof value === 'number' || typeof value === 'boolean' || typeof value === 'bigint') {
    return String(value);
  }
  return null;
}

// ---- Decoder ----
//
// Reconstructing nodes from sentinel markers happens in two passes per parent,
// after children are recursively decoded so inner sentinels resolve first:
//
//   1. expandPaired — same-parent pairing. The opener and closer markers live
//      in the same children list (typical for inline content like a `strong`
//      sentinel that sits next to text inside a paragraph).
//
//   2. expandCrossSibling — cross-block pairing. The opener landed in one
//      block sibling's text, the closer in a later one. Produced when an
//      unsupported block-level node was encoded with each marker wrapped in
//      its own paragraph.
//
// A producer's parser may split a single opener mid-tag across adjacent text
// nodes; mergeFragmentedTags stitches them before the regex runs.

const ESCAPED_OPENER = escapeRegex(SENTINEL_OPENER);
const ESCAPED_CLOSER = escapeRegex(SENTINEL_CLOSER);
// Matches a single opener marker. Group 1 = tag, group 2 = attrs.
const OPENER_REGEX = new RegExp(`${ESCAPED_OPENER}\\s*(\\w+)([^${SENTINEL_CLOSER}]*)${ESCAPED_CLOSER}`);
// Matches any marker (opener or closer). Group 1 = 'end ' for closers
// (undefined for openers), group 2 = tag. Shared `g` regex is safe here:
// scanMarkers iterates it via matchAll, which works on a clone and never
// touches this instance's lastIndex.
const MARKER_REGEX = new RegExp(`${ESCAPED_OPENER}\\s*(end\\s+)?(\\w+)[^${SENTINEL_CLOSER}]*${ESCAPED_CLOSER}`, 'g');

function escapeRegex(value: string): string {
  return value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

function makeCloserRegex(rawTag: string): RegExp {
  return new RegExp(`${ESCAPED_OPENER}\\s*end\\s+${escapeRegex(rawTag)}\\s*${ESCAPED_CLOSER}`);
}

export function decodeSentinels(rootNode: RichTextRoot): RichTextRoot {
  const tablesDecoded = decodeMarkdownTables(rootNode);
  if (!subtreeHasMarkers(tablesDecoded.children)) return tablesDecoded;
  const recursed = tablesDecoded.children.map(decodeNode);
  return { type: 'root', children: expandCrossSibling(expandInChildren(recursed)) };
}

function decodeMarkdownTables(rootNode: RichTextRoot): RichTextRoot {
  return { type: 'root', children: reparseChildrenForTables(rootNode.children) };
}

const RECURSE_INTO = new Set(['blockquote', 'listOrdered', 'listUnordered', 'listItem']);

function reparseChildrenForTables(children: RichTextNode[]): RichTextNode[] {
  const recursed = children.map(child =>
    child.children && RECURSE_INTO.has(child.type)
      ? { ...child, children: reparseChildrenForTables(child.children) }
      : child,
  );

  const result: RichTextNode[] = [];
  let i = 0;
  while (i < recursed.length) {
    const child = recursed[i]!;

    if (child.type === 'paragraph' && child.children) {
      const table = tryParseTableFromInline(child.children);
      if (table) {
        result.push(table);
        i++;
        continue;
      }
    }

    if (isInline(child)) {
      let end = i;
      while (end < recursed.length && isInline(recursed[end]!)) end++;
      const table = tryParseTableFromInline(recursed.slice(i, end));
      if (table) {
        result.push(table);
        i = end;
        continue;
      }
    }

    result.push(child);
    i++;
  }
  return result;
}

const BLOCK_TYPES = new Set([
  'paragraph',
  'heading1',
  'heading2',
  'heading3',
  'heading4',
  'heading5',
  'heading6',
  'blockquote',
  'listOrdered',
  'listUnordered',
  'listItem',
  'code',
  'table',
  'tableRow',
  'tableCell',
  'thematicBreak',
]);

function isInline(node: RichTextNode): boolean {
  return !BLOCK_TYPES.has(node.type);
}

function tryParseTableFromInline(inline: RichTextNode[]): RichTextNode | null {
  if (inline.length === 0) return null;

  const rows = splitIntoRows(inline);
  if (rows.length < 2) return null;

  const headerCells = splitRowAtPipes(rows[0]!);
  const separatorCells = splitRowAtPipes(rows[1]!);
  if (!headerCells || !separatorCells) return null;
  if (separatorCells.length !== headerCells.length) return null;
  if (!separatorCells.every(isSeparatorCell)) return null;

  const bodyCells: RichTextNode[][][] = [];
  for (const row of rows.slice(2)) {
    const cells = splitRowAtPipes(row);
    if (!cells || cells.length !== headerCells.length) return null;
    bodyCells.push(cells);
  }

  return {
    type: 'table',
    children: [buildTableRow(headerCells, true), ...bodyCells.map(cells => buildTableRow(cells, false))],
  };
}

function splitIntoRows(inline: RichTextNode[]): RichTextNode[][] {
  const rows: RichTextNode[][] = [[]];
  const push = (n: RichTextNode) => rows[rows.length - 1]!.push(n);

  for (const child of inline) {
    if (child.type === 'break') {
      rows.push([]);
      continue;
    }
    if (child.type === 'text' && child.value?.includes('\n')) {
      const [head, ...tail] = child.value.split('\n');
      if (head) push({ type: 'text', value: head });
      for (const seg of tail) {
        rows.push([]);
        if (seg) push({ type: 'text', value: seg });
      }
      continue;
    }
    push(child);
  }
  return rows;
}

function isSeparatorCell(cell: RichTextNode[]): boolean {
  if (cell.length !== 1) return false;
  const node = cell[0];
  return node?.type === 'text' && node.value === '---';
}

function splitRowAtPipes(row: RichTextNode[]): RichTextNode[][] | null {
  const cells: RichTextNode[][] = [];
  let current: RichTextNode[] = [];
  let started = false;

  for (const node of row) {
    if (node.type !== 'text' || node.value === undefined) {
      current.push(node);
      continue;
    }

    const segments = splitOnUnescapedPipe(node.value);
    for (let i = 0; i < segments.length; i++) {
      if (i > 0) {
        if (!started) {
          if (hasNonWhitespace(current)) return null;
          started = true;
        } else {
          cells.push(current);
        }
        current = [];
      }
      if (segments[i] !== '') current.push({ type: 'text', value: segments[i]! });
    }
  }

  if (!started || hasNonWhitespace(current)) return null;
  return cells.map(trimCellContent);
}

function hasNonWhitespace(nodes: RichTextNode[]): boolean {
  return nodes.some(n => n.type !== 'text' || (n.value !== undefined && n.value.trim() !== ''));
}

function splitOnUnescapedPipe(text: string): string[] {
  const segments: string[] = [];
  let current = '';
  for (let i = 0; i < text.length; i++) {
    const c = text[i];
    if (c === '\\' && i + 1 < text.length) {
      current += c + text[i + 1];
      i++;
      continue;
    }
    if (c === '|') {
      segments.push(current);
      current = '';
      continue;
    }
    current += c;
  }
  segments.push(current);
  return segments;
}

function trimCellContent(cell: RichTextNode[]): RichTextNode[] {
  const result = cell.map(node =>
    node.type === 'text' && node.value !== undefined ? { ...node, value: unescapeCellText(node.value) } : node,
  );
  const first = result[0];
  if (first?.type === 'text' && first.value !== undefined) {
    const trimmed = first.value.replace(/^\s+/, '');
    if (trimmed === '') result.shift();
    else result[0] = { ...first, value: trimmed };
  }
  const last = result[result.length - 1];
  if (last?.type === 'text' && last.value !== undefined) {
    const trimmed = last.value.replace(/\s+$/, '');
    if (trimmed === '') result.pop();
    else result[result.length - 1] = { ...last, value: trimmed };
  }
  return result;
}

function unescapeCellText(value: string): string {
  return value.replace(/\\\|/g, '|').replace(/\\\\/g, '\\');
}

function buildTableRow(cells: RichTextNode[][], header: boolean): RichTextNode {
  return {
    type: 'tableRow',
    children: cells.map(content => ({
      type: 'tableCell',
      ...(header ? { data: { header: true } } : {}),
      children: content,
    })),
  };
}

function decodeNode(node: RichTextNode): RichTextNode {
  if (!node.children || !subtreeHasMarkers(node.children)) return node;

  const recursed = node.children.map(decodeNode);
  const expanded = expandCrossSibling(expandInChildren(recursed));
  return { ...node, children: expanded };
}

function subtreeHasMarkers(children: RichTextNode[]): boolean {
  for (const child of children) {
    if (child.type === 'text' && child.value?.includes(SENTINEL_OPENER)) return true;
    if (child.children && subtreeHasMarkers(child.children)) return true;
  }
  return false;
}

function expandInChildren(children: RichTextNode[]): RichTextNode[] {
  if (!children.some(c => c.type === 'text' && c.value?.includes(SENTINEL_OPENER))) return children;
  return expandPaired(mergeFragmentedTags(children));
}

// If a producer's parser split a single opener across adjacent text nodes,
// stitch them back so the regex can match the marker as a whole.
function mergeFragmentedTags(children: RichTextNode[]): RichTextNode[] {
  const result: RichTextNode[] = [];
  for (let i = 0; i < children.length; i++) {
    const child = children[i];
    if (!child) continue;
    const next = children[i + 1];
    if (
      child.type === 'text' &&
      child.value &&
      child.value.lastIndexOf(SENTINEL_OPENER) > child.value.lastIndexOf(SENTINEL_CLOSER) &&
      next?.type === 'text' &&
      next.value
    ) {
      result.push({ type: 'text', value: child.value + next.value });
      i++;
    } else {
      result.push(child);
    }
  }
  return result;
}

// Walk children left-to-right. For each text node, look for an opener; if
// found, locate its matching closer (possibly in a later sibling text) and
// reconstruct the node from the content between them. Self-closing markers
// (`【 type … / 】`) emit a node with no children directly, no closer search.
function expandPaired(children: RichTextNode[]): RichTextNode[] {
  const result: RichTextNode[] = [];
  let remaining: RichTextNode[] = children;

  while (remaining.length > 0) {
    const head = remaining[0]!;
    const headValue = head.type === 'text' ? head.value : undefined;
    const openerMatch = headValue ? OPENER_REGEX.exec(headValue) : null;
    const openerTag = openerMatch?.[1];

    if (!openerMatch || !openerTag || openerTag === 'end' || !headValue) {
      result.push(head);
      remaining = remaining.slice(1);
      continue;
    }

    const attrsRaw = openerMatch[2] ?? '';
    const beforeOpener = headValue.substring(0, openerMatch.index);
    const afterOpener = headValue.substring(openerMatch.index + openerMatch[0].length);

    // Self-closing marker — `attrs` ends with whitespace + `/`. Emit the
    // node with empty children, skip the closer search.
    if (SELF_CLOSE_REGEX.test(attrsRaw)) {
      if (beforeOpener) result.push({ type: 'text', value: beforeOpener });
      const { tagName, attrs } = normalizeLegacy(openerTag, attrsRaw.replace(SELF_CLOSE_REGEX, ''));
      result.push(buildNode(tagName, attrs, []));
      remaining = afterOpener ? [{ type: 'text', value: afterOpener }, ...remaining.slice(1)] : remaining.slice(1);
      continue;
    }

    const searchSpace: RichTextNode[] = afterOpener
      ? [{ type: 'text', value: afterOpener }, ...remaining.slice(1)]
      : remaining.slice(1);
    const closed = findMatchingCloserInline(searchSpace, openerTag);

    if (!closed) {
      result.push(head);
      remaining = remaining.slice(1);
      continue;
    }

    if (beforeOpener) result.push({ type: 'text', value: beforeOpener });
    const { tagName, attrs } = normalizeLegacy(openerTag, attrsRaw);
    result.push(decodeNode(buildNode(tagName, attrs, closed.before)));
    remaining = closed.after;
  }

  return result;
}

// `/\s*$` — `/` at the very end of the attrs region (with optional
// trailing whitespace). String attribute values are always quoted by
// `serializeValue`, so the closing `"` separates any `/` inside the
// value from the trailing slash; numeric/boolean values can't end in
// `/`. A `/` at the tail of `attrsRaw` is unambiguously a self-close
// marker.
const SELF_CLOSE_REGEX = /\/\s*$/;

// For each child, look for an opener in its text descendants; if found,
// search later siblings for a matching closer and reconstruct the node from
// everything in between.
function expandCrossSibling(children: RichTextNode[]): RichTextNode[] {
  const result: RichTextNode[] = [];
  let i = 0;

  while (i < children.length) {
    const current = children[i];
    if (!current) {
      i++;
      continue;
    }

    const opener = findOpenerInBlock(current);
    if (!opener) {
      result.push(current);
      i++;
      continue;
    }

    const closer = findMatchingCloserAcrossSiblings(children, i + 1, opener.rawTag);
    if (!closer) {
      result.push(current);
      i++;
      continue;
    }

    const contentNodes: RichTextNode[] = [...opener.afterOpenerNodes];
    for (let k = i + 1; k < closer.matchedAt; k++) {
      const mid = children[k];
      if (mid) contentNodes.push(mid);
    }
    contentNodes.push(...closer.before);

    result.push(...opener.beforeNodes);
    result.push(decodeNode(buildNode(opener.tagName, opener.attrs, contentNodes)));
    result.push(...closer.after);

    i = closer.matchedAt + 1;
  }

  return result;
}

interface MarkerHit {
  nodeIndex: number;
  start: number;
  end: number;
  tag: string;
  isCloser: boolean;
}

function* scanMarkers(nodes: RichTextNode[]): Generator<MarkerHit> {
  for (const [i, node] of nodes.entries()) {
    if (node.type !== 'text' || !node.value) continue;

    for (const match of node.value.matchAll(MARKER_REGEX)) {
      yield {
        nodeIndex: i,
        start: match.index,
        end: match.index + match[0].length,
        tag: match[2]!,
        isCloser: match[1] !== undefined,
      };
    }
  }
}

function* scanMarkersAcrossSiblings(
  siblings: RichTextNode[],
  startIdx: number,
): Generator<MarkerHit & { siblingIndex: number; children: RichTextNode[] }> {
  for (let j = startIdx; j < siblings.length; j++) {
    const sibling = siblings[j];
    if (!sibling?.children) continue;
    const children = sibling.children;
    for (const hit of scanMarkers(children)) {
      yield { ...hit, siblingIndex: j, children };
    }
  }
}

// Walk `hits` left-to-right for the closer that pairs with an already-opened
// outer marker for `tag`. Counts nested openers (depth++) and closers
// (depth--) of the same tag so that `【 foo 】 ... 【 foo 】 ... 【 end foo 】 ... 【 end foo 】`
// pairs the outer opener with the second closer, not the first. Returns null
// when no balanced closer exists.
function findBalancedCloser<Hit extends MarkerHit>(hits: Iterable<Hit>, tag: string): Hit | null {
  let depth = 1;
  for (const hit of hits) {
    if (hit.tag !== tag) continue;
    depth += hit.isCloser ? -1 : 1;
    if (depth === 0) return hit;
  }
  return null;
}

function findMatchingCloserInline(
  children: RichTextNode[],
  tag: string,
): { before: RichTextNode[]; after: RichTextNode[] } | null {
  const hit = findBalancedCloser(scanMarkers(children), tag);
  return hit ? splitTextAt(children, hit) : null;
}

// Like findMatchingCloserInline, but walks block-level siblings starting at
// `startIdx` and descends one level into each sibling's `children` to find
// text nodes. Used when an outer marker's opener and closer land in different
// block siblings.
function findMatchingCloserAcrossSiblings(
  siblings: RichTextNode[],
  startIdx: number,
  tag: string,
): { matchedAt: number; before: RichTextNode[]; after: RichTextNode[] } | null {
  const hit = findBalancedCloser(scanMarkersAcrossSiblings(siblings, startIdx), tag);
  if (!hit) return null;

  const { before, after } = splitTextAt(hit.children, hit);
  // Drop a leading empty/whitespace text node left over after the closer.
  const first = after[0];
  return {
    matchedAt: hit.siblingIndex,
    before,
    after: first?.type === 'text' && first.value?.trim() === '' ? after.slice(1) : after,
  };
}

// Split `children` around the marker at `at`, which lives inside
// `children[at.nodeIndex]`'s text value.
function splitTextAt(children: RichTextNode[], at: MarkerHit): { before: RichTextNode[]; after: RichTextNode[] } {
  const child = children[at.nodeIndex]!;
  const value = child.type === 'text' && child.value !== undefined ? child.value : '';
  const beforeText = value.substring(0, at.start);
  const afterText = value.substring(at.end);

  const before: RichTextNode[] = [...children.slice(0, at.nodeIndex)];
  if (beforeText) before.push({ type: 'text', value: beforeText });

  const after: RichTextNode[] = [];
  if (afterText) after.push({ type: 'text', value: afterText });
  after.push(...children.slice(at.nodeIndex + 1));

  return { before, after };
}

function findOpenerInBlock(node: RichTextNode): {
  rawTag: string;
  tagName: string;
  attrs: Record<string, unknown>;
  beforeNodes: RichTextNode[];
  afterOpenerNodes: RichTextNode[];
} | null {
  if (!node.children) return null;

  for (let i = 0; i < node.children.length; i++) {
    const child = node.children[i];
    if (!child || child.type !== 'text' || !child.value) continue;

    const match = OPENER_REGEX.exec(child.value);
    if (!match) continue;

    const rawTag = match[1] ?? '';
    if (rawTag === 'end') continue;

    // If a closer already lives in this same block, expandPaired would have
    // resolved the pair — skip and let the next iteration look elsewhere.
    const closerRegex = makeCloserRegex(rawTag);
    const afterOpener = child.value.substring(match.index + match[0].length);
    if (closerRegex.test(afterOpener)) continue;
    if (node.children.slice(i + 1).some(s => s.type === 'text' && s.value !== undefined && closerRegex.test(s.value))) {
      continue;
    }

    const { tagName, attrs } = normalizeLegacy(rawTag, match[2] ?? '');
    const beforeText = child.value.substring(0, match.index);
    const beforeNodes: RichTextNode[] = [...node.children.slice(0, i)];
    if (beforeText) beforeNodes.push({ type: 'text', value: beforeText });

    const afterOpenerNodes: RichTextNode[] = [];
    if (afterOpener.trim()) afterOpenerNodes.push({ type: 'text', value: afterOpener });
    afterOpenerNodes.push(...node.children.slice(i + 1));

    return { rawTag, tagName, attrs, beforeNodes, afterOpenerNodes };
  }

  return null;
}

function buildNode(type: string, data: Record<string, unknown>, children: RichTextNode[]): RichTextNode {
  const node: RichTextNode = { type };
  if (Object.keys(data).length > 0) node.data = data;
  if (children.length > 0) node.children = children;
  return node;
}

// ---- Legacy alias normalization ----
//
// Production content (sync-worker era, AsanaFormatter, etc.) emits a few
// sentinel forms that don't match modern conventions: positional args
// (`【 highlighted #ff0000 】` instead of `color="#ff0000"`) and pre-RFC tag
// spellings (`header N` for `headingN`, `highlighted` for `highlight`).
// Decoder accepts both shapes; encoder always emits the modern form.

interface LegacyMapping {
  type: string;
  positionalArg?: string;
}

const LEGACY_TAG_MAP: Record<string, LegacyMapping> = {
  highlight: { type: 'highlight', positionalArg: 'color' },
  highlighted: { type: 'highlight', positionalArg: 'color' },
  header: { type: 'heading', positionalArg: 'level' },
  code: { type: 'code', positionalArg: 'lang' },
};

function normalizeLegacy(rawTag: string, rawArgs: string): { tagName: string; attrs: Record<string, unknown> } {
  const mapping = LEGACY_TAG_MAP[rawTag];
  const attrs: Record<string, unknown> = {};
  const trimmed = rawArgs.trim();

  if (trimmed && /^\w+=/.test(trimmed)) {
    const tagName = mapping && mapping.positionalArg !== 'level' ? mapping.type : rawTag;
    // Value is a JSON literal: quoted string, true/false/null, or number;
    // JSON.parse recovers the typed value. A quoted-string value carrying
    // textual `true` / `42` decodes as the string, not the typed primitive.
    const attrRegex = /(\w+)=("[^"]*"|true|false|null|-?\d+(?:\.\d+)?)/g;
    let match: RegExpExecArray | null;
    while ((match = attrRegex.exec(rawArgs)) !== null) {
      const key = match[1];
      const raw = match[2];
      if (key !== undefined && raw !== undefined) {
        try {
          attrs[key] = JSON.parse(raw) as unknown;
        } catch {
          attrs[key] = raw;
        }
      }
    }
    return { tagName, attrs };
  }

  if (!mapping) return { tagName: rawTag, attrs };

  const positionalArg = mapping.positionalArg;
  const firstPart = trimmed ? trimmed.split(/\s+/)[0] : undefined;

  if (positionalArg && firstPart) {
    if (positionalArg === 'level') {
      return { tagName: `heading${firstPart}`, attrs };
    }
    attrs[positionalArg] = firstPart;
  }

  return { tagName: mapping.type, attrs };
}