import {
  docToHtml,
  docToMarkdown,
  docToPlainText,
  editorSchema,
  extractOutline,
  extractMentionUserIds,
  extractWikilinkSlugs,
  type OutlineEntry,
} from '@dorfteich/shared';
import { Node } from 'prosemirror-model';
import { yXmlFragmentToProseMirrorRootNode } from 'y-prosemirror';
import * as Y from 'yjs';

/**
 * The Yjs XmlFragment name the editor binds to — TipTap's collaboration
 * extension defaults to "default" (#25). api (`apps/api/src/pages/yjs-content.ts`),
 * web, and collab must all agree on this or Yjs states become unreadable across
 * them. This file deliberately mirrors the api's derivation (the shared
 * functions come from `@dorfteich/shared`, #24); the two were kept separate on
 * purpose rather than abstracted prematurely (see the M3 handoff).
 */
const FRAGMENT_NAME = 'default';

/** Thrown for state bytes that are not a well-formed Yjs update for this schema. */
export class InvalidPageStateError extends Error {}

function docFromDoc(ydoc: Y.Doc): Node {
  try {
    return yXmlFragmentToProseMirrorRootNode(ydoc.getXmlFragment(FRAGMENT_NAME), editorSchema);
  } catch (error) {
    throw new InvalidPageStateError(error instanceof Error ? error.message : 'invalid Yjs state');
  }
}

export interface DerivedPageContent {
  plainText: string;
  markdown: string;
  html: string;
  outline: OutlineEntry[];
  /** fileIds of every `image` node embedded in the document — keeps
   * `Attachment.pageId` pointed at the page that embeds the file (issue #31),
   * mirroring the api's REST save path. */
  imageFileIds: string[];
  /** Distinct target slugs of every `[[wikilink]]`, for the `page_links`
   * index (issue #47). */
  wikilinkSlugs: string[];
  /** Distinct resolved user ids of every `@mention`, for the
   * `page_mentions` index and the mention notifications (issue #151). */
  mentionUserIds: string[];
}

function imageFileIdsOf(doc: Node): string[] {
  const ids: string[] = [];
  doc.descendants((node) => {
    if (node.type.name === 'image' && typeof node.attrs.fileId === 'string') {
      ids.push(node.attrs.fileId);
    }
  });
  return ids;
}

/**
 * Decode a live Yjs document into the derived representations stored in
 * `page_content_cache` (issue #23/#35), using the shared editor schema (#24)
 * so the cache matches exactly what the api derives from the same state.
 */
export function deriveContentFromDoc(ydoc: Y.Doc): DerivedPageContent {
  const doc = docFromDoc(ydoc);
  return {
    plainText: docToPlainText(doc),
    markdown: docToMarkdown(doc),
    html: docToHtml(doc),
    outline: extractOutline(doc),
    imageFileIds: imageFileIdsOf(doc),
    wikilinkSlugs: extractWikilinkSlugs(doc),
    mentionUserIds: extractMentionUserIds(doc),
  };
}