document-version.ts

type DocumentVersion = {
  // CouchDB's own ID system
  _id: string;

  // Your document history ID - the same across all versions of a document
  historyId: string;

  // The _id of the ancestor document (undefined if first version)
  parentId: string;

  // Indicates if this version is archived or not
  archived: boolean;

  // Utility flags. Might be useful in future implementations of reconciliation
  // algorithms, or the construction of a changelog feature
  createdAt: Date;
};

save-document.ts

const saveDocumentVersion = async ({ _id, doc }) => {
  // Avoid saving a document version that's already archived
  delete doc.archived;

  const newDoc = {
    ...doc,
    createdAt: new Date().toISOString(),
  };

  let parentDoc;

  if (doc.parentId) {
    parentDoc = await loadDocument(doc.parentId);
  }

  if (parentDoc) {
    // Rely on parentDoc to get historyId and parentId
    newDoc.historyId = parentDoc.historyId;
    newDoc.parentId = parentDoc._id;
  } else {
    newDoc.historyId = await generateHistoryId();
  }

  const savedDoc = await saveDocument(newDoc);

  // Archives the parent document only after new version is saved
  // (sends `parentDoc.archived = true` to CouchDB)
  if (parentDoc) {
    await archiveDocument(parentDoc);
  }

  return savedDoc;
};