✨(backend) add util to extract text from Ydoc content

Documents content is stored in the Ydoc format. We need a util
to extract it as xml/text.

src/backend/core/utils.py

@@ -0,0 +1,25 @@
+"""Utils for the core app."""
+
+import base64
+
+import y_py as Y
+from bs4 import BeautifulSoup
+
+
+def base64_yjs_to_xml(base64_string):
+    """Extract xml from base64 yjs document."""
+
+    decoded_bytes = base64.b64decode(base64_string)
+    uint8_array = bytearray(decoded_bytes)
+
+    doc = Y.YDoc()  # pylint: disable=E1101
+    Y.apply_update(doc, uint8_array)  # pylint: disable=E1101
+    return str(doc.get_xml_element("document-store"))
+
+
+def base64_yjs_to_text(base64_string):
+    """Extract text from base64 yjs document."""
+
+    blocknote_structure = base64_yjs_to_xml(base64_string)
+    soup = BeautifulSoup(blocknote_structure, "html.parser")
+    return soup.get_text(separator=" ").strip()