✨(backend) add duplicate action to the document API endpoint

We took this opportunity to refactor the way access is controlled on
media attachments. We now add the media key to a list on the document
instance each time a media is uploaded to a document. This list is
passed along when a document is duplicated, allowing us to grant
access to readers on the new document, even if they don't have or
lost access to the original document.

We also propose an option to reproduce the same access rights on the
duplicate document as what was in place on the original document.
This can be requested by passing the "with_accesses=true" option in
the query string.

The tricky point is that we need to extract attachment keys from the
existing documents and set them on the new "attachments" field that is
now used to track access rights on media files.

src/backend/core/utils.py

@@ -1,10 +1,52 @@
 """Utils for the core app."""
 
 import base64
+import re
 
 import y_py as Y
 from bs4 import BeautifulSoup
 
+from core import enums
+
+
+def filter_descendants(paths, root_paths, skip_sorting=False):
+    """
+    Filters paths to keep only those that are descendants of any path in root_paths.
+
+    A path is considered a descendant of a root path if it starts with the root path.
+    If `skip_sorting` is not set to True, the function will sort both lists before
+    processing because both `paths` and `root_paths` need to be in lexicographic order
+    before going through the algorithm.
+
+    Args:
+        paths (iterable of str): List of paths to be filtered.
+        root_paths (iterable of str): List of paths to check as potential prefixes.
+        skip_sorting (bool): If True, assumes both `paths` and `root_paths` are already sorted.
+
+    Returns:
+        list of str: A list of sorted paths that are descendants of any path in `root_paths`.
+    """
+    results = []
+    i = 0
+    n = len(root_paths)
+
+    if not skip_sorting:
+        paths.sort()
+        root_paths.sort()
+
+    for path in paths:
+        # Try to find a matching prefix in the sorted accessible paths
+        while i < n:
+            if path.startswith(root_paths[i]):
+                results.append(path)
+                break
+            if root_paths[i] < path:
+                i += 1
+            else:
+                # If paths[i] > path, no need to keep searching
+                break
+    return results
+
 
 def base64_yjs_to_xml(base64_string):
     """Extract xml from base64 yjs document."""
@@ -23,3 +65,9 @@ def base64_yjs_to_text(base64_string):
     blocknote_structure = base64_yjs_to_xml(base64_string)
     soup = BeautifulSoup(blocknote_structure, "html.parser")
     return soup.get_text(separator=" ").strip()
+
+
+def extract_attachments(content):
+    """Helper method to extract media paths from a document's content."""
+    xml_content = base64_yjs_to_xml(content)
+    return re.findall(enums.MEDIA_STORAGE_URL_EXTRACT, xml_content)