✨(backend) add async triggers to enable document indexation with find

On document content or permission changes, start a celery job that will call the
indexation API of the app "Find".

Signed-off-by: Fabre Florian <ffabre@hybird.org>

src/backend/core/tasks/find.py

@@ -0,0 +1,96 @@
+"""Trigger document indexation using celery task."""
+
+from logging import getLogger
+
+from django.conf import settings
+from django.core.cache import cache
+from django.db import transaction
+
+from core import models
+from core.services.search_indexers import (
+    FindDocumentIndexer,
+    get_batch_accesses_by_users_and_teams,
+)
+
+from impress.celery_app import app
+
+logger = getLogger(__file__)
+
+
+def document_indexer_debounce_key(document_id):
+    """Returns debounce cache key"""
+    return f"doc-indexer-debounce-{document_id}"
+
+
+def incr_counter(key):
+    """Increase or reset counter"""
+    try:
+        return cache.incr(key)
+    except ValueError:
+        cache.set(key, 1)
+        return 1
+
+
+def decr_counter(key):
+    """Decrease or reset counter"""
+    try:
+        return cache.decr(key)
+    except ValueError:
+        cache.set(key, 0)
+        return 0
+
+
+@app.task
+def document_indexer_task(document_id):
+    """Send indexation query for a document using celery task."""
+    key = document_indexer_debounce_key(document_id)
+
+    # check if the counter : if still up, skip the task. only the last one
+    # within the countdown delay will do the query.
+    if decr_counter(key) > 0:
+        logger.info("Skip document %s indexation", document_id)
+        return
+
+    doc = models.Document.objects.get(pk=document_id)
+    indexer = FindDocumentIndexer()
+    accesses = get_batch_accesses_by_users_and_teams((doc.path,))
+
+    data = indexer.serialize_document(document=doc, accesses=accesses)
+
+    logger.info("Start document %s indexation", document_id)
+    indexer.push(data)
+
+
+def trigger_document_indexer(document, on_commit=False):
+    """
+    Trigger indexation task with debounce a delay set by the SEARCH_INDEXER_COUNTDOWN setting.
+
+    Args:
+        document (Document): The document instance.
+        on_commit (bool): Wait for the end of the transaction before starting the task
+            (some fields may be in wrong state within the transaction)
+    """
+
+    if document.deleted_at or document.ancestors_deleted_at:
+        pass
+
+    if on_commit:
+
+        def _aux():
+            trigger_document_indexer(document, on_commit=False)
+
+        transaction.on_commit(_aux)
+    else:
+        key = document_indexer_debounce_key(document.pk)
+        countdown = getattr(settings, "SEARCH_INDEXER_COUNTDOWN", 1)
+
+        logger.info(
+            "Add task for document %s indexation in %.2f seconds",
+            document.pk, countdown
+        )
+
+        # Each time this method is called during the countdown, we increment the
+        # counter and each task decrease it, so the index be run only once.
+        incr_counter(key)
+
+        document_indexer_task.apply_async(args=[document.pk], countdown=countdown)