Add persistence to chromadb

Saves chromadb to specified persistence folder (with default being .chroma_db). Purge correctly purges persistence folder.

server.py

@@ -64,6 +64,7 @@ parser.add_argument("--prompt-model", help="Load a custom prompt generation mode
 parser.add_argument("--embedding-model", help="Load a custom text embedding model")
 parser.add_argument("--chroma-host", help="Host IP for a remote ChromaDB instance")
 parser.add_argument("--chroma-port", help="HTTP port for a remote ChromaDB instance (defaults to 8000)")
+parser.add_argument("--chroma-folder", help="Path for chromadb persistence folder", default='.chroma_db')
 
 sd_group = parser.add_mutually_exclusive_group()
 
@@ -247,8 +248,8 @@ if "chromadb" in modules:
     # Also disable chromadb telemetry
     posthog.capture = lambda *args, **kwargs: None
     if args.chroma_host is None:
-        chromadb_client = chromadb.Client(Settings(anonymized_telemetry=False))
-        print("ChromaDB is running in-memory. It will be cleared when the server is restarted!")
+        chromadb_client = chromadb.Client(Settings(anonymized_telemetry=False, persist_directory=args.chroma_folder, chroma_db_impl='duckdb+parquet'))
+        print(f"ChromaDB is running in-memory with persistence. Persistence is stored in {args.chroma_folder}. Can be cleared by deleting the folder or purging db.")
     else:
         chroma_port=(
             args.chroma_port if args.chroma_port else DEFAULT_CHROMA_PORT
@@ -732,8 +733,11 @@ def chromadb_purge():
         name=f"chat-{chat_id_md5}", embedding_function=chromadb_embed_fn
     )
 
-    deleted = collection.delete()
-    print("ChromaDB embeddings deleted", len(deleted))
+    count = collection.count()
+    collection.delete()
+    #Write deletion to persistent folder
+    chromadb_client.persist()
+    print("ChromaDB embeddings deleted", count)
     return 'Ok', 200
 
 
@@ -788,7 +792,7 @@ def chromadb_export():
     data = request.get_json()
     if "chat_id" not in data or not isinstance(data["chat_id"], str):
         abort(400, '"chat_id" is required')
-        
+    
     chat_id_md5 = hashlib.md5(data["chat_id"].encode()).hexdigest()
     collection = chromadb_client.get_or_create_collection(
         name=f"chat-{chat_id_md5}", embedding_function=chromadb_embed_fn