core[patch],community[patch]: Move file chat history back to community (#20834)

Marking as patch since we haven't had releases in between. This just reverting part of a PR from yesterday.

libs/community/langchain_community/chat_message_histories/file.py

@@ -1,5 +1,40 @@
-from langchain_core.chat_history import FileChatMessageHistory
+import json
+from pathlib import Path
+from typing import List
 
-__all__ = [
-    "FileChatMessageHistory",
-]
+from langchain_core.chat_history import (
+    BaseChatMessageHistory,
+)
+from langchain_core.messages import BaseMessage, messages_from_dict, messages_to_dict
+
+
+class FileChatMessageHistory(BaseChatMessageHistory):
+    """Chat message history that stores history in a local file."""
+
+    def __init__(self, file_path: str) -> None:
+        """Initialize the file path for the chat history.
+
+        Args:
+            file_path: The path to the local file to store the chat history.
+        """
+        self.file_path = Path(file_path)
+        if not self.file_path.exists():
+            self.file_path.touch()
+            self.file_path.write_text(json.dumps([]))
+
+    @property
+    def messages(self) -> List[BaseMessage]:  # type: ignore
+        """Retrieve the messages from the local file"""
+        items = json.loads(self.file_path.read_text())
+        messages = messages_from_dict(items)
+        return messages
+
+    def add_message(self, message: BaseMessage) -> None:
+        """Append the message to the record in the local file"""
+        messages = messages_to_dict(self.messages)
+        messages.append(messages_to_dict([message])[0])
+        self.file_path.write_text(json.dumps(messages))
+
+    def clear(self) -> None:
+        """Clear session memory from the local file"""
+        self.file_path.write_text(json.dumps([]))