chat: added clear_cache() function and test

chatmastermind/chat.py

@@ -82,6 +82,17 @@ def write_dir(dir_path: pathlib.Path,
         message.to_file(file_path)
 
 
+def clear_dir(dir_path: pathlib.Path,
+              glob: Optional[str] = None) -> None:
+    """
+    Deletes all Message files in the given directory.
+    """
+    file_iter = dir_path.glob(glob) if glob else dir_path.iterdir()
+    for file_path in file_iter:
+        if file_path.is_file() and file_path.suffix in Message.file_suffixes:
+            file_path.unlink(missing_ok=True)
+
+
 @dataclass
 class Chat:
     """
@@ -289,3 +300,12 @@ class ChatDB(Chat):
                   msgs if msgs else self.messages,
                   self.file_suffix,
                   self.get_next_fid)
+
+    def clear_cache(self) -> None:
+        """
+        Deletes all Message files from the cache dir and removes those messages from
+        the internal list.
+        """
+        clear_dir(self.cache_path, self.glob)
+        # only keep messages from DB dir (or those that have not yet been written)
+        self.messages = [m for m in self.messages if not m.file_path or m.file_path.parent.samefile(self.db_path)]