Config warnings (#1006)

* Fix docstring

* Warn when min/max config values are invalid

* Better retrieval of optional config values

* Less restrictive default max opponent rating

* CONFIG.get() not needed since defaults inserted

* Matchmaking handles creating challenges

* opponent_rating_difference has no default

* Specify which game challenges will be ignored

lib/config.py

@@ -70,7 +70,7 @@ def config_assert(assertion: bool, error_message: str) -> None:
 
 
 def config_warn(assertion: bool, warning_message: str) -> None:
-    """Raise an exception if an assertion is false."""
+    """Print a warning message if an assertion is false."""
     if not assertion:
         logger.warning(warning_message)
 
@@ -297,6 +297,23 @@ def validate_config(CONFIG: CONFIG_DICT_TYPE) -> None:
     config_assert(CONFIG["challenge"]["preference"] in ["none", "human", "bot"],
                   "challenge.preference should be `none`, `human`, or `bot`.")
 
+    min_max_template = ("challenge.max_{setting} < challenge.min_{setting} will result "
+                        "in no {game_type} challenges being accepted.")
+    for setting in ["increment", "base", "days"]:
+        game_type = "correspondence" if setting == "days" else "real-time"
+        config_warn(CONFIG["challenge"][f"min_{setting}"] <= CONFIG["challenge"][f"max_{setting}"],
+                    min_max_template.format(setting=setting, game_type=game_type))
+
+    matchmaking = CONFIG["matchmaking"]
+    matchmaking_enabled = matchmaking["allow_matchmaking"]
+
+    if matchmaking_enabled:
+        config_warn(matchmaking["opponent_min_rating"] <= matchmaking["opponent_max_rating"],
+                    "matchmaking.opponent_max_rating < matchmaking.opponent_min_rating will result in "
+                    "no challenges being created.")
+        config_warn(matchmaking.get("opponent_rating_difference", 0) >= 0,
+                    "matchmaking.opponent_rating_difference < 0 will result in no challenges being created.")
+
     pgn_directory = CONFIG["pgn_directory"]
     in_docker = os.environ.get("LICHESS_BOT_DOCKER")
     config_warn(not pgn_directory or not in_docker, "Games will be saved to '{}', please ensure this folder is in a mounted "
@@ -310,9 +327,6 @@ def validate_config(CONFIG: CONFIG_DICT_TYPE) -> None:
                   f"The `pgn_file_grouping` choice of `{config_pgn_choice}` is not valid. "
                   f"Please choose from {valid_pgn_grouping_options}.")
 
-    matchmaking = CONFIG.get("matchmaking") or {}
-    matchmaking_enabled = matchmaking.get("allow_matchmaking") or False
-
     def has_valid_list(name: str) -> bool:
         entries = matchmaking.get(name)
         return isinstance(entries, list) and entries[0] is not None