1 files changed, 89 insertions, 0 deletions
diff --git a/python/cru/_error.py b/python/cru/_error.py
new file mode 100644
index 0000000..e53c787
--- /dev/null
+++ b/python/cru/_error.py
@@ -0,0 +1,89 @@
+from __future__ import annotations
+
+from typing import NoReturn, cast, overload
+
+
+class CruException(Exception):
+    """Base exception class of all exceptions in cru."""
+
+    @overload
+    def __init__(
+        self,
+        message: None = None,
+        *args,
+        user_message: str,
+        **kwargs,
+    ): ...
+
+    @overload
+    def __init__(
+        self,
+        message: str,
+        *args,
+        user_message: str | None = None,
+        **kwargs,
+    ): ...
+
+    def __init__(
+        self,
+        message: str | None = None,
+        *args,
+        user_message: str | None = None,
+        **kwargs,
+    ):
+        if message is None:
+            message = user_message
+
+        super().__init__(
+            message,
+            *args,
+            **kwargs,
+        )
+        self._message: str
+        self._message = cast(str, message)
+        self._user_message = user_message
+
+    @property
+    def message(self) -> str:
+        return self._message
+
+    def get_user_message(self) -> str | None:
+        return self._user_message
+
+    def get_message(self, use_user: bool = True) -> str:
+        if use_user and self._user_message is not None:
+            return self._user_message
+        else:
+            return self._message
+
+    @property
+    def is_internal(self) -> bool:
+        return False
+
+    @property
+    def is_logic_error(self) -> bool:
+        return False
+
+
+class CruLogicError(CruException):
+    """Raised when a logic error occurs."""
+
+    @property
+    def is_logic_error(self) -> bool:
+        return True
+
+
+class CruInternalError(CruException):
+    """Raised when an internal error occurs."""
+
+    @property
+    def is_internal(self) -> bool:
+        return True
+
+
+class CruUnreachableError(CruInternalError):
+    """Raised when a code path is unreachable."""
+
+
+def cru_unreachable() -> NoReturn:
+    raise CruUnreachableError("Code should not reach here!")