apply suggestion + add update and remove

- add update function
- add remove function

lib/charms/operator_libs_linux/v0/grub.py

@@ -21,6 +21,7 @@
 
 import logging
 import os
+import subprocess
 from pathlib import Path
 from typing import Dict, List, Mapping, Optional, Set
 
@@ -56,10 +57,35 @@
 #   info -f grub -n 'Simple configuration'
 """
 
+# TODO: add better description to lib
+
 
 class ValidationError(ValueError):
     """Exception representing value validation error."""
 
+    def __init__(self, key: str, message: str) -> None:
+        self._key = key
+        self._message = message
+        super().__init__(message)
+
+    @property
+    def key(self) -> str:
+        """Get name of key, which cause this error."""
+        return self._key
+
+    @property
+    def message(self) -> str:
+        """Get error message."""
+        return self._message
+
+
+class IsContainerError(Exception):
+    """Exception if local machine is container."""
+
+
+class ApplyError(Exception):
+    """Exception if applying new config failed."""
+
 
 def _parse_config(data: str) -> Dict[str, str]:
     """Parse config file lines.
@@ -109,6 +135,12 @@ def _save_config(path: Path, config: Dict[str, str], header: str = CONFIG_HEADER
     logger.info("grub config file %s was saved", path)
 
 
+def is_container() -> bool:
+    """Help function to see if local machine is container."""
+    # TODO: implement it
+    return False
+
+
 class GrubConfig(Mapping[str, str]):
     """Grub config object.
 
@@ -122,6 +154,10 @@ class GrubConfig(Mapping[str, str]):
 
     _lazy_data: Optional[Dict[str, str]] = None
 
+    def __init__(self, charm_name: Optional[str] = None) -> None:
+        """Initialize the grub config."""
+        self._charm_name = charm_name
+
     def __contains__(self, key: str) -> bool:
         """Check if key is in config."""
         return key in self._data
@@ -147,6 +183,25 @@ def _data(self) -> Dict[str, str]:
 
         return data
 
+    def _apply(self):
+        """Check if an update to /boot/grub/grub.cfg is available."""
+        try:
+            subprocess.check_call(f"grub-mkconfig -o {GRUB_CONFIG}", stderr=subprocess.STDOUT)
+            subprocess.check_call(["/usr/sbin/update-grub"], stderr=subprocess.STDOUT)
+        except subprocess.CalledProcessError as error:
+            logger.exception(error)
+            raise ApplyError("New config check failed.") from error
+
+    def _save_grub_configuration(self) -> None:
+        """Save current gru configuration."""
+        logger.info("saving new grub config to %s", GRUB_CONFIG)
+        applied_configs = {self.path, *self.applied_configs}  # using set to drop duplicity
+        registered_configs = os.linesep.join(
+            FILE_LINE_IN_DESCRIPTION.format(path=path) for path in applied_configs
+        )
+        header = CONFIG_HEADER + CONFIG_DESCRIPTION.format(configs=registered_configs)
+        _save_config(GRUB_CONFIG, self._data, header)
+
     def _set_value(self, key: str, value: str) -> bool:
         """Set new value for key."""
         logger.debug("setting new value %s for key %s", value, key)
@@ -162,31 +217,77 @@ def _set_value(self, key: str, value: str) -> bool:
                 current_value,
                 value,
             )
-            raise ValidationError(f"key {key} already exists and its value is {current_value}")
+            raise ValidationError(
+                f"key {key} already exists and its value is {current_value}", key
+            )
 
         return False
 
-    @property
-    def registered_configs(self) -> List[Path]:
-        """Return list of charms which registered config here."""
-        return [config.absolute() for config in LIB_CONFIG_DIRECTORY.glob("*") if config.is_file()]
-
-    def update(self, charm_name: str, config: Dict[str, str]) -> Set[str]:
-        """Update the Grub configuration."""
+    def _update(self, config: Dict[str, str]) -> Set[str]:
+        """Update data in object."""
+        logger.debug("updating current config")
         changed_keys = set()
         for key, value in config.items():
             changed = self._set_value(key, value)
             if changed:
                 changed_keys.add(key)
 
+        return changed_keys
+
+    @property
+    def charm_name(self) -> str:
+        """Get charm name or use value obtained from JUJU_UNIT_NAME env."""
+        if self._charm_name is None:
+            self._charm_name, *_ = os.getenv("JUJU_UNIT_NAME", "unknown").split("/")
+
+        return self._charm_name
+
+    @property
+    def path(self) -> Path:
+        """Return path for charm config."""
+        return LIB_CONFIG_DIRECTORY / self.charm_name
+
+    @property
+    def applied_configs(self) -> List[Path]:
+        """Return list of charms which registered config here."""
+        return [config.absolute() for config in LIB_CONFIG_DIRECTORY.glob("*") if config.is_file()]
+
+    def remove(self) -> None:
+        """Remove config for charm.
+
+        This function will remove config file for charm and re-create the `95-juju-charm.cfg`
+        grub config file without changes made by this charm.
+        """
+        self.path.unlink()
+        logger.info("charm config file %s was removed", self.path)
+        config = {}
+        for path in self.applied_configs:
+            _config = _load_config(path)
+            logger.debug("load config file %s", path)
+            config.update(_config)
+
+        self._lazy_data = config
+        self._save_grub_configuration()
+        self._apply()
+
+    def update(self, config: Dict[str, str]) -> Set[str]:
+        """Update the Grub configuration."""
+        if is_container():
+            raise IsContainerError("Could not configure grub config on container.")
+
+        snapshot = self._data.copy()
+        try:
+            changed_keys = self._update(config)
+            self._save_grub_configuration()
+            self._apply()
+        except ValidationError:
+            self._lazy_data = snapshot
+            raise
+        except ApplyError:
+            self._lazy_data = snapshot
+            self._save_grub_configuration()  # save snapshot copy of grub config
+            raise
+
         logger.debug("saving copy of charm config to %s", LIB_CONFIG_DIRECTORY)
-        _save_config(LIB_CONFIG_DIRECTORY / charm_name, config)
-        # TODO: check if config is valid `grub-mkconfig -o <path>``
-        logger.info("saving new grub config to %s", GRUB_CONFIG)
-        registered_configs = os.linesep.join(
-            FILE_LINE_IN_DESCRIPTION.format(path=path) for path in self.registered_configs
-        )
-        header = CONFIG_HEADER + CONFIG_DESCRIPTION.format(configs=registered_configs)
-        _save_config(GRUB_CONFIG, self._data, header)
-        # TODO: update grub, https://git.launchpad.net/charm-sysconfig/tree/src/lib/lib_sysconfig.py
+        _save_config(LIB_CONFIG_DIRECTORY / self.charm_name, config)
         return changed_keys