ci/package_checks: add check for frozen packages

Add a simple configuration file for the CI checks,
that includes dates for a package freeze.

Packages updates for packages in `common/iso_packages.txt` result in
either a notice outside of freeze periods, or a warning in freeze periods.

common/CI/config.yaml

@@ -0,0 +1,4 @@
+---
+freeze:
+  start: null
+  end: null

common/CI/package_checks.py

@@ -6,6 +6,7 @@
 import re
 import subprocess
 from dataclasses import dataclass
+from datetime import datetime, timezone
 from enum import Enum
 from typing import Any, Dict, List, Optional, TextIO, Tuple, Union
 from urllib import request
@@ -14,6 +15,32 @@
 import yaml
 
 
+@dataclass
+class FreezeConfig:
+    start: Optional[datetime]
+    end: Optional[datetime]
+
+    def active(self) -> bool:
+        now = datetime.now(tz=timezone.utc)
+
+        if self.start is None:
+            return False
+
+        return now > self.start and (self.end is None or now < self.end)
+
+
+@dataclass
+class Config:
+    freeze: FreezeConfig
+
+    @staticmethod
+    def load(stream: Any) -> 'Config':
+        return Config(**yaml.safe_load(stream))
+
+    def __post_init__(self) -> None:
+        self.freeze = FreezeConfig(**self.freeze)  # type: ignore
+
+
 class Git:
     def __init__(self, path: str):
         self.path = path
@@ -66,6 +93,8 @@ def untracked_files(self) -> List[str]:
 
 class Level(str, Enum):
     __str__ = Enum.__str__
+    DEBUG = 'debug'
+    NOTICE = 'notice'
     ERROR = 'error'
     WARNING = 'warning'
 
@@ -109,6 +138,7 @@ def _property(self, key: str) -> str:
 class PullRequestCheck:
     _package_files = ['package.yml']
     _two_letter_dirs = ['py']
+    _config: Optional[Config] = None
 
     def __init__(self, git: Git, files: List[str], commits: List[str], base: Optional[str]):
         self.git = git
@@ -119,6 +149,14 @@ def __init__(self, git: Git, files: List[str], commits: List[str], base: Optiona
     def run(self) -> List[Result]:
         raise NotImplementedError
 
+    @property
+    def config(self) -> Config:
+        if self._config is None:
+            with self._open(os.path.join('common', 'CI', 'config.yaml')) as f:
+                self._config = Config.load(f)
+
+        return self._config
+
     @property
     def package_files(self) -> List[str]:
         return self._filter_packages(self.files)
@@ -160,6 +198,14 @@ def package_file(self, package: str, file: str) -> str:
     def package_dir(self, package: str) -> str:
         return os.path.join('packages', self._package_subdir(package), package)
 
+    @staticmethod
+    def package_for(path: str) -> str:
+        parts = path.split("/")
+        if len(parts) != 3 or parts[0] != "packages":
+            return ""
+
+        return parts[2]
+
     def _package_subdir(self, package: str) -> str:
         package = package.lower()
 
@@ -189,6 +235,36 @@ def _check_commit(self, commit: str) -> List[Result]:
         return results
 
 
+class FrozenPackage(PullRequestCheck):
+    __packages: Optional[List[str]] = None
+    __message_normal = ('This package is included in the ISO. '
+                        'Consider validating the functionality in a newly built ISO.')
+    __message_freeze = ('This package is included in the ISO and is currently frozen. '
+                        'It can only be updated to fix critical bugs, '
+                        'in consultation with multiple Solus staff members.')
+
+    def run(self) -> List[Result]:
+        return [self._make_result(f)
+                for f in self.package_files
+                if not self._is_frozen(f)]
+
+    def _make_result(self, file: str) -> Result:
+        if self.config.freeze.active():
+            return Result(message=self.__message_freeze, file=file, level=Level.WARNING)
+
+        return Result(message=self.__message_normal, file=file, level=Level.NOTICE)
+
+    def _is_frozen(self, file: str) -> bool:
+        return self.package_for(file) in self._packages()
+
+    def _packages(self) -> List[str]:
+        if self.__packages is None:
+            with self._open(os.path.join('common', 'iso_packages.txt')) as file:
+                self.__packages = [line.strip() for line in file]
+
+        return self.__packages
+
+
 class Homepage(PullRequestCheck):
     _error = '`homepage` is not set'
     _level = Level.ERROR
@@ -481,6 +557,7 @@ def _commit_package_yaml(self, ref: str) -> Optional[Dict[str, Any]]:
 class Checker:
     checks = [
         CommitMessage,
+        FrozenPackage,
         Homepage,
         PackageBumped,
         PackageDependenciesOrder,