Implement really basic checking

No arguments, no timeouts, no nothing. But it remembers the return
codes, so that counts.

The example has been updated to work with the library.

checklib.py

@@ -1,7 +1,10 @@
 import sys
 import traceback
 import argparse
-from enums import Enum
+from enum import Enum
+from typing import NoReturn
+from functools import total_ordering
+import abc # Temporary: the only abstract method is Check.check(), until it can fall back to using Check.measure()
 
 """
 CheckLib: a simple wrapper around Icinga checks dealing with common
@@ -10,18 +13,24 @@ code like correct error codes and output formatting
 The main class is `Check`, other classes are just helpers.
 """
 
+@total_ordering
 class Result(Enum):
 	"""
 	Enumeration of possible check results.
 
-	The values are related return codes.
+	The values are related return codes. Results can be compared, "larger"
+	means worse status. WARNING < UNKNOWN < CRITICAL
 	"""
 	OK = 0
 	WARNING = 1
 	CRITICAL = 2
 	UNKNOWN = 3
 
-class Check:
+	def __lt__(self, other):
+		ordering = (Result.OK, Result.WARNING, Result.UNKNOWN, Result.CRITICAL)
+		return ordering.index(self) < ordering.index(other)
+
+class Check(abc.ABC):
 	"""
 	The class representing the check.
 
@@ -38,7 +47,7 @@ class Check:
 			   ArgumentParser, e.g. adding more parameters
 			1. self.args = argparse.parse_args(sys.argv)
 			1. check(): the function to check state and populate
-			   self.result, self.short_message and so on.
+			   self.result, self.short_status and so on.
 			1. sys.exit with the relevant exit code according to
 			   self.result
 			- If anything fails, e.g. by raising an exception,
@@ -55,13 +64,101 @@ class Check:
 	are used.
 	"""
 
+	# mypy wants __init__ defined before run, because it is otherwise confused
+	# by using self.result before assignment. I do not like tools dictating me
+	# how to code, but this seems to be a change small enough to be granted an
+	# exception. (But I had to at least write this here…)
+	def __init__(self):
+		"""
+		Initialises the check.
+
+		This method may be overridden. If so, super().__init__() should be
+		called early in order for our attributes to be available. (It is not
+		recommended to not call this initialization.)
+		"""
+
+		# We do not know what the result is unless somebody fills it in.
+		self.result = Result.UNKNOWN
+		self.short_status = None
+		self.long_status = None
+
+		# TODO: Initialize argparser
+
+	@staticmethod
+	def _bail_out() -> NoReturn:
+		"""
+		A last-resort fail function.
+
+		Does not make any assumptions, just prints traceback (if any) and exits
+		with UNKNOWN status.
+
+		Not meant to be called by subclasses.
+		"""
+		
+		short_status = 'Error, checklib bailing out!' # FIXME: do not hardcode name.
+		long_status = 'No details known :-('
+
+		e_type, e_value, e_tb = sys.exc_info()
+		if e_type is not None:
+			short_status = f'EXCEPTION: {repr(e_value)}'
+			long_status = traceback.format_exc()
+
+		# Let's just hope here that the lines do not contain '|' (which would
+		# mark performance data following)…
+		print(short_status)
+		if long_status: print(long_status)
+		sys.exit(Result.UNKNOWN.value)
+
 	@classmethod
-	def run(cls, *args, **kwargs):
+	def run(cls, *args, **kwargs) -> NoReturn:
 		"""
 		This method implements the checking start-to-end.
 
 		The arguments, if any, are passed to the __init__ of the class.
+
+		Please run this method on the class, do not create instances. This
+		allows to construct the instance in a `try` block that handles possible
+		exceptions in compliance with the Plugin API.
+
+		However, unless we do a dark Python magic with descriptors and stuff,
+		it is not possible for us to know how you call it. So we cannot even
+		warn you if you do the wrong thing.
 		"""
 
 		try:
-			
+			inst = cls(*args, **kwargs)
+			# TODO: Add argparse arguments
+			# TODO: Parse arguments into inst.args
+			# TODO: Prime the timer
+			inst.check()
+			# No code from subclass should be run from this moment, so we allow
+			# ourself to modify the instance. (This is potentially controversial.)
+
+			if inst.short_status is None:
+				inst.short_status = 'UNKNOWN: No status supplied!'
+				inst.result = max(inst.result, Result.UNKNOWN)
+			print(inst.short_status)
+
+			if inst.long_status is not None:
+				print(inst.long_status)
+
+			return_value = inst.result.value
+			assert isinstance(return_value, int)
+
+		except BaseException:
+			# We catch everything here, even exits. The idea is that the
+			# subclass should not exit on its own. This however means that it
+			# is harder to fail fast from methods other than check() – FIXME.
+			# TODO: Special handling for timeouts
+			Check._bail_out()
+
+		# The only happy-path exit.
+		sys.exit(return_value)
+	
+	@abc.abstractmethod
+	def check(self):
+		"""
+		This function does the checking. Subclasses should 
+		"""
+		# TODO: Fallback for self.measure()
+		...

example.py

@@ -1,9 +1,11 @@
+#!/usr/bin/env python3
+
 from checklib import Check, Result
 
 class MyCheck(Check):
 	def check(self):
-		self.result.state = Result.UNKNOWN
-		self.result.short_message = 'I don\'t know :-)'
+		self.result = Result.UNKNOWN
+		self.short_status = 'I don\'t know :-)'
 	
 	def add_arguments(self):
 		pass
@@ -12,3 +14,7 @@ class MyCheck(Check):
 
 	# If defining __init__, call super().__init__ first -- it populates
 	# self.result, self.argumentparser and so on.
+
+
+if __name__ == '__main__':
+	MyCheck.run()