#!/usr/bin/python
# General utilities for Python programs.
# This is intended to be imported with "from offog import *".
# Adam Sampson <ats@offog.org>

import sys, os, stat, subprocess

def warn(*args):
	print >>sys.stderr, "".join(map(str, args))

def die(*args):
	warn(*args)
	sys.exit(1)

def run_command(*args):
	"""Run a command; die if it exits non-zero."""
	rc = subprocess.call(*args)
	if rc != 0:
		die("Command failed with returncode ", rc, ": ", args)

def ensure_dir(dir):
	"""Like os.makedirs, but don't fail if the directory already exists."""
	try:
		st = os.lstat(dir)
		if stat.S_ISDIR(st.st_mode):
			return
	except OSError:
		pass
	os.makedirs(dir)

class memoised:
	"""Decorator to memoise a function."""
	def __init__(self, function):
		self.memo = {}
		self.function = function
	def __call__(self, *args, **kwargs):
		key = (args, tuple(kwargs.items()))
		if key in self.memo:
			return self.memo[key]
		r = apply(self.function, args, kwargs)
		self.memo[key] = r
		return r

class push_dir:
	"""Context guard to change directory."""
	def __init__(self, dir):
		self.dir = dir
	def __enter__(self):
		self.previous = os.getcwd()
		os.chdir(self.dir)
	def __exit__(self, type, value, traceback):
		os.chdir(self.previous)

class temporary_dir:
	"""Context guard to create a temporary directory.
	The directory will be forcibly removed at exit."""
	def __init__(self, dir):
		self.dir = dir
	def __enter__(self):
		os.makedirs(self.dir)
	def __exit__(self, type, value, traceback):
		subprocess.check_call(["rm", "-fr", self.dir])