import fstype

class FrozenException(Exception): pass
class NotLoadedYet(Exception): pass

class FSObject(object):
	def __init__(self, path):
		if type(self) == FSObject:
			raise TypeError("FSObject is an abstract class and cannot be initialized.")
		self.path = path
		self.exists = False
		self.accessible = False
		self.marked = False
		self.tagged = False
		self.frozen = False
		self.loaded = False
		self.islink = False
		self.brokenlink = False
		self.stat = None
		self.infostring = None
		self.permissions = None
		self.type = fstype.Unknown

	# load() reads useful information about the file from the file system
	# and caches it in instance attributes.
	def load(self):
		self.stop_if_frozen()
		self.loaded = True

		import os
		try:
			self.stat = os.stat(self.path)
			self.islink = os.path.islink(self.path)
			self.exists = True
			self.accessible = True

			if os.path.isdir(self.path):
				self.type = fstype.Directory
				self.infostring = ' %d' % len(os.listdir(self.path))
			elif os.path.isfile(self.path):
				self.type = fstype.File
				self.infostring = ' %d' % self.stat.st_size
			else:
				self.type = fstype.Unknown
				self.infostring = None

		except OSError:
			self.islink = False
			self.infostring = None
			self.type = fstype.Nonexistent
			self.exists = False
			self.accessible = False

	def load_once(self):
		self.stop_if_frozen()
		if not self.loaded:
			self.load()
			return True
		return False

	def load_if_outdated(self):
		self.stop_if_frozen()
		if self.load_once(): return True

		import os
		real_mtime = os.stat(self.path).st_mtime
		cached_mtime = self.stat.st_mtime

		if real_mtime != cached_mtime:
			self.load()
			return True
		return False

	def clone(self):
		clone = type(self)(self.path)
		for key in iter(self.__dict__):
			clone.__dict__[key] = self.__dict__[key]
		return clone

	def frozen_clone(self):
		clone = self.clone()
		clone.frozen = True
		return clone

	def stop_if_frozen(self):
		if self.frozen: raise FrozenException('Cannot modify datastructure while it is frozen')