from workspaceObject import WorkspaceObject
from slipnet import slipnet

class Letter(WorkspaceObject):
	def __init__(self,string,position,length):
		WorkspaceObject.__init__(self,string)
		from workspace import workspace
		workspace.objects += [ self ]
		string.objects += [self ]
		self.leftStringPosition = position
		self.leftmost = self.leftStringPosition == 1
		self.rightStringPosition = position
		self.rightmost = self.rightStringPosition == length

	def describe(self,position,length):
		if length == 1:
			self.addDescription(slipnet.stringPositionCategory,slipnet.single)
		if self.leftmost and length > 1: # ? why check length ?
			self.addDescription(slipnet.stringPositionCategory,slipnet.leftmost)
		if self.rightmost and length > 1: # ? why check length ?
			self.addDescription(slipnet.stringPositionCategory,slipnet.rightmost)
		if length > 2 and position * 2 == length + 1:
			self.addDescription(slipnet.stringPositionCategory,slipnet.middle)

	def __repr__(self):
		return '<Letter: %s>' % self.__str__()

	def __str__(self):
		if not self.string:
			return ''
		i = self.leftStringPosition - 1
		if len(self.string) <= i:
			raise ValueError, 'len(self.string) <= self.leftStringPosition :: %d <= %d' % (len(self.string),self.leftStringPosition)
		return self.string[ i ]

	def distinguishingDescriptor(self,descriptor):
		"""Whether no other object of the same type (letter) has the same descriptor"""
		if not WorkspaceObject.distinguishingDescriptor(self,descriptor):
			return False
		for objekt in self.string.objects:
			# check to see if they are of the same type
			if isinstance(objekt,Letter) and objekt != self:
				# check all descriptions for the descriptor
				for description in objekt.descriptions:
					if description.descriptor == descriptor:
						return False
		return True