class Expression:
	# This object represents all the needed initial data about an expression that is to be parsed.
	
	expression = "" # The formula to parse as a string.
#	correct_response = 0
	wrong_response = 0 # The incorrect response that was entered by the student.
	variables = [] # A list of Variable.
	
	def __init__(self, expression_string, variables, wrong_response):
		self.expression = expression_string
		self.variables = variables
		self.wrong_response = wrong_response
		
class Variable:
	# This object represents a variable that is found in the formula. It encodes the name, the type of variable
	# and the starting point from which to look for mutations in the variable's value.
	
	name = ""
	type = ""
	starting_point = 0
#	ending_point = 0
	
	VARIABLE_TYPES = {
		"i" : "Interest",
		"I" : "Interest",
		"n" : "Time",
		"N" : "Time",
		"k" : "Installment",
		"K" : "Installment"
	}
	
	def __init__(self, name, type, starting_point = 0, ending_point = 0):
		self.name = name
		self.type = type
		self.starting_point = starting_point
		self.ending_point = ending_point
		
	@staticmethod
	def get_variable_type(variable_name):
		# Utilitie function to get the variable's type from it's name.
		# For example, a variable with 'i' in its name is an Interest type.
		# Returns the variable's type as a string or 'Unknown' otherwise.
		if not variable_name in Variable.VARIABLE_TYPES:
			return "Unknown"
		return Variable.VARIABLE_TYPES[variable_name]