# Based on: http://springfans.com/ieeeSoftware/accChange.pdf

class DecisionTable(models.Model):
	"""Decision Table"""
	
	code = models.CharField(unique=True, max_length=8, verbose_name="Unique code for finding a decision table in code")
	name = models.CharField(blank=True, max_length=100, verbose_name="User friendly name for decision table")

	def __unicode__(self):
		return u"Table"
	
	
class Rule(models.Model):
	
	table = models.ForeignKey(DecisionTable)
	code = models.CharField(unique=True, max_length=8, verbose_name="Unique code for looking up decision tables")
	name = models.CharField(max_length=128, verbose_name="User friendly description of decision table")
	priority = PositionField(collection="decision_table")

	def test(self, facts):
		for condition in self.condition.all():
			if not condition.test(facts):
				return False
		return True

	def __unicode__(self):
		return u"R%d: %s" % (self.code, self.name)


RESPONSE_CHOICES = (
	("Yes", True),
	("No", False),
)


class Condition(models.Model):
	"""Boolean condition (e.g. condition must be true / condition must be false)."""
	
	rule = models.ForeignKey(Rule)
	name = models.CharField(blank=False, max_length=128, verbose_name="User friendly description of rule condition")
	value = models.BooleanField(required=True, default=False, choices=RESPONSE_CHOICES)

	def test(self, facts):
		return facts[self.name]==self.value
		
	def __unicode__(self):
		return u"C%d: %s" % (self.code, self.name)


class Action(models.Model):
	"""Data returned by rule"""
	
	rule = models.ForeignKey(Rule)
	code = models.CharField(unique=True, max_length=8, verbose_name="Unique code for identifying actions in code.")
	name = models.CharField(blank=False, max_length=128, verbose_name="User friendly description of rule action")
	order = PositionField("rule")

	def __unicode__(self):
		return u"A%d: %s" % (self.code, self.name)