mlk

from peak.events.trellis import *

##
## Example #1: Bank accounts and policy enforcement (validation)
##


class Account(Component):
    balance = attr(0)
    interest_rate = attr(1.0)
    policy = attr()

    @maintain
    def enforce_policy(self):
        if self.policy is not None:
            self.policy.check_account(self)


class StrictPolicy(Component):
    min_balance = attr(200)

    def check_account(self, account):
        if account.balance < self.min_balance:
            raise ValueError("Can't withdraw funds")


class RelaxedPolicy(Component):
    min_balance = attr(500)
    # This rate only applies if balance > min_balance
    interest_rate = attr(1.05)

    def check_account(self, account):
        if account.balance < 0:
            raise ValueError("Can't have negative balance")
        if account.balance >= self.min_balance:
            account.interest_rate = self.interest_rate
        else:
            account.interest_rate = 1.0


class CreditPolicy(Component):
    # This rate applies to accounts with negative balance
    interest_rate = attr(0.85)

    def check_account(self, account):
        if account.balance < 0:
            account.interest_rate = self.interest_rate
        else:
            account.interest_rate = 1.0


##########################################
##########################################

from nose.tools import *

acc = Account(balance=1000, policy=StrictPolicy())
assert_raises(ValueError, setattr, acc, 'balance', 100)
assert acc.balance == 1000
assert acc.interest_rate == 1.0

acc.policy = RelaxedPolicy()
assert acc.interest_rate == 1.05
acc.policy.min_balance = 2000
assert acc.interest_rate == 1.0

acc.balance = 100
assert_raises(ValueError, setattr, acc, 'balance', -100)

acc.policy = CreditPolicy()
assert acc.interest_rate == 1.0
acc.balance = -100
assert acc.interest_rate == 0.85