Real order systems keep an audit trail, every state the order has passed through, in order. Record it as the machine moves, and note that a rejected event must not leave a trace.
The order starts its history in cart. Update fire so each successful transition appends the new state.
fire(event): on a successful transition, append the new state to self.history; rejected events change nothingclass Order:
TRANSITIONS = {
"cart": {"checkout": "pending"},
"pending": {"pay": "paid", "cancel": "cancelled"},
"paid": {"ship": "shipped", "refund": "cancelled"},
"shipped": {"deliver": "delivered"},
"delivered": {},
"cancelled": {},
}
def __init__(self):
self.state = "cart"
self.history = ["cart"]
def fire(self, event):
"""Advance on an allowed event and record the new state in history."""
# TODO: same allowed-event check against TRANSITIONS as before, but now
# the audit trail matters. A successful move updates self.state and adds
# the state just entered to the end of self.history; a rejected event
# must leave self.state and self.history exactly as they were.
pass
def can(self, event):
return event in self.TRANSITIONS.get(self.state, {})
def available_events(self):
return list(self.TRANSITIONS.get(self.state, {}).keys())
def is_terminal(self):
return len(self.TRANSITIONS.get(self.state, {})) == 0
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Real order systems keep an audit trail, every state the order has passed through, in order. Record it as the machine moves, and note that a rejected event must not leave a trace.
The order starts its history in cart. Update fire so each successful transition appends the new state.
fire(event): on a successful transition, append the new state to self.history; rejected events change nothingPress Run Tests or ⌘↩ to check your solution.