diff --git a/budget/models.py b/budget/models.py index 5783703..a92281b 100644 --- a/budget/models.py +++ b/budget/models.py @@ -45,10 +45,57 @@ class Project(db.Model): for person in self.members: balance = should_receive[person] - should_pay[person] - balances[person.id] = round(balance, 2) + balances[person] = round(balance, 2) return balances + def settle_bill(self): + """Return a list of transactions that could be made to settle the bill""" + balances = self.balance + credits, debts = list(), list() + transactions = list() + # Create lists of credits and debts + for person in balances.keys(): + if balances[person] > 0: + credits.append({"person": person, "balance": balances[person]}) + elif balances[person] < 0: + debts.append({"person": person, "balance": -balances[person]}) + # Try and find exact matches + for credit in credits: + match = self.exactmatch(credit["balance"], debts) + if match: + for m in match: + transactions.append({"ower": m["person"], "payer": credit["person"], "amount": m["balance"]}) + debts.remove(m) + credits.remove(credit) + # Split any remaining debts & credits + while credits and debts: + if credits[0]["balance"] > debts[0]["balance"]: + transactions.append({"ower": debts[0]["person"], "payer": credits[0]["person"], "amount": debts[0]["balance"]}) + credits[0]["balance"] = credits[0]["balance"] - debts[0]["balance"] + del debts[0] + else: + transactions.append({"ower": debts[0]["person"], "payer": credits[0]["person"], "amount": credits[0]["balance"]}) + debts[0]["balance"] = debts[0]["balance"] - credits[0]["balance"] + del credits[0] + return transactions + + def exactmatch(self, credit, debts): + """Recursively try and find subsets of 'debts' whose sum is equal to credit""" + if not debts: + return [] + if debts[0]["balance"] > credit: + return self.exactmatch(credit, debts[1:]) + elif debts[0]["balance"] == credit: + return [debts[0]] + else: + match = self.exactmatch(credit-debts[0]["balance"], debts[1:]) + if match: + match.append(debts[0]) + else: + match = self.exactmatch(credit, debts[1:]) + return match + def has_bills(self): """return if the project do have bills or not""" return self.get_bills().count() > 0 diff --git a/budget/templates/layout.html b/budget/templates/layout.html index 293ce75..ceee769 100644 --- a/budget/templates/layout.html +++ b/budget/templates/layout.html @@ -54,7 +54,10 @@