Rewrite brmbar v3 in Python because Perl has lousy Qt bindings

Complete 1:1 reimplementation of existing Perl codebase.

brmbar3/brmbar/Shop.py

@@ -0,0 +1,50 @@
+import brmbar
+from .Currency import Currency
+from .Account import Account
+
+import psycopg2
+from contextlib import closing
+
+class Shop:
+	""" BrmBar Shop
+
+	Business logic so that only interaction is left in the hands
+	of the frontend scripts. """
+	def __init__(self, db, currency, profits, cash):
+		self.db = db
+		self.currency = currency # brmbar.Currency
+		self.profits = profits # income brmbar.Account for brmbar profit margins on items
+		self.cash = cash # our operational ("wallet") cash account
+
+	@classmethod
+	def new_with_defaults(cls, db):
+		return cls(db,
+			currency = Currency.default(db),
+			profits = Account.load(db, name = "BrmBar Profits"),
+			cash = Account.load(db, name = "BrmBar Cash"))
+
+	def sell(self, item, user, amount = 1):
+		# Sale: Currency conversion from item currency to shop currency
+		(buy, sell) = item.currency.rates(self.currency)
+		cost = amount * sell
+		profit = amount * (sell - buy)
+
+		transaction = self._transaction(responsible = user, description = "BrmBar sale of {}x {} to {}".format(amount, item.name, user.name))
+		item.credit(transaction, amount, user.name)
+		user.debit(transaction, cost, item.name) # debit (increase) on a _debt_ account
+		self.profits.debit(transaction, profit, "Margin on " + item.name)
+		self.db.commit()
+
+		return cost
+
+	def add_credit(self, credit, user):
+		transaction = self._transaction(responsible = user, description = "BrmBar credit replenishment for " + user.name)
+		self.cash.debit(transaction, credit, user.name)
+		user.credit(transaction, credit, "Credit replenishment")
+		self.db.commit()
+
+	def _transaction(self, responsible, description):
+		with closing(self.db.cursor()) as cur:
+			cur.execute("INSERT INTO transactions (responsible, description) VALUES (%s, %s) RETURNING id", [responsible.id, description])
+			transaction = cur.fetchone()[0]
+		return transaction