Rewrite brmbar v3 in Python because Perl has lousy Qt bindings

Complete 1:1 reimplementation of existing Perl codebase.

brmbar3/brmbar/Currency.py

@@ -0,0 +1,77 @@
+import psycopg2
+from contextlib import closing
+
+class Currency:
+	""" Currency
+	
+	Each account has a currency (1 Kč, 1 Club Maté, ...), pairs of
+	currencies have (asymmetric) exchange rates. """
+	def __init__(self, db, id, name):
+		self.db = db
+		self.id = id
+		self.name = name
+
+	@classmethod
+	def default(cls, db):
+		""" Default wallet currency """
+		return cls.load(db, name = "Kč")
+
+	@classmethod
+	def load(cls, db, id = None, name = None):
+		""" Constructor for existing currency """
+		if id is not None:
+			with closing(db.cursor()) as cur:
+				cur.execute("SELECT name FROM currencies WHERE id = %s", [id])
+				name = cur.fetchone()[0]
+		elif name is not None:
+			with closing(db.cursor()) as cur:
+				cur.execute("SELECT id FROM currencies WHERE name = %s", [name])
+				id = cur.fetchone()[0]
+		else:
+			raise NameError("Currency.load(): Specify either id or name")
+		return cls(db, name = name, id = id)
+
+	@classmethod
+	def create(cls, db, name):
+		""" Constructor for new currency """
+		with closing(db.cursor()) as cur:
+			cur.execute("INSERT INTO currencies (name) VALUES (?) RETURNING id", [name])
+			id = cur.fetchone()[0]
+		return cls.new(db, name = name, id = id)
+
+	def rates(self, other):
+		""" Return tuple ($buy, $sell) of rates of $self in relation to $other (brmbar.Currency):
+		$buy is the price of $self in means of $other when buying it (into brmbar)
+		$sell is the price of $self in means of $other when selling it (from brmbar) """
+		with closing(self.db.cursor()) as cur:
+
+			cur.execute("SELECT rate, rate_dir FROM exchange_rates WHERE target = %s AND source = %s", [self.id, other.id])
+			res = cur.fetchone()
+			if res is None:
+				raise NameError("Currency.rate(): Unknown conversion " + other.name() + " to " + self.name())
+			buy_rate, buy_rate_dir = res
+			buy = buy_rate if buy_rate_dir == "target_to_source" else 1/buy_rate
+
+			cur.execute("SELECT rate, rate_dir FROM exchange_rates WHERE target = %s AND source = %s", [other.id, self.id])
+			res = cur.fetchone()
+			if res is None:
+				raise NameError("Currency.rate(): Unknown conversion " + self.name() + " to " + other.name())
+			sell_rate, sell_rate_dir = res
+			sell = sell_rate if sell_rate_dir == "source_to_target" else 1/sell_rate
+
+			return (buy, sell)
+
+	def convert(self, amount, target):
+		with closing(self.db.cursor()) as cur:
+			cur.execute("SELECT rate, rate_dir FROM exchange_rates WHERE target = %s AND source = %s AND valid_since <= NOW() ORDER BY valid_since ASC LIMIT 1", [target.id, self.id])
+			res = cur.fetchone()
+			if res is None:
+				raise NameError("Currency.convert(): Unknown conversion " + self.name() + " to " + other.name())
+			if rate_dir == "source_to_target":
+				resamount = amount * rate
+			else:
+				resamount = amount / rate
+			return resamount
+
+	def str(self, amount):
+		return str(amount) + " " + self.name