Feature/currencies (#541)

Now each project can have a currency, default to None.
Each bill can use a different currency, and a conversion to project default currency is done on settle.

Fix #512

1 files changed, 46 insertions, 0 deletions

diff --git a/ihatemoney/currency_convertor.py b/ihatemoney/currency_convertor.py
new file mode 100644
index 0000000..75fa834
--- /dev/null
+++ b/ihatemoney/currency_convertor.py
@@ -0,0 +1,46 @@
+from cachetools import TTLCache, cached
+import requests
+
+
+class Singleton(type):
+    _instances = {}
+
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instances:
+            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
+        return cls._instances[cls]
+
+
+class CurrencyConverter(object, metaclass=Singleton):
+    # Get exchange rates
+    default = "No Currency"
+    api_url = "https://api.exchangeratesapi.io/latest?base=USD"
+
+    def __init__(self):
+        pass
+
+    @cached(cache=TTLCache(maxsize=1, ttl=86400))
+    def get_rates(self):
+        rates = requests.get(self.api_url).json()["rates"]
+        rates[self.default] = 1.0
+        return rates
+
+    def get_currencies(self):
+        rates = [rate for rate in self.get_rates()]
+        rates.sort(key=lambda rate: "" if rate == self.default else rate)
+        return rates
+
+    def exchange_currency(self, amount, source_currency, dest_currency):
+        if (
+            source_currency == dest_currency
+            or source_currency == self.default
+            or dest_currency == self.default
+        ):
+            return amount
+
+        rates = self.get_rates()
+        source_rate = rates[source_currency]
+        dest_rate = rates[dest_currency]
+        new_amount = (float(amount) / source_rate) * dest_rate
+        # round to two digits because we are dealing with money
+        return round(new_amount, 2)