New algorithm when switching currencies

Fixes #599

Be careful, when switching to no currency, all bills are first converted
to the last known currency, and currency is erased

ihatemoney/forms.py

@@ -152,7 +152,7 @@ class EditProjectForm(FlaskForm):
 
         project.contact_email = self.contact_email.data
         project.logging_preference = self.logging_preference
-        project.default_currency = self.default_currency.data
+        project.switch_currency(self.default_currency.data)
 
         return project
 

ihatemoney/models.py

@@ -17,6 +17,7 @@ from sqlalchemy_continuum import make_versioned, version_class
 from sqlalchemy_continuum.plugins import FlaskPlugin
 from werkzeug.security import generate_password_hash
 
+from ihatemoney.currency_convertor import CurrencyConverter
 from ihatemoney.patch_sqlalchemy_continuum import PatchedBuilder
 from ihatemoney.versioning import (
     ConditionalVersioningManager,
@@ -263,6 +264,34 @@ class Project(db.Model):
             )
         return pretty_bills
 
+    def switch_currency(self, new_currency):
+        # Update converted currency
+        if new_currency != self.default_currency:
+            for bill in self.get_bills():
+                if bill.original_currency == new_currency:
+                    continue
+
+                if new_currency == CurrencyConverter.no_currency:
+                    # Use old currency to flatten all amount before stripping
+                    bill.converted_amount = CurrencyConverter().exchange_currency(
+                        bill.amount, bill.original_currency, self.default_currency
+                    )
+                    # Strip currency
+                    bill.amount = bill.converted_amount
+                    bill.original_currency = CurrencyConverter.no_currency
+                else:
+                    # Switch to new currency for everyone
+                    bill.converted_amount = CurrencyConverter().exchange_currency(
+                        bill.amount, bill.original_currency, new_currency
+                    )
+                    # Add the currency for previously un-currency-ied
+                    if bill.original_currency == CurrencyConverter.no_currency:
+                        bill.original_currency = new_currency
+                db.session.add(bill)
+        self.default_currency = new_currency
+        db.session.add(self)
+        db.session.commit()
+
     def remove_member(self, member_id):
         """Remove a member from the project.
 

ihatemoney/web.py

@@ -414,31 +414,7 @@ def edit_project():
 
     # Edit form
     if edit_form.validate_on_submit():
-        old_currency = g.project.default_currency
         project = edit_form.update(g.project)
-        # Update converted currency
-        if project.default_currency != old_currency:
-            for bill in project.get_bills():
-                if bill.original_currency == project.default_currency:
-                    continue
-
-                if project.default_currency == CurrencyConverter.no_currency:
-                    # Use old currency to flatten all amount before stripping
-                    bill.converted_amount = CurrencyConverter().exchange_currency(
-                        bill.amount, bill.original_currency, old_currency
-                    )
-                    # Strip currency
-                    bill.amount = bill.converted_amount
-                    bill.original_currency = CurrencyConverter.no_currency
-                else:
-                    # Switch to new currency for everyone
-                    bill.converted_amount = CurrencyConverter().exchange_currency(
-                        bill.amount, bill.original_currency, project.default_currency
-                    )
-                    # Add the currency for previously un-currency-ied
-                    if bill.original_currency == CurrencyConverter.no_currency:
-                        bill.original_currency = project.default_currency
-                db.session.add(bill)
 
         db.session.add(project)
         db.session.commit()