Rework currency switching (#661)

Co-authored-by: Alexis Métaireau <alexis@notmyidea.org>

Currency switching is both simpler and less powerful. This was done primarily for users, to have a clear and logical understanding, but the code is also simpler. The main change is that it is now forbidden to switch a project to "no currency" if bills don't share the same currency.

Also, tests assume that projects are created without currency, as in the web UI.

ihatemoney/api/common.py

@@ -69,7 +69,7 @@ class ProjectHandler(Resource):
         return "DELETED"
 
     def put(self, project):
-        form = EditProjectForm(meta={"csrf": False})
+        form = EditProjectForm(id=project.id, meta={"csrf": False})
         if form.validate() and current_app.config.get("ALLOW_PUBLIC_PROJECT_CREATION"):
             form.update(project)
             db.session.commit()

ihatemoney/forms.py

@@ -1,5 +1,6 @@
 from datetime import datetime
 from re import match
+from types import SimpleNamespace
 
 import email_validator
 from flask import request
@@ -110,6 +111,14 @@ class EditProjectForm(FlaskForm):
     default_currency = SelectField(_("Default Currency"), validators=[DataRequired()])
 
     def __init__(self, *args, **kwargs):
+        if not hasattr(self, "id"):
+            # We must access the project to validate the default currency, using its id.
+            # In ProjectForm, 'id' is provided, but not in this base class, so it *must*
+            # be provided by callers.
+            # Since id can be defined as a WTForms.StringField, we mimics it,
+            # using an object that can have a 'data' attribute.
+            # It defaults to empty string to ensure that query run smoothly.
+            self.id = SimpleNamespace(data=kwargs.pop("id", ""))
         super().__init__(*args, **kwargs)
         self.default_currency.choices = [
             (currency_name, render_localized_currency(currency_name, detailed=True))
@@ -142,6 +151,22 @@ class EditProjectForm(FlaskForm):
         )
         return project
 
+    def validate_default_currency(form, field):
+        project = Project.query.get(form.id.data)
+        if (
+            project is not None
+            and field.data == CurrencyConverter.no_currency
+            and project.has_multiple_currencies()
+        ):
+            raise ValidationError(
+                _(
+                    (
+                        "This project cannot be set to 'no currency'"
+                        " because it contains bills in multiple currencies."
+                    )
+                )
+            )
+
     def update(self, project):
         """Update the project with the information from the form"""
         project.name = self.name.data
@@ -152,7 +177,7 @@ 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,
@@ -139,7 +140,7 @@ class Project(db.Model):
                 "spent": sum(
                     [
                         bill.pay_each() * member.weight
-                        for bill in self.get_bills().all()
+                        for bill in self.get_bills_unordered().all()
                         if member in bill.owers
                     ]
                 ),
@@ -156,7 +157,7 @@ class Project(db.Model):
         :rtype dict:
         """
         monthly = defaultdict(lambda: defaultdict(float))
-        for bill in self.get_bills().all():
+        for bill in self.get_bills_unordered().all():
             monthly[bill.date.year][bill.date.month] += bill.converted_amount
         return monthly
 
@@ -215,15 +216,25 @@ class Project(db.Model):
 
     def has_bills(self):
         """return if the project do have bills or not"""
-        return self.get_bills().count() > 0
+        return self.get_bills_unordered().count() > 0
 
-    def get_bills(self):
-        """Return the list of bills related to this project"""
+    def has_multiple_currencies(self):
+        """Return if multiple currencies are used"""
+        return self.get_bills_unordered().group_by(Bill.original_currency).count() > 1
+
+    def get_bills_unordered(self):
+        """Base query for bill list"""
         return (
             Bill.query.join(Person, Project)
             .filter(Bill.payer_id == Person.id)
             .filter(Person.project_id == Project.id)
             .filter(Project.id == self.id)
+        )
+
+    def get_bills(self):
+        """Return the list of bills related to this project"""
+        return (
+            self.get_bills_unordered()
             .order_by(Bill.date.desc())
             .order_by(Bill.creation_date.desc())
             .order_by(Bill.id.desc())
@@ -232,11 +243,8 @@ class Project(db.Model):
     def get_member_bills(self, member_id):
         """Return the list of bills related to a specific member"""
         return (
-            Bill.query.join(Person, Project)
-            .filter(Bill.payer_id == Person.id)
-            .filter(Person.project_id == Project.id)
+            self.get_bills_unordered()
             .filter(Person.id == member_id)
-            .filter(Project.id == self.id)
             .order_by(Bill.date.desc())
             .order_by(Bill.id.desc())
         )
@@ -263,6 +271,41 @@ class Project(db.Model):
             )
         return pretty_bills
 
+    def switch_currency(self, new_currency):
+        if new_currency == self.default_currency:
+            return
+        # Update converted currency
+        if new_currency == CurrencyConverter.no_currency:
+            if self.has_multiple_currencies():
+                raise ValueError(f"Can't unset currency of project {self.id}")
+
+            for bill in self.get_bills_unordered():
+                # We are removing the currency, and we already checked that all bills
+                # had the same currency: it means that we can simply strip the currency
+                # without converting the amounts. We basically ignore the current default_currency
+
+                # Reset converted amount in case it was different from the original amount
+                bill.converted_amount = bill.amount
+                # Strip currency
+                bill.original_currency = CurrencyConverter.no_currency
+                db.session.add(bill)
+        else:
+            for bill in self.get_bills_unordered():
+                if bill.original_currency == CurrencyConverter.no_currency:
+                    # Bills that were created without currency will be set to the new currency
+                    bill.original_currency = new_currency
+                    bill.converted_amount = bill.amount
+                else:
+                    # Convert amount for others, without touching original_currency
+                    bill.converted_amount = CurrencyConverter().exchange_currency(
+                        bill.amount, 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/templates/dashboard.html

@@ -5,7 +5,7 @@
     <thead><tr><th>{{ _("Project") }}</th><th>{{ _("Number of members") }}</th><th>{{ _("Number of bills") }}</th><th>{{_("Newest bill")}}</th><th>{{_("Oldest bill")}}</th><th>{{_("Actions")}}</th></tr></thead>
     <tbody>{% for project in projects|sort(attribute='name') %}
         <tr>
-        <td><a href="{{ url_for(".list_bills", project_id=project.id) }}" title="{{ project.name }}">{{ project.name }}</a></td><td>{{ project.members | count }}</td><td>{{ project.get_bills().count() }}</td>
+        <td><a href="{{ url_for(".list_bills", project_id=project.id) }}" title="{{ project.name }}">{{ project.name }}</a></td><td>{{ project.members | count }}</td><td>{{ project.get_bills_unordered().count() }}</td>
         {% if project.has_bills() %}
         <td>{{ project.get_bills().all()[0].date }}</td>
         <td>{{ project.get_bills().all()[-1].date }}</td>

ihatemoney/tests/budget_test.py

@@ -4,11 +4,14 @@ import json
 import re
 from time import sleep
 import unittest
+from unittest.mock import MagicMock
 
 from flask import session
+import pytest
 from werkzeug.security import check_password_hash, generate_password_hash
 
 from ihatemoney import models
+from ihatemoney.currency_convertor import CurrencyConverter
 from ihatemoney.tests.common.ihatemoney_testcase import IhatemoneyTestCase
 from ihatemoney.versioning import LoggingMode
 
@@ -802,7 +805,8 @@ class BudgetTestCase(IhatemoneyTestCase):
         self.assertEqual(response.status_code, 200)
 
     def test_statistics(self):
-        self.post_project("raclette")
+        # Output is checked with the USD sign
+        self.post_project("raclette", default_currency="USD")
 
         # add members
         self.client.post("/raclette/members/add", data={"name": "zorglub", "weight": 2})
@@ -1443,6 +1447,225 @@ class BudgetTestCase(IhatemoneyTestCase):
         member = models.Person.query.filter(models.Person.id == 1).one_or_none()
         self.assertEqual(member, None)
 
+    def test_currency_switch(self):
+
+        mock_data = {"USD": 1, "EUR": 0.8, "CAD": 1.2, CurrencyConverter.no_currency: 1}
+        converter = CurrencyConverter()
+        converter.get_rates = MagicMock(return_value=mock_data)
+
+        # A project should be editable
+        self.post_project("raclette")
+
+        # add members
+        self.client.post("/raclette/members/add", data={"name": "zorglub"})
+        self.client.post("/raclette/members/add", data={"name": "fred"})
+        self.client.post("/raclette/members/add", data={"name": "tata"})
+
+        # create bills
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2016-12-31",
+                "what": "fromage à raclette",
+                "payer": 1,
+                "payed_for": [1, 2, 3],
+                "amount": "10.0",
+            },
+        )
+
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2016-12-31",
+                "what": "red wine",
+                "payer": 2,
+                "payed_for": [1, 3],
+                "amount": "20",
+            },
+        )
+
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2017-01-01",
+                "what": "refund",
+                "payer": 3,
+                "payed_for": [2],
+                "amount": "13.33",
+            },
+        )
+
+        project = models.Project.query.get("raclette")
+
+        # First all converted_amount should be the same as amount, with no currency
+        for bill in project.get_bills():
+            assert bill.original_currency == CurrencyConverter.no_currency
+            assert bill.amount == bill.converted_amount
+
+        # Then, switch to EUR, all bills must have been changed to this currency
+        project.switch_currency("EUR")
+        for bill in project.get_bills():
+            assert bill.original_currency == "EUR"
+            assert bill.amount == bill.converted_amount
+
+        # Add a bill in EUR, the current default currency
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2017-01-01",
+                "what": "refund from EUR",
+                "payer": 3,
+                "payed_for": [2],
+                "amount": "20",
+                "original_currency": "EUR",
+            },
+        )
+        last_bill = project.get_bills().first()
+        assert last_bill.converted_amount == last_bill.amount
+
+        # Erase all currencies
+        project.switch_currency(CurrencyConverter.no_currency)
+        for bill in project.get_bills():
+            assert bill.original_currency == CurrencyConverter.no_currency
+            assert bill.amount == bill.converted_amount
+
+        # Let's go back to EUR to test conversion
+        project.switch_currency("EUR")
+        # This is a bill in CAD
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2017-01-01",
+                "what": "Poutine",
+                "payer": 3,
+                "payed_for": [2],
+                "amount": "18",
+                "original_currency": "CAD",
+            },
+        )
+        last_bill = project.get_bills().first()
+        expected_amount = converter.exchange_currency(last_bill.amount, "CAD", "EUR")
+        assert last_bill.converted_amount == expected_amount
+
+        # Switch to USD. Now, NO bill should be in USD, since they already had a currency
+        project.switch_currency("USD")
+        for bill in project.get_bills():
+            assert bill.original_currency != "USD"
+            expected_amount = converter.exchange_currency(
+                bill.amount, bill.original_currency, "USD"
+            )
+            assert bill.converted_amount == expected_amount
+
+        # Switching back to no currency must fail
+        with pytest.raises(ValueError):
+            project.switch_currency(CurrencyConverter.no_currency)
+
+        # It also must fails with a nice error using the form
+        resp = self.client.post(
+            "/raclette/edit",
+            data={
+                "name": "demonstration",
+                "password": "demo",
+                "contact_email": "demo@notmyidea.org",
+                "project_history": "y",
+                "default_currency": converter.no_currency,
+            },
+        )
+        # A user displayed error should be generated, and its currency should be the same.
+        self.assertStatus(200, resp)
+        self.assertIn('<p class="alert alert-danger">', resp.data.decode("utf-8"))
+        self.assertEqual(models.Project.query.get("raclette").default_currency, "USD")
+
+    def test_currency_switch_to_bill_currency(self):
+
+        mock_data = {"USD": 1, "EUR": 0.8, "CAD": 1.2, CurrencyConverter.no_currency: 1}
+        converter = CurrencyConverter()
+        converter.get_rates = MagicMock(return_value=mock_data)
+
+        # Default currency is 'XXX', but we should start from a project with a currency
+        self.post_project("raclette", default_currency="USD")
+
+        # add members
+        self.client.post("/raclette/members/add", data={"name": "zorglub"})
+        self.client.post("/raclette/members/add", data={"name": "fred"})
+
+        # Bill with a different currency than project's default
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2016-12-31",
+                "what": "fromage à raclette",
+                "payer": 1,
+                "payed_for": [1, 2],
+                "amount": "10.0",
+                "original_currency": "EUR",
+            },
+        )
+
+        project = models.Project.query.get("raclette")
+
+        bill = project.get_bills().first()
+        assert bill.converted_amount == converter.exchange_currency(
+            bill.amount, "EUR", "USD"
+        )
+
+        # And switch project to the currency from the bill we created
+        project.switch_currency("EUR")
+        bill = project.get_bills().first()
+        assert bill.converted_amount == bill.amount
+
+    def test_currency_switch_to_no_currency(self):
+
+        mock_data = {"USD": 1, "EUR": 0.8, "CAD": 1.2, CurrencyConverter.no_currency: 1}
+        converter = CurrencyConverter()
+        converter.get_rates = MagicMock(return_value=mock_data)
+
+        # Default currency is 'XXX', but we should start from a project with a currency
+        self.post_project("raclette", default_currency="USD")
+
+        # add members
+        self.client.post("/raclette/members/add", data={"name": "zorglub"})
+        self.client.post("/raclette/members/add", data={"name": "fred"})
+
+        # Bills with a different currency than project's default
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2016-12-31",
+                "what": "fromage à raclette",
+                "payer": 1,
+                "payed_for": [1, 2],
+                "amount": "10.0",
+                "original_currency": "EUR",
+            },
+        )
+
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2017-01-01",
+                "what": "aspirine",
+                "payer": 2,
+                "payed_for": [1, 2],
+                "amount": "5.0",
+                "original_currency": "EUR",
+            },
+        )
+
+        project = models.Project.query.get("raclette")
+
+        for bill in project.get_bills_unordered():
+            assert bill.converted_amount == converter.exchange_currency(
+                bill.amount, "EUR", "USD"
+            )
+
+        # And switch project to no currency: amount should be equal to what was submitted
+        project.switch_currency(converter.no_currency)
+        no_currency_bills = [
+            (bill.amount, bill.converted_amount) for bill in project.get_bills()
+        ]
+        assert no_currency_bills == [(5.0, 5.0), (10.0, 10.0)]
+
 
 if __name__ == "__main__":
     unittest.main()

ihatemoney/tests/common/ihatemoney_testcase.py

@@ -30,7 +30,7 @@ class BaseTestCase(TestCase):
             follow_redirects=True,
         )
 
-    def post_project(self, name, follow_redirects=True):
+    def post_project(self, name, follow_redirects=True, default_currency="XXX"):
         """Create a fake project"""
         # create the project
         return self.client.post(
@@ -40,18 +40,18 @@ class BaseTestCase(TestCase):
                 "id": name,
                 "password": name,
                 "contact_email": f"{name}@notmyidea.org",
-                "default_currency": "USD",
+                "default_currency": default_currency,
             },
             follow_redirects=follow_redirects,
         )
 
-    def create_project(self, name):
+    def create_project(self, name, default_currency="XXX"):
         project = models.Project(
             id=name,
             name=str(name),
             password=generate_password_hash(name),
             contact_email=f"{name}@notmyidea.org",
-            default_currency="USD",
+            default_currency=default_currency,
         )
         models.db.session.add(project)
         models.db.session.commit()

ihatemoney/tests/history_test.py

@@ -25,7 +25,7 @@ class HistoryTestCase(IhatemoneyTestCase):
             "name": "demo",
             "contact_email": "demo@notmyidea.org",
             "password": "demo",
-            "default_currency": "USD",
+            "default_currency": "XXX",
         }
 
         if logging_preference != LoggingMode.DISABLED:
@@ -78,7 +78,7 @@ class HistoryTestCase(IhatemoneyTestCase):
             "contact_email": "demo2@notmyidea.org",
             "password": "123456",
             "project_history": "y",
-            "default_currency": "USD",
+            "default_currency": "USD",  # Currency changed from default
         }
 
         resp = self.client.post("/demo/edit", data=new_data, follow_redirects=True)
@@ -103,7 +103,7 @@ class HistoryTestCase(IhatemoneyTestCase):
             resp.data.decode("utf-8").index("Project renamed "),
             resp.data.decode("utf-8").index("Project private code changed"),
         )
-        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 4)
+        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 5)
         self.assertNotIn("127.0.0.1", resp.data.decode("utf-8"))
 
     def test_project_privacy_edit(self):
@@ -284,7 +284,7 @@ class HistoryTestCase(IhatemoneyTestCase):
         self.assertIn(
             "Some entries below contain IP addresses,", resp.data.decode("utf-8")
         )
-        self.assertEqual(resp.data.decode("utf-8").count("127.0.0.1"), 10)
+        self.assertEqual(resp.data.decode("utf-8").count("127.0.0.1"), 12)
         self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 1)
 
         # Generate more operations to confirm additional IP info isn't recorded
@@ -292,8 +292,8 @@ class HistoryTestCase(IhatemoneyTestCase):
 
         resp = self.client.get("/demo/history")
         self.assertEqual(resp.status_code, 200)
-        self.assertEqual(resp.data.decode("utf-8").count("127.0.0.1"), 10)
-        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 6)
+        self.assertEqual(resp.data.decode("utf-8").count("127.0.0.1"), 12)
+        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 7)
 
         # Clear IP Data
         resp = self.client.post("/demo/strip_ip_addresses", follow_redirects=True)
@@ -311,7 +311,7 @@ class HistoryTestCase(IhatemoneyTestCase):
             "Some entries below contain IP addresses,", resp.data.decode("utf-8")
         )
         self.assertEqual(resp.data.decode("utf-8").count("127.0.0.1"), 0)
-        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 16)
+        self.assertEqual(resp.data.decode("utf-8").count("<td> -- </td>"), 19)
 
     def test_logs_for_common_actions(self):
         # adds a member to this project

ihatemoney/tests/main_test.py

@@ -240,7 +240,7 @@ class EmailFailureTestCase(IhatemoneyTestCase):
 
 class TestCurrencyConverter(unittest.TestCase):
     converter = CurrencyConverter()
-    mock_data = {"USD": 1, "EUR": 0.8115}
+    mock_data = {"USD": 1, "EUR": 0.8, "CAD": 1.2, CurrencyConverter.no_currency: 1}
     converter.get_rates = MagicMock(return_value=mock_data)
 
     def test_only_one_instance(self):
@@ -249,11 +249,14 @@ class TestCurrencyConverter(unittest.TestCase):
         self.assertEqual(one, two)
 
     def test_get_currencies(self):
-        self.assertCountEqual(self.converter.get_currencies(), ["USD", "EUR"])
+        self.assertCountEqual(
+            self.converter.get_currencies(),
+            ["USD", "EUR", "CAD", CurrencyConverter.no_currency],
+        )
 
     def test_exchange_currency(self):
         result = self.converter.exchange_currency(100, "USD", "EUR")
-        self.assertEqual(result, 81.15)
+        self.assertEqual(result, 80.0)
 
 
 if __name__ == "__main__":

ihatemoney/web.py

@@ -36,7 +36,6 @@ from sqlalchemy_continuum import Operation
 from werkzeug.exceptions import NotFound
 from werkzeug.security import check_password_hash, generate_password_hash
 
-from ihatemoney.currency_convertor import CurrencyConverter
 from ihatemoney.forms import (
     AdminAuthenticationForm,
     AuthenticationForm,
@@ -400,7 +399,7 @@ def reset_password():
 
 @main.route("/<project_id>/edit", methods=["GET", "POST"])
 def edit_project():
-    edit_form = EditProjectForm()
+    edit_form = EditProjectForm(id=g.project.id)
     import_form = UploadForm()
     # Import form
     if import_form.validate_on_submit():
@@ -415,17 +414,6 @@ def edit_project():
     # Edit form
     if edit_form.validate_on_submit():
         project = edit_form.update(g.project)
-        # Update converted currency
-        if project.default_currency != CurrencyConverter.no_currency:
-            for bill in project.get_bills():
-
-                if bill.original_currency == CurrencyConverter.no_currency:
-                    bill.original_currency = project.default_currency
-
-                bill.converted_amount = CurrencyConverter().exchange_currency(
-                    bill.amount, bill.original_currency, project.default_currency
-                )
-                db.session.add(bill)
 
         db.session.add(project)
         db.session.commit()