Invoicing: Allow to show exchange rates based on sources/rules (#3122)

src/pretix/base/services/currencies.py

@@ -0,0 +1,145 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+from datetime import date, datetime, timedelta
+from decimal import Decimal
+
+import requests
+from django.conf import settings
+from django.db.models import Max
+from django.dispatch import receiver
+from django.utils.translation import gettext_lazy as _
+from lxml import etree
+
+from pretix.base.models import ExchangeRate
+from pretix.base.signals import periodic_task
+from pretix.celery_app import app
+
+SOURCE_NAMES = {
+    None: _('European Central Bank'),  # backwards-compatibility
+    'eu:ecb:eurofxref-daily': _('European Central Bank'),
+    'cz:cnb:rate-fixing-daily': _('Czech National Bank'),
+}
+
+
+@receiver(signal=periodic_task)
+def fetch_rates(sender, **kwargs):
+    if not settings.FETCH_ECB_RATES:
+        return
+
+    source_tasks = {
+        'eu:ecb:eurofxref-daily': fetch_ecb_rates,
+        'cz:cnb:rate-fixing-daily': fetch_cnb_cz_rates,
+    }
+
+    for source_name, task in source_tasks.items():
+        last_source_date = ExchangeRate.objects.filter(source=source_name).aggregate(m=Max('source_date'))['m']
+        if last_source_date and last_source_date >= date.today():
+            # We assume that the rates we fetch are only updated daily
+            continue
+
+        last_fetch_date = ExchangeRate.objects.filter(source=source_name).aggregate(m=Max('updated'))['m']
+        if last_fetch_date and last_fetch_date >= datetime.utcnow() - timedelta(hours=1):
+            # Only try to fetch once per hour
+            continue
+
+        # Today's rate not yet published, let's try to fetch it
+        task.apply_async()
+
+
+@app.task()
+def fetch_ecb_rates():
+    """
+    Fetches currency rates from the European Central Bank.
+    """
+    d = 'https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml'
+    r = requests.get(d)
+    r.raise_for_status()
+
+    # File looks like this:
+    # <?xml version="1.0" encoding="UTF-8"?>
+    # <gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01"
+    #                  xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
+    #   <gesmes:subject>Reference rates</gesmes:subject>
+    #   <gesmes:Sender>
+    #       <gesmes:name>European Central Bank</gesmes:name>
+    #   </gesmes:Sender>
+    #   <Cube>
+    #       <Cube time="2023-02-14">
+    #           <Cube currency="USD" rate="1.0759"/>
+    #           ...
+    #       </Cube>
+    #   </Cube>
+    # </gesmes:Envelope>
+
+    root = etree.fromstring(r.content)
+    namespaces = {
+        'gesmes': 'http://www.gesmes.org/xml/2002-08-01',
+        'eurofxref': 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref'
+    }
+    outercube = root.xpath('./eurofxref:Cube/eurofxref:Cube[@time]', namespaces=namespaces)[0]
+    source_date = date.fromisoformat(outercube.get("time"))
+
+    for cube in outercube.xpath('./eurofxref:Cube[@currency][@rate]', namespaces=namespaces):
+        currency = cube.get('currency')
+        rate = Decimal(cube.get('rate'))
+        ExchangeRate.objects.update_or_create(
+            source='eu:ecb:eurofxref-daily',
+            source_currency='EUR',
+            other_currency=currency,
+            defaults=dict(
+                source_date=source_date,
+                rate=rate,
+            )
+        )
+
+
+@app.task()
+def fetch_cnb_cz_rates():
+    """
+    Fetches currency rates from the Czech National Bank.
+    """
+    d = f'https://www.cnb.cz/en/financial-markets/foreign-exchange-market/central-bank-exchange-rate-fixing/' \
+        f'central-bank-exchange-rate-fixing/daily.txt?date={date.today().strftime("%d.%m.%Y")}'
+    r = requests.get(d)
+    r.raise_for_status()
+
+    lines = r.text.splitlines()
+
+    # File looks like this:
+    # 14 Feb 2023 #32
+    # Country|Currency|Amount|Code|Rate
+    # Australia|dollar|1|AUD|15.412
+
+    source_date = datetime.strptime(lines[0].split("#")[0].strip(), "%d %b %Y").date()
+
+    for line in lines[2:]:
+        country, currency, amount, code, rate = line.split("|")
+        rate = Decimal(rate).quantize(Decimal('0.000001')) / int(amount)
+        ExchangeRate.objects.update_or_create(
+            source='cz:cnb:rate-fixing-daily',
+            source_currency=code,
+            other_currency='CZK',
+            defaults=dict(
+                source_date=source_date,
+                rate=rate,
+            )
+        )