Tax rules and reverse charge (#559)

Tax rules and reverse charge

src/pretix/base/models/tax.py

@@ -0,0 +1,174 @@
+from decimal import Decimal
+
+from django.db import models
+from django.utils.formats import localize
+from django.utils.translation import ugettext_lazy as _
+from django_countries.fields import CountryField
+from i18nfield.fields import I18nCharField
+
+from pretix.base.decimal import round_decimal
+from pretix.base.models.base import LoggedModel
+
+
+class TaxedPrice:
+    def __init__(self, *, gross: Decimal, net: Decimal, tax: Decimal, rate: Decimal, name: str):
+        if net + tax != gross:
+            raise ValueError('Net value and tax value need to add to the gross value')
+        self.gross = gross
+        self.net = net
+        self.tax = tax
+        self.rate = rate
+        self.name = name
+
+    def __repr__(self):
+        return '{} + {}% = {}'.format(localize(self.net), localize(self.rate), localize(self.gross))
+
+
+TAXED_ZERO = TaxedPrice(
+    gross=Decimal('0.00'),
+    net=Decimal('0.00'),
+    tax=Decimal('0.00'),
+    rate=Decimal('0.00'),
+    name=''
+)
+
+EU_COUNTRIES = {
+    'AT', 'BE', 'BG', 'HR', 'CY', 'CZ', 'DK', 'EE', 'FI', 'FR', 'DE', 'GR', 'HU', 'IE', 'IT', 'LV', 'LT', 'LU', 'MT',
+    'NL', 'PL', 'PT', 'RO', 'SK', 'SI', 'ES', 'SE', 'GB'
+}
+EU_CURRENCIES = {
+    'BG': 'BGN',
+    'GB': 'GBP',
+    'HR': 'HRK',
+    'CZ': 'CZK',
+    'DK': 'DKK',
+    'HU': 'HUF',
+    'PL': 'PLN',
+    'RO': 'RON',
+    'SE': 'SEK'
+}
+
+
+class TaxRule(LoggedModel):
+    event = models.ForeignKey('Event', related_name='tax_rules')
+    name = I18nCharField(
+        verbose_name=_('Name'),
+        help_text=_('Should be short, e.g. "VAT"'),
+        max_length=190,
+    )
+    rate = models.DecimalField(
+        max_digits=10,
+        decimal_places=2,
+        verbose_name=_("Tax rate")
+    )
+    price_includes_tax = models.BooleanField(
+        verbose_name=_("The configured product prices include the tax amount"),
+        default=True,
+    )
+    eu_reverse_charge = models.BooleanField(
+        verbose_name=_("Use EU reverse charge taxation rules"),
+        default=False,
+        help_text=_("Not recommended. Most events will NOT be qualified for reverse charge since the place of "
+                    "taxation is the location of the event. This option disables charging VAT for all customers "
+                    "outside the EU and for business customers in different EU countries that do not "
+                    "customers who entered a valid EU VAT ID. Only enable this option after consulting a tax counsel. "
+                    "No warranty given for correct tax calculation. USE AT YOUR OWN RISK.")
+    )
+    home_country = CountryField(
+        verbose_name=_('Merchant country'),
+        blank=True,
+        help_text=_('Your country of residence. This is the country the EU reverse charge rule will not apply in, '
+                    'if configured above.'),
+    )
+
+    @classmethod
+    def zero(cls):
+        return cls(
+            event=None,
+            name='',
+            rate=Decimal('0.00'),
+            price_includes_tax=True,
+            eu_reverse_charge=False
+        )
+
+    def clean(self):
+        if self.eu_reverse_charge and not self.home_country:
+            raise ValueError(_('You need to set your home country to use the reverse charge feature.'))
+
+    def __str__(self):
+        if self.price_includes_tax:
+            s = _('incl. {rate} {name}').format(rate=self.rate, name=self.name)
+        else:
+            s = _('plus {rate} {name}').format(rate=self.rate, name=self.name)
+        if self.eu_reverse_charge:
+            s += ' ({})'.format(_('reverse charge enabled'))
+        return str(s)
+
+    def tax(self, base_price, base_price_is='auto'):
+        if self.rate == Decimal('0.00'):
+            return TaxedPrice(
+                net=base_price, gross=base_price, tax=Decimal('0.00'),
+                rate=self.rate, name=self.name
+            )
+
+        if base_price_is == 'auto':
+            if self.price_includes_tax:
+                base_price_is = 'gross'
+            else:
+                base_price_is = 'net'
+
+        if base_price_is == 'gross':
+            gross = base_price
+            net = gross - round_decimal(base_price * (1 - 100 / (100 + self.rate)))
+        elif base_price_is == 'net':
+            net = base_price
+            gross = round_decimal(net * (1 + self.rate / 100))
+        else:
+            raise ValueError('Unknown base price type: {}'.format(base_price_is))
+
+        return TaxedPrice(
+            net=net, gross=gross, tax=gross - net,
+            rate=self.rate, name=self.name
+        )
+
+    def is_reverse_charge(self, invoice_address):
+        if not self.eu_reverse_charge:
+            return False
+
+        if not invoice_address or not invoice_address.country:
+            return False
+
+        if str(invoice_address.country) not in EU_COUNTRIES:
+            return False
+
+        if invoice_address.country == self.home_country:
+            return False
+
+        if invoice_address.is_business and invoice_address.vat_id and invoice_address.vat_id_validated:
+            return True
+
+        return False
+
+    def tax_applicable(self, invoice_address):
+        if not self.eu_reverse_charge:
+            # No reverse charge rules? Always apply VAT!
+            return True
+
+        if not invoice_address or not invoice_address.country:
+            # No country specified? Always apply VAT!
+            return True
+
+        if str(invoice_address.country) not in EU_COUNTRIES:
+            # Non-EU country? Never apply VAT!
+            return False
+
+        if invoice_address.country == self.home_country:
+            # Within same EU country? Always apply VAT!
+            return True
+
+        if invoice_address.is_business and invoice_address.vat_id and invoice_address.vat_id_validated:
+            # Reverse charge case
+            return False
+
+        # Consumer in different EU country / invalid VAT
+        return True