create SQL composite type currency_basket

liberapay/constants.py

@@ -7,6 +7,7 @@
 import re
 
 from jinja2 import StrictUndefined
+from mangopay.utils import Money
 from pando.utils import utc
 
 
@@ -238,4 +239,6 @@ def make_standard_tip(label, weekly):
 
 USERNAME_MAX_SIZE = 32
 
+ZERO = {c: Money(D_ZERO, c) for c in ('EUR', 'USD', None)}
+
 del _

liberapay/main.py

@@ -26,7 +26,7 @@
 from liberapay.models.repository import refetch_repos
 from liberapay.security import authentication, csrf, set_default_security_headers
 from liberapay.utils import b64decode_s, b64encode_s, erase_cookie, http_caching, i18n, set_cookie
-from liberapay.utils.currencies import fetch_currency_exchange_rates
+from liberapay.utils.currencies import MoneyBasket, fetch_currency_exchange_rates
 from liberapay.utils.state_chain import (
     attach_environ_to_request, create_response_object, canonize, insert_constants,
     _dispatch_path_to_filesystem, merge_exception_into_response, return_500_for_exception,
@@ -43,6 +43,7 @@
 # ===================
 
 json.register_encoder(Money, lambda m: {'amount': str(m.amount), 'currency': m.currency})
+json.register_encoder(MoneyBasket, lambda b: list(b))
 
 website.renderer_default = 'unspecified'  # require explicit renderer, to avoid escaping bugs
 

liberapay/utils/currencies.py

@@ -6,7 +6,7 @@
 import requests
 import xmltodict
 
-from liberapay.constants import D_CENT, D_ZERO
+from liberapay.constants import D_CENT, D_ZERO, ZERO
 from liberapay.website import website
 
 
@@ -28,6 +28,62 @@ def _convert(self, c):
 Money.zero = lambda m: Money(D_ZERO, m.currency)
 
 
+class MoneyBasket(object):
+
+    def __init__(self, eur=ZERO['EUR'], usd=ZERO['USD']):
+        assert eur.currency == 'EUR'
+        assert usd.currency == 'USD'
+        self.eur = eur
+        self.usd = usd
+
+    def __iter__(self):
+        return iter((self.eur, self.usd))
+
+    def __eq__(self, other):
+        if isinstance(other, self.__class__):
+            return self.__dict__ == other.__dict__
+        return False
+
+    def __add__(self, other):
+        r = self.__class__(self.eur, self.usd)
+        if isinstance(other, self.__class__):
+            for k, v in other.__dict__.items():
+                if k in r.__dict__:
+                    r.__dict__[k] += v
+                else:
+                    r.__dict__[k] = v
+        elif isinstance(other, Money):
+            k = other.currency.lower()
+            if k in r.__dict__:
+                r.__dict__[k] += other
+            else:
+                r.__dict__[k] = other
+        else:
+            raise TypeError(other)
+        return r
+
+    def __sub__(self, other):
+        r = self.__class__(self.eur, self.usd)
+        if isinstance(other, self.__class__):
+            for k, v in other.__dict__.items():
+                if k in r.__dict__:
+                    r.__dict__[k] -= v
+                else:
+                    r.__dict__[k] = -v
+        elif isinstance(other, Money):
+            k = other.currency.lower()
+            if k in r.__dict__:
+                r.__dict__[k] -= other
+            else:
+                r.__dict__[k] = -other
+        else:
+            raise TypeError(other)
+        return r
+
+    def __repr__(self):
+        return b'%s[%s, %s]' % (self.__class__.__name__, self.eur, self.usd)
+
+
 def fetch_currency_exchange_rates(db):
     currencies = set(db.one("SELECT array_to_json(enum_range(NULL::currency))"))
     r = requests.get('https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml')

liberapay/wireup.py

@@ -42,7 +42,7 @@
 from liberapay.models import DB
 from liberapay.security.authentication import ANON
 from liberapay.utils import find_files, markdown, mkdir_p
-from liberapay.utils.currencies import get_currency_exchange_rates
+from liberapay.utils.currencies import MoneyBasket, get_currency_exchange_rates
 from liberapay.utils.emails import compile_email_spt
 from liberapay.utils.http_caching import asset_etag
 from liberapay.utils.i18n import (
@@ -110,6 +110,18 @@ def cast_currency_amount(v, cursor):
     oid = db.one("SELECT 'currency_amount'::regtype::oid")
     register_type(new_type((oid,), _str('currency_amount'), cast_currency_amount))
 
+    def adapt_money_basket(b):
+        return AsIs(b'(%s,%s)::currency_basket' % (b.eur.amount, b.usd.amount))
+    register_adapter(MoneyBasket, adapt_money_basket)
+
+    def cast_currency_basket(v, cursor):
+        if v is None:
+            return None
+        eur, usd = v[1:-1].split(',')
+        return MoneyBasket(Money(eur, 'EUR'), Money(usd, 'USD'))
+    oid = db.one("SELECT 'currency_basket'::regtype::oid")
+    register_type(new_type((oid,), _str('currency_basket'), cast_currency_basket))
+
     use_qc = not env.override_query_cache
     qc1 = QueryCache(db, threshold=(1 if use_qc else 0))
     qc5 = QueryCache(db, threshold=(5 if use_qc else 0))

sql/currencies.sql

@@ -240,6 +240,98 @@ CREATE OPERATOR <= (
 );
 
 
+-- Basket type: amounts in multiple currencies
+
+CREATE TYPE currency_basket AS (EUR numeric, USD numeric);
+
+CREATE FUNCTION currency_basket_add(currency_basket, currency_amount)
+RETURNS currency_basket AS $$
+    BEGIN
+        IF ($2.currency = 'EUR') THEN
+            RETURN ($1.EUR + $2.amount, $1.USD);
+        ELSIF ($2.currency = 'USD') THEN
+            RETURN ($1.EUR, $1.USD + $2.amount);
+        ELSE
+            RAISE 'unknown currency %', $2.currency;
+        END IF;
+    END;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
+
+CREATE OPERATOR + (
+    leftarg = currency_basket,
+    rightarg = currency_amount,
+    procedure = currency_basket_add,
+    commutator = +
+);
+
+CREATE FUNCTION currency_basket_add(currency_basket, currency_basket)
+RETURNS currency_basket AS $$
+    BEGIN RETURN ($1.EUR + $2.EUR, $1.USD + $2.USD); END;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
+
+CREATE OPERATOR + (
+    leftarg = currency_basket,
+    rightarg = currency_basket,
+    procedure = currency_basket_add,
+    commutator = +
+);
+
+CREATE FUNCTION currency_basket_sub(currency_basket, currency_amount)
+RETURNS currency_basket AS $$
+    BEGIN
+        IF ($2.currency = 'EUR') THEN
+            RETURN ($1.EUR - $2.amount, $1.USD);
+        ELSIF ($2.currency = 'USD') THEN
+            RETURN ($1.EUR, $1.USD - $2.amount);
+        ELSE
+            RAISE 'unknown currency %', $2.currency;
+        END IF;
+    END;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
+
+CREATE OPERATOR - (
+    leftarg = currency_basket,
+    rightarg = currency_amount,
+    procedure = currency_basket_sub
+);
+
+CREATE FUNCTION currency_basket_sub(currency_basket, currency_basket)
+RETURNS currency_basket AS $$
+    BEGIN RETURN ($1.EUR - $2.EUR, $1.USD - $2.USD); END;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
+
+CREATE OPERATOR - (
+    leftarg = currency_basket,
+    rightarg = currency_basket,
+    procedure = currency_basket_sub
+);
+
+CREATE FUNCTION currency_basket_contains(currency_basket, currency_amount)
+RETURNS boolean AS $$
+    BEGIN
+        IF ($2.currency = 'EUR') THEN
+            RETURN ($1.EUR >= $2.amount);
+        ELSIF ($2.currency = 'USD') THEN
+            RETURN ($1.USD >= $2.amount);
+        ELSE
+            RAISE 'unknown currency %', $2.currency;
+        END IF;
+    END;
+$$ LANGUAGE plpgsql IMMUTABLE STRICT;
+
+CREATE OPERATOR >= (
+    leftarg = currency_basket,
+    rightarg = currency_amount,
+    procedure = currency_basket_contains
+);
+
+CREATE AGGREGATE basket_sum(currency_amount) (
+    sfunc = currency_basket_add,
+    stype = currency_basket,
+    initcond = '(0.00,0.00)'
+);
+
+
 -- Exchange rates
 
 CREATE TABLE currency_exchange_rates