Use date for market currency conversion

Author: Evernight

src/fava_portfolio_returns/api/investments.py

@@ -18,7 +18,7 @@
 
 def group_stats(p: FilteredPortfolio, start_date: datetime.date, end_date: datetime.date):
     balance = p.balance_at(end_date)
-    cost_value = cost_value_of_inv(p.pricer, p.target_currency, balance)
+    cost_value = cost_value_of_inv(p.pricer, p.target_currency, balance, end_date)
     market_value = market_value_of_inv(p.pricer, p.target_currency, balance, end_date, record=True)
     # reduce to units (i.e. removing cost attribute) after calculating market value, because convert.get_value() only works with positions held at cost
     # this will convert for example CORP -> USD (cost currency) -> EUR (target currency), instead of CORP -> EUR.

src/fava_portfolio_returns/api/portfolio.py

@@ -61,6 +61,9 @@ def portfolio_values(
             if posting.meta["category"] is Cat.ASSET and posting.cost:
                 # ex. (CORP, USD)
                 currency_pairs.add((posting.units.currency, posting.cost.currency))
+                # also add data points for indirect conversion to target currency
+                if posting.cost.currency != p.target_currency:
+                    currency_pairs.add((posting.cost.currency, p.target_currency))
 
     def first(x):
         return x[0]
@@ -112,8 +115,8 @@ def first(x):
             # Clamp start_date in case we cut off data at the beginning.
             clamp_date = max(date, start_date)
             market = market_value_of_inv(p.pricer, p.target_currency, balance, clamp_date)
-            cost = cost_value_of_inv(p.pricer, p.target_currency, balance)
-            cash = -inv_to_currency(p.pricer, p.target_currency, cf_balance)  # sum of cash flows
+            cost = cost_value_of_inv(p.pricer, p.target_currency, balance, clamp_date)
+            cash = -inv_to_currency(p.pricer, p.target_currency, cf_balance, clamp_date)  # sum of cash flows
             values.append(PortfolioValue(date=clamp_date, market=market, cost=cost, cash=cash))
 
     return values

src/fava_portfolio_returns/core/currencies_test.py

@@ -0,0 +1,59 @@
+import datetime
+import unittest
+
+from fava_portfolio_returns.returns.simple import SimpleReturns
+from fava_portfolio_returns.test.test import BEANGROW_CONFIG_CORP
+from fava_portfolio_returns.test.test import load_portfolio_str
+
+from fava_portfolio_returns.test.test import approx2
+
+class CurrenciesTest(unittest.TestCase):
+    def test_indirect_currency_conversion(self):
+        p = load_portfolio_str(
+            """
+plugin "beancount.plugins.auto_accounts"
+plugin "beancount.plugins.implicit_prices"
+
+2020-01-01 commodity CORP
+  name: "Example Stock"
+
+2020-01-01 commodity CURRENCY_BASE
+2020-01-01 commodity CURRENCY_TARGET
+
+2020-01-01 price CURRENCY_BASE  2 CURRENCY_TARGET
+
+2020-01-01 * "Buy 100 CORP @ 2 CURRENCY_BASE"
+  Assets:Cash                           -100.00 CURRENCY_BASE
+  Assets:CORP                                50 CORP {2 CURRENCY_BASE}
+
+2020-01-04 price CURRENCY_BASE 3 CURRENCY_TARGET
+
+2020-02-01 price CORP  3 CURRENCY_BASE
+2020-03-03 price CURRENCY_BASE  5 CURRENCY_TARGET
+            """,
+            BEANGROW_CONFIG_CORP,
+        )
+        p.target_currency = 'CURRENCY_TARGET'
+
+        # Cost basis of 100 CURRENCY_BASE = 200 CURRENCY_TARGET
+        assert p.cash_at(datetime.date(2020, 1, 1)) == 200 
+        # Cost basis of 100 CURRENCY_BASE = 300 CURRENCY_TARGET
+        assert p.cash_at(datetime.date(2020, 1, 5)) == 300
+        # Cost basis of 100 CURRENCY_BASE = 300 CURRENCY_TARGET
+        assert p.cash_at(datetime.date(2020, 2, 1)) == 300
+        # Cost basis of 100 CURRENCY_BASE = 500 CURRENCY_TARGET
+        assert p.cash_at(datetime.date(2020, 3, 3)) == 500
+
+        returns = SimpleReturns().series(p, datetime.date(2020, 1, 1), datetime.date(2020, 4, 1))
+        assert returns == [
+            # 200 CURRENCY_TARGET = 100 CURRENCY_BASE invested
+            (datetime.date(2020, 1, 1), 0.0),
+            # currency rate changing doesn't change the cost basis 
+            # (300 CURRENCY_TARGET invested)
+            (datetime.date(2020, 1, 4), 0.0),
+            # investment has acrually grown
+            # (300 CURRENCY_TARGET invested, 50 CORP valued at 150 CURRENCY_BASE = 450 CURRENCY_TARGET)
+            (datetime.date(2020, 2, 1), 0.5),
+            # currency rate changing again doesn't change the cost basis (500 CURRENCY_TARGET invested)
+            (datetime.date(2020, 3, 3), 0.5),
+        ]

src/fava_portfolio_returns/core/portfolio.py

@@ -176,7 +176,7 @@ def cash_at(self, date: datetime.date) -> Decimal:
                 if cash_flow.date > date:
                     break
                 balance.add_amount(cash_flow.amount)
-        return -inv_to_currency(self.pricer, self.target_currency, balance)
+        return -inv_to_currency(self.pricer, self.target_currency, balance, date)
 
 
 def get_target_currency(account_data_list: list[AccountData]) -> str:

src/fava_portfolio_returns/core/utils.py

@@ -20,9 +20,9 @@ def __init__(self, source: str, target: str, date: Optional[datetime.date]):
         )
 
 
-def cost_value_of_inv(pricer: Pricer, target_currency: str, balance: Inventory) -> Decimal:
+def cost_value_of_inv(pricer: Pricer, target_currency: str, balance: Inventory, date: datetime.date) -> Decimal:
     cost_balance = balance.reduce(convert.get_cost)
-    return inv_to_currency(pricer, target_currency, cost_balance)
+    return inv_to_currency(pricer, target_currency, cost_balance, date)
 
 
 def market_value_of_inv(
@@ -36,7 +36,7 @@ def market_value_of_inv(
         value_balance = balance.reduce(convert.get_value, pricer.price_map, date)
 
     # then convert to target currency
-    return inv_to_currency(pricer, target_currency, value_balance)
+    return inv_to_currency(pricer, target_currency, value_balance, date)
 
 
 def inv_to_currency(
@@ -71,4 +71,7 @@ def get_prices(pricer: Pricer, pair: tuple[str, str]) -> list[tuple[datetime.dat
     """
     :param tuple pair:  (currency, target_currency), e.g. (CORP, USD)
     """
-    return prices.get_all_prices(pricer.price_map, pair)
+    try:
+        return prices.get_all_prices(pricer.price_map, pair)
+    except:
+        raise ValueError(f"Missing prices for currency pair {pair}")