From 54ee68976b193aadc024e3318cab362f93654c17 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Sat, 22 Nov 2008 20:32:58 +0000
Subject: [PATCH] support converting amounts to cost, using their saved price.
 And do this by default for auto-balancing transactions, as ledger seems to.

---
 Ledger/Amount.hs | 12 ++++++++++++
 Ledger/Entry.hs  |  5 +++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/Ledger/Amount.hs b/Ledger/Amount.hs
index 1843afc7b..ff43cd0ec 100644
--- a/Ledger/Amount.hs
+++ b/Ledger/Amount.hs
@@ -71,6 +71,14 @@ amountop :: (Double -> Double -> Double) -> Amount -> Amount -> Amount
 amountop op a@(Amount ac aq ap) b@(Amount bc bq bp) = 
     Amount bc ((quantity $ convertAmountTo bc a) `op` bq) Nothing
 
+-- | Convert an amount to the commodity of its saved price, if any.
+costOfAmount :: Amount -> Amount
+costOfAmount a@(Amount _ _ Nothing) = a
+costOfAmount a@(Amount _ q (Just price))
+    | isZeroMixedAmount price = nullamt
+    | otherwise = Amount pc (pq*q) Nothing
+    where (Amount pc pq _) = head $ amounts price
+
 -- | Convert an amount to the specified commodity using the appropriate
 -- exchange rate (which is currently always 1).
 convertAmountTo :: Commodity -> Amount -> Amount
@@ -137,6 +145,10 @@ normaliseMixedAmount (Mixed as) = Mixed $ map sum $ grouped
       symbols = sort $ nub $ map (symbol . commodity) as
       hassymbol s a = s == (symbol $ commodity a)
 
+-- | Convert a mixed amount's component amounts to the commodity of their
+-- saved price, if any.
+costOfMixedAmount :: MixedAmount -> MixedAmount
+costOfMixedAmount (Mixed as) = Mixed $ map costOfAmount as
 
 -- | The empty simple amount.
 nullamt :: Amount
diff --git a/Ledger/Entry.hs b/Ledger/Entry.hs
index eda52d45a..82367cedb 100644
--- a/Ledger/Entry.hs
+++ b/Ledger/Entry.hs
@@ -76,8 +76,9 @@ isEntryBalanced (Entry {etransactions=ts}) =
 -- | Fill in a missing balance in this entry, if we have enough
 -- information to do that. Excluding virtual transactions, there should be
 -- at most one missing balance. Otherwise, raise an error.
+-- The new balance will be converted to cost basis if possible.
 balanceEntry :: Entry -> Entry
-balanceEntry e@(Entry{etransactions=ts}) = e{etransactions=ts'}
+balanceEntry e@Entry{etransactions=ts} = e{etransactions=ts'}
     where 
       (withamounts, missingamounts) = partition hasAmount $ filter isReal ts
       ts' = case (length missingamounts) of
@@ -86,5 +87,5 @@ balanceEntry e@(Entry{etransactions=ts}) = e{etransactions=ts'}
               otherwise -> error $ "could not balance this entry, too many missing amounts:\n" ++ show e
       otherstotal = sum $ map tamount withamounts
       balance t
-          | isReal t && not (hasAmount t) = t{tamount = -otherstotal}
+          | isReal t && not (hasAmount t) = t{tamount = costOfMixedAmount (-otherstotal)}
           | otherwise = t