prices: improve precision

bin/hledger-prices.hs

@@ -13,7 +13,7 @@ import Data.Maybe
 import Data.String.Here
 import Data.Time
 import qualified Data.Text as T
-import Control.Monad
+import Control.Monad (when)
 import Hledger.Cli
 
 ------------------------------------------------------------------------------
@@ -30,6 +30,13 @@ Print all prices from the journal.
 showPrice :: MarketPrice -> String
 showPrice mp = unwords ["P", show $ mpdate mp, T.unpack . quoteCommoditySymbolIfNeeded $ mpcommodity mp, showAmountWithZeroCommodity $ mpamount mp]
 
+divideAmount' :: Amount -> Quantity -> Amount
+divideAmount' a d = a' where
+    a' = (a `divideAmount` d) { astyle = style' }
+    style' = (astyle a) { asprecision = precision' }
+    extPrecision = (1+) . floor . logBase 10 $ (realToFrac d :: Double)
+    precision' = extPrecision + asprecision (astyle a)
+
 amountCost :: Day -> Amount -> Maybe MarketPrice
 amountCost d a =
     case aprice a of
@@ -37,7 +44,7 @@ amountCost d a =
         UnitPrice pa -> Just
             MarketPrice { mpdate = d, mpcommodity = acommodity a, mpamount = pa }
         TotalPrice pa -> Just
-            MarketPrice { mpdate = d, mpcommodity = acommodity a, mpamount = pa `divideAmount` abs (aquantity a) }
+            MarketPrice { mpdate = d, mpcommodity = acommodity a, mpamount = pa `divideAmount'` abs (aquantity a) }
 
 postingCosts :: Posting -> [MarketPrice]
 postingCosts p = mapMaybe (amountCost date) . amounts $ pamount p  where

tests/bin/prices.test

@@ -34,8 +34,13 @@ P 2016/2/1 EUR $1.05
 2016/1/2 spend
     expenses             20 EUR @ $1.07
     assets:bank
+
+2016/1/3 spend
+    expenses             20 EUR @@ $21.45
+    assets:bank
 >>>
 P 2016-01-02 EUR $1.07
+P 2016-01-03 EUR $1.0725
 P 2016-01-01 EUR $1.06
 P 2016-02-01 EUR $1.05
 >>>2