bal: support --value-at in single column balance reports

hledger-lib/Hledger/Reports/BalanceReport.hs

@@ -4,7 +4,7 @@ Balance report, used by the balance command.
 
 -}
 
-{-# LANGUAGE FlexibleInstances, ScopedTypeVariables, OverloadedStrings #-}
+{-# LANGUAGE FlexibleInstances, RecordWildCards, ScopedTypeVariables, OverloadedStrings #-}
 
 module Hledger.Reports.BalanceReport (
   BalanceReport,
@@ -172,25 +172,41 @@ brNegate (is, tot) = (map brItemNegate is, -tot)
 -- | Convert all the posting amounts in a BalanceReport to their
 -- default valuation commodities. This means using the Journal's most
 -- recent applicable market prices before the valuation date.
--- The valuation date is the specified report end date if any,
--- otherwise the current date, otherwise the journal's end date.
+-- The valuation date is set with --value-at and can be:
+-- each posting's date,
+-- the last day in the report period (or in the journal if no period,
+-- or gives an error if journal is empty - shouldn't happen),
+-- or today's date (gives an error if today_ is not set in ReportOpts),
+-- or a specified date.
 brValue :: ReportOpts -> Journal -> BalanceReport -> BalanceReport
-brValue ropts j r =
-  let mvaluationdate = periodEnd (period_ ropts) <|> today_ ropts <|> journalEndDate False j
-  in case mvaluationdate of
-    Nothing -> r
-    Just d  -> r'
-      where
-        -- prices are in parse order - sort into date then parse order,
-        -- & reversed for quick lookup of the latest price.
-        prices = reverse $ sortOn mpdate $ jmarketprices j
-        (items,total) = r
-        r' =
-          dbg8 "market prices" prices `seq`
-          dbg8 "valuation date" d `seq`
-          dbg8 "brValue"
-            ([(n, n', i, mixedAmountValue prices d a) |(n,n',i,a) <- items], mixedAmountValue prices d total)
+brValue ropts@ReportOpts{..} j (items, total) =
+  ([ (n, n', i, mixedAmountValue prices d a) | (n,n',i,a) <- items ]
+  ,mixedAmountValue prices d total
+  )
+  where
+    -- prices are in parse order - sort into date then parse order,
+    -- & reversed for quick lookup of the latest price.
+    prices = reverse $ sortOn mpdate $ jmarketprices j
+    d = case value_at_ of
+      AtTransaction -> error' "sorry, --value-at=transaction is not yet supported with balance reports"  -- XXX
+      AtPeriod      -> fromMaybe (error' "brValue: expected a non-empty journal") mperiodorjournallastday  -- XXX shouldn't happen
+      AtNow         -> case today_ of
+                         Just d  -> d
+                         Nothing -> error' "brValue: ReportOpts today_ is unset so could not satisfy --value-at=now"
+      AtDate d      -> d
 
+    -- Get the last day of the report period.
+    -- Will be Nothing if no report period is specified, or also
+    -- if ReportOpts does not have today_ set, since we need that
+    -- to get the report period robustly.
+    mperiodlastday :: Maybe Day = do
+      t <- today_
+      let q = queryFromOpts t ropts
+      qend <- queryEndDate False q
+      return $ addDays (-1) qend
+
+    mperiodorjournallastday = mperiodlastday <|> journalEndDate False j
+    
 -- -- | Find the best commodity to convert to when asked to show the
 -- -- market value of this commodity on the given date. That is, the one
 -- -- in which it has most recently been market-priced, ie the commodity