273 lines
12 KiB
Haskell
273 lines
12 KiB
Haskell
{-|
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Convert amounts to some related value in various ways. This involves
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looking up historical market prices (exchange rates) between commodities.
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-}
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{-# LANGUAGE NamedFieldPuns #-}
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE RecordWildCards #-}
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{-# LANGUAGE ScopedTypeVariables #-}
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module Hledger.Data.Valuation (
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amountValueAtDate
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,amountApplyValuation
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,mixedAmountValueAtDate
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,mixedAmountApplyValuation
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,marketPriceReverse
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,priceDirectiveToMarketPrice
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,priceLookup
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,tests_Valuation
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)
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where
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import Control.Applicative ((<|>))
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import Data.Decimal (roundTo)
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import Data.Function (on)
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import Data.Graph.Inductive (Gr, Node, NodeMap, mkMapGraph, mkNode, lab, out, sp)
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import Data.List
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-- import Data.List.Extra (nubSortBy)
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import qualified Data.Map as M
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import Data.Maybe
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import qualified Data.Text as T
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import Data.Time.Calendar (Day)
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import Safe (headMay)
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import Hledger.Utils
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import Hledger.Data.Types
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import Hledger.Data.Amount
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import Hledger.Data.Dates (parsedate)
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tests_Valuation = tests "Valuation" [
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tests_priceLookup
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]
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------------------------------------------------------------------------------
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-- Valuation
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-- Apply a specified valuation to this mixed amount, using the provided
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-- prices db, commodity styles, period-end/current dates,
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-- and whether this is for a multiperiod report or not.
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mixedAmountApplyValuation :: [PriceDirective] -> M.Map CommoditySymbol AmountStyle -> Day -> Day -> Bool -> ValuationType -> MixedAmount -> MixedAmount
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mixedAmountApplyValuation prices styles periodend today ismultiperiod v (Mixed as) =
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Mixed $ map (amountApplyValuation prices styles periodend today ismultiperiod v) as
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-- | Find the market value of each component amount in the given
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-- commodity, or its default valuation commodity, at the given
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-- valuation date, using the given market prices.
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-- When market prices available on that date are not sufficient to
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-- calculate the value, amounts are left unchanged.
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mixedAmountValueAtDate :: [PriceDirective] -> M.Map CommoditySymbol AmountStyle -> Maybe CommoditySymbol -> Day -> MixedAmount -> MixedAmount
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mixedAmountValueAtDate prices styles mc d (Mixed as) = Mixed $ map (amountValueAtDate prices styles mc d) as
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-- | Apply a specified valuation to this amount, using the provided
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-- prices db, commodity styles, period-end/current dates,
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-- and whether this is for a multiperiod report or not.
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amountApplyValuation :: [PriceDirective] -> M.Map CommoditySymbol AmountStyle -> Day -> Day -> Bool -> ValuationType -> Amount -> Amount
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amountApplyValuation prices styles periodend today ismultiperiod v a =
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case v of
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AtCost Nothing -> amountToCost styles a
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AtCost mc -> amountValueAtDate prices styles mc periodend $ amountToCost styles a
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AtEnd mc -> amountValueAtDate prices styles mc periodend a
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AtNow mc -> amountValueAtDate prices styles mc today a
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AtDefault mc | ismultiperiod -> amountValueAtDate prices styles mc periodend a
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AtDefault mc -> amountValueAtDate prices styles mc today a
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AtDate d mc -> amountValueAtDate prices styles mc d a
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-- | Find the market value of this amount in the given valuation
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-- commodity if any, otherwise the default valuation commodity, at the
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-- given valuation date. (The default valuation commodity is the
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-- commodity of the latest applicable market price before the
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-- valuation date.)
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--
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-- The returned amount will have its commodity's canonical style applied,
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-- but with the precision adjusted to show all significant decimal digits
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-- up to a maximum of 8. (experimental)
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--
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-- If the market prices available on that date are not sufficient to
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-- calculate this value, the amount is left unchanged.
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amountValueAtDate :: [PriceDirective] -> M.Map CommoditySymbol AmountStyle -> Maybe CommoditySymbol -> Day -> Amount -> Amount
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amountValueAtDate pricedirectives styles mto d a =
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case priceLookup pricedirectives d (acommodity a) mto of
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Nothing -> a
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Just (comm, rate) ->
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-- setNaturalPrecisionUpTo 8 $ -- XXX force higher precision in case amount appears to be zero ?
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-- Make default display style use precision 2 instead of 0 ?
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-- Leave as is for now; mentioned in manual.
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styleAmount styles
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amount{acommodity=comm, aquantity=rate * aquantity a}
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------------------------------------------------------------------------------
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-- Building a price graph
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-- | Convert a list of market price directives in parse order to a
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-- graph of all prices in effect on a given day, allowing efficient
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-- lookup of exchange rates between commodity pairs.
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pricesAtDate :: [PriceDirective] -> Day -> PriceGraph
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pricesAtDate pricedirectives d = PriceGraph{prGraph=g, prNodemap=m, prDeclaredPairs=dps}
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where
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-- build the graph and associated node map
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(g :: Gr CommoditySymbol Quantity, m :: NodeMap CommoditySymbol) =
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mkMapGraph
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(dbg5 "g nodelabels" $ sort allcomms) -- this must include all nodes mentioned in edges
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(dbg5 "g edges" $ [(mpfrom, mpto, mprate) | MarketPrice{..} <- prices])
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where
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prices = declaredprices ++ reverseprices
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allcomms = map mpfrom prices
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-- get the latest (on or before date d) declared price for each commodity pair
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declaredprices :: [MarketPrice] =
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dbg5 "declaredprices" $
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-- XXX Data.List.Extra.nubSortBy might be more efficient (n Log n vs n^2 ?)
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-- but is not in ghc 7.10, 8.0 stackage snapshots
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nub $ sortBy (compare `on` (\(MarketPrice{..})->(mpfrom,mpto))) $ -- keep only the first (ie newest and latest parsed) price for each pair
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map snd $ -- discard the parse order label
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sortBy (flip compare `on` (\(parseorder,mp)->(mpdate mp,parseorder))) $ -- sort with newest dates and latest parse order first
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zip [1..] $ -- label with parse order
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map priceDirectiveToMarketPrice $
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filter ((<=d).pddate) pricedirectives -- consider only price declarations up to the valuation date
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-- infer additional reverse prices where not already declared
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reverseprices =
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dbg5 "reverseprices" $
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map marketPriceReverse declaredprices \\ declaredprices
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-- remember which edges correspond to declared prices
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dps = [(node m mpfrom, node m mpto) | MarketPrice{..} <- declaredprices ]
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priceDirectiveToMarketPrice :: PriceDirective -> MarketPrice
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priceDirectiveToMarketPrice PriceDirective{..} =
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MarketPrice{ mpdate = pddate
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, mpfrom = pdcommodity
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, mpto = acommodity pdamount
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, mprate = aquantity pdamount
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}
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marketPriceReverse :: MarketPrice -> MarketPrice
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marketPriceReverse mp@MarketPrice{..} = mp{mpfrom=mpto, mpto=mpfrom, mprate=1/mprate}
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------------------------------------------------------------------------------
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-- Market price lookup
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tests_priceLookup =
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let
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d = parsedate
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a q c = amount{acommodity=c, aquantity=q}
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p date from q to = PriceDirective{pddate=d date, pdcommodity=from, pdamount=a q to}
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ps1 = [
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p "2000/01/01" "A" 10 "B"
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,p "2000/01/01" "B" 10 "C"
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,p "2000/01/01" "C" 10 "D"
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,p "2000/01/01" "E" 2 "D"
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,p "2001/01/01" "A" 11 "B"
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]
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in tests "priceLookup" [
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priceLookup ps1 (d "1999/01/01") "A" Nothing `is` Nothing
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,priceLookup ps1 (d "2000/01/01") "A" Nothing `is` Just ("B",10)
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,priceLookup ps1 (d "2000/01/01") "B" (Just "A") `is` Just ("A",0.1)
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,priceLookup ps1 (d "2000/01/01") "A" (Just "E") `is` Just ("E",500)
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]
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-- | Given a list of price directives in parse order, find the market
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-- value at the given date of one unit of a given source commodity, in
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-- a different specified valuation commodity, or a default valuation
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-- commodity.
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--
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-- When the valuation commodity is specified, this looks for, in order:
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--
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-- - a price declaration giving the exchange rate from source
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-- commodity to valuation commodity ("declared price").
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--
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-- - a price declaration from valuation to source commodity, which
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-- gets inverted ("reverse price").
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--
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-- - the shortest chain of prices (declared or reverse) leading from
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-- source commodity to valuation commodity, which gets collapsed
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-- into a single synthetic exchange rate ("indirect price").
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--
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-- When the valuation commodity is not specified, this looks for the
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-- latest applicable declared price, and converts to the commodity
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-- mentioned in that price (the default valuation commodity).
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--
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-- Note this default valuation commodity can vary across successive
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-- calls for different dates, since it depends on the price
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-- declarations in each period.
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--
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-- This returns the valuation commodity that was specified or
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-- inferred, and the quantity of it that one unit of the source
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-- commodity is worth. Or if no applicable market price or chain of
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-- prices can be found, or the source commodity and the valuation
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-- commodity are the same, returns Nothing.
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--
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-- A 'PriceGraph' is built each time this is called, which is probably
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-- wasteful when looking up multiple prices on the same day; it could
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-- be built at a higher level, or memoised.
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--
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priceLookup :: [PriceDirective] -> Day -> CommoditySymbol -> Maybe CommoditySymbol -> Maybe (CommoditySymbol, Quantity)
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priceLookup pricedirectives d from mto =
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let
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-- build a graph of the commodity exchange rates in effect on this day
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-- XXX should hide these fgl details better
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PriceGraph{prGraph=g, prNodemap=m, prDeclaredPairs=dps} = pricesAtDate pricedirectives d
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fromnode = node m from
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mto' = mto <|> mdefaultto
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where
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-- If to is unspecified, try to pick a default valuation commodity from declared prices (only).
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-- XXX how to choose ? Take lowest sorted ?
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-- Take first, hoping current order is useful ? <-
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-- Keep parse order in label and take latest parsed ?
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mdefaultto =
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dbg4 ("default valuation commodity for "++T.unpack from) $
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headMay [t | (f,t,_) <- out g fromnode, (f,t) `elem` dps] >>= lab g
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in
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case mto' of
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Nothing -> Nothing
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Just to | to==from -> Nothing
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Just to ->
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-- We have a commodity to convert to. Find the most direct price available.
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case mindirectprice of
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Nothing -> Nothing
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Just q -> Just (to, q)
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where
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tonode = node m to
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mindirectprice :: Maybe Quantity =
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-- Find the shortest path, if any, between from and to.
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case sp fromnode tonode g :: Maybe [Node] of
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Nothing -> Nothing
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Just nodes ->
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dbg ("market price "++intercalate "->" (map T.unpack comms)) $
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Just $ product $ pathEdgeLabels g nodes -- convert to a single exchange rate
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where comms = catMaybes $ map (lab g) nodes
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-- log a message and a Maybe Quantity, hiding Just/Nothing and limiting decimal places
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dbg msg = dbg4With (((msg++": ")++) . maybe "" (show . roundTo 8))
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------------------------------------------------------------------------------
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-- fgl helpers
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-- | Look up an existing graph node by its label.
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-- (If the node does not exist, a new one will be generated, but not
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-- persisted in the nodemap.)
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node :: Ord a => NodeMap a -> a -> Node
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node m = fst . fst . mkNode m
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-- | Convert a valid path within the given graph to the corresponding
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-- edge labels. When there are multiple edges between two nodes, the
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-- lowest-sorting label is used.
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pathEdgeLabels :: (Show b, Ord b) => Gr a b -> [Node] -> [b]
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pathEdgeLabels g = map frommaybe . map (nodesEdgeLabel g) . pathEdges
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where frommaybe = fromMaybe (error' "pathEdgeLabels: expected no Nothings here")
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-- | Convert a path to node pairs representing the path's edges.
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pathEdges :: [Node] -> [(Node,Node)]
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pathEdges p = [(f,t) | f:t:_ <- tails p]
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-- | Get the label of a graph edge from one node to another.
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-- When there are multiple such edges, the lowest-sorting label is used.
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nodesEdgeLabel :: Ord b => Gr a b -> (Node, Node) -> Maybe b
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nodesEdgeLabel g (from,to) = headMay $ sort [l | (_,t,l) <- out g from, t==to]
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------------------------------------------------------------------------------
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