54 lines
1.5 KiB
Haskell
54 lines
1.5 KiB
Haskell
{-|
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Find historical exchange rates between two commodities.
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-}
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE RecordWildCards #-}
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module Hledger.Data.Prices (
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Prices
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,nullPrices
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,toPrices
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,priceLookup
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,tests_Prices
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)
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where
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import Data.List
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import qualified Data.Text as T
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import Data.Time.Calendar (Day)
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import Hledger.Utils
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import Hledger.Data.Types
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-- | A database of historical market prices for multiple commodites,
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-- allowing fast lookup of exchange rates between commodity pairs on a
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-- given date.
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data Prices = Prices {
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prPrices :: [MarketPrice] -- ^ For now, just a list of price declarations sorted by date then parse order.
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}
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nullPrices = toPrices []
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-- | Convert a list of market prices in declaration order to a 'Prices' db.
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toPrices :: [MarketPrice] -> Prices
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toPrices declaredprices = Prices{prPrices = reverse $ sortOn mpdate declaredprices}
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-- | Find the market value of one unit of the given commodity on the
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-- given date in its default valuation commodity (the commodity of the
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-- latest applicable price before the valuation date).
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-- Returns Nothing if there's no applicable price.
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priceLookup :: Prices -> Day -> CommoditySymbol -> Maybe Amount
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priceLookup Prices{..} valuationdate c =
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case filter (\MarketPrice{..} -> mpcommodity==c && mpdate<=valuationdate) prPrices of
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[] -> dbg Nothing
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ps' -> dbg $ Just $ mpamount $ head ps'
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where
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dbg = dbg8 ("using market price for "++T.unpack c)
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tests_Prices = tests "Prices" [
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]
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