hledger scripting exercise

average-cashflow.hs

#!/usr/bin/env runhaskell
{-
Print monthly average cashflow by account.

$ average-cashflow.hs YEAR [JOURNALFILE]

-}

module Main where

import Hledger
import Data.Maybe (catMaybes)
import Control.Monad (forM_)
import Text.Printf (printf)
import Safe (headDef)
import System.Environment (getArgs)

-- needs Hledger.Data.Dates spanFromSmartDate
matchMonth y m = Date $ spanFromSmartDate nulldate (show y, show m, "")

allOneCommodity = all (\(Mixed as) -> let c = acommodity $ head as in all ((==c).acommodity) as)

averageMixedAmounts ms
  | null ms = mixed $ num 0
  | allOneCommodity ms = let Mixed [a@Amount{aquantity=q}] = sum ms in Mixed [a{aquantity=q / fromIntegral (length ms)}]
  | otherwise = error "Can't calculate the average of multi-commodity amounts."

main = do
  -- parse args
  year:rest <- getArgs
  deffile <- defaultJournalPath
  let file = headDef deffile rest
  -- read file
  j <- readJournalFile Nothing Nothing file >>= either error' return
  -- calculate averages
  let accts = journalAccountNames j
      months = [1..12]
      acctbalsbymonth = [(m, map (\(a,_,_,bal)->(a,bal)) $ fst $ accountsReport defreportopts (matchMonth year m) j) | m <- months]
      monthlyBalsForAcct a = catMaybes [lookup a monthbals | (_,monthbals) <- acctbalsbymonth]
      averagebalbyacct = [(a, averageMixedAmounts $ monthlyBalsForAcct a) | a <- accts]
  -- display report
  printf "Average monthly cashflow by account in %s\n" year
  forM_ averagebalbyacct $ \(a,b) -> printf "%12s  %s\n" (showMixedAmount b) a