#!/usr/bin/env runhaskell
-- | Calculations for FIRE (financial independence, retire early)
module Main where
import Hledger
import Data.Decimal (DecimalRaw, roundTo)
import Data.Either (fromRight)
import Data.Time.Calendar (Day)
import Data.Time.Clock (UTCTime(utctDay), getCurrentTime)
import Data.Text (pack)

main = do
  j <- getJournal
  today <- getCurrentTime >>= return . utctDay
  say ["savings rate:", show $ savingsRate j today]
  say ["target fund:", show $ targetFund j today]
  say ["when free:", show $ whenFreedom j today]

say = putStrLn . unwords

getJournal :: IO Journal
getJournal = do
  jp <- defaultJournalPath
  let opts = definputopts { auto_ = True }
  ej <- readJournalFile opts jp
  return $ fromRight undefined ej

-- | Helper for getting the total out of a balance report.
getTotal :: Journal -> Day -> String -> Quantity
getTotal j d q = head $ map aquantity $ total
  where
    opts = defreportopts { balancetype_ = CumulativeChange }
    (query, _) = parseQuery d $ pack q
    (_, (Mixed total)) = balanceReport opts query j

-- | These are the accounts that I consider a part of my savings and not my
-- cash-spending accounts.
savingsAccounts :: [String]
savingsAccounts =
  [ "as:me:save", "as:me:vest" ]

-- | Savings rate is a FIRE staple. Basically take your savings and divide it by
-- your income on a monthly basis.
--
savingsRate :: Journal -> Day -> Quantity
savingsRate j d = roundTo 2 $ monthlySavings / monthlyIncome
  where
    monthlySavings = sum $ map (getTotal j d) $ map appendMonthly savingsAccounts
    appendMonthly s = s ++ " --monthly"
    monthlyIncome = getTotal j d "^in --monthly"

-- | The target fund is simply 25x your annual expenditure.
--
-- This is going to be incomplete until I have a full year of
-- expenses.. currently, I just use my most recent quarter times 4 as a proxy
-- for the yearly expenses.
--
-- Assumptions: 4% withdrawal rate, 3-5% return on investments.
--
targetFund :: Journal -> Day -> Quantity
targetFund j d = 25 * yearlyExpenses
  where
    yearlyExpenses = 4 * quarterlyExpenses
    quarterlyExpenses = sum $ map aquantity $ total
    (query, _) = parseQuery d $ pack "^ex -p thisquarter --forecast cur:USD"
    (_, (Mixed total)) = balanceReport opts query j
    opts = defreportopts

-- | How long until I can live off of my savings and investment returns?
--
-- Return integer is number of months until I'm free.
--
whenFreedom :: Journal -> Day -> Quantity
whenFreedom j d = roundTo 1 $ targetFund j d / monthlySavings
  where
    monthlySavings = sum $ map (getTotal j d) $ map appendMonthly savingsAccounts
    appendMonthly s = s ++ " --monthly"