module Internal.Budget (readBudget) where

import Control.Monad.Except
import Data.Decimal hiding (allocate)
import Data.Foldable
import Internal.Database
import Internal.Types.Main
import Internal.Utils
import RIO hiding (to)
import qualified RIO.List as L
import qualified RIO.Map as M
import qualified RIO.NonEmpty as NE
import qualified RIO.Text as T
import RIO.Time

readBudget
  :: (MonadInsertError m, MonadFinance m)
  => Budget
  -> m (Either CommitR [Tx CommitR])
readBudget
  b@Budget
    { bgtLabel
    , bgtIncomes
    , bgtTransfers
    , bgtShadowTransfers
    , bgtPretax
    , bgtTax
    , bgtPosttax
    , bgtInterval
    } =
    eitherHash CTBudget b return $ \key -> do
      spanRes <- getSpan
      case spanRes of
        Nothing -> return []
        Just budgetSpan -> do
          (intAllos, _) <- combineError intAlloRes acntRes (,)
          let res1 = mapErrors (readIncome key bgtLabel intAllos budgetSpan) bgtIncomes
          let res2 = expandTransfers key bgtLabel budgetSpan bgtTransfers
          txs <- combineError (concat <$> res1) res2 (++)
          shadow <- addShadowTransfers bgtShadowTransfers txs
          return $ txs ++ shadow
    where
      acntRes = mapErrors isNotIncomeAcnt alloAcnts
      intAlloRes = combineError3 pre_ tax_ post_ (,,)
      pre_ = sortAllos bgtPretax
      tax_ = sortAllos bgtTax
      post_ = sortAllos bgtPosttax
      sortAllos = liftExcept . mapErrors sortAllo
      alloAcnts =
        (alloAcnt <$> bgtPretax)
          ++ (alloAcnt <$> bgtTax)
          ++ (alloAcnt <$> bgtPosttax)
      getSpan = do
        globalSpan <- askDBState kmBudgetInterval
        case bgtInterval of
          Nothing -> return $ Just globalSpan
          Just bi -> do
            localSpan <- liftExcept $ resolveDaySpan bi
            return $ intersectDaySpan globalSpan localSpan

sortAllo :: MultiAllocation v -> InsertExcept (DaySpanAllocation v)
sortAllo a@Allocation {alloAmts = as} = do
  bs <- foldSpan [] $ L.sortOn amtWhen as
  return $ a {alloAmts = reverse bs}
  where
    foldSpan acc [] = return acc
    foldSpan acc (x : xs) = do
      let start = amtWhen x
      res <- case xs of
        [] -> resolveDaySpan start
        (y : _) -> resolveDaySpan_ (intStart $ amtWhen y) start
      foldSpan (x {amtWhen = res} : acc) xs

--------------------------------------------------------------------------------
-- Income

-- TODO this will scan the interval allocations fully each time
-- iteration which is a total waste, but the fix requires turning this
-- loop into a fold which I don't feel like doing now :(
readIncome
  :: (MonadInsertError m, MonadFinance m)
  => CommitR
  -> T.Text
  -> IntAllocations
  -> DaySpan
  -> Income
  -> m [Tx CommitR]
readIncome
  key
  name
  (intPre, intTax, intPost)
  ds
  Income
    { incWhen
    , incCurrency
    , incFrom = TaggedAcnt {taAcnt = srcAcnt, taTags = srcTags}
    , incPretax
    , incPosttax
    , incTaxes
    , incToBal = TaggedAcnt {taAcnt = destAcnt, taTags = destTags}
    , incGross
    , incPayPeriod
    , incPriority
    } =
    combineErrorM
      (combineError incRes nonIncRes (,))
      (combineError cpRes dayRes (,))
      $ \_ (cp, days) -> do
        let gross = realFracToDecimal (cpPrec cp) incGross
        foldDays (allocate cp gross) start days
    where
      incRes = isIncomeAcnt srcAcnt
      nonIncRes =
        mapErrors isNotIncomeAcnt $
          destAcnt
            : (alloAcnt <$> incPretax)
            ++ (alloAcnt <$> incTaxes)
            ++ (alloAcnt <$> incPosttax)
      cpRes = lookupCurrency incCurrency
      dayRes = liftExcept $ expandDatePat ds incWhen
      start = fromGregorian' $ pStart incPayPeriod
      pType' = pType incPayPeriod
      flatPre = concatMap flattenAllo incPretax
      flatTax = concatMap flattenAllo incTaxes
      flatPost = concatMap flattenAllo incPosttax
      sumAllos = sum . fmap faValue
      -- TODO ensure these are all the "correct" accounts
      allocate cp gross prevDay day = do
        scaler <- liftExcept $ periodScaler pType' prevDay day
        let precision = cpPrec cp
        let (preDeductions, pre) =
              allocatePre precision gross $
                flatPre ++ concatMap (selectAllos day) intPre
        let tax =
              allocateTax precision gross preDeductions scaler $
                flatTax ++ concatMap (selectAllos day) intTax
            aftertaxGross = gross - sumAllos (tax ++ pre)
        let post =
              allocatePost precision aftertaxGross $
                flatPost ++ concatMap (selectAllos day) intPost
        -- TODO double or rational here?
        let src =
              Entry
                { eAcnt = srcAcnt
                , eValue = ()
                , eComment = ""
                , eTags = srcTags
                }
        let dest =
              Entry
                { eAcnt = destAcnt
                , eValue = ()
                , eComment = "balance after deductions"
                , eTags = destTags
                }
        let allos = allo2Trans <$> (pre ++ tax ++ post)
        let primary =
              EntrySet
                { esTotalValue = gross
                , esCurrency = cpID cp
                , esFrom = HalfEntrySet {hesPrimary = src, hesOther = []}
                , esTo = HalfEntrySet {hesPrimary = dest, hesOther = allos}
                }
        return $
          Tx
            { txCommit = key
            , txDate = day
            , txPrimary = Left primary
            , txOther = []
            , txDescr = ""
            , txBudget = name
            , txPriority = incPriority
            }

periodScaler
  :: PeriodType
  -> Day
  -> Day
  -> InsertExcept PeriodScaler
periodScaler pt prev cur = return scale
  where
    n = workingDays wds prev cur
    wds = case pt of
      Hourly HourlyPeriod {hpWorkingDays} -> hpWorkingDays
      Daily ds -> ds
    scale prec x = case pt of
      Hourly HourlyPeriod {hpAnnualHours, hpDailyHours} ->
        realFracToDecimal prec (x / fromIntegral hpAnnualHours)
          * fromIntegral hpDailyHours
          * fromIntegral n
      Daily _ -> realFracToDecimal prec (x * fromIntegral n / 365.25)

-- ASSUME start < end
workingDays :: [Weekday] -> Day -> Day -> Natural
workingDays wds start end = fromIntegral $ daysFull + daysTail
  where
    interval = diffDays end start
    (nFull, nPart) = divMod interval 7
    daysFull = fromIntegral (length wds') * nFull
    daysTail = fromIntegral $ length $ takeWhile (< nPart) wds'
    startDay = dayOfWeek start
    wds' = L.sort $ (\x -> diff (fromWeekday x) startDay) <$> L.nub wds
    diff a b = fromIntegral $ mod (fromEnum a - fromEnum b) 7

-- ASSUME days is a sorted list
foldDays
  :: MonadInsertError m
  => (Day -> Day -> m a)
  -> Day
  -> [Day]
  -> m [a]
foldDays f start days = case NE.nonEmpty days of
  Nothing -> return []
  Just ds
    | any (start >) ds ->
        throwError $
          InsertException [PeriodError start $ minimum ds]
    | otherwise ->
        combineErrors $
          snd $
            L.mapAccumL (\prevDay day -> (day, f prevDay day)) start days

isIncomeAcnt :: (MonadInsertError m, MonadFinance m) => AcntID -> m ()
isIncomeAcnt = checkAcntType IncomeT

isNotIncomeAcnt :: (MonadInsertError m, MonadFinance m) => AcntID -> m ()
isNotIncomeAcnt = checkAcntTypes (AssetT :| [EquityT, ExpenseT, LiabilityT])

checkAcntType
  :: (MonadInsertError m, MonadFinance m)
  => AcntType
  -> AcntID
  -> m ()
checkAcntType t = checkAcntTypes (t :| [])

checkAcntTypes
  :: (MonadInsertError m, MonadFinance m)
  => NE.NonEmpty AcntType
  -> AcntID
  -> m ()
checkAcntTypes ts i = void $ go =<< lookupAccountType i
  where
    go t
      | t `L.elem` ts = return i
      | otherwise = throwError $ InsertException [AccountError i ts]

flattenAllo :: SingleAllocation v -> [FlatAllocation v]
flattenAllo Allocation {alloAmts, alloTo} = fmap go alloAmts
  where
    go Amount {amtValue, amtDesc} =
      FlatAllocation
        { faTo = alloTo
        , faValue = amtValue
        , faDesc = amtDesc
        }

-- ASSUME allocations are sorted
selectAllos :: Day -> DaySpanAllocation v -> [FlatAllocation v]
selectAllos day Allocation {alloAmts, alloTo} =
  go <$> filter ((`inDaySpan` day) . amtWhen) alloAmts
  where
    go Amount {amtValue, amtDesc} =
      FlatAllocation
        { faTo = alloTo
        , faValue = amtValue
        , faDesc = amtDesc
        }

allo2Trans :: FlatAllocation Decimal -> Entry AcntID LinkDeferred TagID
allo2Trans FlatAllocation {faValue, faTo = TaggedAcnt {taAcnt, taTags}, faDesc} =
  Entry
    { eValue = LinkDeferred (EntryFixed faValue)
    , eComment = faDesc
    , eAcnt = taAcnt
    , eTags = taTags
    }

allocatePre
  :: Precision
  -> Decimal
  -> [FlatAllocation PretaxValue]
  -> (M.Map T.Text Decimal, [FlatAllocation Decimal])
allocatePre precision gross = L.mapAccumR go M.empty
  where
    go m f@FlatAllocation {faValue = PretaxValue {preCategory, preValue, prePercent}} =
      let v =
            if prePercent
              then gross *. (preValue / 100)
              else realFracToDecimal precision preValue
       in (mapAdd_ preCategory v m, f {faValue = v})

allocateTax
  :: Precision
  -> Decimal
  -> M.Map T.Text Decimal
  -> PeriodScaler
  -> [FlatAllocation TaxValue]
  -> [FlatAllocation Decimal]
allocateTax precision gross preDeds f = fmap (fmap go)
  where
    go TaxValue {tvCategories, tvMethod} =
      let agi = gross - sum (mapMaybe (`M.lookup` preDeds) tvCategories)
       in case tvMethod of
            TMPercent p -> agi *. p / 100
            TMBracket TaxProgression {tpDeductible, tpBrackets} ->
              let taxDed = f precision tpDeductible
               in foldBracket f precision (agi - taxDed) tpBrackets

-- | Compute effective tax percentage of a bracket
-- The algorithm can be thought of in three phases:
-- 1. Find the highest tax bracket by looping backward until the AGI is less
--    than the bracket limit
-- 2. Computing the tax in the top bracket by subtracting the AGI from the
--    bracket limit and multiplying by the tax percentage.
-- 3. Adding all lower brackets, which are just the limit of the bracket less
--    the amount of the lower bracket times the percentage.
--
-- In reality, this can all be done with one loop, but it isn't clear these
-- three steps are implemented from this alone.
foldBracket :: PeriodScaler -> Precision -> Decimal -> [TaxBracket] -> Decimal
foldBracket f prec agi bs = fst $ foldr go (0, agi) $ L.sortOn tbLowerLimit bs
  where
    go TaxBracket {tbLowerLimit, tbPercent} a@(acc, remain) =
      let l = f prec tbLowerLimit
       in if remain >= l
            then (acc + (remain - l) *. (tbPercent / 100), l)
            else a

allocatePost
  :: Precision
  -> Decimal
  -> [FlatAllocation PosttaxValue]
  -> [FlatAllocation Decimal]
allocatePost prec aftertax = fmap (fmap go)
  where
    go PosttaxValue {postValue, postPercent}
      | postPercent = aftertax *. (postValue / 100)
      | otherwise = realFracToDecimal prec postValue

--------------------------------------------------------------------------------
-- shadow transfers

-- TODO this is going to be O(n*m), which might be a problem?
addShadowTransfers
  :: (MonadInsertError m, MonadFinance m)
  => [ShadowTransfer]
  -> [Tx CommitR]
  -> m [Tx CommitR]
addShadowTransfers ms = mapErrors go
  where
    go tx = do
      es <- catMaybes <$> mapErrors (fromShadow tx) ms
      return $ tx {txOther = Right <$> es}

fromShadow
  :: (MonadInsertError m, MonadFinance m)
  => Tx CommitR
  -> ShadowTransfer
  -> m (Maybe ShadowEntrySet)
fromShadow tx ShadowTransfer {stFrom, stTo, stDesc, stRatio, stCurrency, stMatch} = do
  cp <- lookupCurrency stCurrency
  res <- liftExcept $ shadowMatches stMatch tx
  let es = entryPair stFrom stTo (cpID cp) stDesc stRatio ()
  return $ if not res then Nothing else Just es

shadowMatches :: TransferMatcher -> Tx CommitR -> InsertExcept Bool
shadowMatches TransferMatcher {tmFrom, tmTo, tmDate, tmVal} Tx {txPrimary, txDate} = do
  -- NOTE this will only match against the primary entry set since those
  -- are what are guaranteed to exist from a transfer
  valRes <- case txPrimary of
    Left es -> valMatches tmVal $ toRational $ esTotalValue es
    Right _ -> return True
  return $
    memberMaybe fa tmFrom
      && memberMaybe ta tmTo
      && maybe True (`dateMatches` txDate) tmDate
      && valRes
  where
    fa = either getAcntFrom getAcntFrom txPrimary
    ta = either getAcntTo getAcntTo txPrimary
    getAcntFrom = getAcnt esFrom
    getAcntTo = getAcnt esTo
    getAcnt f = eAcnt . hesPrimary . f
    memberMaybe x AcntSet {asList, asInclude} =
      (if asInclude then id else not) $ x `elem` asList

--------------------------------------------------------------------------------
-- random

alloAcnt :: Allocation w v -> AcntID
alloAcnt = taAcnt . alloTo

type IntAllocations =
  ( [DaySpanAllocation PretaxValue]
  , [DaySpanAllocation TaxValue]
  , [DaySpanAllocation PosttaxValue]
  )

type DaySpanAllocation = Allocation DaySpan

type PeriodScaler = Precision -> Double -> Decimal

data FlatAllocation v = FlatAllocation
  { faValue :: !v
  , faDesc :: !T.Text
  , faTo :: !TaggedAcnt
  }
  deriving (Functor, Show)