{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE CPP #-}
{-|

A 'TransactionModifier' is a rule that modifies certain 'Transaction's,
typically adding automated postings to them. 

-}
module Hledger.Data.TransactionModifier (
    transactionModifierToFunction
)
where

import Data.Maybe
#if !(MIN_VERSION_base(4,11,0))
import Data.Monoid ((<>))
#endif
import qualified Data.Text as T
import Data.Time.Calendar
import Hledger.Data.Types
import Hledger.Data.Dates
import Hledger.Data.Amount
import Hledger.Data.Transaction
import Hledger.Query
import Hledger.Utils.UTF8IOCompat (error')
import Hledger.Utils.Debug

-- $setup
-- >>> :set -XOverloadedStrings
-- >>> import Hledger.Data.Posting
-- >>> import Hledger.Data.Transaction
-- >>> import Hledger.Data.Journal

-- | Converts a 'TransactionModifier' to a 'Transaction'-transforming function,
-- which applies the modification(s) specified by the TransactionModifier.
-- Currently this means adding automated postings when certain other postings are present.
-- The postings of the transformed transaction will reference it in the usual 
-- way (ie, 'txnTieKnot' is called).
--
-- >>> putStr $ showTransaction $ transactionModifierToFunction (TransactionModifier "" ["pong" `post` usd 2]) nulltransaction{tpostings=["ping" `post` usd 1]}
-- 0000/01/01
--     ping           $1.00
--     pong           $2.00
-- <BLANKLINE>
-- >>> putStr $ showTransaction $ transactionModifierToFunction (TransactionModifier "miss" ["pong" `post` usd 2]) nulltransaction{tpostings=["ping" `post` usd 1]}
-- 0000/01/01
--     ping           $1.00
-- <BLANKLINE>
-- >>> putStr $ showTransaction $ transactionModifierToFunction (TransactionModifier "ping" ["pong" `post` amount{amultiplier=True, aquantity=3}]) nulltransaction{tpostings=["ping" `post` usd 2]}
-- 0000/01/01
--     ping           $2.00
--     pong           $6.00
-- <BLANKLINE>
--
transactionModifierToFunction :: TransactionModifier -> (Transaction -> Transaction)
transactionModifierToFunction mt = 
  \t@(tpostings -> ps) -> txnTieKnot t{ tpostings=generatePostings ps } -- TODO add modifier txn comment/tags ?
  where
    q = simplifyQuery $ tmParseQuery mt (error' "a transaction modifier's query cannot depend on current date")
    mods = map tmPostingRuleToFunction $ tmpostingrules mt
    generatePostings ps = [p' | p <- ps
                              , p' <- if q `matchesPosting` p then p:[ m p | m <- mods] else [p]]
    
-- | Parse the 'Query' from a 'TransactionModifier's 'tmquerytxt', 
-- and return it as a function requiring the current date. 
--
-- >>> tmParseQuery (TransactionModifier "" []) undefined
-- Any
-- >>> tmParseQuery (TransactionModifier "ping" []) undefined
-- Acct "ping"
-- >>> tmParseQuery (TransactionModifier "date:2016" []) undefined
-- Date (DateSpan 2016)
-- >>> tmParseQuery (TransactionModifier "date:today" []) (read "2017-01-01")
-- Date (DateSpan 2017/01/01)
tmParseQuery :: TransactionModifier -> (Day -> Query)
tmParseQuery mt = fst . flip parseQuery (tmquerytxt mt)

-- | Converts a 'TransactionModifier''s posting rule to a 'Posting'-generating function,
-- which will be used to make a new posting based on the old one (an "automated posting").
-- The new posting's amount can optionally be the old posting's amount multiplied by a constant.
-- If the old posting had a total-priced amount, the new posting's multiplied amount will be unit-priced. 
tmPostingRuleToFunction :: TMPostingRule -> (Posting -> Posting)
tmPostingRuleToFunction pr = 
  \p -> renderPostingCommentDates $ pr
      { pdate = pdate p
      , pdate2 = pdate2 p
      , pamount = amount' p
      }
  where
    amount' = case postingRuleMultiplier pr of
        Nothing -> const $ pamount pr
        Just n  -> \p ->
          -- Multiply the old posting's amount by the posting rule's multiplier.
          let
            pramount = dbg6 "pramount" $ head $ amounts $ pamount pr
            matchedamount = dbg6 "matchedamount" $ pamount p
            -- Handle a matched amount with a total price carefully so as to keep the transaction balanced (#928).
            -- Approach 1: convert to a unit price and increase the display precision slightly
            -- Mixed as = dbg6 "multipliedamount" $ n `multiplyMixedAmount` mixedAmountTotalPriceToUnitPrice matchedamount 
            -- Approach 2: multiply the total price (keeping it positive) as well as the quantity 
            Mixed as = dbg6 "multipliedamount" $ n `multiplyMixedAmountAndPrice` matchedamount 
          in
            case acommodity pramount of
              "" -> Mixed as
              -- TODO multipliers with commodity symbols are not yet a documented feature.
              -- For now: in addition to multiplying the quantity, it also replaces the 
              -- matched amount's commodity, display style, and price with those of the posting rule.   
              c  -> Mixed [a{acommodity = c, astyle = astyle pramount, aprice = aprice pramount} | a <- as]

postingRuleMultiplier :: TMPostingRule -> Maybe Quantity
postingRuleMultiplier p =
    case amounts $ pamount p of
        [a] | amultiplier a -> Just $ aquantity a
        _                   -> Nothing

renderPostingCommentDates :: Posting -> Posting
renderPostingCommentDates p = p { pcomment = comment' }
    where
        datesComment = T.concat $ catMaybes [T.pack . showDate <$> pdate p, ("=" <>) . T.pack . showDate <$> pdate2 p]
        comment'
            | T.null datesComment = pcomment p
            | otherwise = T.intercalate "\n" $ filter (not . T.null) [T.strip $ pcomment p, "[" <> datesComment <> "]"]