-----------------------------------------------------------------------------
--
-- Module      :  QifParser
-- Copyright   :  (c) Jonathan Kochems
-- License     :  BSD3
--
-- Maintainer  :  Jonathan Kochems <jonathan.kochems@google.com>
-- Stability   :  unstable
-- Portability :
--
--
--
-----------------------------------------------------------------------------
module QifParser where

import           QifData
import           Text.ParserCombinators.Parsec

{- **************************************************
    Parsers for transaction fields
*************************************************** -}
-- | Helper type to tag transaction field data
data TransactionField
  = D String
  | P String
  | M String
  | T String

-- | Parser for date field in transaction
date_parser :: GenParser Char st TransactionField
date_parser = do
  _ <- string "D"
  date <- manyTill (noneOf ['\n', '\r']) (newline_or_eof)
  return $ D date

-- | Parser for description field in transaction
description_parser :: GenParser Char st TransactionField
description_parser = do
  _ <- string "P"
  description <- manyTill (noneOf ['\n', '\r']) newline_or_eof
  return $ P description

-- | Parser for text field in transaction
text_parser :: GenParser Char st TransactionField
text_parser = do
  _ <- string "M"
  text <- manyTill (noneOf ['\n', '\r']) newline_or_eof
  return $ M text

-- | Parser for balance field in transaction
balance_parser :: GenParser Char st TransactionField
balance_parser = do
  _ <- string "T"
  balance <- manyTill (noneOf ['\n', '\r']) newline_or_eof
  return $ T balance

{- **************************************************
    transactions
*************************************************** -}
-- | Parser for one whole transaction
transaction_parser :: GenParser Char st Transaction
transaction_parser = do
  fields <-
    manyTill
      (choice [date_parser, description_parser, text_parser, balance_parser])
      (try $ lookAhead $ seperator_parser)
  return $
    foldl
      fieldToTransaction
      Transaction {date = "", description = "", text = "", balance = ""}
      fields
  where
    fieldToTransaction trans (D date) = trans {date = date}
    fieldToTransaction trans (P desc) = trans {description = desc}
    fieldToTransaction trans (M text) = trans {text = text}
    fieldToTransaction trans (T bal)  = trans {balance = bal}

-- | Parser for transaction seperator '^'
seperator_parser :: GenParser Char st ()
seperator_parser = do
  _ <- string "^"
  _ <- newline_or_eof
  return ()

-- | Parser for a list of transactions
transactions_parser :: GenParser Char st [Transaction]
transactions_parser = sepEndBy transaction_parser seperator_parser

{- **************************************************
    Qif file
*************************************************** -}
-- | Parser for type of qif (Bank, CCard, etc.)
type_parser :: GenParser Char st String
type_parser = do
  _ <- string "!Type:"
  typeinfo <- manyTill (noneOf ['\n', '\r']) newline_or_eof
  return typeinfo

-- | Parser for a qif file
qif_file_parser :: GenParser Char st Qif
qif_file_parser = do
  typeinfo <- type_parser
  transactions <- transactions_parser
  return Qif {typeinfo = typeinfo, transactions = transactions}

-- | obtain qif from string
qifFromString s =
  fromRight (Qif {typeinfo = "Bank", transactions = []}) $
  parse qif_file_parser "(unknown)" s

-- | IO Monad helper function: reads and parses qif file
-- * if parsing successful returns qif data structure, otherwise returns "empty" qif
parse_qif_file filename = do
  contents <- readFile filename
  return $ qifFromString contents

{- **************************************************
    Helper functions
*************************************************** -}
-- | test out parser on string
-- test_parser p s = parse p "(unknown)" s
-- | parses newline but throws away '\n'
newline_skip = do
  _ <- newline
  return ()

-- | skips newline but also succeeds at end-of-file
newline_or_eof = choice [newline_skip, eof]

-- | quick and dirty Either exception handling with default value
fromRight d (Right x) = x
fromRight d _         = d