module Darcs.Patch.Repair
    ( Repair(..), RepairToFL(..), mapMaybeSnd, Check(..) )
    where

import Darcs.Prelude

import Darcs.Patch.Apply ( Apply(..) )
import Darcs.Patch.ApplyMonad ( ApplyMonad )
import Darcs.Patch.Witnesses.Ordered ( FL(..), RL(..), mapFL, mapRL, (+>+) )
import Darcs.Util.Printer ( Doc )

import Data.Maybe ( catMaybes, listToMaybe )


class Check p where
    isInconsistent :: p wX wY -> Maybe Doc
    isInconsistent _ = Nothing

-- |'Repair' and 'RepairToFL' deal with repairing old patches that were were
-- written out due to bugs or that we no longer wish to support. 'Repair' is
-- implemented by collections of patches (FL, Named, PatchInfoAnd) that might
-- need repairing.
class Repair p where
    applyAndTryToFix
      :: ApplyMonad (ApplyState p) m => p wX wY -> m (Maybe (String, p wX wY))

-- |'RepairToFL' is implemented by single patches that can be repaired (Prim,
-- Patch, RepoPatchV2) There is a default so that patch types with no current
-- legacy problems don't need to have an implementation.
class Apply p => RepairToFL p where
    applyAndTryToFixFL
      :: ApplyMonad (ApplyState p) m => p wX wY -> m (Maybe (String, FL p wX wY))
    applyAndTryToFixFL p = do apply p; return Nothing

mapMaybeSnd :: (a -> b) -> Maybe (c, a) -> Maybe (c, b)
mapMaybeSnd f (Just (a,b)) = Just (a,f b)
mapMaybeSnd _ Nothing = Nothing

instance Check p => Check (FL p) where
    isInconsistent = listToMaybe . catMaybes . mapFL isInconsistent

instance Check p => Check (RL p) where
    isInconsistent = listToMaybe . catMaybes . mapRL isInconsistent

instance RepairToFL p => Repair (FL p) where
    applyAndTryToFix NilFL = return Nothing
    applyAndTryToFix (p :>: ps) = do
      mp <- applyAndTryToFixFL p
      mps <- applyAndTryToFix ps
      return $
        case (mp, mps) of
          (Nothing, Nothing) -> Nothing
          (Just (e, p'), Nothing) -> Just (e, p' +>+ ps)
          (Nothing, Just (e, ps')) -> Just (e, p :>: ps')
          (Just (e, p'), Just (es, ps')) -> Just (e ++ "\n" ++ es, p' +>+ ps')