module Data.Algorithm.Diff3 (Hunk(..), diff3, merge) where
import Prelude hiding ((<>))
import Data.Algorithm.Diff
import Data.Monoid (Monoid, mempty, mappend)
data Hunk a = LeftChange [a]
| RightChange [a]
| Unchanged [a]
| Conflict [a] [a] [a]
deriving (Eq, Show)
instance Functor Hunk where
fmap f (LeftChange ls) = LeftChange (map f ls)
fmap f (RightChange rs) = RightChange (map f rs)
fmap f (Unchanged os) = Unchanged (map f os)
fmap f (Conflict ls os rs) = Conflict (map f ls) (map f os) (map f rs)
diff3 :: Eq a => [a] -> [a] -> [a] -> [Hunk a]
diff3 a o b = step (getDiff o a) (getDiff o b)
where
step [] [] = []
step [] ob = toHunk [] ob
step oa [] = toHunk oa []
step oa ob =
let (conflictHunk, ra, rb) = shortestConflict oa ob
(matchHunk, ra', rb') = shortestMatch ra rb
in conflictHunk ++ matchHunk ++ step ra' rb'
merge :: [Hunk a] -> Either [Hunk a] [a]
merge hunks = maybe (Left hunks) Right $ go hunks
where
go [] = Just []
go ((Conflict _ _ _):_) = Nothing
go ((LeftChange l):t) = fmap (l ++) $ go t
go ((RightChange r):t) = fmap (r ++) $ go t
go ((Unchanged o):t) = fmap (o ++) $ go t
toHunk :: [Diff a] -> [Diff a] -> [Hunk a]
toHunk [] [] = mempty
toHunk a [] = [LeftChange $ takeSecond a]
toHunk [] b = [RightChange $ takeSecond b]
toHunk a b
| all isB a && all isB b = [Unchanged $ takeFirst a]
| all isB a = [RightChange $ takeSecond b]
| all isB b = [LeftChange $ takeSecond a]
| otherwise = [Conflict (takeSecond a) (takeFirst a) (takeSecond b)]
takeSecond :: [Diff a] -> [a]
takeSecond [] = []
takeSecond (Second x:xs) = x:takeSecond xs
takeSecond (Both x _:xs) = x:takeSecond xs
takeSecond (_:xs) = takeSecond xs
takeFirst :: [Diff a] -> [a]
takeFirst [] = []
takeFirst (First x :xs) = x:takeFirst xs
takeFirst (Both x _:xs) = x:takeFirst xs
takeFirst (_:xs) = takeFirst xs
isB :: Diff a -> Bool
isB (Both _ _) = True
isB _ = False
{-# INLINE isB #-}
shortestMatch :: [Diff a] -> [Diff a] -> ([Hunk a], [Diff a], [Diff a])
shortestMatch oa ob = go oa ob [] []
where
go (x@(Both _ _):xs) (y@(Both _ _):ys) accX accY = go xs ys (accX ++ [x]) (accY ++ [y])
go xs ys accX accY = (toHunk accX accY, xs, ys)
shortestConflict :: [Diff a] -> [Diff a] -> ([Hunk a], [Diff a], [Diff a])
shortestConflict l r =
let (hunk, rA, rB) = go l r
in (uncurry toHunk hunk, rA, rB)
where
go [] b = (([], b), [], [])
go a [] = ((a, []), [], [])
go a b =
let (as, ta) = break isBoth a
(bs, tb) = break isBoth b
am = sum $ map motion as
bm = sum $ map motion bs
(as', ta') = if bm > am then incurMotion (bm-am) ta else ([], ta)
(bs', tb') = if am > bm then incurMotion (am-bm) tb else ([], tb)
in if am == bm
then ((as, bs), ta, tb)
else ((as ++ as', bs ++ bs'), [], []) <> go ta' tb'
isBoth (Both _ _) = True
isBoth _ = False
motion (Second _) = 0
motion _ = 1
incurMotion :: Int -> [Diff a] -> ([Diff a], [Diff a])
incurMotion _ [] = ([], [])
incurMotion 0 as = ([], as)
incurMotion n (a@(Both _ _):as) = ([a], []) <> incurMotion (pred n) as
incurMotion n (a@(First _):as) = ([a], []) <> incurMotion (pred n) as
incurMotion n (a:as) = ([a], []) <> incurMotion n as
infixr 6 <>
(<>) :: Monoid m => m -> m -> m
(<>) = mappend
{-# INLINE (<>) #-}