the start of a rewrite using what was learned from bzip2

compress.cabal

@@ -41,6 +41,7 @@ common deps
     TypeOperators,
     TypeSynonymInstances,
     UndecidableInstances,
+    ViewPatterns,
   mixins:
     base hiding (Prelude),
     relude (Relude as Prelude),
@@ -76,6 +77,7 @@ common deps
      Compress.PrefixTree
      Compress.WordMarkovStats
      Compress.LengthDistancePairs
+     Compress.MoveToFrontTransform
      Data.Dirs
      Data.FiniteBit
      Data.HuffmanTree

src/Compress/BurrowsWheeler.hs

@@ -3,25 +3,50 @@
 module Compress.BurrowsWheeler where
 -- import qualified Data.CircularList as CL
 import qualified Relude.Unsafe as U
--- import Compress.BurrowsWheeler (toBurrowsWheeler)
 
+import Data.ByteString.Lazy qualified as BSL
+import Relude.Unsafe qualified as U
 
-toBurrowsWheeler (x:xs) = map U.head . sortOn (U.tail) . take (pred . length $ xs) .  tails $ xs'
+data BurrowsWheelerMetadata a = BurrowsWheelerMetadata
+  { originPtr :: Word,
+    transformed :: a
+  }
+  deriving (Functor, Show, Generic)
+
+type BurrowsWheelerOutput = BurrowsWheelerMetadata LByteString
+
+toBurrowsWheeler :: LByteString -> BurrowsWheelerOutput
+toBurrowsWheeler bs =
+  BurrowsWheelerMetadata originPtr
+    . BSL.pack
+    . map (`BSL.index` (bsLen - 1))
+    $ sortedCycles
   where
-    xs' = toList $ (x :| xs) <> (x :| [])
+    sortedCycles =
+      sort
+        . take bsLen
+        . BSL.tails
+        $ (bs <> bs)
 
-toCounts :: forall a b . (Eq a, Eq b, Num b, Enum b, Bounded a, Bounded b) => [a] -> [(a, b)]
-toCounts = reverse . foldl' f []
+    originPtr =
+      succ
+        . fst
+        . U.fromJust
+        . find (BSL.isPrefixOf bs . snd)
+        . zip [0 ..]
+        $ sortedCycles
+
+    bsLen :: (Integral a) => a
+    bsLen = fromIntegral . BSL.length $ bs
+
+unBurrowsWheeler :: BurrowsWheelerOutput -> LByteString
+unBurrowsWheeler (BurrowsWheelerMetadata {..}) =
+  (U.!! (fromIntegral originPtr))
+    . sort
+    . (U.!! (pred . fromIntegral . BSL.length $ transformed))
+    . iterate (zipWith BSL.cons unpacked . sort)
+    . map BSL.singleton
+    . BSL.unpack
+    $ transformed
   where
-    f [] x = [(x, 0)]
-    f ((x, count) : xs) newVal
-      | x == newVal && count == maxBound = (x, 0) : (x, count) : xs
-      | x == newVal = (x, succ count) : xs
-      | otherwise = (newVal, 0) : (x, count) : xs
-
-
--- toBurrowsWheeler xs = map last . sort . map (findLyndonWord) . take (length xs) . tails $ xs'
---   where
---     xs' = xs ++ xs
-
--- findLyndonWord (x : xs) = (x :|) . map snd . takeWhile (uncurry (<=)) . zip (x : xs) $ xs
+    unpacked = BSL.unpack transformed

src/Compress/Huffman.hs

@@ -20,7 +20,6 @@ import Data.Bits as B
 import Data.Maybe (fromMaybe)
 import Data.Maybe qualified as My
 import Data.PQueue qualified as PQ
-import Codec.Winery qualified as C
 import Data.Text qualified as T
 import Data.Text.IO qualified as TIO
 import Data.Vector.Unboxed qualified as V

src/Compress/MoveToFrontTransform.hs

@@ -0,0 +1,49 @@
+module Compress.MoveToFrontTransform where
+
+import Data.ByteString.Lazy qualified as BSL
+import qualified Data.Containers.ListUtils as LU
+import qualified Relude.Unsafe as U
+import qualified Data.ByteString as S
+
+
+data MoveToFrontMetadata a = MoveToFrontMetadata {
+  startingStack :: [Word8],
+  transformed :: a
+                                                 } deriving (Functor, Show, Generic)
+
+type MoveToFrontOutput = MoveToFrontMetadata LByteString
+
+moveToFront :: LByteString -> MoveToFrontOutput
+moveToFront bs = MoveToFrontMetadata startingStack . moveToFront' startingStack $ bs
+  where
+    startingStack = LU.nubIntOn fromEnum . BSL.unpack $ bs
+    
+    moveToFront' :: [Word8] -> LByteString -> LByteString
+    moveToFront' s "" = BSL.empty
+    moveToFront' s (BSL.uncons -> Just (x, xs)) = BSL.cons stackIndex recurse
+      where
+        stackIndex :: Word8
+        stackIndex =
+          fromIntegral
+            . fromMaybe (length s)
+            . fmap fst
+            . find ((==) x . snd)
+            . zip [0 ..]
+            $ s
+    
+        recurse = moveToFront' s' xs
+    
+        s' :: [Word8]
+        s' = removeAndPrepend x s
+
+removeAndPrepend x = (x :) . filter (/= x)
+
+unMoveToFront :: MoveToFrontOutput -> LByteString
+unMoveToFront (MoveToFrontMetadata {..}) = unMoveToFront' startingStack transformed
+  where
+    unMoveToFront' s bs | BSL.null bs = BSL.empty
+    unMoveToFront' s (BSL.uncons -> Just (loc, xs)) = BSL.cons byte $ unMoveToFront' s' xs
+      where
+        byte = s U.!! (fromEnum loc)
+
+        s' = removeAndPrepend byte s