Use comonads

src/Main.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE DeriveAnyClass      #-}
+{-# LANGUAGE DeriveFunctor       #-}
 {-# LANGUAGE DeriveGeneric       #-}
 {-# LANGUAGE OverloadedStrings   #-}
 {-# LANGUAGE RecordWildCards     #-}
@@ -9,6 +10,8 @@ module Main where
 
 import           Codec.Picture
 import           Codec.Picture.Extra   (scaleBilinear)
+import           Control.Comonad       (extend, extract)
+import           Control.Comonad.Store (Store, experiment, seek, store)
 import           Control.Exception     (SomeException, try)
 import           Control.Monad         (forM_, void, when)
 import           Data.Bits
@@ -21,7 +24,8 @@ import           Pipes
 import           Pipes.Files
 import qualified Pipes.Prelude         as P
 import           Pipes.Safe            (runSafeT)
-import           System.Directory    (createDirectoryIfMissing, createFileLink)
+import           System.Directory      (createDirectoryIfMissing,
+                                        createFileLink)
 import           System.FilePath       (takeFileName, (</>))
 
 
@@ -46,7 +50,6 @@ instance BK.Metric Fingerprint where
     let xored = a `xor` b
     in foldr (\shiftA acc -> acc + if 1 `shift` shiftA .&. xored > 0 then 1 else 0) 0 [0..63]
 
-
 fingerprint :: Alg -> DynamicImage -> Word64
 fingerprint alg = hash . grey . scale . convertRGB8
   where
@@ -54,17 +57,25 @@ fingerprint alg = hash . grey . scale . convertRGB8
     scale = scaleBilinear 8 8
     grey :: Image PixelRGB8 -> Image Pixel8
     grey = pixelMap (\(PixelRGB8 r g b) -> ceiling ((fromIntegral r * (0.3 :: Double)) + (fromIntegral g * 0.59) + (fromIntegral b * 0.11)))
+    indexes = [(x,y) | x <- [0..7], y <- [0..7]]
+    hashWith :: Image Pixel8 -> (Store (Int, Int) Pixel8 -> Bool) -> Word64
+    hashWith img f =
+      let s = store (uncurry (pixelAt img)) (0,0)
+          img' = extend f s
+          at pos = extract $ seek pos img'
+      in foldr (\(shiftA, b) acc -> if b then 1 `shift` shiftA .|. acc else acc) 0 $ zip [0..] $ map at indexes
     hash :: Image Pixel8 -> Word64
-    hash = case alg of
-                Average -> averageHash
-                DHash -> dhash
-    dhash :: Image Pixel8 -> Word64
-    dhash img =
-      foldr (\(shiftA, b) acc -> if b then 1 `shift` shiftA .|. acc else acc) 0 $ zip [0..] [(x < 7) && (pixelAt img x y > pixelAt img (x+1) y) | x <- [0..7], y <- [0..7]]
-    averageHash :: Image Pixel8 -> Word64
-    averageHash img = -- the average fingerprint method
-      let avg = fromIntegral (foldl' (\acc (x,y) -> acc + fromIntegral (pixelAt img x y)) (0 :: Int) [(x,y) | x <- [0..7], y <- [0..7]] `div` 64)
-      in foldr (\(shiftA, b) acc -> if b then 1 `shift` shiftA .|. acc else acc) 0 $ zip [0..] [pixelAt img x y > avg | x <- [0..7], y <- [0..7]]
+    hash img = case alg of
+                Average ->
+                  let avg = fromIntegral (foldl' (\acc (x,y) -> acc + fromIntegral (pixelAt img x y)) (0 :: Int) [(x,y) | (x,y) <- indexes] `div` 64)
+                  in img `hashWith` (avgAlg avg)
+                DHash -> img `hashWith` dAlg
+    dAlg :: Store (Int, Int) Pixel8 -> Bool
+    dAlg img = case experiment (\(x,y) -> [(x,y), (succ x `mod` 8, y)]) img of
+                    [l,r] -> l > r
+                    _     -> False
+    avgAlg :: Pixel8 -> Store (Int, Int) Pixel8 -> Bool
+    avgAlg avg img = extract img > avg
 
 main :: IO ()
 main = do