1 files changed, 26 insertions, 12 deletions

diff --git a/Hosts.hs b/Hosts.hs
index 4f8788f..669fd09 100644
--- a/Hosts.hs
+++ b/Hosts.hs
@@ -9,6 +9,9 @@ module Hosts
     , empty
     , hasName
     , hasAddr
+    , encode
+    , decode
+    , diff
     ) where
 
 import Data.Maybe
@@ -22,6 +25,7 @@ import qualified Data.ByteString.Lazy.Char8 as L
 import System.IO.Unsafe (unsafePerformIO)
 import Control.Exception as Exception (IOException(..),catch)
 import Control.Applicative ( (<$>), (<*>) )
+import Control.Monad (mplus)
 import Network.Socket
 
 handleIO_ h a = Exception.catch a (\(_ :: IOException) -> h)
@@ -51,7 +55,9 @@ data Hosts = Hosts
     }
 
 instance Show Hosts where
-    show hosts = L.unpack . L.unlines . map snd . Map.assocs $ numline hosts
+    show = L.unpack . encode
+
+encode = L.unlines . map snd . Map.assocs . numline
 
 parseLine s = (addr,names)
  where
@@ -71,6 +77,9 @@ empty = Hosts { lineCount = 0
 
 parseHosts fname = do
     input <- L.readFile fname
+    decode input
+
+decode input = do
     let ls = L.lines input
         ans = map (\l->(parseLine l,l)) ls
         hosts = foldl' upd empty ans
@@ -150,14 +159,19 @@ assignNewName addr name hosts =
     if hasName name hosts then hosts
                           else assignName0 True addr name hosts
 
-{-
-main = do
-    args <- getArgs
-    let fname = args !! 0
-    p <- parseHosts fname
-    let addr = (fromJust $ inet_pton "fdee:0abe:1f80:31c7:d1af:bce0:0f6c:91d2")
-        p'   = assignName addr "bigshift" p
-        p''  = assignNewName addr "poopy" p'
-    putStr $ show p''
-    return ()
--}
+-- Returns a list of bytestrings intended to show the
+-- differences between the two host databases.  It is
+-- assumed that no lines are deleted, only altered or
+-- appended.
+diff :: Hosts -> Hosts -> [L.ByteString]
+diff as bs = cs
+ where
+    [as',bs'] = map (L.lines . Hosts.encode) [as,bs]
+    ext xs = map Just xs ++ repeat Nothing
+    ds = takeWhile (isJust . uncurry mplus) $ zip (ext as') (ext bs')
+    es = filter (uncurry (/=)) ds
+    cs = do
+        (a,b) <- es
+        [a,b] <- return $ map maybeToList [a,b]
+        fmap ("- " <>) a ++ fmap ("+ " <>) b
+