Abstract the string table into a newtype

lib/Language/Elna/Object/StringTable.hs

@@ -0,0 +1,44 @@
+module Language.Elna.Object.StringTable
+    ( StringTable
+    , append
+    , elem
+    , index
+    , encode
+    , size
+    ) where
+
+import Data.ByteString (StrictByteString)
+import qualified Data.ByteString as ByteString
+import Language.Elna.Object.Elf
+import Prelude hiding (elem)
+
+newtype StringTable = StringTable StrictByteString
+    deriving Eq
+
+instance Semigroup StringTable
+  where
+    (StringTable x) <> (StringTable y) = StringTable $ x <> ByteString.drop 1 y
+
+instance Monoid StringTable
+  where
+    mempty = StringTable "\0"
+
+size :: StringTable -> Elf32_Word
+size (StringTable container) =
+    fromIntegral $ ByteString.length container
+
+elem :: StrictByteString -> StringTable -> Bool
+elem needle (StringTable container) =
+    ("\0" <> needle <> "\0") `ByteString.isInfixOf` container
+
+append :: StrictByteString -> StringTable -> StringTable
+append element (StringTable container) =
+    StringTable $ container <> element <> "\0"
+
+index :: Elf32_Word -> StringTable -> StrictByteString
+index stringTableIndex (StringTable stringTable)
+    = ByteString.takeWhile (/= 0)
+    $ ByteString.drop (fromIntegral stringTableIndex) stringTable
+
+encode :: StringTable -> StrictByteString
+encode (StringTable container) = container