[haskell] Implemented pagination and systems list api call

haskell/src/SpaceTraders/Database/Systems.hs

@@ -0,0 +1,23 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module SpaceTraders.Database.Systems
+  ( addSystems
+  , getSystems
+  ) where
+
+import Data.Aeson
+import Data.Maybe
+import qualified Database.SQLite.Simple as S
+
+import Data.Text.Encoding (encodeUtf8Builder)
+import Data.ByteString.Builder(toLazyByteString)
+
+import SpaceTraders.Model.System
+
+addSystems :: S.Connection -> [System] -> IO ()
+addSystems conn systems = S.withTransaction conn $ S.executeMany conn "INSERT INTO systems(data) VALUES (json(?));" $ S.Only <$> map encode systems
+
+getSystems :: S.Connection -> IO [System]
+getSystems conn = do
+  ret <- S.query_ conn "SELECT data from systems;"
+  return . catMaybes $ map (decode . toLazyByteString . encodeUtf8Builder . head) ret