Move SQL out of API and into separate modules

Create modules for each Table in our SQL database. This cleans up the handler
bodies at the expense of introducing more files and indirection.

src/Trips.hs

@@ -0,0 +1,27 @@
+{-# LANGUAGE OverloadedStrings #-}
+--------------------------------------------------------------------------------
+module Trips where
+--------------------------------------------------------------------------------
+import Data.Function ((&))
+import Database.SQLite.Simple
+
+import qualified Types as T
+--------------------------------------------------------------------------------
+
+-- | Create a new `trip` in `dbFile`.
+create :: FilePath -> T.Trip -> IO ()
+create dbFile trip = withConnection dbFile $ \conn ->
+  execute conn "INSERT INTO Trips (username,destination,startDate,endDate,comment) VALUES (?,?,?,?,?)"
+    (trip & T.tripFields)
+
+-- | Delete a trip from `dbFile` using its `tripPK` Primary Key.
+delete :: FilePath -> T.TripPK -> IO ()
+delete dbFile tripPK =
+  withConnection dbFile $ \conn -> do
+    execute conn "DELETE FROM Trips WHERE username = ? AND destination = ? and startDate = ?"
+      (tripPK & T.tripPKFields)
+
+-- | Return a list of all of the trips in `dbFile`.
+list :: FilePath -> IO [T.Trip]
+list dbFile = withConnection dbFile $ \conn ->
+  query_ conn "SELECT * FROM Trips"