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diff --git a/users/wpcarro/assessments/tt/src/Sessions.hs b/users/wpcarro/assessments/tt/src/Sessions.hs
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+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+--------------------------------------------------------------------------------
+module Sessions where
+--------------------------------------------------------------------------------
+import Database.SQLite.Simple
+
+import qualified Data.Time.Clock as Clock
+import qualified Types as T
+import qualified System.Random as Random
+--------------------------------------------------------------------------------
+
+-- | Return True if `session` was created at most three hours ago.
+isValid :: T.StoredSession -> IO Bool
+isValid session = do
+  t1 <- Clock.getCurrentTime
+  let t0 = T.storedSessionTsCreated session in
+    pure $ Clock.diffUTCTime t1 t0 <= 3 * 60 * 60
+
+-- | Lookup the session by UUID.
+get :: FilePath -> T.SessionUUID -> IO (Maybe T.StoredSession)
+get dbFile uuid = withConnection dbFile $ \conn -> do
+  res <- query conn "SELECT uuid,username,tsCreated FROM Sessions WHERE uuid = ?" (Only uuid)
+  case res of
+    [x] -> pure (Just x)
+    _ -> pure Nothing
+
+-- | Lookup the session stored under `username` in `dbFile`.
+find :: FilePath -> T.Username -> IO (Maybe T.StoredSession)
+find dbFile username = withConnection dbFile $ \conn -> do
+  res <- query conn "SELECT uuid,username,tsCreated FROM Sessions WHERE username = ?" (Only username)
+  case res of
+    [x] -> pure (Just x)
+    _ -> pure Nothing
+
+-- | Create a session under the `username` key in `dbFile`.
+create :: FilePath -> T.Username -> IO T.SessionUUID
+create dbFile username = withConnection dbFile $ \conn -> do
+  now <- Clock.getCurrentTime
+  uuid <- Random.randomIO
+  execute conn "INSERT INTO Sessions (uuid,username,tsCreated) VALUES (?,?,?)"
+    (T.SessionUUID uuid, username, now)
+  pure (T.SessionUUID uuid)
+
+-- | Reset the tsCreated field to the current time to ensure the token is valid.
+refresh :: FilePath -> T.SessionUUID -> IO ()
+refresh dbFile uuid = withConnection dbFile $ \conn -> do
+  now <- Clock.getCurrentTime
+  execute conn "UPDATE Sessions SET tsCreated = ? WHERE uuid = ?"
+    (now, uuid)
+  pure ()
+
+-- | Delete the session under `username` from `dbFile`.
+delete :: FilePath -> T.SessionUUID -> IO ()
+delete dbFile uuid = withConnection dbFile $ \conn ->
+  execute conn "DELETE FROM Sessions WHERE uuid = ?" (Only uuid)
+
+-- | Find or create a session in the Sessions table. If a session exists,
+-- refresh the token's validity.
+findOrCreate :: FilePath -> T.Account -> IO T.SessionUUID
+findOrCreate dbFile account =
+  let username = T.accountUsername account in do
+    mSession <- find dbFile username
+    case mSession of
+      Nothing -> create dbFile username
+      Just session ->
+        let uuid = T.storedSessionUUID session in do
+          refresh dbFile uuid
+          pure uuid
+
+-- | Return a list of all sessions in the Sessions table.
+list :: FilePath -> IO [T.StoredSession]
+list dbFile = withConnection dbFile $ \conn ->
+  query_ conn "SELECT uuid,username,tsCreated FROM Sessions"