Merge branch 'sandbox/MasseR/2-opds' of MasseR/ebook-manager into master

Closes #2

ebook-manager.cabal

@@ -25,6 +25,7 @@ executable ebook-manager
                      , Database
                      , Database.Book
                      , Database.Channel
+                     , Database.Tag
                      , Database.Schema
                      , Database.User
                      , Datastore

migrations/V1.1__Channel_visibility.sql

@@ -0,0 +1 @@
+alter table channels add column visibility text NOT NULL default 'Private';

src/API.hs

@@ -27,8 +27,8 @@ data Index = Index
 
 type API = Get '[HTML] (AppView Index)
       :<|> Users.API
-      :<|> "api" :> Channels.API
+      :<|> "api" :> "current" :> Channels.API
-      :<|> "api" :> Books.API
+      :<|> "api" :> "current" :> Books.API
       :<|> "api" :> "1" :> Catalogue.VersionedAPI 1
       :<|> "api" :> "current" :> Catalogue.VersionedAPI 1
 

src/API/Books.hs

@@ -21,9 +21,9 @@ import ClassyPrelude
 import Server.Auth
 import Servant.Auth as SA
 import Data.Aeson
-import API.Channels (JsonChannel(..))
 import Database.Book
 import Database.Channel
+import Database.Tag
 import Database
 import Control.Lens
 import Data.Generics.Product
@@ -36,15 +36,17 @@ import Crypto.Hash (digestFromByteString)
 
 data JsonBook = JsonBook { identifier :: BookID
                          , contentType :: Text
-                         , title :: Maybe Text
+                         , title :: Text
                          , description :: Maybe Text
-                         , channels :: [JsonChannel] }
+                         , channels :: [Text]
+                         , tags :: [Text] }
               deriving (Generic, Show)
 
 data PostBook = PostBook { contentType :: Text
-                         , title :: Maybe Text
+                         , title :: Text
                          , description :: Maybe Text
-                         , channels :: [JsonChannel] }
+                         , channels :: [Text]
+                         , tags :: [Text] }
               deriving (Generic, Show)
 
 
@@ -59,7 +61,9 @@ type BaseAPI = "books" :> Get '[JSON] [JsonBook]
        :<|> "books" :> ReqBody '[JSON] PostBook :> Post '[JSON] JsonBook
        :<|> "books" :> Capture "book_id" BookID :> "meta" :> ReqBody '[JSON] JsonBook :> Put '[JSON] JsonBook
        :<|> "books" :> Capture "book_id" BookID :> ReqBody '[OctetStream] ByteString :> Put '[JSON] NoContent
-       :<|> "books" :> Capture "book_id" BookID :> Get '[OctetStream] ByteString
+       :<|> GetBook
+
+type GetBook = "books" :> Capture "book_id" BookID :> Get '[OctetStream] ByteString
 
 handler :: ServerT API AppM
 handler user = listBooksHandler user
@@ -95,9 +99,9 @@ postBookMetaHandler auth PostBook{..} = flip requireLoggedIn auth $ \SafeUser{us
 
 
 putBookMetaHandler :: AuthResult SafeUser -> BookID -> JsonBook -> AppM JsonBook
-putBookMetaHandler auth bookId b@JsonBook{..}
+putBookMetaHandler auth bookId JsonBook{..}
   | bookId == identifier = requireBookOwner auth bookId $ \SafeUser{username=owner} ->
-        maybe (throwM err403) (const (return b)) =<< runDB (updateBook UpdateBook{..})
+        maybe (throwM err403) (return . view (super @JsonBook)) =<< runDB (updateBook UpdateBook{..})
   | otherwise = throwM err403
 
 listBooksHandler :: AuthResult SafeUser -> AppM [JsonBook]
@@ -105,5 +109,6 @@ listBooksHandler = requireLoggedIn $ \user -> do
   runDB (usersBooks (view (field @"username") user) >>= mapM augment)
     where
       augment Book{identifier=bookId,contentType,title,description} = do
-        channels <- fmap (\Channel{..} -> JsonChannel{..}) <$> booksChannels bookId
+        channels <- fmap (view (field @"channel")) <$> booksChannels bookId
+        tags <- fmap (view (field @"tag")) <$> booksTags bookId
         pure JsonBook{identifier=bookId,..}

src/API/Catalogue.hs

@@ -17,14 +17,16 @@
 module API.Catalogue (VersionedAPI, handler) where
 
 import Types
-import Servant
+import Servant hiding (contentType)
 import ClassyPrelude
 import GHC.TypeLits
 import Server.Auth
 import Servant.Auth as SA
 import Servant.XML
 import qualified Database.Channel as Channel
+import Database.Book (Book(..))
 import Database
+import qualified API.Books
 
 -- This is my first try on going to versioned apis, things might change
 -- I think my rule of thumb is that you can add new things as you want, but
@@ -96,18 +98,40 @@ instance ToNode (Catalog 1) where
 
 class Monad m => VersionedCatalog m (v :: Nat) where
   getChannels :: SafeUser -> m (Catalog v)
+  getBooks :: Channel.ChannelID -> SafeUser -> m (Catalog v)
 
 instance VersionedCatalog AppM 1 where
   getChannels = getChannelsV1
+  getBooks = getBooksV1
+
+relUrl :: Link -> Rel
+relUrl x = Rel ("/api/current/" <> (pack . uriPath . linkURI $ x))
+
+getBooksV1 :: Channel.ChannelID -> SafeUser -> AppM (Catalog 1)
+getBooksV1 channelID SafeUser{username} = do
+  updated <- liftIO getCurrentTime
+  let self = relUrl selfUrl
+      start = relUrl startUrl
+      selfUrl = safeLink (Proxy @(BaseAPI 1)) (Proxy @(ChannelCatalog 1)) channelID
+      startUrl = safeLink (Proxy @(BaseAPI 1)) (Proxy @(RootCatalog 1))
+      pagination = Pagination Nothing Nothing
+  entries <- map (toEntry updated) <$> runDB (Channel.channelBooks username channelID)
+  pure CatalogV1{..}
+  where
+    toEntry updated Book{description,title,identifier=bookId} =
+      let content = fromMaybe "no content" description
+          identifier = pack . show $ bookId
+          link = Right (Acquisition (relUrl (safeLink (Proxy @API.Books.BaseAPI) (Proxy @API.Books.GetBook) bookId)))
+      in EntryV1{..}
 
 getChannelsV1 :: SafeUser -> AppM (Catalog 1)
 getChannelsV1 SafeUser{username} = do
   updated <- liftIO getCurrentTime
-  let self = Rel ("/api/current/" <> selfUrl)
+  let self = relUrl selfUrl
       -- I'm not sure if this safe link approach is really useable with this
       -- api hierarchy since I can't access the topmost api from here. Also
       -- authentication would bring a little bit of extra effort as well
-      selfUrl = pack . uriPath . linkURI $ safeLink (Proxy @(BaseAPI 1)) (Proxy @(RootCatalog 1))
+      selfUrl = safeLink (Proxy @(BaseAPI 1)) (Proxy @(RootCatalog 1))
       start = self
       pagination = Pagination Nothing Nothing
   entries <- map (fromChannel updated) <$> runDB (Channel.userChannels username)
@@ -115,8 +139,8 @@ getChannelsV1 SafeUser{username} = do
   where
     fromChannel :: UTCTime -> Channel.Channel -> Entry 1
     fromChannel updated Channel.Channel{..} =
-      let url = pack . uriPath . linkURI $ safeLink (Proxy @(BaseAPI 1)) (Proxy @(ChannelCatalog 1)) identifier
+      let url = safeLink (Proxy @(BaseAPI 1)) (Proxy @(ChannelCatalog 1)) identifier
-          self = Rel ("/api/current/" <> url)
+          self = relUrl url
       in EntryV1 channel channel updated channel (Left $ SubSection self)
 
 type VersionedAPI (v :: Nat) = Auth '[SA.BasicAuth, SA.JWT] SafeUser :> BaseAPI v
@@ -133,7 +157,7 @@ handler auth = catalogRoot :<|> catalogChannels
   where
     catalogChannels :: Channel.ChannelID -> AppM (Catalog v)
     -- Channel specific catalog returns tags inside the catalog
-    catalogChannels _ = throwM err403{errBody="Not implemented"}
+    catalogChannels identifier = flip requireLoggedIn auth (getBooks identifier)
     catalogRoot :: AppM (Catalog v)
     -- catalog root returns channels
     catalogRoot = flip requireLoggedIn auth getChannels

src/API/Channels.hs

@@ -11,6 +11,8 @@
 {-# Language FlexibleInstances #-}
 {-# Language TypeApplications #-}
 {-# Language DataKinds #-}
+{-# Language DuplicateRecordFields #-}
+{-# Language NamedFieldPuns #-}
 module API.Channels (API, handler, JsonChannel(..)) where
 
 import Servant
@@ -25,18 +27,37 @@ import Data.Aeson
 import Control.Lens
 import Data.Generics.Product
 
-data JsonChannel = JsonChannel { channel :: Text } deriving (Show, Generic)
+data JsonChannel = JsonChannel { channel :: Text
+                               , visibility :: Visibility }
+                 deriving (Show, Generic)
+data UpdateChannel = UpdateChannel { identifier :: ChannelID
+                                   , channel :: Text
+                                   , visibility :: Visibility }
+                 deriving (Show, Generic)
 
 instance ToJSON JsonChannel
 instance FromJSON JsonChannel
+instance ToJSON UpdateChannel
+instance FromJSON UpdateChannel
 
 type API = Auth '[SA.BasicAuth, SA.Cookie, SA.JWT] SafeUser :> BaseAPI
 
-type BaseAPI = "channels" :> ReqBody '[JSON] JsonChannel :> Put '[JSON] JsonChannel
+type BaseAPI = "channels" :> ReqBody '[JSON] JsonChannel :> Post '[JSON] UpdateChannel
+          :<|> "channels" :> Capture "channel_id" ChannelID :> ReqBody '[JSON] UpdateChannel :> Put '[JSON] UpdateChannel
           :<|> "channels" :> Get '[JSON] [JsonChannel]
 
 handler :: ServerT API AppM
-handler user = newChannelHandler user :<|> listChannelsHandler user
+handler user = newChannelHandler user :<|> updateChannelHandler user :<|> listChannelsHandler user
+
+requireChannelOwner :: AuthResult SafeUser -> ChannelID -> (SafeUser -> AppM a) -> AppM a
+requireChannelOwner auth channelId f = flip requireLoggedIn auth $ \u@SafeUser{username} -> do
+  unlessM (runDB . channelExists $ channelId) $ throwM err404
+  runDB (isChannelOwner channelId username) >>= \o -> if o then f u else throwM err403
+
+updateChannelHandler :: AuthResult SafeUser -> ChannelID -> UpdateChannel -> AppM UpdateChannel
+updateChannelHandler auth channelId UpdateChannel{visibility} = requireChannelOwner auth channelId $ \_ -> do
+  mChannel <- fmap toChannel <$> runDB (updateChannelPrivacy channelId visibility)
+  maybe (throwM err403) return mChannel
 
 listChannelsHandler :: AuthResult SafeUser -> AppM [JsonChannel]
 listChannelsHandler = requireLoggedIn $ \user ->
@@ -44,8 +65,11 @@ listChannelsHandler = requireLoggedIn $ \user ->
   -- use the 'channel' accessor somehow or export it
   fmap (\Channel{..} -> JsonChannel{..}) <$> runDB (userChannels (view (field @"username") user))
 
-newChannelHandler :: AuthResult SafeUser -> JsonChannel -> AppM JsonChannel
+newChannelHandler :: AuthResult SafeUser -> JsonChannel -> AppM UpdateChannel
-newChannelHandler auth ch@JsonChannel{..} = flip requireLoggedIn auth $ \user -> do
+newChannelHandler auth JsonChannel{..} = flip requireLoggedIn auth $ \user -> do
   $logInfo $ "Creating channel for user " <> pack (show user)
-  runDB (insertChannel (view (field @"username") user) channel)
+  mChannel <- fmap toChannel <$> runDB (insertChannel (view (field @"username") user) channel visibility)
-  return ch
+  maybe (throwM err403{errBody="Could not create the channel"}) return mChannel
+
+toChannel :: Channel -> UpdateChannel
+toChannel Channel{..} = UpdateChannel{..}

src/Database.hs

@@ -11,6 +11,7 @@ module Database
   , fromRel
   , fromRels
   , toRel
+  , transaction
   , SeldaT )
   where
 
@@ -18,7 +19,7 @@ import Data.Generics.Product
 import Control.Lens (view)
 import Data.Pool (Pool, withResource)
 import Database.Selda.Backend (SeldaConnection, runSeldaT, SeldaT)
-import Database.Selda (query, select)
+import Database.Selda (query, select, transaction)
 import Database.Selda.Generic (gen, fromRel, fromRels, toRel)
 import ClassyPrelude
 

src/Database/Book.hs

@@ -18,11 +18,17 @@ module Database.Book
   , BookID) where
 
 import ClassyPrelude
-import Database.Schema
+import Database.Schema (books, users, Username, Book(..), BookID(..), UserID, HashDigest(..))
 import Database
 import Database.Selda
 import Database.Selda.Generic
 
+import Control.Lens (view)
+import Data.Generics.Product
+
+import Database.Tag (booksTags, attachTag, clearTags)
+import Database.Channel (booksChannels, attachChannel, clearChannels)
+
 usersBooks :: (MonadSelda m, MonadMask m, MonadIO m) => Username -> m [Book]
 usersBooks username = fromRels <$> query q
   where
@@ -45,7 +51,7 @@ getBook identifier owner = listToMaybe . fromRels <$> query q
       return book
 
 data InsertBook = InsertBook { contentType :: Text
-                             , title :: Maybe Text
+                             , title :: Text
                              , description :: Maybe Text
                              , owner :: Username }
 
@@ -62,9 +68,12 @@ insertBook InsertBook{..} = do
 
 data UpdateBook = UpdateBook { identifier :: BookID
                              , contentType :: Text
-                             , title :: Maybe Text
+                             , title :: Text
                              , description :: Maybe Text
-                             , owner :: Username }
+                             , owner :: Username
+                             , tags :: [Text]
+                             , channels :: [Text] }
+                deriving (Show, Generic)
 
 bookExists :: (MonadSelda m, MonadMask m, MonadIO m) => BookID -> m Bool
 bookExists identifier = not . null <$> query q
@@ -87,17 +96,32 @@ bookOwner' identifier username = do
   return (userId :*: bookId)
 
 updateBook :: (MonadSelda m, MonadMask m, MonadIO m) => UpdateBook -> m (Maybe UpdateBook)
-updateBook book@UpdateBook{..} = do
+updateBook UpdateBook{..} = do
+  clearTags identifier >> connectTags
+  clearChannels identifier >> connectChannels
+  updateBook'
+  getUpdateBook identifier owner
+  where
+    connectTags = mapM_ (attachTag owner identifier) tags
+    connectChannels = mapM_ (attachChannel owner identifier) channels
+    updateBook' = do
       mUserId <- query (bookOwner' identifier owner)
-  forM (listToMaybe mUserId) $ \_userId -> do
+      forM_ (listToMaybe mUserId) $ \_userId -> do
         update_ (gen books) predicate (\b -> b `with` [ pContentType := literal contentType
                                                       , pTitle := literal title
                                                       , pDescription := literal description ])
-    return book
-  where
     _ :*: _ :*: pContentType :*: pTitle :*: pDescription :*: _ = selectors (gen books)
     predicate (bookId :*: _) = bookId .== literal identifier
 
+
+getUpdateBook :: (MonadMask m, MonadIO m, MonadSelda m) => BookID -> Username -> m (Maybe UpdateBook)
+getUpdateBook bookId username = do
+  mBook <- getBook bookId username
+  forM mBook $ \Book{..} -> do
+    channels <- map (view (field @"channel")) <$> booksChannels bookId
+    tags <- map (view (field @"tag")) <$> booksTags bookId
+    return UpdateBook{owner=username,..}
+
 setContent :: (MonadSelda m, MonadMask m, MonadIO m) => BookID -> Username -> HashDigest -> m ()
 setContent identifier owner digest = do
   mOwner <- query (bookOwner' identifier owner)

src/Database/Channel.hs

@@ -1,46 +1,127 @@
 {-# Language TypeApplications #-}
 {-# Language DataKinds #-}
+{-# Language NamedFieldPuns #-}
 module Database.Channel
   ( userChannels
   , insertChannel
+  , channelExists
+  , isChannelOwner
+  , updateChannelPrivacy
+  , attachChannel
+  , Visibility(..)
+  , clearChannels
   , booksChannels
+  , channelBooks
   , Channel(..)
-  , ChannelID )
+  , ChannelID(..) )
   where
 
 import ClassyPrelude
 import Database.Schema
 import Database
 import Database.Selda
+import Database.Selda.Generic
+
+import Control.Monad.Trans.Maybe
+
+getChannel :: (MonadSelda m, MonadMask m, MonadIO m) => ChannelID -> m (Maybe Channel)
+getChannel identifier = listToMaybe . fromRels <$> query q
+  where
+    q = do
+      ch@(channelId :*: _) <- select (gen channels)
+      restrict (channelId .== literal identifier)
+      return ch
+
+channelExists :: (MonadSelda m, MonadMask m, MonadIO m) => ChannelID -> m Bool
+channelExists identifier = not . null <$> getChannel identifier
+
+isChannelOwner :: (MonadSelda m, MonadIO m, MonadMask m) => ChannelID -> Username -> m Bool
+isChannelOwner identifier username = not . null <$> query q
+  where
+    q = do
+      userId :*: _ :*: username' :*: _ <- select (gen users)
+      channelId :*: _ :*: channelOwner :*: _ <- select (gen channels)
+      restrict (userId .== channelOwner)
+      restrict (username' .== literal username)
+      restrict (channelId .== literal identifier)
+      return channelId
 
 userChannels :: (MonadMask m, MonadIO m) => Username -> SeldaT m [Channel]
 userChannels username = fromRels <$> query q
   where
     q = do
       userId :*: _ :*: username' :*: _ <- select (gen users)
-      channel@(_ :*: _ :*: owner) <- select (gen channels)
+      channel@(_ :*: _ :*: owner :*: _) <- select (gen channels)
       restrict (owner .== userId)
       restrict (username' .== literal username)
       return channel
 
-insertChannel :: (MonadMask m, MonadIO m) => Username -> Text -> SeldaT m ()
+updateChannelPrivacy :: (MonadMask m, MonadIO m, MonadSelda m) => ChannelID -> Visibility -> m (Maybe Channel)
-insertChannel username channel = do
+updateChannelPrivacy channelId visibility = do
-  mUserId <- listToMaybe <$> getUser
+  void $ update (gen channels) predicate (\channel -> channel `with` [pVis := literal visibility])
-  void $ forM mUserId $ \userId ->
+  getChannel channelId
-    insertUnless (gen channels) (doesNotExist userId) [ def :*: channel :*: userId ]
   where
-    doesNotExist userId (_ :*: channel' :*: userId') = channel' .== literal channel .&& userId' .== literal userId
+    predicate (channelId' :*: _) = channelId' .== literal channelId
+    _ :*: _ :*: _ :*: pVis = selectors (gen channels)
+
+insertChannel :: (MonadMask m, MonadIO m, MonadSelda m) => Username -> Text -> Visibility -> m (Maybe Channel)
+insertChannel username channel visibility = runMaybeT $ do
+  userId <- MaybeT (listToMaybe <$> getUser)
+  channelId <- toChannelId <$> MaybeT (insertUnless (gen channels) (doesNotExist userId) [ def :*: channel :*: userId :*: visibility ])
+  MaybeT (listToMaybe . fromRels <$> query (q channelId))
+  where
+    q channelId = do
+      ch@(channelId' :*: _) <- select (gen channels)
+      restrict (channelId' .== literal channelId)
+      return ch
+    toChannelId = ChannelID . fromRowId
+    doesNotExist userId (_ :*: channel' :*: userId' :*: _) = channel' .== literal channel .&& userId' .== literal userId
     getUser = query $ do
       userId :*: _ :*: user :*: _ <- select (gen users)
       restrict (user .== literal username)
       return userId
 
-booksChannels :: (MonadMask m, MonadIO m) => BookID -> SeldaT m [Channel]
+channelBooks :: (MonadSelda m, MonadMask m, MonadIO m) => Username -> ChannelID -> m [Book]
-booksChannels contentHash = fromRels <$> query q
+channelBooks username identifier = fromRels <$> query q
   where
     q = do
-      channelId :*: contentHash' <- select (gen bookChannels)
+      channelId :*: bookId' <- select (gen bookChannels)
+      channelId' :*: _ :*: owner :*: _ <- select (gen channels)
+      userId :*: _ :*: username' :*: _ <- select (gen users)
+      book@(bookId :*: _) <- select (gen books)
+      restrict (username' .== literal username .&& owner .== userId)
+      restrict (channelId .== literal identifier .&& channelId .== channelId')
+      restrict (bookId .== bookId')
+      return book
+
+booksChannels :: (MonadSelda m, MonadMask m, MonadIO m) => BookID -> m [Channel]
+booksChannels bookId = fromRels <$> query q
+  where
+    q = do
+      channelId :*: bookId' <- select (gen bookChannels)
       ch@(channelId' :*: _) <- select (gen channels)
       restrict (channelId .== channelId')
-      restrict (contentHash' .== literal contentHash)
+      restrict (bookId' .== literal bookId)
       return ch
+
+attachChannel :: (MonadMask m, MonadIO m, MonadSelda m) => Username -> BookID -> Text -> m ()
+attachChannel username bookId channel = do
+  mCh <- fromRels <$> query channelQ
+  forM_ mCh $ \Channel{identifier} ->
+    whenM (null <$> query (attachQ identifier)) $
+      void $ insertGen bookChannels [BookChannel identifier bookId]
+  where
+    attachQ channelId = do
+      (channelId' :*: bookId') <- select (gen bookChannels)
+      restrict (channelId' .== literal channelId .&& bookId' .== literal bookId)
+      return channelId'
+    channelQ = do
+      userId :*: _ :*: username' :*: _ <- select (gen users)
+      ch@(_ :*: channel' :*: owner :*: _) <- select (gen channels)
+      restrict (username' .== literal username)
+      restrict (owner .== userId)
+      restrict (channel' .== literal channel)
+      return ch
+
+clearChannels :: (MonadMask m, MonadIO m, MonadSelda m) => BookID -> m Int
+clearChannels bookId = deleteFrom (gen bookChannels) (\(_ :*: bookId') -> bookId' .== literal bookId)

src/Database/Schema.hs

@@ -42,9 +42,9 @@ instance SqlType Username where
 
 newtype UserID = UserID {unUserID :: Int} deriving (Show)
 
-newtype BookID = BookID {unBookID :: Int} deriving (Show, ToJSON, FromJSON, FromHttpApiData, Eq, Ord)
+newtype BookID = BookID {unBookID :: Int} deriving (Show, ToJSON, FromJSON, FromHttpApiData, Eq, Ord, ToHttpApiData)
 
-newtype ChannelID = ChannelID {unChannelID :: Int} deriving (Show, ToHttpApiData, FromHttpApiData)
+newtype ChannelID = ChannelID {unChannelID :: Int} deriving (Show, ToHttpApiData, FromHttpApiData, ToJSON, FromJSON)
 
 newtype TagID = TagID {unTagID :: Int} deriving (Show)
 
@@ -101,7 +101,7 @@ newtype HashDigest = HashDigest { unHex :: ByteString } deriving Show
 data Book = Book { identifier :: BookID
                  , contentHash :: Maybe HashDigest
                  , contentType :: Text
-                 , title :: Maybe Text
+                 , title :: Text
                  , description :: Maybe Text
                  , owner :: UserID }
           deriving (Show, Generic)
@@ -124,9 +124,22 @@ data Tag = Tag { identifier :: TagID
                , owner :: UserID }
          deriving (Show, Generic)
 
+data Visibility = Public | Private | Followers
+                deriving (Show, Read, Generic)
+
+instance ToJSON Visibility
+instance FromJSON Visibility
+
+instance SqlType Visibility where
+  mkLit = LCustom . LText . pack . show
+  fromSql (SqlString x) = fromMaybe (error "fromSql: Not a valid visibility token") . readMay . unpack $ x
+  fromSql _             = error "fromSql: Not a valid visibility token"
+  defaultValue = mkLit Private
+
 data Channel = Channel { identifier :: ChannelID
                        , channel :: Text
-                       , owner :: UserID }
+                       , owner :: UserID
+                       , visibility :: Visibility }
              deriving (Show, Generic)
 
 tags :: GenTable Tag

src/Database/Tag.hs

@@ -0,0 +1,61 @@
+{-# Language TypeApplications #-}
+{-# Language TypeOperators #-}
+{-# Language DataKinds #-}
+{-# Language DuplicateRecordFields #-}
+{-# Language NamedFieldPuns #-}
+module Database.Tag
+  ( def
+  , booksTags
+  , attachTag
+  , upsertTag
+  , clearTags
+  , Tag(..) ) where
+
+import ClassyPrelude
+import Database.Schema
+import Database
+import Database.Selda
+import Database.Selda.Generic
+import Control.Monad.Trans.Maybe
+
+upsertTag :: (MonadMask m, MonadIO m, MonadSelda m) => Username -> Text -> m (Maybe Tag)
+upsertTag username tag = runMaybeT $ do
+  userId <- MaybeT (listToMaybe <$> query userQ)
+  void $ lift $ upsert (gen tags) (predicate userId) id [toRel (Tag def tag userId)]
+  MaybeT (listToMaybe . fromRels <$> query (tagQ userId))
+  where
+    predicate userId (_ :*: tag' :*: owner) = tag' .== literal tag .&& owner .== literal userId
+    tagQ userId = do
+      t@(_ :*: tag' :*: owner) <- select (gen tags)
+      restrict (tag' .== literal tag .&& owner .== literal userId)
+      return t
+    userQ = do
+      userId :*: _ :*: username' :*: _ <- select (gen users)
+      restrict (username' .== literal username)
+      return userId
+
+booksTags :: (MonadMask m, MonadIO m, MonadSelda m) => BookID -> m [Tag]
+booksTags bookId = fromRels <$> query q
+  where
+    q = do
+      tagId :*: bookId' <- select (gen bookTags)
+      tag@(tagId' :*: _) <- select (gen tags)
+      restrict (tagId .== tagId')
+      restrict (bookId' .== literal bookId)
+      return tag
+
+attachTag :: (MonadMask m, MonadIO m, MonadSelda m) => Username -> BookID -> Text -> m ()
+attachTag username bookId tag = do
+  maybeT <- upsertTag username tag
+  forM_ maybeT $ \Tag{identifier} -> do
+    whenM (null <$> query (tagQ identifier)) $
+      void $ insertGen bookTags [BookTag identifier bookId]
+  where
+    tagQ tagId = do
+      (tagId' :*: bookId') <- select (gen bookTags)
+      restrict (tagId' .== literal tagId .&& bookId' .== literal bookId)
+      return tagId'
+
+clearTags :: (MonadMask m, MonadIO m, MonadSelda m) => BookID -> m Int
+clearTags bookId = deleteFrom (gen bookTags) (\(_ :*: bookId') -> bookId' .== literal bookId)
+