-- | An HSet is a sub-hash table in Redis, indexed by both a key and a subkey.

module HLRDB.Structures.HSet where

import Database.Redis as Redis
import HLRDB.Primitives.Redis
import HLRDB.Internal
import Control.Monad.State

-- I wanted to only have the list get/set commands, but ultimately
-- decided to include the single commands separately because `hset`
-- has a return value which specifies whether a subkey was created or not,
-- whereas hmset does not, and this can be critically useful. Amusingly,
-- even the standard `set` command does not return this information.


-- | Retrieve all elements of an HSet
hgetall :: MonadRedis m => RedisHSet a s b -> a -> m [ (s,b) ]
hgetall p@(RHSet (E _ _ d) (HSET _ ds)) =
   (fmap . fmap) (\(s,b) -> (ds s , d (pure b)))
 . unwrap
 . Redis.hgetall
 . primKey p

-- | Lookup via key and subkey
hget :: MonadRedis m => RedisHSet a s b -> a -> s -> m (Maybe b)
hget p@(RHSet (E _ _ d) (HSET e _)) k =
    (fmap . fmap) (d . pure)
  . unwrap
  . Redis.hget (primKey p k)
  . e

-- | Lookup via key and subkeys, pairing each given subkey with the lookup result
hmget :: (MonadRedis m , Traversable t) => RedisHSet a s b -> a -> t s -> m (t (s , Maybe b))
hmget p@(RHSet (E _ _ d) (HSET e _)) k t = do
  let f = (fmap . fmap . fmap) (d . pure) . fixEmpty (unwrap . Redis.hmget (primKey p k)) id . fmap e
  let xs = foldr (:) [] t
  reifyTraversal t <$> liftRedis (f xs)
  where
    reifyTraversal :: Traversable t => t a -> [ b ] -> t (a,b)
    reifyTraversal tr bs = evalState (traverse g tr) bs
      where
        g a = do
          xs <- Control.Monad.State.get
          case xs of
            [] -> error "Impossible in hmget: unexpected data size in HLRDB.Structures.HSet.hmget"
            (b:bs') -> do
              put bs'
              return (a,b)

-- | Set via key and subkey
hset :: MonadRedis m => RedisHSet a s b -> a -> s -> b -> m (ActionPerformed Creation)
hset p@(RHSet (E _ eb _) (HSET e _)) k s =
    unwrapCreatedBool
  . Redis.hset (primKey p k) (e s)
  . runIdentity
  . eb

-- | Set via key and subkeys
hmset :: (MonadRedis m , Traversable t) => RedisHSet a s b -> a -> t (s , b) -> m ()
hmset p@(RHSet (E _ eb _) (HSET e _)) k =
    fixEmpty (ignore . unwrap . Redis.hmset (primKey p k)) (\(s,b) -> (e s , runIdentity $ eb b))

-- | Delete via key and subkeys
hdel :: (MonadRedis m , Traversable t) => RedisHSet a s b -> a -> t s -> m (ActionPerformed Deletion)
hdel p@(RHSet _ (HSET e _)) k =
    fmap Deleted
  . fixEmpty' (unwrap . Redis.hdel (primKey p k)) e

-- | Set a value only if it does not currently exist in the HSET
hsetnx :: MonadRedis m => RedisHSet a s b -> a -> s -> b -> m (ActionPerformed Creation)
hsetnx p@(RHSet (E _ eb _) (HSET e _)) k s =
    unwrapCreatedBool
  . Redis.hsetnx (primKey p k) (e s)
  . runIdentity
  . eb

-- | Use a cursor to iterate a collection
hscan :: RedisHSet a s b -> a -> Cursor -> Redis (Maybe Cursor , [ (s , b) ])
hscan p@(RHSet (E _ _ d) (HSET _ d')) k =
  let f (a,b) = (d' a , d (pure b)) in
    unwrapCursor (fmap f)
  . Redis.hscan (primKey p k)