{-# OPTIONS_GHC -XEmptyDataDecls #-}
--
-- (c) 2009, Sigbjorn Finne.
-- 
-- Example of how to create and execute LINQ queries
-- from Haskell beyond basic 'where' queries (cf. LinqQuery.hs)
--
-- To test, call 'whereSelectIt' from GHCi.
--
module LinqSelect where

import Data.Int
import NET
import NET.System.Func
import NET.System.Collections.Generic.Queue
import NET.System.Collections.Generic.List as List
import NET.System.Linq.Enumerable
import NET.System.Linq.IOrderedEnumerable

instance NET.System.Linq.IOrderedEnumerable.IOrderedEnumerable (Queue_ a b) where
  instanceName_IOrderedEnumerable _ = ""

newQueue :: NET.Type a => a -> IO (Queue () a)
newQueue a = newGeneric "System.Collections.Generic.Queue" a

whereSelectIt :: IO ()
whereSelectIt = do
 dict <- newQueue ""
 mapM_ (flip enqueue dict) ["Harry", "Dick", "Jan"]
  -- simple predicate for picking strings longer than the given length.
 let predicate v = return (length v > 2)
 putStrLn "Performing the query.."
 d0 <- dict # whereQ predicate
 d1 <- (d0 `asTypeOf` dict) # orderBy (\ x -> return (length x))
 d  <- (d1 `asTypeOf` dict) # select  (\ x -> return (x ++ show (length x)))
 putStrLn "..query done; predicate not yet invoked.."
 vs <- d # getList
 putStrLn ("Query result: " ++ show vs)
 putStrLn "Running some extra LINQ operations over query result.."
 let showRes c act = d # act >>= \ v -> putStrLn (c ++ ": " ++ show v)
 showRes "First element" first
 showRes "Number of elements" NET.System.Linq.Enumerable.count
 showRes "Contains Jan3?" (NET.System.Linq.Enumerable.contains "Jan3")
 showRes "Contains Jan4?" (NET.System.Linq.Enumerable.contains "Jan4")
 showRes "Has Jan4?" (NET.System.Linq.Enumerable.any_1 (\ x -> return (x == "Jan4")))
 showRes "Has Jan3?" (NET.System.Linq.Enumerable.any_1 (\ x -> return (x == "Jan3")))

 d2  <- NET.System.Linq.Enumerable.concat d d
 vs  <- d2 # getList 
 putStrLn ("Query result: " ++ show vs)

 dict # enqueue "Bob!"
 d2  <- NET.System.Linq.Enumerable.union d d
 vs <-  d2 # getList 
 putStrLn ("2nd query result: " ++ show vs)
 
getList :: (Type a, Result a) => Queue () a -> IO [a]
getList q = do
 ls    <- q # toList
 count <- ls # getField "Count" ()
 mapM (\ i -> ls # List.get_Item i) [(0::Int32)..(count-1)]