{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications    #-}
{-|
Module      : HsLua.Marshalling.Userdata
Copyright   : © 2007–2012 Gracjan Polak;
              © 2012–2016 Ömer Sinan Ağacan;
              © 2017-2021 Albert Krewinkel
License     : MIT
Maintainer  : Albert Krewinkel <tarleb+hslua@zeitkraut.de>
Stability   : beta
Portability : non-portable (depends on GHC)

Convenience functions to use Haskell values as Lua userdata.
-}
module HsLua.Marshalling.Userdata
  ( pushIterator
  ) where

import Control.Monad (void)
import HsLua.Core as Lua

-- | Pushes three values to the stack that can be used in a generic for
-- loop to lazily iterate over all values in the list. Keeps the
-- remaining list in a userdata state.
pushIterator :: forall a e. LuaError e
             => (a -> LuaE e NumResults)  -- ^ the values to push
             -> [a]                       -- ^ list to iterate over lazily
             -> LuaE e NumResults
pushIterator :: (a -> LuaE e NumResults) -> [a] -> LuaE e NumResults
pushIterator a -> LuaE e NumResults
pushValues [a]
xs = do
  -- push initial state
  LuaE e NumResults -> LuaE e ()
forall e. LuaError e => HaskellFunction e -> LuaE e ()
pushHaskellFunction LuaE e NumResults
nextItem
  LuaE e ()
pushInitialState
  LuaE e ()
forall e. LuaE e ()
pushnil
  NumResults -> LuaE e NumResults
forall (m :: * -> *) a. Monad m => a -> m a
return (CInt -> NumResults
NumResults CInt
3)
  where
    nextItem :: LuaE e NumResults
    nextItem :: LuaE e NumResults
nextItem = do
      Maybe [a]
props <- StackIndex -> Name -> LuaE e (Maybe [a])
forall a e. StackIndex -> Name -> LuaE e (Maybe a)
fromuserdata @[a] (CInt -> StackIndex
nthBottom CInt
1) Name
statename
      case Maybe [a]
props of
        Maybe [a]
Nothing -> String -> LuaE e NumResults
forall e a. LuaError e => String -> LuaE e a
failLua
          String
"Error in iterator: could not retrieve iterator state."
        Just [] -> NumResults
2 NumResults -> LuaE e () -> LuaE e NumResults
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ (LuaE e ()
forall e. LuaE e ()
pushnil LuaE e () -> LuaE e () -> LuaE e ()
forall (f :: * -> *) a b. Applicative f => f a -> f b -> f b
*> LuaE e ()
forall e. LuaE e ()
pushnil)  -- end loop
        Just (a
y:[a]
ys) -> do
          Bool
success <- StackIndex -> Name -> [a] -> LuaE e Bool
forall a e. StackIndex -> Name -> a -> LuaE e Bool
putuserdata @[a] (CInt -> StackIndex
nthBottom CInt
1) Name
statename [a]
ys
          if Bool -> Bool
not Bool
success
            then String -> LuaE e NumResults
forall e a. LuaError e => String -> LuaE e a
failLua String
"Error in iterator: could not update iterator state."
            else a -> LuaE e NumResults
pushValues a
y

    statename :: Name
    statename :: Name
statename = Name
"HsLua iterator state"

    pushInitialState :: LuaE e ()
    pushInitialState :: LuaE e ()
pushInitialState = do
      [a] -> LuaE e ()
forall a e. a -> LuaE e ()
newhsuserdata @[a] [a]
xs
      LuaE e Bool -> LuaE e ()
forall (f :: * -> *) a. Functor f => f a -> f ()
void (Name -> LuaE e Bool
forall e. Name -> LuaE e Bool
newudmetatable Name
statename)
      StackIndex -> LuaE e ()
forall e. StackIndex -> LuaE e ()
setmetatable (CInt -> StackIndex
nth CInt
2)