{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}

{- |
Module      :  Neovim.Context.Internal
Description :  Abstract description of the plugin provider's internal context
Copyright   :  (c) Sebastian Witte
License     :  Apache-2.0

Maintainer  :  woozletoff@gmail.com
Stability   :  experimental
Portability :  GHC

To shorten function and data type names, import this qualfied as @Internal@.
-}
module Neovim.Context.Internal where

import Neovim.Classes (
    AnsiStyle,
    Doc,
    NFData,
    Pretty (pretty),
    deepseq,
 )
import Neovim.Exceptions (
    NeovimException (..),
    exceptionToDoc,
 )
import Neovim.Plugin.Classes (
    FunctionName (..),
    FunctionalityDescription,
    HasFunctionName (nvimMethod),
    NeovimEventId (..),
    NvimMethod,
    Subscription (..),
    SubscriptionId (..),
 )
import Neovim.Plugin.IPC (SomeMessage)

import Data.Map (Map)
import qualified Data.Map as Map
import Data.MessagePack (Object)
import Data.Monoid (Ap (Ap))
import Data.Text (Text, pack)
import System.Log.Logger (errorM)
import UnliftIO (
    Exception (fromException),
    Handler (..),
    MVar,
    MonadIO (..),
    MonadUnliftIO,
    SomeException,
    TMVar,
    TQueue,
    TVar,
    atomically,
    catches,
    modifyTVar',
    newEmptyMVar,
    newEmptyTMVarIO,
    newTMVarIO,
    newTQueueIO,
    newTVarIO,
    putTMVar,
    readTVar,
    takeTMVar,
    throwIO,
    try,
 )

import Prettyprinter (viaShow)

import Conduit (MonadThrow)
import Control.Exception (
    ArithException,
    ArrayException,
    ErrorCall,
    PatternMatchFail,
 )
import qualified Control.Monad.Fail as Fail
import Control.Monad.Reader (
    MonadReader (ask, local),
    ReaderT (..),
    asks,
    void,
 )
import Prelude

{- | This is the environment in which all plugins are initially started.

 Functions have to run in this transformer stack to communicate with neovim.
 If parts of your own functions dont need to communicate with neovim, it is
 good practice to factor them out. This allows you to write tests and spot
 errors easier. Essentially, you should treat this similar to 'IO' in general
 haskell programs.
-}
newtype Neovim env a = Neovim
    {unNeovim :: ReaderT (Config env) IO a}
    deriving newtype (Functor, Applicative, Monad, MonadIO, MonadThrow, MonadUnliftIO)
    deriving (Semigroup, Monoid) via (Ap (Neovim env) a)

-- | User facing instance declaration for the reader state.
instance MonadReader env (Neovim env) where
    ask = Neovim $ asks customConfig
    local f (Neovim a) = do
        r <- Neovim ask
        liftIO $ runReaderT a (r{customConfig = f (customConfig r)})

instance Fail.MonadFail (Neovim env) where
    fail = throwIO . ErrorMessage . pretty

-- | Same as 'ask' for the 'InternalConfig'.
ask' :: Neovim env (Config env)
ask' = Neovim ask

-- | Same as 'asks' for the 'InternalConfig'.
asks' :: (Config env -> a) -> Neovim env a
asks' = Neovim . asks

exceptionHandlers :: [Handler IO (Either (Doc ann) a)]
exceptionHandlers =
    [ Handler $ \(_ :: ArithException) -> ret "ArithException (e.g. division by 0)"
    , Handler $ \(_ :: ArrayException) -> ret "ArrayException"
    , Handler $ \(_ :: ErrorCall) -> ret "ErrorCall (e.g. call of undefined or error"
    , Handler $ \(_ :: PatternMatchFail) -> ret "Pattern match failure"
    , Handler $ \(_ :: SomeException) -> ret "Unhandled exception"
    ]
  where
    ret = return . Left

-- | Initialize a 'Neovim' context by supplying an 'InternalEnvironment'.
runNeovim ::
    NFData a =>
    Config env ->
    Neovim env a ->
    IO (Either (Doc AnsiStyle) a)
runNeovim = runNeovimInternal (\a -> a `deepseq` return a)

runNeovimInternal ::
    (a -> IO a) ->
    Config env ->
    Neovim env a ->
    IO (Either (Doc AnsiStyle) a)
runNeovimInternal f r (Neovim a) =
    (try . runReaderT a) r >>= \case
        Left e -> case fromException e of
            Just e' ->
                return . Left . exceptionToDoc $ (e' :: NeovimException)
            Nothing -> do
                liftIO . errorM "Context" $ "Converting Exception to Error message: " ++ show e
                (return . Left . viaShow) e
        Right res ->
            (Right <$> f res) `catches` exceptionHandlers

{- | Create a new unique function name. To prevent possible name clashes, digits
 are stripped from the given suffix.
-}
newUniqueFunctionName :: Neovim env FunctionName
newUniqueFunctionName = do
    tu <- asks' uniqueCounter
    -- reverseing the integer string should distribute the first character more
    -- evently and hence cause faster termination for comparisons.
    fmap (F . pack . reverse . show) . liftIO . atomically $ do
        u <- readTVar tu
        modifyTVar' tu succ
        return u

{- | This data type is used to dispatch a remote function call to the appopriate
 recipient.
-}
newtype FunctionType
    = -- | 'Stateful' functions are handled within a special thread, the 'TQueue'
      -- is the communication endpoint for the arguments we have to pass.
      Stateful (TQueue SomeMessage)

instance Pretty FunctionType where
    pretty = \case
        Stateful _ -> "\\os -> Neovim env o"

-- | Type of the values stored in the function map.
type FunctionMapEntry = (FunctionalityDescription, FunctionType)

{- | A function map is a map containing the names of functions as keys and some
 context dependent value which contains all the necessary information to
 execute that function in the intended way.

 This type is only used internally and handles two distinct cases. One case
 is a direct function call, wich is simply a function that accepts a list of
 'Object' values and returns a result in the 'Neovim' context. The second
 case is calling a function that has a persistent state. This is mediated to
 a thread that reads from a 'TQueue'. (NB: persistent currently means, that
 state is stored for as long as the plugin provider is running and not
 restarted.)
-}
type FunctionMap = Map NvimMethod FunctionMapEntry

-- | Create a new function map from the given list of 'FunctionMapEntry' values.
mkFunctionMap :: [FunctionMapEntry] -> FunctionMap
mkFunctionMap = Map.fromList . map (\e -> (nvimMethod (fst e), e))

data Subscriptions = Subscriptions
    { nextSubscriptionId :: SubscriptionId
    , byEventId :: Map NeovimEventId [Subscription]
    }

{- | Subscribe to an event. When the event is received, the given callback function
 is run. It is usually necessary to call the appropriate API function in order for
 /neovim/ to send the notifications to /nvim-hs/. The returned subscription can be
 used to 'unsubscribe'.
-}
subscribe :: Text -> ([Object] -> Neovim env ()) -> Neovim env Subscription
subscribe event action = do
    let eventId = NeovimEventId event
    cfg <- ask'
    let subscriptions' = subscriptions cfg
    atomically $ do
        s <- takeTMVar subscriptions'
        let subscriptionId = nextSubscriptionId s
        let newSubscription =
                Subscription
                    { subId = subscriptionId
                    , subEventId = eventId
                    , subAction = void . runNeovim cfg . action
                    }
        putTMVar
            subscriptions'
            s
                { nextSubscriptionId = succ subscriptionId
                , byEventId = Map.insertWith (<>) eventId [newSubscription] (byEventId s)
                }
        pure newSubscription

-- | Remove the subscription that has been returned by 'subscribe'.
unsubscribe :: Subscription -> Neovim env ()
unsubscribe subscription = do
    subscriptions' <- asks' subscriptions
    void . atomically $ do
        s <- takeTMVar subscriptions'
        let eventId = subEventId subscription
            deleteSubscription = Just . filter ((/= subId subscription) . subId)
        putTMVar
            subscriptions'
            s
                { byEventId = Map.update deleteSubscription eventId (byEventId s)
                }

{- | A wrapper for a reader value that contains extra fields required to
 communicate with the messagepack-rpc components and provide necessary data to
 provide other globally available operations.

 Note that you most probably do not want to change the fields prefixed with an
 underscore.
-}
data Config env = Config
    -- Global settings; initialized once
    { eventQueue :: TQueue SomeMessage
    -- ^ A queue of messages that the event handler will propagate to
    -- appropriate threads and handlers.
    , transitionTo :: MVar StateTransition
    -- ^ The main thread will wait for this 'MVar' to be filled with a value
    -- and then perform an action appropriate for the value of type
    -- 'StateTransition'.
    , providerName :: TMVar (Either String Int)
    -- ^ Since nvim-hs must have its "Neovim.RPC.SocketReader" and
    -- "Neovim.RPC.EventHandler" running to determine the actual channel id
    -- (i.e. the 'Int' value here) this field can only be set properly later.
    -- Hence, the value of this field is put in an 'TMVar'.
    -- Name that is used to identify this provider. Assigning such a name is
    -- done in the neovim config (e.g. ~\/.nvim\/nvimrc).
    , uniqueCounter :: TVar Integer
    -- ^ This 'TVar' is used to generate uniqe function names on the side of
    -- /nvim-hs/. This is useful if you don't want to overwrite existing
    -- functions or if you create autocmd functions.
    , globalFunctionMap :: TMVar FunctionMap
    -- ^ This map is used to dispatch received messagepack function calls to
    -- it's appropriate targets.
    , -- Local settings; intialized for each stateful component

      pluginSettings :: Maybe (PluginSettings env)
    -- ^ In a registered functionality this field contains a function (and
    -- possibly some context dependent values) to register new functionality.
    , subscriptions :: TMVar Subscriptions
    -- ^ Plugins can dynamically subscribe to events that neovim sends.
    , customConfig :: env
    -- ^ Plugin author supplyable custom configuration. Queried on the
    -- user-facing side with 'ask' or 'asks'.
    }

{- | Convenient helper to create a new config for the given state and read-only
 config.

 Sets the 'pluginSettings' field to 'Nothing'.
-}
retypeConfig :: env -> Config anotherEnv -> Config env
retypeConfig r cfg = cfg{pluginSettings = Nothing, customConfig = r}

{- | This GADT is used to share information between stateless and stateful
 plugin threads since they work fundamentally in the same way. They both
 contain a function to register some functionality in the plugin provider
 as well as some values which are specific to the one or the other context.
-}
data PluginSettings env where
    StatefulSettings ::
        ( FunctionalityDescription ->
          ([Object] -> Neovim env Object) ->
          TQueue SomeMessage ->
          TVar (Map NvimMethod ([Object] -> Neovim env Object)) ->
          Neovim env (Maybe FunctionMapEntry)
        ) ->
        TQueue SomeMessage ->
        TVar (Map NvimMethod ([Object] -> Neovim env Object)) ->
        PluginSettings env

{- | Create a new 'InternalConfig' object by providing the minimal amount of
 necessary information.

 This function should only be called once per /nvim-hs/ session since the
 arguments are shared across processes.
-}
newConfig :: IO (Maybe String) -> IO env -> IO (Config env)
newConfig ioProviderName r =
    Config
        <$> newTQueueIO
        <*> newEmptyMVar
        <*> (maybe newEmptyTMVarIO (newTMVarIO . Left) =<< ioProviderName)
        <*> newTVarIO 100
        <*> newEmptyTMVarIO
        <*> pure Nothing
        <*> newTMVarIO (Subscriptions (SubscriptionId 1) mempty)
        <*> r

-- | The state that the plugin provider wants to transition to.
data StateTransition
    = -- | Quit the plugin provider.
      Quit
    | -- | Restart the plugin provider.
      Restart
    | -- | The plugin provider failed to start or some other error occured.
      Failure (Doc AnsiStyle)
    | -- | The plugin provider started successfully.
      InitSuccess
    deriving (Show)