{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ExplicitForAll #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}

-- |
-- Module: Capnp.Convert
-- Description: Convert between messages, typed capnproto values, and (lazy)bytestring(builders).
--
-- This module provides various helper functions to convert between messages, types defined
-- in capnproto schema (called "values" in the rest of this module's documentation),
-- bytestrings (both lazy and strict), and bytestring builders.
--
-- Note that most of the functions which decode messages or raw bytes do *not* need to be
-- run inside of an instance of 'MonadLimit'; they choose an appropriate limit based on the
-- size of the input.
--
-- Note that not all conversions exist or necessarily make sense.
module Capnp.Convert
  ( msgToBuilder,
    msgToLBS,
    msgToBS,
    bsToMsg,
    lbsToMsg,
    -- new API
    msgToRaw,
    msgToParsed,
    bsToRaw,
    bsToParsed,
    lbsToRaw,
    lbsToParsed,
    parsedToRaw,
    parsedToMsg,
    parsedToBuilder,
    parsedToBS,
    parsedToLBS,
  )
where

import Capnp.Classes (Parse (encode, parse))
import qualified Capnp.Message as M
import Capnp.Mutability (Mutability (..), freeze)
import qualified Capnp.Repr as R
import qualified Capnp.Untyped as U
import Control.Monad.Catch (MonadThrow)
import qualified Data.ByteString as BS
import qualified Data.ByteString.Builder as BB
import qualified Data.ByteString.Lazy as LBS

{- TODO: unused currently, but we should put it back into service for things like
   msgToParsed.

-- | Compute a reasonable limit based on the size of a message. The limit
-- is the total number of words in all of the message's segments, multiplied
-- by 10 to provide some slack for decoding default values.
limitFromMsg :: (MonadThrow m, M.MonadReadMessage mut m) => M.Message mut -> m WordCount
limitFromMsg msg = do
    messageWords <- countMessageWords
    pure (messageWords * 10)
  where
    countMessageWords = do
        segCount <- M.numSegs msg
        foldlM
            (\total i -> do
                words <- M.getSegment msg i >>= M.numWords
                pure (words + total)
            )
            0
            [0..segCount - 1]
-}

-- | Convert an immutable message to a bytestring 'BB.Builder'.
-- To convert a mutable message, 'freeze' it first.
msgToBuilder :: M.Message 'Const -> BB.Builder
msgToBuilder = M.encode

-- | Convert an immutable message to a lazy 'LBS.ByteString'.
-- To convert a mutable message, 'freeze' it first.
msgToLBS :: M.Message 'Const -> LBS.ByteString
msgToLBS = BB.toLazyByteString . msgToBuilder

-- | Convert an immutable message to a strict 'BS.ByteString'.
-- To convert a mutable message, 'freeze' it first.
msgToBS :: M.Message 'Const -> BS.ByteString
msgToBS = LBS.toStrict . msgToLBS

-- | Convert a strict 'BS.ByteString' to a message.
bsToMsg :: MonadThrow m => BS.ByteString -> m (M.Message 'Const)
bsToMsg = M.decode

-- | Convert a lazy 'LBS.ByteString' to a message.
lbsToMsg :: MonadThrow m => LBS.ByteString -> m (M.Message 'Const)
lbsToMsg = bsToMsg . LBS.toStrict

-- | Get the root pointer of a message, wrapped as a 'R.Raw'.
msgToRaw :: forall a m mut. (U.ReadCtx m mut, R.IsStruct a) => M.Message mut -> m (R.Raw a mut)
msgToRaw = fmap R.Raw . U.rootPtr

-- | Get the root pointer of a message, as a parsed ADT.
msgToParsed :: forall a m pa. (U.ReadCtx m 'Const, R.IsStruct a, Parse a pa) => M.Message 'Const -> m pa
msgToParsed msg = msgToRaw msg >>= parse

-- | Like 'msgToRaw', but takes a (strict) bytestring.
bsToRaw :: forall a m. (U.ReadCtx m 'Const, R.IsStruct a) => BS.ByteString -> m (R.Raw a 'Const)
bsToRaw bs = bsToMsg bs >>= msgToRaw

-- | Like 'msgToParsed', but takes a (strict) bytestring.
bsToParsed :: forall a pa m. (U.ReadCtx m 'Const, R.IsStruct a, Parse a pa) => BS.ByteString -> m pa
bsToParsed bs = bsToRaw bs >>= parse

-- | Like 'msgToRaw', but takes a (lazy) bytestring.
lbsToRaw :: forall a m. (U.ReadCtx m 'Const, R.IsStruct a) => LBS.ByteString -> m (R.Raw a 'Const)
lbsToRaw = bsToRaw . LBS.toStrict

-- | Like 'msgToParsed', but takes a (lazzy) bytestring.
lbsToParsed :: forall a pa m. (U.ReadCtx m 'Const, R.IsStruct a, Parse a pa) => LBS.ByteString -> m pa
lbsToParsed = bsToParsed . LBS.toStrict

-- | Serialize the parsed form of a struct into its 'R.Raw' form, and make it the root
-- of its message.
parsedToRaw :: forall a m pa s. (U.RWCtx m s, R.IsStruct a, Parse a pa) => pa -> m (R.Raw a ('Mut s))
parsedToRaw p = do
  msg <- M.newMessage Nothing
  value@(R.Raw struct) <- encode msg p
  U.setRoot struct
  pure value

-- | Serialize the parsed form of a struct into a message with that value as its
-- root, returning the message.
parsedToMsg :: forall a m pa s. (U.RWCtx m s, R.IsStruct a, Parse a pa) => pa -> m (M.Message ('Mut s))
parsedToMsg p = do
  root <- parsedToRaw p
  pure $ U.message @(R.Raw a) root

-- | Serialize the parsed form of a struct and return it as a 'BB.Builder'
parsedToBuilder :: forall a m pa s. (U.RWCtx m s, R.IsStruct a, Parse a pa) => pa -> m BB.Builder
parsedToBuilder p = msgToBuilder <$> (parsedToMsg p >>= freeze)

-- | Serialize the parsed form of a struct and return it as a lazy 'LBS.ByteString'
parsedToLBS :: forall a m pa s. (U.RWCtx m s, R.IsStruct a, Parse a pa) => pa -> m LBS.ByteString
parsedToLBS = fmap BB.toLazyByteString . parsedToBuilder

-- | Serialize the parsed form of a struct and return it as a strict 'BS.ByteString'
parsedToBS :: forall a m pa s. (U.RWCtx m s, R.IsStruct a, Parse a pa) => pa -> m BS.ByteString
parsedToBS = fmap LBS.toStrict . parsedToLBS