{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}

module Capnp.GenHelpers
  ( dataField,
    ptrField,
    groupField,
    voidField,
    readVariant,
    Mutability (..),
    TypeParam,
    newStruct,
    parseEnum,
    encodeEnum,
    getPtrConst,
    BS.ByteString,
    module F,
    module Capnp.Accessors,

    -- * Re-exports from the standard library.
    Proxy (..),
  )
where

import Capnp.Accessors
import qualified Capnp.Basics as NB
import Capnp.Bits
import qualified Capnp.Classes as NC
import Capnp.Constraints (TypeParam)
import Capnp.Convert (bsToRaw)
import Capnp.Fields as F
import Capnp.Message (Mutability (..))
import qualified Capnp.Message as M
import qualified Capnp.Repr as R
import Capnp.TraversalLimit (evalLimitT)
import qualified Capnp.Untyped as U
import Data.Bits
import qualified Data.ByteString as BS
import Data.Functor ((<&>))
import Data.Maybe (fromJust)
import Data.Proxy (Proxy (..))
import Data.Word

dataField ::
  forall b a sz.
  ( R.ReprFor b ~ 'R.Data sz,
    NC.IsWord (R.UntypedData sz)
  ) =>
  BitCount ->
  Word16 ->
  BitCount ->
  Word64 ->
  F.Field 'F.Slot a b
dataField shift index nbits defaultValue =
  F.Field $
    F.DataField @sz
      F.DataFieldLoc
        { shift,
          index,
          mask = ((1 `shiftL` fromIntegral nbits) - 1) `shiftL` fromIntegral shift,
          defaultValue
        }

ptrField :: forall a b. R.IsPtr b => Word16 -> F.Field 'F.Slot a b
ptrField = F.Field . F.PtrField @(R.PtrReprFor (R.ReprFor b))

groupField :: (R.ReprFor b ~ 'R.Ptr ('Just 'R.Struct)) => F.Field 'F.Group a b
groupField = F.Field F.GroupField

voidField :: (R.ReprFor b ~ 'R.Data 'R.Sz0) => F.Field 'F.Slot a b
voidField = F.Field F.VoidField

-- | Like 'readField', but accepts a variant. Warning: *DOES NOT CHECK* that the
-- variant is the one that is set. This should only be used by generated code.
readVariant ::
  forall k a b mut m.
  ( R.IsStruct a,
    U.ReadCtx m mut
  ) =>
  F.Variant k a b ->
  R.Raw a mut ->
  m (R.Raw b mut)
readVariant F.Variant {field} = readField field

newStruct :: forall a m s. (U.RWCtx m s, NC.TypedStruct a) => () -> M.Message ('Mut s) -> m (R.Raw a ('Mut s))
newStruct () msg = R.Raw . R.fromRaw <$> NC.new @NB.AnyStruct (NC.numStructWords @a, NC.numStructPtrs @a) msg

parseEnum ::
  (R.ReprFor a ~ 'R.Data 'R.Sz16, Enum a, Applicative m) =>
  R.Raw a 'Const ->
  m a
parseEnum (R.Raw n) = pure $ toEnum $ fromIntegral n

encodeEnum ::
  forall a m s.
  (R.ReprFor a ~ 'R.Data 'R.Sz16, Enum a, U.RWCtx m s) =>
  M.Message ('Mut s) ->
  a ->
  m (R.Raw a ('Mut s))
encodeEnum _msg value = pure $ R.Raw $ fromIntegral $ fromEnum @a value

-- | Get a pointer from a ByteString, where the root object is a struct with
-- one pointer, which is the pointer we will retrieve. This is only safe for
-- trusted inputs; it reads the message with a traversal limit of 'maxBound'
-- (and so is suseptable to denial of service attacks), and it calls 'error'
-- if decoding is not successful.
--
-- The purpose of this is for defining constants of pointer type from a schema.
getPtrConst :: forall a. R.IsPtr a => BS.ByteString -> R.Raw a 'Const
getPtrConst bytes = fromJust $ evalLimitT maxBound $ do
  R.Raw root <- bsToRaw @NB.AnyStruct bytes
  U.getPtr 0 root
    >>= R.fromPtr @(R.PtrReprFor (R.ReprFor a)) (U.message @U.Struct root)
    <&> R.Raw