{-# LANGUAGE DeriveFoldable #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE DerivingStrategies #-}

module Data.Bytes.Parser.Types
  ( Parser
  , Result (..)
  , Slice (..)
  ) where

import Data.Bytes.Parser.Internal (Parser (..))

-- | The result of running a parser.
data Result e a
  = -- | An error message indicating what went wrong.
    Failure e
  | -- | The parsed value and the number of bytes
    -- remaining in parsed slice.
    Success {-# UNPACK #-} !(Slice a)
  deriving stock (Eq, Show, Foldable, Functor)

{- | Slicing metadata (an offset and a length) accompanied
by a value. This does not represent a slice into the
value. This type is intended to be used as the result
of an executed parser. In this context the slicing metadata
describe a slice into to the array (or byte array) that
from which the value was parsed.

It is often useful to check the @length@ when a parser
succeeds since a non-zero length indicates that there
was additional unconsumed input. The @offset@ is only
ever needed to construct a new slice (via @Bytes@ or
@SmallVector@) from the remaining input.
-}
data Slice a = Slice
  { offset :: {-# UNPACK #-} !Int
  -- ^ Offset into the array.
  , length :: {-# UNPACK #-} !Int
  -- ^ Length of the slice.
  , value :: a
  -- ^ The structured data that was successfully parsed.
  }
  deriving stock (Eq, Show, Foldable, Functor)