Make.hs

{-# LANGUAGE AllowAmbiguousTypes       #-}
{-# LANGUAGE DataKinds                 #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE GADTs                     #-}
{-# LANGUAGE InstanceSigs              #-}
{-# LANGUAGE PolyKinds                 #-}
{-# LANGUAGE TypeFamilies              #-}
{-# LANGUAGE UndecidableInstances      #-}

{- |
  This module provides functions to make values
  out of a registry. The general algorithm is the following

   1. for a given value type search in the existing list of values
      a value with the same type. If found return it

   2. if not found search a function having the desired output type
      if found, now try to recursively make all the input parameters.
      Keep a stack of the current types trying to be built.

   3. when trying to make an input parameter if the current input type
      is already in the types trying to be built then there is a cycle.
      Return an error in that case

   4. when a value has been constructed place it on top of the existing value
      list so that it can be reused by other functions

-}
module Data.Registry.Make where

import           Data.Dynamic
import           Data.Registry.Internal.Make
import           Data.Registry.Internal.Stack
import           Data.Registry.Internal.Types
import           Data.Registry.Registry
import qualified Prelude                         (error)
import           Protolude                       as P hiding (Constructor)
import           Type.Reflection

-- | Make an element of type 'a' out of the registry
make :: forall a ins out . (Typeable a) => Registry ins out -> a
make registry =
  -- if the registry is an unchecked one, built with +:
  -- this may fail
  case makeEither registry of
    Right a -> a
    Left  e -> Prelude.error (toS e)

-- | Make an element of type 'a' out of the registry, for a registry
--   which was possibly created with +:
makeEither :: forall a ins out . (Typeable a) => Registry ins out -> Either Text a
makeEither = makeEitherWithContext (Context [(someTypeRep (Proxy :: Proxy a), Nothing)])

-- * SPECIALIZED VALUES

-- | make for specialized values
makeSpecialized :: forall a b ins out . (Typeable a, Typeable b) => Registry ins out -> b
makeSpecialized registry =
  case makeSpecializedEither @a @b registry of
    Right a -> a
    Left  e -> Prelude.error (toS e)

-- | make for specialized values
makeSpecializedPath :: forall path b ins out . (PathToTypeReps path, Typeable b) => Registry ins out -> b
makeSpecializedPath registry =
  case makeSpecializedPathEither @path @b registry of
    Right a -> a
    Left  e -> Prelude.error (toS e)

-- | makeEither for specialized values, in case you are using an unchecked registry
makeSpecializedEither :: forall a b ins out . (Typeable a, Typeable b) => Registry ins out -> Either Text b
makeSpecializedEither = makeEitherWithContext (Context [(someTypeRep (Proxy :: Proxy a), Nothing), (someTypeRep (Proxy :: Proxy b), Nothing)])

-- | makeEither for specialized values along a path, in case you are using an unchecked registry
makeSpecializedPathEither :: forall path b ins out . (PathToTypeReps path, Typeable b) => Registry ins out -> Either Text b
makeSpecializedPathEither = makeEitherWithContext (Context ((, Nothing) <$> toList (someTypeReps (Proxy :: Proxy path))))

-- | This version of make only execute checks at runtime
--   this can speed-up compilation when writing tests or in ghci
makeEitherWithContext :: forall a ins out . (Typeable a) => Context -> Registry ins out -> Either Text a
makeEitherWithContext context registry =
  let values          = _values registry
      functions       = _functions registry
      specializations = _specializations registry
      modifiers       = _modifiers registry
      targetType      = someTypeRep (Proxy :: Proxy a)
  in
      --  use the makeUntyped function to create an element of the target type from a list of values and functions
      --  the list of values is kept as some State so that newly created values can be added to the current state
      case
        runStackWithValues values
          (makeUntyped targetType context functions specializations modifiers)

      of
        Left e ->
          Left $
             "\nThe registry is"
          <> "\n\n" <> show registry
          <> "=====================\n"
          <> "\nCould not create a " <> show targetType <> " out of the registry:"
          <> "\n\n" <> e
          <> "\n\nYou can check the registry displayed above the ===== line to verify the current values and constructors\n"


        Right Nothing ->
          Left $
          show registry
          <> "\n could not create a " <> show targetType <> " out of the registry"
          <> "\n\nYou can check the registry displayed above the ===== line to verify the current values and constructors\n"

        Right (Just result) -> fromMaybe
          (Left $ "could not cast the computed value to a " <> show targetType <> ". The value is of type: " <> show (valueDynTypeRep result))
          (Right <$> fromDynamic (valueDyn result))