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module Mind
  ( NeuronIndex (..)
  , getNeuronIndex

  , Edge (..)
  
  , Network (..)
  , createEmptyNetwork
  , connectNeurons
  , compute
  ) where

import Data.Ix

-- index different neuron types
data NeuronIndex = Input Int | Internal Int | Output Int deriving (Show, Eq)

getNeuronIndex :: NeuronIndex -> Int
getNeuronIndex (Input i)    = i
getNeuronIndex (Internal i) = i
getNeuronIndex (Output i)   = i

-- define incident edges
newtype Edge = Edge (NeuronIndex, Float) deriving (Show, Eq)

-- define networks
data Network = Network 
  { numInput :: Int
  , internalNeurons :: [[Edge]]
  , outputNeurons :: [[Edge]]
  } deriving (Show, Eq)

-- create a completely empty network
createEmptyNetwork :: Int -> Int -> Int -> Network
createEmptyNetwork i h o = Network i (replicate h []) (replicate o [])


-- connect two neurons together with a new edge
connectNeurons :: Network -> NeuronIndex -> NeuronIndex -> Float -> Maybe Network
-- internal sink
connectNeurons (Network i h o) source (Internal sink) weight = 
  if (validSource (Network i h o) source) then do
    newH <- insertEdge h sink $ Edge (source, weight)
    return $ Network i newH o
  else Nothing
-- output sink
connectNeurons (Network i h o) source (Output sink) weight = 
  if (validSource (Network i h o) source) then do
    newO <- insertEdge o sink $ Edge (source, weight)
    return $ Network i h newO
  else Nothing
-- 
connectNeurons _ _ (Input _) _ = Nothing



-- helpers for connectNeurons

-- check if a given NeuronIndex can be used as a valid source
validSource :: Network -> NeuronIndex -> Bool
validSource _ (Output _) = False
validSource (Network i _ _) (Input x) = 
  if (inRange (0, i) x) 
  then True else False
validSource (Network _ h _) (Internal x) = 
  if (inRange (0, length h) x)
  then True else False

-- insert a new edge into a neuron list, possibly failing
insertEdge :: [[Edge]] -> Int -> Edge -> Maybe [[Edge]]
insertEdge ns i e 
  | (inRange (0, length ns) i) = let (front, es:back) = splitAt i ns
    in Just $ front ++ [e:es] ++ back
  | otherwise = Nothing


-- network computation
compute :: Network -> [Float] -> [Float] -> Maybe ([Float], [Float])
compute net input state = undefined