-- |
-- Module      :  Phonetic.Languages.Permutations.ArrMini
-- Copyright   :  (c) OleksandrZhabenko 2021
-- License     :  MIT
-- Stability   :  Experimental
-- Maintainer  :  olexandr543@yahoo.com
--
-- Special permutations functions for the phonetic-languages series of packages. This
-- module uses no vectors, but instead uses arrays.

module Phonetic.Languages.Permutations.ArrMini (
  genPairwisePermutations
  , pairsSwapP
  , genPairwisePermutationsArrN
  , genPairwisePermutationsArr
  , genPairwisePermutationsLN
  , genPairwisePermutationsL
  , genPairwisePermutationsArrLN
  , genPairwisePermutationsArrL
) where

import GHC.Arr

genPairwisePermutations :: Int -> Array Int [Int]
genPairwisePermutations n = listArray (0,(n*(n-1)) `quot` 2) . pairsSwapP . take n $ [0..]
{-# INLINE genPairwisePermutations #-}

pairsSwapP :: [Int] -> [[Int]]
pairsSwapP xs = xs:[swap2Ls k m xs | k <- xs, m <- xs , k < m]
{-# INLINABLE pairsSwapP #-}

-- | The first two arguments are considered not equal, though it is not checked.
swap2ns :: Int -> Int -> Int -> Int
swap2ns k m n
 | n /= k = if n /= m then n else k
 | otherwise = m
{-# INLINE swap2ns #-}

swap2Ls :: Int -> Int -> [Int] -> [Int]
swap2Ls k m = map (swap2ns k m)
{-# INLINE swap2Ls #-}

genPairwisePermutationsArrN :: Int -> Array Int (Array Int [Int])
genPairwisePermutationsArrN n = amap genPairwisePermutations . listArray (0,n - 2) $ [2..n]
{-# INLINE genPairwisePermutationsArrN #-}

genPairwisePermutationsArr :: Array Int (Array Int [Int])
genPairwisePermutationsArr = genPairwisePermutationsArrN 10
{-# INLINE genPairwisePermutationsArr #-}

genPairwisePermutationsLN :: Int -> [Array Int Int]
genPairwisePermutationsLN n = map (\xs -> listArray (0,n - 1) xs) . pairsSwapP . take n $ [0..]
{-# INLINE genPairwisePermutationsLN #-}

genPairwisePermutationsL :: [Array Int Int]
genPairwisePermutationsL = genPairwisePermutationsLN 10
{-# INLINE genPairwisePermutationsL #-}

genPairwisePermutationsArrLN :: Int -> Array Int [Array Int Int]
genPairwisePermutationsArrLN n = amap genPairwisePermutationsLN . listArray (0,n - 2) $ [2..n]
{-# INLINE genPairwisePermutationsArrLN #-}

genPairwisePermutationsArrL :: Array Int [Array Int Int]
genPairwisePermutationsArrL = genPairwisePermutationsArrLN 10
{-# INLINE genPairwisePermutationsArrL #-}