Util.hs

{-# LANGUAGE NoImplicitPrelude #-}

module Imj.Util
    ( -- * List utilities
      showListOrSingleton
    , replicateElements
    , range
      -- * String utilities
    , commonPrefix
    , commonSuffix
      -- * Math utilities
    , randomRsIO
    , clamp
      -- * Reexports
    , Int64
    ) where

import           Imj.Prelude

import           Data.Int(Int64)
import           Data.List(reverse)
import           Data.Text(Text, pack)

import           Control.Arrow( first )

import           System.Random( Random(..)
                              , getStdRandom
                              , split )


{-# INLINABLE showListOrSingleton #-}
-- | If list is a singleton, show the element, else show the list.
showListOrSingleton :: Show a => [a] -> Text
showListOrSingleton [e] = pack $ show e
showListOrSingleton l   = pack $ show l

{-# INLINE replicateElements #-}
-- | Replicates each list element n times and concatenates the result.
replicateElements :: Int -> [a] -> [a]
replicateElements n = concatMap (replicate n)

{-# INLINABLE range #-}
{- | Builds a range with no constraint on the order of bounds:

@
range 3 5 == [3,4,5]
range 5 3 == [5,4,3]
@
-}
range :: Enum a => Ord a
      => a -- ^ First inclusive bound
      -> a -- ^ Second inclusive bound
      -> [a]
range n m =
  if m < n
    then
      [n,(pred n)..m]
    else
      [n..m]

-- | Returns a list of random values uniformly distributed in the closed interval
-- [lo,hi].
--
-- It is unspecified what happens if lo>hi
randomRsIO :: Random a
           => a -- ^ lo : lower bound
           -> a -- ^ hi : upper bound
           -> IO [a]
randomRsIO from to =
  getStdRandom $ split >>> first (randomRs (from, to))

commonPrefix :: String -> String -> String
commonPrefix (x:xs) (y:ys)
    | x == y    = x : commonPrefix xs ys
commonPrefix _ _ = []

commonSuffix :: String -> String -> String
commonSuffix s s' = reverse $ commonPrefix (reverse s) (reverse s')


-- | Expects the bounds to be in the right order.
{-# INLINABLE clamp #-}
clamp :: Ord a
      => a
      -- ^ The value
      -> a
      -- ^ The inclusive minimum bound
      -> a
      -- ^ The inclusive maximum bound
      -> a
clamp n min_ max_
  | n < min_ = min_
  | n > max_ = max_
  | otherwise = n