{-# LANGUAGE OverloadedStrings #-}

{-|
Module      : Text.Numerals.Prefix
Description : A module used to define /numeric prefixes/ for /long/ and /short scales/.
Maintainer  : hapytexeu+gh@gmail.com
Stability   : experimental
Portability : POSIX

A module that defines /Latin/ prefixes. These prefixes are used to construct names for the /long/ and /short scales/.
So the /m/, /b/, /tr/ in /million/, /billion/, /trillion/.
-}

module Text.Numerals.Prefix (
    -- * Latin prefixes
    latinPrefixes, latinPrefixes', latinPrefix
  ) where

import Data.Text(Text)
import Data.Vector(Vector, (!?), fromList)

-- | A list of /Latin/ prefixes, used for the /long/ and /short scale/.
latinPrefixes' :: [Text]  -- ^ A list of 'Text' objects. This makes explicit recursion more convenient.
latinPrefixes' = [
    "m"
  , "b"
  , "tr"
  , "quadr"
  , "quint"
  , "sext"
  , "sept"
  , "oct"
  , "non"
  , "dec"
  , "undec"
  , "duodec"
  , "tredec"
  , "quattuordec"
  , "quindec"
  , "sedec"
  , "septendec"
  , "octodec"
  , "novendec"
  , "vigint"
  , "unvigint"
  , "duovigint"
  , "tresvigint"
  , "quattuorvigint"
  , "quinvigint"
  , "sesvigint"
  , "septemvigint"
  , "octovigint"
  , "novemvigint"
  , "trigint"
  , "untrigint"
  , "duotrigint"
  , "trestrigint"
  , "quattuortrigint"
  , "quintrigint"
  , "sestrigint"
  , "septentrigint"
  , "octotrigint"
  , "noventrigint"
  , "quadragint"
  ]

-- | The /Latin/ prefixes in a 'Vector' for /O(1)/ lookup.
latinPrefixes :: Vector Text  -- ^ A 'Vector' of 'Text' objects to allow fast lookup.
latinPrefixes = fromList latinPrefixes'

-- | Lookup the given /Latin/ prefix for the given value.
latinPrefix :: Integral i
  => i  -- ^ The value to map on a Latin prefix.
  -> Maybe Text  -- ^ The corresponding Latin prefix, given this exists.
latinPrefix n = latinPrefixes !? (fromIntegral n - 1)