{-|

Module:      Password
Description: a simple password manager
Copyright:   (C) 2018 Jonathan Lamothe
License:     LGPLv3 (or later)
Maintainer:  jlamothe1980@gmail.com

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this program.  If not, see
<https://www.gnu.org/licenses/>.

-}

{-# LANGUAGE TemplateHaskell #-}

module Password (
  -- * Data Types
  PWDatabase, PWData(..), PWPolicy (..), PWSalt,
  -- ** Lenses
  -- $lenses
  -- *** PWData
  pwPolicy, pwSalt,
  -- *** PWPolicy
  pwLength, pwUpper, pwLower, pwDigits, pwSpecial,
  -- ** Default Instances
  newPWData, newPWPolicy, newPWSalt,
  -- * Functions
  validatePWPolicy
  ) where

import Control.Lens (makeLenses, (^.))
import Data.Char (isUpper, isLower, isDigit, isAlphaNum)
import qualified Data.ByteString as B
import qualified Data.Map as M
import Data.Maybe (fromMaybe)
import System.Random (RandomGen, randoms, split)

-- | a mapping of service names to password data
type PWDatabase = M.Map String PWData

-- | data necessary to construct a password
data PWData = PWData
  { _pwPolicy :: PWPolicy
  -- ^ the password policy
  , _pwSalt :: B.ByteString
  -- ^ random data used to generate the password
  } deriving (Eq, Show)

-- | defines a password policy
data PWPolicy = PWPolicy
  { _pwLength :: Int
  -- ^ password length
  , _pwUpper :: Int
  -- ^ the minimum number of upper case characters
  , _pwLower :: Int
  -- ^ the minimum number of lower case characters
  , _pwDigits :: Int
  -- ^ the minimum number of digits
  , _pwSpecial :: Maybe Int
  -- ^ the minimum number of non-alphanumeric characters (not allowed
  -- if @"Nothing"@)
  } deriving (Eq, Show)

-- | the "salt" used to generate a password
type PWSalt = B.ByteString

-- $lenses The following functions are automatically generated by
-- @makeLenses@. See the
-- [lens](http://hackage.haskell.org/package/lens) package for further
-- details.

makeLenses ''PWPolicy
makeLenses ''PWData

-- | builds a new @'PWData'@
newPWData
  :: RandomGen g
  => g
  -- ^ the random generator to use
  -> (PWData, g)
  -- ^ the result and new random generator
newPWData g = (result, g') where
  result = PWData newPWPolicy salt
  (salt, g') = newPWSalt g

-- | default password policy
newPWPolicy :: PWPolicy
newPWPolicy = PWPolicy 16 0 0 0 (Just 0)

-- | builds a new salt
newPWSalt
  :: RandomGen g
  => g
  -- ^ the random generator to use
  -> (PWSalt, g)
  -- ^ the result and new random generator
newPWSalt g = (result, g2) where
  result = B.pack $ take 256 $ randoms g1
  (g1, g2) = split g

-- | validates a password policy
validatePWPolicy
  :: PWPolicy
  -- ^ the policy being validated
  -> Bool
  -- ^ indicates whether or not the policy is valid
validatePWPolicy x = and
  [ needed <= x^.pwLength
  , x^.pwLength >= 0
  , x^.pwUpper >= 0
  , x^.pwLower >= 0
  , x^.pwDigits >= 0
  , fromMaybe 0 (x^.pwSpecial) >= 0
  ] where
    needed = x^.pwUpper + x^.pwLower + x^.pwDigits + special
    special = fromMaybe 0 $ x^.pwSpecial

--jl