-- Copyright 2020 United States Government as represented by the Administrator
-- of the National Aeronautics and Space Administration. All Rights Reserved.
--
-- Disclaimers
--
-- Licensed under the Apache License, Version 2.0 (the "License"); you may
-- not use this file except in compliance with the License. You may obtain a
-- copy of the License at
--
--      https://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-- License for the specific language governing permissions and limitations
-- under the License.
--
-- | Auxiliary functions for working with values of type 'String'.
module Data.String.Extra
    (
      -- * Safe I/O
      safeReadFile

      -- * String transformation
    , pascalCase

      -- * String sanitization
    , sanitizeLCIdentifier
    , sanitizeUCIdentifier
    )
  where

-- External imports
import Control.Exception ( catch )
import Data.Char         ( toLower, toUpper )
import System.IO.Error   ( isDoesNotExistError )

-- * Safe I/O

-- | Safely read a file into a 'String', returning a 'Left' error message if
-- the file cannot be opened.

-- This function could also be placed in System.IO. However, we decide to
-- include it in this module for symmetry with an analogous function for
-- ByteString, included in Data.ByteString.Extra.
safeReadFile :: FilePath -> IO (Either String String)
safeReadFile :: String -> IO (Either String String)
safeReadFile String
fp =
  IO (Either String String)
-> (IOError -> IO (Either String String))
-> IO (Either String String)
forall e a. Exception e => IO a -> (e -> IO a) -> IO a
catch (String -> Either String String
forall a. a -> Either String a
forall (m :: * -> *) a. Monad m => a -> m a
return (String -> Either String String)
-> IO String -> IO (Either String String)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> String -> IO String
readFile String
fp) ((IOError -> IO (Either String String))
 -> IO (Either String String))
-> (IOError -> IO (Either String String))
-> IO (Either String String)
forall a b. (a -> b) -> a -> b
$ \IOError
e ->
    if IOError -> Bool
isDoesNotExistError IOError
e
      then Either String String -> IO (Either String String)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return (Either String String -> IO (Either String String))
-> Either String String -> IO (Either String String)
forall a b. (a -> b) -> a -> b
$ String -> Either String String
forall a b. a -> Either a b
Left (String -> Either String String) -> String -> Either String String
forall a b. (a -> b) -> a -> b
$ String -> String
strStringFileNotFound String
fp
      else Either String String -> IO (Either String String)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return (Either String String -> IO (Either String String))
-> Either String String -> IO (Either String String)
forall a b. (a -> b) -> a -> b
$ String -> Either String String
forall a b. a -> Either a b
Left (String -> Either String String) -> String -> Either String String
forall a b. (a -> b) -> a -> b
$ String -> String
strStringCannotOpenFile String
fp

-- ** Error messages

-- | File-not-found message.
strStringFileNotFound :: FilePath -> String
strStringFileNotFound :: String -> String
strStringFileNotFound String
fp = String
"File not found: " String -> String -> String
forall a. [a] -> [a] -> [a]
++ String
fp

-- | Cannot-open-file message.
strStringCannotOpenFile :: FilePath -> String
strStringCannotOpenFile :: String -> String
strStringCannotOpenFile String
fp = String
"Error opening file: " String -> String -> String
forall a. [a] -> [a] -> [a]
++ String
fp

-- * Transformation

-- | Convert a string with underscores to PascalCase.
pascalCase :: String -> String
pascalCase :: String -> String
pascalCase = (String -> String) -> [String] -> String
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap String -> String
capitalize ([String] -> String) -> (String -> [String]) -> String -> String
forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> [String]
parts
  where
    capitalize :: String -> String
capitalize (Char
x:String
xs) = Char -> Char
toUpper Char
x Char -> String -> String
forall a. a -> [a] -> [a]
: (Char -> Char) -> String -> String
forall a b. (a -> b) -> [a] -> [b]
map Char -> Char
toLower String
xs
    capitalize [] = []

    parts :: String -> [String]
    parts :: String -> [String]
parts String
"" = []
    parts String
s =
      let (String
l, String
r) = (Char -> Bool) -> String -> (String, String)
forall a. (a -> Bool) -> [a] -> ([a], [a])
break (Char -> Char -> Bool
forall a. Eq a => a -> a -> Bool
== Char
'_') String
s
      in String
l String -> [String] -> [String]
forall a. a -> [a] -> [a]
: case String
r of
               []     -> []
               (Char
_:String
rs) -> String -> [String]
parts String
rs

-- * Sanitization

-- | Remove extraneous characters from an identifier and make the starting
-- character lowercase.
--
-- This function currently replaces hyphens with underscores.
sanitizeLCIdentifier :: String -> String
sanitizeLCIdentifier :: String -> String
sanitizeLCIdentifier = String -> String
headToLower (String -> String) -> (String -> String) -> String -> String
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Char -> Char) -> String -> String
forall a b. (a -> b) -> [a] -> [b]
map Char -> Char
sanitizeCharacter
  where
    sanitizeCharacter :: Char -> Char
sanitizeCharacter Char
'-' = Char
'_'
    sanitizeCharacter Char
x   = Char
x

    headToLower :: [Char] -> [Char]
    headToLower :: String -> String
headToLower []     = []
    headToLower (Char
x:String
xs) = Char -> Char
toLower Char
x Char -> String -> String
forall a. a -> [a] -> [a]
: String
xs

-- | Remove extraneous characters from an identifier and make the starting
-- character uppercase.
--
-- This function currently replaces hyphens with underscores.
sanitizeUCIdentifier :: String -> String
sanitizeUCIdentifier :: String -> String
sanitizeUCIdentifier = String -> String
headToUpper (String -> String) -> (String -> String) -> String -> String
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Char -> Char) -> String -> String
forall a b. (a -> b) -> [a] -> [b]
map Char -> Char
sanitizeCharacter
  where
    sanitizeCharacter :: Char -> Char
sanitizeCharacter Char
'-' = Char
'_'
    sanitizeCharacter Char
x   = Char
x

    headToUpper :: [Char] -> [Char]
    headToUpper :: String -> String
headToUpper []     = []
    headToUpper (Char
x:String
xs) = Char -> Char
toUpper Char
x Char -> String -> String
forall a. a -> [a] -> [a]
: String
xs