Add program version in help and a separate --version flag

src/Arguments.hs

@@ -5,12 +5,14 @@ module Arguments (
   ) where
 
 import Data.Monoid ((<>))
+import Data.Version (showVersion)
 import Options.Applicative
+import qualified Paths_hablo as Hablo (version)
 import System.Directory (doesDirectoryExist, doesFileExist, makeAbsolute)
-import System.Exit (die)
+import System.Exit (die, exitSuccess)
 import System.FilePath.Posix (dropTrailingPathSeparator, isValid)
 
-data Arguments = Arguments {
+data Arguments = BlogConfig {
       sourceDir :: FilePath
     , blogName :: Maybe String
     , previewArticlesCount :: Int
@@ -18,9 +20,10 @@ data Arguments = Arguments {
     , bannerPath :: Maybe FilePath
     , headPath :: Maybe FilePath
   }
+  | Version
 
-parseArguments :: Parser Arguments
-parseArguments = Arguments
+blogConfig :: Parser Arguments
+blogConfig = BlogConfig
   <$> argument filePath (metavar "INPUT_DIR")
   <*> option (optional str) (
           metavar "BLOG_NAME"
@@ -58,6 +61,16 @@ parseArguments = Arguments
         <> help "path to the file to add in the blog's head"
       )
 
+version :: Parser Arguments
+version = flag' Version (
+      long "version"
+    <> short 'v'
+    <> help "print the version number"
+  )
+
+arguments :: Parser Arguments
+arguments = blogConfig <|> version
+
 filePath :: ReadM FilePath
 filePath = eitherReader $ \path ->
   if isValid path
@@ -71,16 +84,16 @@ ifNotDie check messageBuilder input = do
     then return ()
     else die $ messageBuilder input
 
-get :: IO Arguments
-get = do
-  arguments <- execParser $ info (parseArguments <**> helper) fullDesc
-  doesDirectoryExist `ifNotDie` noSuchDirectory $ sourceDir arguments
-  absoluteSourceDir <- makeAbsolute $ sourceDir arguments
-  mapM_ (doesFileExist `ifNotDie` noSuchFile) $ bannerPath arguments
-  absoluteBannerPath <- mapM makeAbsolute $ bannerPath arguments
-  mapM_ (doesFileExist `ifNotDie` noSuchFile) $ headPath arguments
-  absoluteHeadPath <- mapM makeAbsolute $ headPath arguments
-  return $ arguments {
+checkAndMakeAbsolute :: Arguments -> IO Arguments
+checkAndMakeAbsolute Version = return Version
+checkAndMakeAbsolute aBlogConfig = do
+  doesDirectoryExist `ifNotDie` noSuchDirectory $ sourceDir aBlogConfig
+  absoluteSourceDir <- makeAbsolute $ sourceDir aBlogConfig
+  mapM_ (doesFileExist `ifNotDie` noSuchFile) $ bannerPath aBlogConfig
+  absoluteBannerPath <- mapM makeAbsolute $ bannerPath aBlogConfig
+  mapM_ (doesFileExist `ifNotDie` noSuchFile) $ headPath aBlogConfig
+  absoluteHeadPath <- mapM makeAbsolute $ headPath aBlogConfig
+  return $ aBlogConfig {
         sourceDir = absoluteSourceDir
       , bannerPath = absoluteBannerPath
       , headPath = absoluteHeadPath
@@ -88,3 +101,13 @@ get = do
   where
     noSuchDirectory = (++ ": no such directory")
     noSuchFile = (++ ": no such file")
+
+get :: IO Arguments
+get = do
+  args <- execParser $
+    info
+      (arguments <**> helper)
+      (fullDesc <> header ("Hablo v" ++ showVersion Hablo.version))
+  case args of
+    Version -> (putStrLn $ showVersion Hablo.version) >> exitSuccess
+    BlogConfig {} -> checkAndMakeAbsolute args