Implement basic hcat functionality

We show a simple UI that informs the user about the possible choices:

- n to show the next page
- q to quit immediately

src/HCat.hs

@@ -4,20 +4,34 @@ module HCat (
 ) where
 
 import System.Environment qualified as Env
-import System.IO (hPutStrLn, stderr)
+import System.IO
 
 import Control.Exception qualified as Exception
 import System.IO.Error qualified as IOError
 
 import Data.Text.IO qualified as TextIO
 
-import HCat.Internal (parseArgs)
+import HCat.Internal
 
 runHCat :: IO ()
 runHCat = do
   fileNameOrError <- parseArgs <$> Env.getArgs
   fileName <- eitherToError fileNameOrError
-  TextIO.readFile fileName >>= TextIO.putStr
+  content <- TextIO.readFile fileName
+  screen <- getTerminalSize
+  let contentPane = screen{screenRows = screenRows screen - 1}
+  showPages $ paginate contentPane content
+
+showPages :: Pages -> IO ()
+showPages [] = pure ()
+showPages (p : ps) = do
+  TextIO.putStr p
+  putStr ">>> (n)ext page or (q)uit?"
+  hFlush stdout
+  cmd <- getUserCommand
+  case cmd of
+    Quit -> pure ()
+    NextPage -> putStrLn "" >> showPages ps
 
 eitherToError :: Show a => Either a b -> IO b
 eitherToError = either (Exception.throwIO . IOError.userError . show) return

src/HCat/Internal.hs

@@ -76,13 +76,18 @@ getTerminalSize :: IO ScreenDimensions
 getTerminalSize = case SysInfo.os of
   "linux" -> tputScreenDimensions
   "darwin" -> tputScreenDimensions
-  _ -> pure $ defaultScreenDimensions{screenRows = 25, screenColumns = 80}
+  _ -> pure defaultScreenDimensions
 
 defaultScreenDimensions :: ScreenDimensions
-defaultScreenDimensions = ScreenDimensions{screenRows = 25, screenColumns = 80}
+defaultScreenDimensions =
+  ScreenDimensions
+    { screenRows = 25
+    , screenColumns = 80
+    }
 
 tputScreenDimensions :: IO ScreenDimensions
-tputScreenDimensions = ScreenDimensions <$> tput "lines" <*> tput "cols"
+tputScreenDimensions =
+  ScreenDimensions <$> tput "lines" <*> tput "cols"
  where
   tput cmd = read <$> P.readProcess "tput" [cmd] ""
 
@@ -94,6 +99,6 @@ getUserCommand = do
   hSetEcho stdin False
   input <- getChar
   case input of
-    ' ' -> pure NextPage
+    'n' -> pure NextPage
     'q' -> pure Quit
     _ -> getUserCommand