Implement wordWrap and paginate

hcat.cabal

@@ -70,4 +70,5 @@ test-suite spec
     , base >=4.13 && <5
     , hcat
     , hspec
+    , quickcheck-instances
   default-language: GHC2021

package.yaml

@@ -52,7 +52,7 @@ tests:
       - hcat
       - hspec
       - QuickCheck
-      # - quickcheck-instances
+      - quickcheck-instances
       # - quickcheck-text
     build-tools: hspec-discover
     verbatim:

src/HCat/Internal.hs

@@ -1,6 +1,9 @@
 -- | Internal module in order to facilitate testability.
 module HCat.Internal where
 
+import Data.Text (Text)
+import Data.Text qualified as T
+
 -- | @parseArgs@ takes a list of strings and returns a single FilePath if there was exactly one element.
 --
 -- >>> parseArgs ["foo"]
@@ -28,3 +31,39 @@ chunksOf n xs@(_ : _)
   | otherwise =
       let (chunk, rest) = splitAt n xs
        in chunk : chunksOf n rest
+
+-- | @wordWrap@ splits the given Text if it is longer than the given margin.
+--
+-- >>> :set -XOverloadedStrings
+-- >>> wordWrap 3 "abcdef"
+-- ["abc","def"]
+--
+-- >>> wordWrap 3 "abc"
+-- ["abc"]
+--
+-- >>> wordWrap 3 "ab"
+-- ["ab"]
+wordWrap :: Int -> Text -> [Text]
+wordWrap n text
+  | n > 0 && T.length text > n =
+      let (line, rest) = T.splitAt n text
+       in line : wordWrap n rest
+  | otherwise = pure text
+
+data ScreenDimensions = ScreenDimensions
+  { screenRows :: Int
+  , screenColumns :: Int
+  }
+  deriving (Show)
+
+-- | @paginate@ transforms a given piece of Text into pages of lines that fit
+-- onto the screen.
+--
+-- >>> paginate ScreenDimensions{screenRows = 2, screenColumns = 2} "foo bar baz"
+-- ["fo\no \n","ba\nr \n","ba\nz\n"]
+paginate :: ScreenDimensions -> Text -> Pages
+paginate (ScreenDimensions rows cols) =
+  fmap T.unlines . chunksOf rows . concatMap (wordWrap cols) . T.lines
+
+type Pages = [Page]
+type Page = Text

test/spec/HCatSpec.hs

@@ -1,12 +1,12 @@
--- {-# LANGUAGE GHC2021 #-}
-
 module HCatSpec (spec) where
 
-import HCat.Internal (chunksOf, parseArgs)
+import HCat.Internal
 
 import Test.Hspec
 import Test.Hspec.QuickCheck (prop)
-import Test.QuickCheck (Positive (getPositive))
+
+import Test.QuickCheck (Positive (getPositive), getNonPositive)
+import Test.QuickCheck.Instances.Text ()
 
 spec :: Spec
 spec = do
@@ -15,6 +15,7 @@ spec = do
       parseArgs ["foo"] `shouldBe` Right "foo"
       parseArgs [] `shouldBe` Left "No filename given!"
       parseArgs ["foo", "bar"] `shouldBe` Left "Only a single file is supported"
+
   describe "chunksOf" $ do
     prop "each chunk contains at most N items" $ \n xs ->
       let chunkLengths = length <$> chunksOf n (xs :: [Int])
@@ -25,3 +26,19 @@ spec = do
     prop "the sum of all lengths is equal to the length of the input" $ \n xs ->
       let chunkLengths = length <$> chunksOf (getPositive n) (xs :: [Int])
        in sum chunkLengths `shouldBe` length xs
+
+  describe "wordWrap" do
+    prop "non positive margins result in empty result" $ \margin ->
+      wordWrap (getNonPositive margin) "abc" `shouldBe` ["abc"]
+
+    it "wraps the given text at the given margin" do
+      wordWrap 4 "abc" `shouldBe` ["abc"]
+      wordWrap 4 "abcdefg" `shouldBe` ["abcd", "efg"]
+
+    prop "concatenating the result equals the input" $ \txt ->
+      let wrapped = wordWrap 4 txt
+       in mconcat wrapped `shouldBe` txt
+
+  describe "paginate" do
+    it "wraps the given text at the given margin" do
+      paginate (ScreenDimensions 3 2) "abcdefghijkl" `shouldBe` ["ab\ncd\nef\n", "gh\nij\nkl\n"]