6 files changed, 65 insertions(+), 4 deletions(-)

M CHANGELOG.md
M src/Data/Text/ParagraphLayout/Internal/Plain.hs
M src/Data/Text/ParagraphLayout/Internal/ResolvedSpan.hs
M src/Data/Text/ParagraphLayout/Internal/Run.hs
M src/Data/Text/ParagraphLayout/Internal/TextContainer.hs
M test/Data/Text/ParagraphLayout/Internal/TextContainerSpec.hs

@@ 4,6 4,8 @@
 
 * Added support for forced (hard) line breaks in the input text.
 
+* Now also trimming white space at the beginning of lines.
+
 * Internally, language tags will be cut at the first invalid character before
   being passed to ICU.
 

@@ 179,7 179,10 @@ hardSplit :: [WithSpan Run] -> ([WithSpan Run], [WithSpan Run])
 hardSplit runs = trimFst $ NonEmpty.last $ splits
     where
         trimFst (runs1, runs2) = (trim runs1, runs2)
-        trim = trimTextsEndPreserve isEndSpace . trimTextsEndPreserve isNewline
+        trim
+            = trimTextsStartPreserve isStartSpace
+            . trimTextsEndPreserve isEndSpace
+            . trimTextsEndPreserve isNewline
         -- TODO: Consider optimising.
         --       We do not need to look for any line breaks further than the
         --       shortest hard break.


@@ 205,7 208,7 @@ softSplits :: [WithSpan Run] -> [([WithSpan Run], [WithSpan Run])]
 softSplits runs = map trimFst splits
     where
         trimFst (runs1, runs2) = (trim runs1, runs2)
-        trim = trimTextsEnd isEndSpace
+        trim = trimTextsStart isStartSpace . trimTextsEnd isEndSpace
         splits = lSplits ++ cSplits
         lSplits = splitTextsBy (map fst . runLineBreaks) runs
         -- TODO: Consider optimising.


@@ 315,6 318,11 @@ runBreaksFromSpan run spanBreaks =
         valid (off, _) = off < runLength
         runLength = lengthWord8 $ getText run
 
+-- | Predicate for characters that can be potentially removed from the
+-- beginning of a line according to the CSS Text Module.
+isStartSpace :: Char -> Bool
+isStartSpace c = c `elem` [' ', '\t']
+
 -- | Predicate for characters that can be potentially removed from the end of
 -- a line according to the CSS Text Module.
 isEndSpace :: Char -> Bool

@@ 45,6 45,7 @@ instance TextContainer a => TextContainer (WithSpan a) where
 instance SeparableTextContainer a => SeparableTextContainer (WithSpan a) where
     splitTextAt8 n (WithSpan rs c) = (WithSpan rs c1, WithSpan rs c2)
         where (c1, c2) = splitTextAt8 n c
+    dropWhileStart p (WithSpan rs c) = WithSpan rs (dropWhileStart p c)
     dropWhileEnd p (WithSpan rs c) = WithSpan rs (dropWhileEnd p c)
 
 splitBySpanIndex :: [WithSpan a] -> [[a]]

@@ 40,6 40,14 @@ instance SeparableTextContainer Run where
             t1 = takeWord8 (fromIntegral n) t
             t2 = dropWord8 (fromIntegral n) t
             t = getText r
+    dropWhileStart p r = r { runText = t', runOffsetInSpan = o' }
+        where
+            t = runText r
+            t' = Text.dropWhile p t
+            l = lengthWord8 t
+            l' = lengthWord8 t'
+            o = runOffsetInSpan r
+            o' = o + l - l'
     dropWhileEnd p r = r { runText = Text.dropWhileEnd p (runText r) }
 
 type ProtoRun = (Zipper, Maybe Direction, ScriptCode)

@@ 2,11 2,14 @@ module Data.Text.ParagraphLayout.Internal.TextContainer
     (SeparableTextContainer
     ,TextContainer
     ,dropWhileEnd
+    ,dropWhileStart
     ,getText
     ,splitTextAt8
     ,splitTextsBy
     ,trimTextsEnd
     ,trimTextsEndPreserve
+    ,trimTextsStart
+    ,trimTextsStartPreserve
     )
 where
 


@@ 33,8 36,12 @@ class TextContainer a => SeparableTextContainer a where
     -- constraints the instance requires.
     splitTextAt8 :: Int -> a -> (a, a)
 
-    -- | Return the prefix remaining after dropping characters that satisfy
-    -- the given predicate from the end of the given `SeparableTextContainer`.
+    -- | Return the suffix remaining after dropping characters that satisfy the
+    -- given predicate from the beginning of the given `SeparableTextContainer`.
+    dropWhileStart :: (Char -> Bool) -> a -> a
+
+    -- | Return the prefix remaining after dropping characters that satisfy the
+    -- given predicate from the end of the given `SeparableTextContainer`.
     dropWhileEnd :: (Char -> Bool) -> a -> a
 
 -- | As a trivial instance, each `Text` can be split directly.


@@ 43,6 50,7 @@ instance SeparableTextContainer Text where
         where
             t1 = takeWord8 (fromIntegral n) t
             t2 = dropWord8 (fromIntegral n) t
+    dropWhileStart = Text.dropWhile
     dropWhileEnd = Text.dropWhileEnd
 
 -- | Treat a list of text containers as a contiguous sequence,


@@ 77,6 85,26 @@ collapse (tc :| tcs)
     | otherwise = tc:tcs
 
 -- | Treat a list of text containers as a contiguous sequence,
+-- and remove a prefix of characters that match the given predicate.
+--
+-- Empty text containers are removed from the output, so the result may
+-- potentially be an empty list.
+trimTextsStart :: SeparableTextContainer a => (Char -> Bool) -> [a] -> [a]
+trimTextsStart p tcs = trimTextsStart' p tcs
+
+-- | Treat a list of text containers as a contiguous sequence,
+-- and remove a prefix of characters that match the given predicate.
+--
+-- Empty text containers are removed from the output except the first one,
+-- which is instead truncated to zero length.
+trimTextsStartPreserve ::
+    SeparableTextContainer a => (Char -> Bool) -> [a] -> [a]
+trimTextsStartPreserve _ [] = []
+trimTextsStartPreserve p ins@(in1:_) = case trimTextsStart' p ins of
+    [] -> [truncateText in1]
+    out -> out
+
+-- | Treat a list of text containers as a contiguous sequence,
 -- and remove a suffix of characters that match the given predicate.
 --
 -- Empty text containers are removed from the output, so the result may


@@ 96,6 124,14 @@ trimTextsEndPreserve p ins@(in1:_) = case trimTextsEnd' p (reverse ins) of
     [] -> [truncateText in1]
     out -> out
 
+trimTextsStart' :: SeparableTextContainer a => (Char -> Bool) -> [a] -> [a]
+trimTextsStart' _ [] = []
+trimTextsStart' p (tc:tcs)
+    | Text.null (getText trimmed) = trimTextsStart' p tcs
+    | otherwise = trimmed:tcs
+    where
+        trimmed = dropWhileStart p tc
+
 trimTextsEnd' :: SeparableTextContainer a => (Char -> Bool) -> [a] -> [a]
 trimTextsEnd' _ [] = []
 trimTextsEnd' p (tc:tcs)

@@ 21,6 21,12 @@ instance SeparableTextContainer ExampleContainer where
             (t1, t2) = splitTextAt8 n t
             o1 = o
             o2 = o + lengthWord8 t1
+    dropWhileStart p (Contain t o) = Contain t' o'
+        where
+            l = lengthWord8 t
+            t' = dropWhileStart p t
+            l' = lengthWord8 t
+            o' = o + l - l'
     dropWhileEnd p (Contain t o) = Contain (dropWhileEnd p t) o
 
 exampleContainers :: [ExampleContainer]