1 files changed, 83 insertions, 0 deletions
diff --git a/src/Erebos/TextFormat/Ansi.hs b/src/Erebos/TextFormat/Ansi.hs
new file mode 100644
index 0000000..faec0ad
--- /dev/null
+++ b/src/Erebos/TextFormat/Ansi.hs
@@ -0,0 +1,83 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Erebos.TextFormat.Ansi (
+    FormattedText,
+
+    AnsiText(..),
+    renderAnsiText,
+) where
+
+import Control.Applicative
+import Control.Monad.State
+import Control.Monad.Writer
+
+import Data.String
+import Data.Text (Text)
+import Data.Text qualified as T
+
+import Erebos.TextFormat.Types
+
+
+newtype AnsiText = AnsiText { fromAnsiText :: Text }
+    deriving (Eq, Ord, Semigroup, Monoid, IsString)
+
+
+data RenderState = RenderState
+    { rsEndedWithNewline :: Bool
+    }
+
+initialRenderState :: RenderState
+initialRenderState = RenderState
+    { rsEndedWithNewline = True
+    }
+
+renderAnsiText :: FormattedText -> AnsiText
+renderAnsiText ft = AnsiText $ T.concat $ execWriter $ flip evalStateT initialRenderState $ go ( Nothing, Nothing ) ft
+  where
+    go :: ( Maybe Color, Maybe Color ) -> FormattedText -> StateT RenderState (Writer [ Text ]) ()
+    go cur@( cfg, cbg ) = \case
+        PlainText text -> do
+            tell [ text ]
+            case T.unsnoc text of
+                Just ( _, c ) -> modify (\s -> s { rsEndedWithNewline = c == '\n' })
+                Nothing -> return ()
+        ConcatenatedText ftexts -> mconcat <$> mapM (go cur) ftexts
+        FormattedText (CustomTextColor fg bg) ftext -> do
+            tell [ ansiColor fg bg ]
+            go ( fg <|> cfg, bg <|> cbg ) ftext
+            tell [ ansiColor
+                (if fg /= cfg then cfg <|> Just DefaultColor else Nothing)
+                (if bg /= cbg then cbg <|> Just DefaultColor else Nothing)
+                ]
+        EndWithNewline ftext -> do
+            go cur ftext
+            gets rsEndedWithNewline >>= \case
+                True -> return ()
+                False -> tell [ "\n" ] >> modify (\s -> s { rsEndedWithNewline = True })
+
+
+ansiColor :: Maybe Color -> Maybe Color -> Text
+ansiColor Nothing Nothing = ""
+ansiColor (Just fg) Nothing = "\ESC[" <> T.pack (show (colorNum fg)) <> "m"
+ansiColor Nothing (Just bg) = "\ESC[" <> T.pack (show (colorNum bg + 10)) <> "m"
+ansiColor (Just fg) (Just bg) = "\ESC[" <> T.pack (show (colorNum fg)) <> ";" <> T.pack (show (colorNum bg + 10)) <> "m"
+
+colorNum :: Color -> Int
+colorNum = \case
+    DefaultColor -> 39
+    Black -> 30
+    Red -> 31
+    Green -> 32
+    Yellow -> 33
+    Blue -> 34
+    Magenta -> 35
+    Cyan -> 36
+    White -> 37
+    BrightBlack -> 90
+    BrightRed -> 91
+    BrightGreen -> 92
+    BrightYellow -> 93
+    BrightBlue -> 94
+    BrightMagenta -> 95
+    BrightCyan -> 96
+    BrightWhite -> 97