{-# LANGUAGE ScopedTypeVariables #-}
module Text.Colour.Capabilities.FromEnv where
import Control.Exception
import qualified System.Console.Terminfo as Terminfo
import System.Environment (lookupEnv)
import System.IO
import Text.Colour.Capabilities
-- | Try to detect how many colours the terminal can handle.
--
-- This is based on the @colors@ capability of the terminfo detected based on the @TERM@ environment variable.
-- If the terminal can handle 8-bit colours and also has the @COLORTERM@ environment variable set to @24bit@ or @truecolor@, then this function will return 'With24BitColours'.
getTerminalCapabilitiesFromEnv :: IO TerminalCapabilities
getTerminalCapabilitiesFromEnv = do
mTerm <- (Just <$> Terminfo.setupTermFromEnv) `catch` (\(_ :: Terminfo.SetupTermError) -> pure Nothing)
case mTerm of
Nothing -> pure WithoutColours
Just term -> do
-- To support https://no-color.org/
mnc <- lookupEnv "NO_COLOR"
case mnc of
Just _ -> pure WithoutColours
Nothing -> do
-- To support 24-bit colour:
-- https://unix.stackexchange.com/questions/450365/check-if-terminal-supports-24-bit-true-color
mct <- lookupEnv "COLORTERM"
pure $ case mct of
Just "truecolor" -> With24BitColours
Just "24bit" -> With24BitColours
_ ->
case Terminfo.getCapability term (Terminfo.tiGetNum "colors") of
Nothing -> WithoutColours
Just c
| c > 256 -> With24BitColours
| c >= 256 -> With8BitColours
| c >= 8 -> With8Colours
| otherwise -> WithoutColours
-- | Try to detect how many colours a given handle can handle.
--
-- This function does the same as 'getTerminalCapabilitiesFromEnv' but returns 'WithoutColours' is not a terminal device.
getTerminalCapabilitiesFromHandle :: Handle -> IO TerminalCapabilities
getTerminalCapabilitiesFromHandle h = do
isTerm <- hIsTerminalDevice h
if isTerm
then getTerminalCapabilitiesFromEnv
else pure WithoutColours