-- Simple program to display a src reference.
-- Reports the filename and location, and shows a section of the file
-- with the cursor on the actual location.  We try to place the
-- important line as near the centre of the screen as possible.

module Main where

import System
import IO             (hSetBuffering,BufferMode(..),stdin,stdout)
import Char           (isSpace,isDigit)
import Run            (runAndReadStdout)
import HighlightStyle (getTerminalSize,cls,goto,highlight,lineWrap
                      ,Highlight(..),Colour(..))

main = do
    args <- System.getArgs
    case args of
      [filename,sline,scol] ->
              let line = (read sline)::Int
                  column = (read scol)::Int in
              display filename line column 0 0
      [filename,sline,scol,sline2,scol2] ->
              let line = (read sline)::Int
                  column = (read scol)::Int
                  endline = (read sline2)::Int
                  endcolumn = (read scol2)::Int in
              display filename line column endline endcolumn
      _ -> do prog <- System.getProgName
              putStrLn ("Usage: "++prog++" srcfile line col [endline endcol]")
              exitWith (ExitFailure 1)

display :: FilePath -> Int -> Int -> Int -> Int -> IO ()
display srcfile line column endline endcolumn = do
    len <- runAndReadStdout ("wc -l "++srcfile)
    let n = read (takeWhile isDigit (dropWhile isSpace len))
    case n of
      0 -> do putStrLn ("File "++srcfile++" not found.")
              exitWith (ExitFailure 1)
      _ -> do (width,height) <- getTerminalSize
              f <- readFile srcfile
              hSetBuffering stdin NoBuffering
              hSetBuffering stdout NoBuffering
              let middle= (height `div` 2) - 1
                  trim  = if line < middle then 0 else line - middle
                  fs    = (expandTabs . unlines . take (height-2)
                          . drop trim . lines) f
                  line' = line-trim
                  (a,b,c) = split (line',column,endline-trim,endcolumn) fs
              putStr (cls ++ goto 1 1 ++ lineWrap False)
              putStr (highlight [Bold] ("---- "++srcfile++" ---- line: "
                                       ++show line++" ---- column: "
                                       ++show column++" ----"))
              if endline==0
                then putStr (goto 1 2 ++ fs ++ goto column (line'+1))
                else putStr (goto 1 2 ++ a
                             ++ highlight [Bold, Foreground Magenta] b ++ c
                             ++ goto column (line'+1))
              System.system ("stty -icanon min 1 -echo")
              awaitQuit
              System.system ("stty icanon echo")
              putStr (goto 1 height)
              return ()

split :: (Int,Int,Int,Int) -> String -> (String,String,String)
split (sl,sc,el,ec) str
  | sl==el    =
    let (a,b) = splitAt (el-1) (lines str)
        (c,d) = splitAt ec (head b)
        (e,f) = splitAt (sc-1) c
    in (unlines a++e, f, unlines (d:tail b))
  | otherwise =
    let ls = lines str
        (a,b)   = splitAt (el-1) (lines str)
        (a',b') = splitAt  ec    (head b)
        (p,q)   = splitAt (sl-1) a
        (p',q') = splitAt (sc-1) (head q)
    in (unlines p++p', unlines (q':tail q)++a', unlines (b':tail b))

awaitQuit :: IO ()
awaitQuit = do
  q <- getChar
  case q of
    'q' -> return ()
    'x' -> return ()
    _   -> awaitQuit

expandTabs :: String -> String
expandTabs = expand 0
  where expand n []         = []
        expand n ('\n':xs)  = '\n': expand 0 xs
        expand 8 ('\t':xs)  = replicate 8     ' ' ++ expand 0 xs
        expand n ('\t':xs)  = replicate (8-n) ' ' ++ expand 0 xs
        expand 8 (x:xs)     = x : expand 1 xs
        expand n (x:xs)     = x : expand (n+1) xs