/*
  dnd.c: Do Not Disturb - one-line output filter.

  Jason Hood, 6 October, 2010.
  Public Domain.
  
  Reads standard input, overwrites to standard output.  Lines are truncated to
  fit the screen.  The final line is kept if -k is given, otherwise it is
  removed.

  v1.01, 13 February, 2011:
  - fixed tab at screen edge;
  * blank the previous line before starting the next one.

  v1.02, 20 June, 2011:
  - Win32: another long line fix (pipe coming from DOS);
  * removed the DOS versions (not much point if you can't see it running).

  v1.03, 30 June, 2011:
  - lines before a blank line were not blanked out.

  v1.04, 9 January, 2012:
  - don't add any characters after a tab at screen edge;
  * just pass through if we've been redirected;
  * read a complete line before writing it;
  * Win32: use window width, not buffer width.

  v1.05, 31 August, 2013:
  - fix col when truncating at a tab.
*/

#define PVERS "1.05"
#define PDATE "31 August, 2013"


#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <io.h>			    // isatty
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else
#include <unistd.h>		    // isatty for UNIX? (djgpp at least)
#endif


#define TAB_SIZE   8


const char helpmsg[] = "\
Do Not Disturb by Jason Hood <jadoxa@yahoo.com.au>.\n\
Version " PVERS " (" PDATE ").  Public Domain.\n\
http://misc.adoxa.vze.com/\n\
\n\
Read lines from standard input, overwrite each line (truncated to screen width)\n\
to standard output.\n\
\n\
... | dnd [-k]\n\
\n\
-k - keep the last line\
";


int main( int argc, char* argv[] )
{
  int	cols, col, len, wid;
  int	ch;
  char	buf[8192];
  char* pos;

#ifdef _WIN32
  CONSOLE_SCREEN_BUFFER_INFO csbi;
#else
  char* col_env;
#endif

  if ((argc == 1 && isatty( 0 )) ||
      (argc == 2 && (strcmp( argv[1], "/?" ) == 0 ||
		     strcmp( argv[1], "-?" ) == 0 ||
		     strcmp( argv[1], "--help" ) == 0)))
  {
    puts( helpmsg );
    return 0;
  }
  if (argc == 2 && strcmp( argv[1], "--version" ) == 0)
  {
    puts( "Do Not Disturb version " PVERS " (" PDATE ")." );
    return 0;
  }

  // If we've been redirected, just pass through.
  if (!isatty( 1 ))
  {
    for (;;)
    {
      len = read( 0, buf, sizeof(buf) );
      if (len == 0)
	break;
      write( 1, buf, len );
    }
    return 0;
  }

  // Stop just before the edge to prevent wrap (not disabling
  // ENABLE_WRAP_AT_EOL_OUTPUT in Windows because it doesn't seem to work when
  // piping from a DOS program, at least in XP).
#ifdef _WIN32
  GetConsoleScreenBufferInfo( GetStdHandle( STD_OUTPUT_HANDLE ), &csbi );
  cols = csbi.srWindow.Right;
#else
  col_env = getenv( "COLUMNS" );
  cols = (col_env) ? atoi( col_env ) - 1 : 79;
#endif

  col = len = wid = 0;
  pos = buf;
  for (;;)
  {
    ch = getchar();
    if (ch == '\n' || ch == EOF)
    {
      if (ch == EOF && wid == 0)
	break;
      if (wid < len)
      {
	memset( pos, ' ', len - wid );
	pos += len - wid;
      }
      *pos++ = '\r';
      write( 1, buf, pos - buf );
      len = wid;
      if (ch == EOF)
	break;
      col = wid = 0;
      pos = buf;
    }
    else if (ch == '\r')
    {
      col = 0;
      *pos++ = ch;
    }
    else if (ch == '\b')
    {
      if (col > 0)
        --col;
      *pos++ = ch;
    }
    else if (ch == '\a')
    {
      *pos++ = ch;
    }
    else if (col < cols)
    {
      if (ch == '\t')
      {
	int c = col + TAB_SIZE - (col % TAB_SIZE);
	if (c < cols)
	{
	  col = c;
	  *pos++ = ch;
	}
      }
      else
      {
	++col;
	*pos++ = ch;
      }
      if (col > wid)
	wid = col;
    }
    if (pos == buf + sizeof(buf))
    {
      write( 1, buf, sizeof(buf) );
      pos = buf;
    }
  }

  if (argc == 1 || strcmp( argv[1], "-k" ) != 0)
  {
    if (len != 0)
    {
      memset( buf, ' ', len );
      buf[len] = '\r';
      write( 1, buf, len + 1 );
    }
  }
  else
  {
    putchar( '\n' );
  }

  return 0;
}