/* overlay - overlay two or more files
**
** Let's say you have these two files:
**
**     "This is file 1."
**     "                 And this is file 2."
**
** "overlay file1 file2" will produce:
**
**     "This is file 1.  And this is file 2."
**
** Copyright (C) 1993 by Jef Poskanzer <jef@mail.acme.com>.
** All rights reserved.
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions
** are met:
** 1. Redistributions of source code must retain the above copyright
**    notice, this list of conditions and the following disclaimer.
** 2. Redistributions in binary form must reproduce the above copyright
**    notice, this list of conditions and the following disclaimer in the
**    documentation and/or other materials provided with the distribution.
** 
** THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
** IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
** ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
** FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
** DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
** OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
** HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
** OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
** SUCH DAMAGE.
*/

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

static char* argv0;

int
main( int argc, char** argv )
    {
    int nfiles, i, j;
    int stdin_used, got_line;
    FILE** fp;
    char a_line[1024], the_line[1024];
    char* cp;

    /* Check args. */
    argv0 = argv[0];
    nfiles = argc - 1;
    if ( nfiles < 2 )
	{
	(void) fprintf( stderr, "usage:  %s file1 file2 ...\n", argv0 );
	exit( 1 );
	}
    
    /* Allocate file pointer array. */
    fp = (FILE**) malloc( nfiles * sizeof(FILE*) );
    if ( fp == (FILE**) 0 )
	{
	(void) fprintf( stderr, "%s: out of memory\n", argv0 );
	exit( 1 );
	}

    /* Open files. */
    stdin_used = 0;
    for ( i = 0; i < nfiles; ++i )
	{
	if ( strcmp( argv[i+1], "-" ) == 0 )
	    {
	    if ( stdin_used )
		{
		(void) fprintf( stderr, "%s: can't use stdin twice\n", argv0 );
		exit( 1 );
		}
	    fp[i] = stdin;
	    stdin_used = 1;
	    }
	else
	    {
	    fp[i] = fopen( argv[i+1], "r" );
	    if ( fp[i] == (FILE*) 0 )
		{
		perror( argv[i+1] );
		exit( 1 );
		}
	    }
	}

    /* Read and overlay lines until all files are done. */
    for (;;)
	{
	/* Clear out the result line. */
	for ( i = 0; i < sizeof(the_line); ++i )
	    the_line[i] = ' ';

	/* Read a line from each still-open file. */
	got_line = 0;
	for ( i = 0; i < nfiles; ++i )
	    {
	    if ( fp[i] != (FILE*) 0 )
		{
		if ( fgets( a_line, sizeof(a_line), fp[i] ) == (char*) 0 )
		    {
		    if ( fp[i] != stdin )
			(void) fclose( fp[i] );
		    fp[i] = (FILE*) 0;
		    }
		else
		    {
		    got_line = 1;
		    /* Add this line to the result line. */
		    for ( j = 0, cp = a_line; *cp != '\0'; ++cp )
			{
			switch ( *cp )
			    {
			    case ' ':
			    ++j;
			    break;

			    case '\t':
			    j = ( ( j / 8 ) + 1 ) * 8;
			    break;

			    case '\n':
			    break;

			    default:
			    the_line[j] = *cp;
			    ++j;
			    break;
			    }
			}
		    }
		}
	    }
	if ( ! got_line )
	    break;

	/* Remove trailing blanks. */
	for ( i = sizeof(the_line) - 2; i > 0; --i )
	    if ( the_line[i] != ' ' )
		break;
	the_line[i+1] = '\0';

	/* And write it out. */
	puts( the_line );
	}

    /* Finished. */
    exit( 0 );
    }