#include <stdio.h>

/* Pos - a text positioning tool */
/* Written by Jonathan Bowen, 15 July 1985 */
/* Version 1.1, October 1985 (error returns improved) */
/* Version 1.2, January 1990 (blank lines give zero-length lines) */

#define USAGE "Usage: pos [ -b ] [ column ] [ file ... ]\n"
#define FALSE 0
#define TRUE 1
#define NUL '\0'
#define HT '\t'
#define LF '\n'
#define SP ' '
#define TABLENGTH 8    /* Must be a power of 2 */
#define MAXLENGTH 256  /* Must be a multiple of TABLENGTH */
#define DEFAULTPOS 40  /* Column positioning */
#define NOPOS (-1)     /* Invalid column position */

extern errno;          /* Global error number */

column = DEFAULTPOS;   /* Column position */
blanks = FALSE;        /* Leading white spaces include tabs */
first  = FALSE;        /* First line used for adjustment */
left   = FALSE;        /* Left margin adjustment */
right  = FALSE;        /* Right margin adjustment */

main(argc, argv)
int argc;
char *argv[];
{
    FILE *fp, *fopen();
    errno = 0;

    if (argc > 1) {
	if ((*++argv)[0] == '-') {
	    switch (*(argv[0]+1)) {
	    case 'b':
		blanks = TRUE;
		argc--;
		*argv++;
		break;
	    case 'U':
		fprintf(stderr,USAGE);
		exit(0);
	    }
	}
    }

    if (argc > 1) {
	if (*(argv[0]) == '-') left = TRUE;
	else if (*(argv[0]) == '+') right = TRUE;
	if ((left || right || (*(argv[0]) == '0')) &&
	    (*(argv[0]+1) == '\0')) /* `-' or `+' or `0' */
	    first = TRUE; /* position calculated from 1st line */
	if (! first) { /* check for valid column */
	    column = abs(atoi(argv[0]));
	    if (((left || right) && (column <= 0)) ||
	      (column>MAXLENGTH)) {
		fprintf(stderr, "pos: Bad column position (1-%d): %d\n",
			MAXLENGTH, column);
		exit(1);
	    }
	}
	if (column == 0) { /* invalid column - assume file name */
	    column = DEFAULTPOS;
	    *argv--;
	}
	else argc--;
    }
    column--;    /* start from column 0 rather than column 1 */

    if (argc == 1) /* no arguments left; read standard input */
	position(stdin);
    else
	while (--argc > 0)
	    if ((fp = fopen(*++argv,"r")) == NULL) {
	    perror(*argv); /* No such file or directory */
	    continue;
	    }
	    else {
	    position(fp);
	    if (fclose(fp) == EOF) {
		perror(*argv); /* Can't close file */
		continue;
		}
	    }
    exit(errno);
}

position(fp)    /* position file fp on standard output */
FILE *fp;
{
    char c;
    char buf[MAXLENGTH+1];
    int len, old, pos, pad, tabs, spaces, i;

    if (first) column = NOPOS;
    while ((c=getc(fp)) != EOF) {
	if (c == '.') { /* lines starting with `.' not mangled */
	    while ((c != LF) && (c != EOF)) {
		putchar(c);
		c = getc(fp);
	    }
	    putchar(LF);
	}
	else {
	len=0;
	pos=0;
	while ((c == SP) || (c == HT)) { /* leading white spaces */
	    if (c == HT) pos |= TABLENGTH-1;
	    pos++;
	    c = getc(fp);
#ifdef DEBUG
	    printf("pos = %d\n",pos);
#endif
	}
	while ((c != LF) && (c != EOF) && (len <= MAXLENGTH)) {
	    /* valid line */
	    old = pos;
	    if (c == HT) pos |= TABLENGTH-1;
	    pos++;
	    if (c == HT) {
		spaces = pos-old;
		for (i=0; i<spaces; i++) buf[len++] = SP;
		/* N.B. No overflow is possible here because
		   MAXLENGTH is a multiple of TABLENGTH */
	    }
	    else buf[len++] = c;
	    c = getc(fp);
#ifdef DEBUG
	    printf("pos = %d, len = %d\n",pos,len);
#endif
	}
	buf[len] = NUL;
	if (len <= MAXLENGTH) { /* no buffer overflow */
	    while (len > 0) { /* trailing white spaces */
		if (buf[len-1] == SP) buf[--len] = NUL;
		else break;
#ifdef DEBUG
		printf("len = %d\n",len);
#endif
	    }
	    if (column == NOPOS) {
		if (left)              column = pos - len;
		else if (right)        column = pos;
		else /* if (center) */ column = pos - len/2;
	    }
	    if (left)              pad = column;
	    else if (right)        pad = column - len;
	    else /* if (center) */ pad = column - len/2;
	    if ((pad < 0) || (len == 0)) pad = 0;
	    if (blanks) {
		tabs   = 0;
		spaces = pad;
	    }
	    else {
		tabs   = pad/TABLENGTH;
		spaces = pad%TABLENGTH;
	    }
	    for (i=0; i<tabs;   i++) putchar(HT);
	    for (i=0; i<spaces; i++) putchar(SP);
	}
	fputs(buf,stdout); /* output string with no newline character */
	while ((c != LF) && (c != EOF)) { /* valid line */
	    c = getc(fp);
	    putchar(c);
	}
	putchar(LF);
	if (c == EOF) return;
	}
    }
}