#include "gbos.h"
/* cut -f N [-d C] [file]: print field N of each line.
 *
 * The delimiter defaults to TAB, like cut(1); -d takes the first character of
 * its argument, so `-d :` works - and since the shell has no quoting, `-d \\s`
 * is how you say space (\\t tab, \\n newline). A line with no delimiter is passed through
 * whole (what GNU cut does without -s), which is usually what you want when
 * filtering mixed output on a 40-column screen. */

#define MAXLINE 80

/* The shell has no quoting, so a space or a tab cannot be typed as an
   argument: "-d ' '" arrives as three tokens. Escapes are how you name them
   here - \s space, \t tab, \n newline, \\ backslash. */
static char unesc1(const char *s, unsigned char *used) {
    *used = 1;
    if (s[0] != '\\' || !s[1]) return s[0];
    *used = 2;
    switch (s[1]) {
        case 's': return ' ';
        case 't': return '\t';
        case 'n': return '\n';
        case 'r': return '\r';
        default: return s[1];
    }
}

void main(void) {
    char *argv[8];
    char line[MAXLINE];
    unsigned char argc = argv_parse(argv, 8);
    char *fv = optval(argv, argc, 'f');
    char *dv = optval(argv, argc, 'd');
    unsigned char dused;
    char delim = dv ? unesc1(dv, &dused) : '\t';
    unsigned char want = fv ? atou(fv) : 1;
    unsigned char len = 0, fd = NOFD, i, field, start, end;
    char *fname = 0;
    int ch;

    if (want == 0) want = 1;
    for (i = 0; i < argc; i++) {
        if (argv[i][0] == '-') continue;
        if (fv == argv[i] || dv == argv[i]) continue;
        fname = argv[i];
        break;
    }
    if (fname) {
        fd = open(fname, O_READ);
        if (fd == EISDIR) {
            puts("cut: is a directory");
            nl();
            sexit(2);
        }
        if (fd == NOFD) {
            puts("cut: no such file");
            nl();
            sexit(2);
        }
    }
    for (;;) {
        if (fd == NOFD) {
            char c = readc();
            ch = (c == EOF) ? -1 : c;
        } else ch = fgetc(fd);
        if (ch == '\r') continue;
        if (ch >= 0 && ch != '\n') {
            if (len < MAXLINE) line[len++] = (char)ch;
            continue;
        }
        if (ch < 0 && len == 0) break;
        /* walk to the wanted field */
        field = 1;
        start = 0;
        for (i = 0; i <= len; i++) {
            if (i == len || line[i] == delim) {
                if (field == want) break;
                field++;
                start = (unsigned char)(i + 1);
            }
        }
        end = i;
        if (field == want && start <= len) writes(line + start, (unsigned char)(end - start));
        nl();
        len = 0;
        if (ch < 0) break;
    }
    if (fd != NOFD) close(fd);
}