// SPDX-License-Identifier: Apache-2.0
//
// chvt N -- show virtual terminal N.
//
// The same name and the same argument as the Linux tool, because it does the
// same thing and nobody should have to learn a second one. Alt+F1..F6 does
// this from the keyboard; this does it from a script, and from a serial
// console where there are no function keys to press.
//
//   chvt        report which terminal is active and which are in use
//   chvt 2      switch to /dev/tty2

#include "types.h"
#include "user.h"
#include "fcntl.h"
#include "posix.h"

// No printf in lib/, and this needs one string and two small numbers.
static void
puts(const char *s)
{
    int n = 0;
    while (s[n]) n++;
    write(1, (void *)s, n);
}

static void
putn(int v)
{
    char b[12];
    int i = 0;
    if (v < 0) { write(1, "-", 1); v = -v; }
    if (v == 0) { write(1, "0", 1); return; }
    while (v > 0) { b[i++] = '0' + (v % 10); v /= 10; }
    while (i-- > 0) write(1, &b[i], 1);
}

static int
num(const char *s)
{
    int v = 0;
    while (*s >= '0' && *s <= '9')
        v = v * 10 + (*s++ - '0');
    return v;
}

int
main(int argc, char *argv[])
{
    // /dev/console rather than fd 0: the caller may have redirected its input,
    // and the terminal being asked about is the machine's, not whichever one
    // this process happens to be reading from.
    int fd = open("/dev/console", O_RDWR);
    if (fd < 0) {
        puts("chvt: cannot open /dev/console\n");
        exit();
    }

    if (argc == 1) {
        struct vt_stat st;
        if (ioctl(fd, VT_GETSTATE, &st) < 0) {
            puts("chvt: VT_GETSTATE failed\n");
            exit();
        }
        puts("active: tty");
        putn(st.v_active);
        puts("\nin use:");
        for (int i = 1; i <= 16; i++)
            if (st.v_state & (1 << i)) {
                puts(" tty");
                putn(i);
            }
        puts("\n");
        exit();
    }

    int n = num(argv[1]);
    if (n < 1) {
        puts("usage: chvt N\n");
        exit();
    }

    // The argument goes by value, not through a pointer -- Linux defines
    // VT_ACTIVATE that way and so does SchOS. Passing a pointer here would
    // switch to whatever the address happened to be.
    if (ioctl(fd, VT_ACTIVATE, (void *)(long)n) < 0) {
        puts("chvt: no terminal ");
        putn(n);
        puts("\n");
        exit();
    }
    exit();
}