// SPDX-License-Identifier: Apache-2.0
// SchOS — minimal init (PID 1)

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

static void
xputs(int fd, const char *s)
{
    int n = 0;
    while (s[n]) n++;
    write(fd, (void *)s, n);
}

int
main(void)
{
    if (getpid() != 1)
        exit();

    // Open console as fd 0; dup to fd 1 (stdout) and fd 2 (stderr).
    if (open("console", O_RDWR) < 0) {
        mknod("console", 1, 1);
        open("console", O_RDWR);
    }
    dup(0);
    dup(0);

    // --- /dev ------------------------------------------------------------
    // Minor numbers under major 1 follow Linux's mem-major layout where it
    // costs nothing (null=2, zero=5, full=7, random=8, urandom=9).
    // /dev/hole (was minor 4) is gone: it backed an abandoned experiment and
    // nothing has referenced it since.
    mkdir("/dev");
    mknod("/dev/console",  1,  1);
    mknod("/dev/null",     1,  2);
    mknod("/dev/keyboard", 1,  3);
    mknod("/dev/zero",     1,  5);
    mknod("/dev/full",     1,  7);
    mknod("/dev/random",   1,  8);
    mknod("/dev/urandom",  1,  9);
    mknod("/dev/fb0",      2,  0);
    mknod("/dev/mouse",    3,  1);
    mknod("/dev/tty",      1,  1); // alias for console — must pass TCGETS ioctl
    mknod("/dev/ttyS0",    4, 64);
    mknod("/dev/stdin",    1,  1);
    mknod("/dev/stdout",   1,  1);
    mknod("/dev/stderr",   1,  1);

    // Raw input events, Linux evdev layout (kernel/dev/input.c). /dev/keyboard
    // and /dev/mouse above are the old character-and-position interfaces; these
    // are the ones with key releases and button transitions, which is what a
    // game or a compositor needs and what neither of the others can express.
    mkdir("/dev/input");
    mknod("/dev/input/event0", 7, 0);   // keyboard
    mknod("/dev/input/event1", 7, 1);   // mouse

    // Raw disks (kernel/dev/disk.c). The minor is the IDE device number, so
    // hda is the disk the kernel booted from and hdb the second channel.
    //
    // Created unconditionally, the same way every other node here is: opening
    // one when no drive is there fails with ENXIO, which is a better answer
    // than a missing path, and it keeps this list a description of the device
    // model rather than of one machine's hardware.
    mknod("/dev/hda",      8,  0);
    mknod("/dev/hdb",      8,  1);

    // --- /proc -----------------------------------------------------------
    // Synthesised status files, major 6 (kernel/dev/procfs.c). These are the
    // global ones; per-process /proc/<pid>/ directories need synthetic
    // directory support in the filesystem, which does not exist yet.
    mkdir("/proc");
    // /proc is a real filesystem now (kernel/fs/procfs.c), not a handful of
    // mknod'd nodes: it has to be, because one directory per process cannot be
    // created ahead of time. This is what makes `ps` and `top` work.
    //
    // The mknod'd global files below still happen, and are simply covered by
    // the mount. They stay for now so that a failure here degrades to the old
    // behaviour instead of losing /proc entirely.
    mount("proc", "/proc", "proc", 0, 0);
    mknod("/proc/meminfo",     6, 1);
    mknod("/proc/uptime",      6, 2);
    mknod("/proc/cpuinfo",     6, 3);
    mknod("/proc/version",     6, 4);
    mknod("/proc/stat",        6, 5);
    mknod("/proc/loadavg",     6, 6);
    mknod("/proc/mounts",      6, 7);
    mknod("/proc/filesystems", 6, 8);
    // SchFS volume summary: label, generation, free space, and the root
    // directory. Reachable whether or not the volume is mounted into the
    // namespace, which is what makes it useful when a mount has gone wrong.
    mknod("/proc/schfs",       6, 9);
    // Write 'c' here to crash on purpose. The crash screen is otherwise the
    // one part of the system that can only be seen by having a bug.
    mknod("/proc/sysrq",       6, 10);
    mknod("/proc/pci",         6, 11);
    mknod("/proc/interrupts",  6, 12);

    mkdir("/sys");

    xputs(1, "\nSchOS\n");
    xputs(1, "init: ready (pid 1)\n");

    for (;;) {
        int pid = fork();
        if (pid < 0) {
            xputs(2, "init: fork failed\n");
            sleep(100);
            continue;
        }

        if (pid == 0) {
            // exec.c auto-enables Linux ABI for musl binaries (entry >= 0x100000).
            // Do NOT call enable_linux_abi() here — it corrupts SchOS syscall
            // numbers for the exec/exit calls that follow in this child.
            // Standardized naming: the shell is always /bin/sh, regardless of
            // which implementation backs it (dash, mksh, etc.) — no ksh/mksh/
            // other aliases are looked up here.
            static char *argv[] = { "sh", 0 };
            exec("/bin/sh", argv);
            xputs(2, "init: no shell found; place sh in /bin\n");
            exit();
        }

        // Reap zombies; the loop restarts the shell when it exits.
        int wpid;
        while ((wpid = wait()) >= 0 && wpid != pid)
            ;
        // Brief pause before restarting so we don't spin on a missing shell.
        sleep(100);
    }
    return 0;
}