use clap::{Arg, ArgMatches, Command};
use lazy_static::lazy_static;
use shitbox::Cmd;
use std::{
    error::Error,
    ffi::CString,
    fs::OpenOptions,
    io::{self, Read, Seek, SeekFrom, Write},
};

const SWAP_MAGIC1: &str = "SWAPSPACE2";
const SWAP_MAGIC2: &str = "SWAP_SPACE";
const SWAP_MAGIC_LENGTH: u64 = 10;
const SWAP_LABEL_LENGTH: u64 = 16;
const SWAP_LABEL_OFFSET: u64 = 1024 + 4 + 4 + 4 + 16;

lazy_static! {
    static ref SWAP_MAGIC_OFFSET: u64 =
        unsafe { libc::sysconf(libc::_SC_PAGESIZE) as u64 - SWAP_MAGIC_LENGTH };
}

#[derive(Debug)]
pub struct Swaplabel;

impl Cmd for Swaplabel {
    fn cli(&self) -> Command {
        Command::new("swaplabel")
            .about("set the label of a swap filesystem")
            .author("Nathan Fisher")
            .version(env!("CARGO_PKG_VERSION"))
            .args([
                Arg::new("label")
                    .help("set the label")
                    .short('L')
                    .visible_short_alias('l')
                    .long("label")
                    .num_args(1)
                    .required(false),
                Arg::new("device").num_args(1).required(true),
            ])
    }

    fn run(&self, matches: &ArgMatches) -> Result<(), Box<dyn Error>> {
        let mut opts = OpenOptions::new();
        let device = matches
            .get_one::<String>("device")
            .ok_or(io::Error::new(io::ErrorKind::Other, "no device given"))?;
        let mut fd = opts.read(true).write(true).open(device)?;
        fd.seek(SeekFrom::Start(*SWAP_MAGIC_OFFSET))?;
        let mut magic = [0; SWAP_MAGIC_LENGTH as usize];
        fd.read_exact(&mut magic)?;
        let m: String = magic.iter().map(|x| *x as char).collect();
        if m.as_str() != SWAP_MAGIC1 && m.as_str() != SWAP_MAGIC2 {
            let msg = format!("{device} is not a swap file or partition");
            println!("Magic String: {m}");
            return Err(io::Error::new(io::ErrorKind::Other, msg).into());
        }
        fd.seek(SeekFrom::Start(SWAP_LABEL_OFFSET))?;
        if let Some(label) = matches.get_one::<String>("label") {
            if label.len() + 1 > SWAP_LABEL_LENGTH as usize {
                return Err(io::Error::new(io::ErrorKind::Other, "label is too long").into());
            }
            let label = CString::new(label.as_str())?;
            fd.write_all(label.as_bytes())?;
        } else {
            let mut label = [0; SWAP_LABEL_LENGTH as usize];
            fd.read_exact(&mut label)?;
            let label: String = label
                .iter()
                .map(|x| *x as char)
                .take_while(|x| *x != '\0')
                .collect();
            println!("label: {label}");
        }
        Ok(())
    }

    fn path(&self) -> Option<shitbox::Path> {
        Some(shitbox::Path::UsrSbin)
    }
}