use std::{
    fs::File,
    io::{Read as _, Seek as _, SeekFrom},
};

use eyre::Context as _;

pub(crate) struct Netdev {
    rx_bytes: File,
    tx_bytes: File,
}

impl Netdev {
    pub fn from_name(name: &str) -> eyre::Result<Self> {
        let rx_bytes = Self::open_netdev(name, "rx_bytes")?;
        let tx_bytes = Self::open_netdev(name, "tx_bytes")?;

        Ok(Self { rx_bytes, tx_bytes })
    }

    fn open_netdev(dev: &str, stat: &str) -> eyre::Result<File> {
        let path = format!("/sys/class/net/{dev}/statistics/{stat}");
        File::open(&path).wrap_err(format!("Failed to open netdev '{dev}'"))
    }

    fn read_bytes(file: &mut File) -> eyre::Result<u64> {
        file.seek(SeekFrom::Start(0))?;
        let mut buf = String::new();
        file.read_to_string(&mut buf)?;
        Ok(buf.trim().parse().unwrap_or(0))
    }

    pub fn rx_bytes(&mut self) -> eyre::Result<u64> {
        Self::read_bytes(&mut self.rx_bytes)
    }

    pub fn tx_bytes(&mut self) -> eyre::Result<u64> {
        Self::read_bytes(&mut self.tx_bytes)
    }
}