use std::{
    collections::HashMap, env, fs::File, io::Read, process::Command, thread::sleep, time::Duration,
};

fn main() {
    let mut args = env::args();

    assert!(
        args.len() > 2,
        "Too few arguments, provide battery id and values with warning levels"
    );
    // Skip process (argc[0])
    args.next();

    // 1: Battery ID
    let bat = args.next().expect("Invalid Battery id");
    let bat_path = format!("/sys/class/power_supply/{bat}");
    let cap_path = format!("{bat_path}/capacity");
    let status_path = format!("{bat_path}/status");

    // 2: Sleep
    let sleep_secs = args
        .next()
        .expect("Invalid sleep duration")
        .parse::<u64>()
        .expect("Invalid sleep value");

    let mut warnings: HashMap<u8, String> = HashMap::new();
    for arg in args {
        let (lvl, value) = arg.split_at(1);
        assert!(
            lvl == "l" || lvl == "n" || lvl == "c",
            "Unknown notification level"
        );
        warnings.insert(
            value.parse::<u8>().expect("Invalid battery value"),
            lvl.to_string(),
        );
    }

    let mut cap_cache = String::new();
    loop {
        let cur_cap = read_file(&cap_path);
        if cur_cap != cap_cache {
            cap_cache.clone_from(&cur_cap);
            if &read_file(&status_path) == "Charging" { continue; };
            let val = cur_cap
                .parse::<u8>()
                .expect("Couldn't parse capacity value");
            if let Some(lvl) = warnings.get(&val) {
                notify(lvl, val);
            };
        }
        sleep(Duration::from_secs(sleep_secs));
    }
}

fn read_file(path: &str) -> String {
    let mut f = File::open(path).expect("Could't open file");
    let mut buf = String::new();
    f.read_to_string(&mut buf).expect("Couldn't read file");
    buf.trim().to_string()
}

fn notify(lvl: &str, remaining: u8) {
    let urgency = match lvl {
        "l" => "low",
        "n" => "normal",
        "c" => "critical",
        _ => unreachable!(),
    };
    let notif = format!("Remaining battery capacity: {remaining}");
    Command::new("notify-send")
        .arg("--app-name=esbnd")
        .arg("--category=device")
        .arg("--icon=battery-low-symbolic")
        .arg("-u")
        .arg(urgency)
        .arg(notif)
        .spawn()
        .expect("Couldn't send notification");
}