use super::{EventSource, SystemEvent, now_unix};
use tokio::fs::File;
use tokio::io::{AsyncBufReadExt, BufReader};
use tokio::sync::mpsc;

pub async fn watch(tx: mpsc::Sender<SystemEvent>) {
    let file = match File::open("/dev/kmsg").await {
        Ok(f) => f,
        Err(e) => {
            log::warn!("kmsg watcher: cannot open /dev/kmsg: {e}");
            return;
        }
    };

    let mut lines = BufReader::new(file).lines();
    while let Ok(Some(line)) = lines.next_line().await {
        if let Some(msg) = parse_kmsg(&line) {
            let _ = tx
                .send(SystemEvent {
                    source: EventSource::Kmsg,
                    raw_line: msg,
                    timestamp: now_unix(),
                })
                .await;
        }
    }
}

fn parse_kmsg(line: &str) -> Option<String> {
    let msg = if let Some(pos) = line.find(';') {
        &line[pos + 1..]
    } else {
        line
    };
    if msg.is_empty() {
        return None;
    }
    Some(msg.to_string())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parses_kmsg_line_with_semicolon() {
        let line = "6,1234,56789,-;usb 1-1: new full-speed USB device number 2";
        assert_eq!(
            parse_kmsg(line),
            Some("usb 1-1: new full-speed USB device number 2".to_string())
        );
    }

    #[test]
    fn parses_kmsg_line_without_semicolon() {
        let line = "plain message without header";
        assert_eq!(parse_kmsg(line), Some("plain message without header".to_string()));
    }

    #[test]
    fn skips_empty_message_after_semicolon() {
        let line = "6,1234,56789,-;";
        assert_eq!(parse_kmsg(line), None);
    }
}