use log::warn;
use std::fmt::Display;
use std::sync::{Arc, LazyLock};
use tokio::io::{self, AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net;
use tokio::sync::{oneshot, watch, Mutex};

pub async fn read_line(prompt: impl Display) -> String {
    read(prompt, false).await
}

pub async fn read_password(prompt: impl Display) -> String {
    read(prompt, true).await
}

fn choice_char(s: &str) -> char {
    s.chars().skip_while(|c| *c != '[').skip(1).next().unwrap()
}

#[test]
fn test_choice_char() {
    assert_eq!('r', choice_char("[r]etry"));
    assert_eq!('b', choice_char("re[b]boot"));
}

/// ```no_run
/// use init::input;
///
/// #[tokio::main(flavor = "current_thread")]
/// async fn main() {
///     tokio::spawn(input::answer_requests_from_stdin());
///     match input::read_choice(["[r]etry","[i]gnore","re[b]oot"]).await {
///         'r' => todo!(),
///         'i' => todo!(),
///         'b' => todo!(),
///         _ => unreachable!(),
///     }
/// }
/// ```
pub async fn read_choice<const N: usize>(choices: [&str; N]) -> char {
    let chars = choices.map(choice_char);

    let mut prompt = String::new();
    for s in choices {
        if !prompt.is_empty() {
            prompt.push_str(", ");
        }
        prompt.push_str(s);
    }
    prompt.push_str("? ");

    loop {
        let line = read_line(&prompt).await;
        let Some(ch) = line.chars().nth(0) else {
            continue;
        };

        for choice in chars {
            if ch == choice {
                return choice;
            }
        }
    }
}

#[derive(Clone, serde::Deserialize, serde::Serialize)]
pub struct InputRequest {
    prompt: String,
    hide: bool,
}

pub type Reply = Arc<Mutex<Option<oneshot::Sender<String>>>>;

static REQ: LazyLock<Mutex<watch::Sender<Option<(InputRequest, Reply)>>>> = LazyLock::new(|| {
    let (tx, _) = watch::channel(None);
    Mutex::new(tx)
});
static READ_MUTEX: Mutex<()> = Mutex::const_new(());

async fn read(prompt: impl Display, hide_input: bool) -> String {
    let _read_lock = READ_MUTEX.lock();

    let req = InputRequest {
        prompt: prompt.to_string(),
        hide: hide_input,
    };

    let (tx, rx) = oneshot::channel();
    let reply = Arc::new(Mutex::new(Some(tx)));

    REQ.lock().await.send_replace(Some((req, reply)));

    let input = rx.await.expect("reply sender should not be closed");

    REQ.lock().await.send_replace(None);

    input
}

pub async fn answer_requests_from_stdin() {
    let mut stdin = BufReader::new(io::stdin()).lines();
    let mut stdout = io::stdout();

    let mut current_req = REQ.lock().await.subscribe();
    current_req.mark_changed();

    loop {
        // TODO check is stdin has been closed (using C-c is enough for now)
        (current_req.changed().await).expect("input request should not close");

        let Some((req, reply)) = current_req.borrow_and_update().clone() else {
            continue;
        };

        // handle hide
        let mut saved_termios = None;
        if req.hide {
            match termios::Termios::from_fd(0) {
                Ok(mut tio) => {
                    saved_termios = Some(tio.clone());
                    tio.c_lflag &= !termios::ECHO;
                    if let Err(e) = termios::tcsetattr(0, termios::TCSAFLUSH, &tio) {
                        warn!("password may be echoed! {e}");
                    }
                }
                Err(e) => {
                    warn!("password may be echoed! {e}");
                }
            }
        }

        // print the prompt and wait for user input
        stdout.write_all(req.prompt.as_bytes()).await.unwrap();
        stdout.flush().await.unwrap();

        tokio::select!(
            r = stdin.next_line() => {
                let Ok(Some(line)) = r else {
                    warn!("stdin closed");
                    return;
                };

                if let Some(tx) = reply.lock().await.take() {
                    let _ = tx.send(line);
                }

                if saved_termios.is_some() {
                    // final '\n' is hidden too so fix it
                    stdout.write_all(b"\n").await.unwrap();
                    stdout.flush().await.unwrap();
                }
            }
            _ = current_req.changed() => {
                // reply came from somewhere else
                stdout.write_all(b"<answered>\n").await.unwrap();
                stdout.flush().await.unwrap();

                current_req.mark_changed();
            }
        );

        // restore term if input was hidden
        if let Some(tio) = saved_termios {
            if let Err(e) = termios::tcsetattr(0, termios::TCSAFLUSH, &tio) {
                warn!("failed to restore pty attrs: {e}");
            }
        }
    }
}

const SOCKET_PATH: &str = "/run/init.sock";

pub async fn answer_requests_from_socket() {
    let Ok(listener) = net::UnixListener::bind(SOCKET_PATH)
        .inspect_err(|e| warn!("failed start input socket listener: {e}"))
    else {
        return;
    };

    loop {
        let Ok((conn, _)) = (listener.accept())
            .await
            .inspect_err(|e| warn!("input socket listener failed: {e}"))
        else {
            return;
        };

        tokio::spawn(handle_connection(conn));
    }
}

#[derive(serde::Deserialize, serde::Serialize)]
enum Message {
    #[serde(rename = "l")]
    Log(Vec<u8>),
    #[serde(rename = "r")]
    Req(Option<InputRequest>),
}

async fn handle_connection(conn: net::UnixStream) {
    use crate::dklog;

    let mut log = dklog::LOG.subscribe();

    let mut current_req = REQ.lock().await.subscribe();
    current_req.mark_changed();

    let (rd, mut wr) = io::split(conn);
    let mut rd = BufReader::new(rd).lines();

    macro_rules! wr {
        ($msg:expr) => {
            let mut buf = serde_json::to_vec(&$msg).unwrap();
            buf.push(b'\n');

            if wr.write_all(&buf).await.is_err() {
                return;
            }
            if wr.flush().await.is_err() {
                return;
            }
        };
    }

    loop {
        tokio::select!(
            r = current_req.changed() => {
                r.expect("input request should not close");
            },
            l = log.next() => {
                let Some(l) = l else { return; };
                wr!(Message::Log(l));
                continue;
            },
        );

        let Some((req, reply)) = current_req.borrow_and_update().clone() else {
            wr!(Message::Req(None));
            continue;
        };

        wr!(Message::Req(Some(req)));

        loop {
            tokio::select!(
                r = rd.next_line() => {
                    let Ok(Some(line)) = r else {
                        return; // closed
                    };

                    if let Some(tx) = reply.lock().await.take() {
                        let _ = tx.send(line);
                    }
                }
                _ = current_req.changed() => {
                    // reply came from somewhere else
                    current_req.mark_changed();
                }
                l = log.next() => {
                    let Some(l) = l else { return; };
                    wr!(Message::Log(l));
                    continue;
                },
            );
            break;
        }
    }
}

pub async fn forward_requests_from_socket() -> eyre::Result<()> {
    let stream = net::UnixStream::connect(SOCKET_PATH).await?;

    let (rd, mut wr) = io::split(stream);
    let mut rd = BufReader::new(rd).lines();

    let (tx, mut rx) = tokio::sync::mpsc::channel(1);

    tokio::spawn(async move {
        loop {
            let Ok(line) = (rd.next_line().await).inspect_err(|e| warn!("socket read error: {e}"))
            else {
                return;
            };

            let Some(line) = line else {
                // end of stream
                return;
            };

            let Ok(msg) = serde_json::from_str::<Message>(&line)
                .inspect_err(|e| warn!("invalid message received: {e}"))
            else {
                continue;
            };

            match msg {
                Message::Req(req) => {
                    if tx.send(req).await.is_err() {
                        // closed
                        return;
                    }
                }
                Message::Log(l) => {
                    let mut out = io::stderr();
                    let _ = out.write_all(&l).await;
                    let _ = out.flush().await;
                }
            };
        }
    });

    // the recv request if any, otherwise wait for the next
    let mut recv = None;

    loop {
        let req = match recv.take() {
            // value already available
            Some(v) => v,
            // no value available, wait for the next
            None => match rx.recv().await {
                Some(v) => v,
                // end of requests
                None => return Ok(()),
            },
        };

        let Some(req) = req else {
            REQ.lock().await.send_replace(None);
            continue;
        };

        tokio::select!(
            mut r = read(req.prompt, req.hide) => {
                r.push('\n');
                wr.write_all(r.as_bytes()).await?;
                wr.flush().await?;
            }
            r = rx.recv() => {
                recv = r
            }
        );
    }
}