#![cfg_attr(target_os = "yggdrasil", feature(yggdrasil_os))]
#![feature(let_chains)]

use std::{
    io::{stderr, stdout, IsTerminal, Read, Stderr, Write},
    ops::{Deref, DerefMut},
    os::fd::AsRawFd,
};

use clap::Parser;
use cross::io::Poll;
use rsh::{
    crypt::{
        client::{self, ClientSocket, Message},
        config::{ClientConfig, SimpleClientKeyStore},
        signature::{SignEd25519, SignatureMethod},
    },
    proto::{ServerMessage, StreamIndex},
};

use std::{
    io::{self, stdin, Stdin, Stdout},
    net::{IpAddr, SocketAddr},
    path::PathBuf,
    process::ExitCode,
    time::Duration,
};

use libterm::{RawMode, RawTerminal};
use rsh::proto::{ClientMessage, TerminalInfo};

pub const PING_TIMEOUT: Duration = Duration::from_secs(3);

#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("I/O error: {0}")]
    Io(#[from] io::Error),
    #[error("Terminal error: {0}")]
    Terminal(#[from] libterm::Error),
    #[error("Disconnected by the server: {0}")]
    Disconnected(String),
    #[error("Timed out")]
    Timeout,
    #[error("Socket error: {0}")]
    Socket(#[from] client::Error),
    #[error("Aborted by user")]
    Abort,
}

#[derive(Debug, Parser)]
struct Args {
    #[clap(short, long)]
    key: PathBuf,
    #[clap(short = 'P', long, default_value_t = 77)]
    port: u16,
    remote: IpAddr,
    command: Vec<String>,
}

struct RawStdin {
    stdin: Stdin,
    raw: Option<RawMode>,
}

pub struct Client {
    poll: Poll,
    socket: ClientSocket,
    stdin: RawStdin,
    stdout: Stdout,
    stderr: Stderr,
    last0: u8,
    last1: u8,
}

pub enum Event<'a, 'b> {
    Data(&'a [u8]),
    Stdin(&'b [u8]),
    Disconnected(&'b str),
}

impl RawStdin {
    pub fn open() -> Result<Self, Error> {
        let stdin = stdin();
        let raw = if stdin.is_terminal() {
            Some(unsafe { RawMode::enter(&stdin) }?)
        } else {
            None
        };
        Ok(Self { stdin, raw })
    }
}

impl Deref for RawStdin {
    type Target = Stdin;

    fn deref(&self) -> &Self::Target {
        &self.stdin
    }
}

impl DerefMut for RawStdin {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.stdin
    }
}

impl AsRawFd for RawStdin {
    fn as_raw_fd(&self) -> std::os::fd::RawFd {
        self.stdin.as_raw_fd()
    }
}

impl Drop for RawStdin {
    fn drop(&mut self) {
        if let Some(raw) = &mut self.raw {
            unsafe { raw.leave(&self.stdin) };
        }
    }
}

impl Client {
    pub fn connect(remote: SocketAddr, crypto_config: ClientConfig) -> Result<Self, Error> {
        let mut poll = Poll::new()?;
        let mut socket = ClientSocket::connect(remote, crypto_config)?;
        let stdin = RawStdin::open()?;
        let stdout = stdout();
        let stderr = stderr();

        poll.add(&stdin)?;
        poll.add(&socket)?;

        let info = terminal_info(&stdout)?;

        Self::handshake(&mut socket, info)?;

        Ok(Self {
            stdin,
            stdout,
            stderr,
            socket,
            poll,
            last0: 0,
            last1: 0,
        })
    }

    fn update_last(&mut self, buffer: &[u8]) -> Result<(), Error> {
        if buffer.len() >= 2 {
            self.last0 = buffer[buffer.len() - 2];
            self.last1 = buffer[buffer.len() - 1];
        } else if buffer.len() >= 1 {
            self.last0 = self.last1;
            self.last1 = buffer[buffer.len() - 1];
        } else {
            self.last0 = self.last1;
            self.last1 = 0;
        }

        if self.last0 == b'\x1B' && self.last1 == b'~' {
            Err(Error::Abort)
        } else {
            Ok(())
        }
    }

    pub fn run(mut self) -> Result<String, Error> {
        let mut recv_buf = [0; 512];

        loop {
            if let Some(message) = self.socket.read(&mut recv_buf)? {
                match message {
                    ServerMessage::Bye(reason) => return Ok(reason.into()),
                    ServerMessage::Output(StreamIndex::Stdout, data) => {
                        self.stdout.write_all(data).ok();
                        self.stdout.flush().ok();
                        continue;
                    }
                    ServerMessage::Output(StreamIndex::Stderr, data) => {
                        self.stderr.write_all(data).ok();
                        self.stderr.flush().ok();
                        continue;
                    }
                    _ => continue,
                }
            }

            let fd = self.poll.wait(None)?.unwrap();

            if fd == self.socket.as_raw_fd() {
                if self.socket.poll()? == 0 {
                    return Ok("".into());
                }
            } else if self.stdin.as_raw_fd() == fd {
                let len = self.stdin.read(&mut recv_buf)?;
                self.update_last(&recv_buf[..len])?;
                self.socket
                    .write_all(&ClientMessage::Input(&recv_buf[..len]))?;
            } else {
                unreachable!()
            }
        }
    }

    fn handshake(socket: &mut ClientSocket, info: TerminalInfo) -> Result<(), Error> {
        let mut recv_buf = [0; 256];
        socket.write_all(&ClientMessage::OpenSession(info))?;
        loop {
            if let Some(message) = socket.read(&mut recv_buf)? {
                match message {
                    ServerMessage::SessionOpen => return Ok(()),
                    _ => return Err(Error::Disconnected("Unexpected server message".into())),
                }
            }

            if socket.poll()? == 0 {
                todo!()
            }
        }
    }
}

fn terminal_info(stdout: &Stdout) -> Result<TerminalInfo, Error> {
    let (columns, rows) = stdout.raw_size()?;
    Ok(TerminalInfo {
        columns: columns as _,
        rows: rows as _,
    })
}

fn run_terminal(remote: SocketAddr, config: ClientConfig) -> Result<(), Error> {
    let reason = Client::connect(remote, config)?.run()?;
    if !reason.is_empty() {
        eprintln!("\nDisconnected: {reason}");
    }
    Ok(())
}

fn run_command(
    remote: SocketAddr,
    config: ClientConfig,
    command: Vec<String>,
) -> Result<ExitCode, Error> {
    let mut poll = Poll::new()?;
    let mut buffer = [0; 512];
    let mut command_string = String::new();
    for (i, word) in command.iter().enumerate() {
        if i != 0 {
            command_string.push(' ');
        }
        command_string.push_str(word);
    }

    let mut stdin = stdin();
    let mut stdout = stdout();
    let mut stderr = stderr();

    let mut socket = ClientSocket::connect(remote, config)?;

    poll.add(&socket)?;
    poll.add(&stdin)?;

    socket.write_all(&ClientMessage::RunCommand(command_string.as_str()))?;

    loop {
        let fd = poll.wait(None)?.unwrap();

        match fd {
            _ if fd == socket.as_raw_fd() => {
                let message = match socket.poll_read(&mut buffer)? {
                    Message::Data(data) => data,
                    Message::Incomplete => continue,
                    Message::Closed => break,
                };

                match message {
                    ServerMessage::Output(StreamIndex::Stdout, output) => {
                        stdout.write_all(output).ok();
                        stdout.flush().ok();
                    }
                    ServerMessage::Output(StreamIndex::Stderr, output) => {
                        stderr.write_all(output).ok();
                        stderr.flush().ok();
                    }
                    _ => todo!(),
                }
            }
            _ if fd == stdin.as_raw_fd() => {
                let len = stdin.read(&mut buffer)?;
                if len == 0 {
                    poll.remove(&stdin)?;
                    socket.write_all(&ClientMessage::CloseStdin)?;
                } else {
                    socket.write_all(&ClientMessage::Input(&buffer[..len]))?;
                }
            }
            _ => unreachable!(),
        }
    }

    Ok(ExitCode::SUCCESS)
}

fn run(args: Args) -> Result<ExitCode, Error> {
    let remote = SocketAddr::new(args.remote, args.port);
    let ed25519 = SignEd25519::load_signing_key(args.key).unwrap();
    let key = SignatureMethod::Ed25519(ed25519);
    let config = ClientConfig::with_default_algorithms(SimpleClientKeyStore::new(key));
    if args.command.is_empty() {
        run_terminal(remote, config).map(|_| ExitCode::SUCCESS)
    } else {
        run_command(remote, config, args.command)
    }
}

fn main() -> ExitCode {
    env_logger::init();
    let args = Args::parse();

    match run(args) {
        Ok(status) => status,
        Err(error) => {
            eprintln!("Error: {error}");
            ExitCode::FAILURE
        }
    }
}