use core::fmt;
use std::{
    fs::File,
    io::{self, PipeReader, PipeWriter, Read, Write},
    os::fd::{AsFd, BorrowedFd},
    process::Stdio,
    sync::{
        Arc,
        atomic::{AtomicBool, Ordering::SeqCst},
    },
};

use nix::poll::{PollFd, PollFlags};

pub enum Input {
    Null,
    Stdin,
    Pipe(PipeReader),
    File(File),
}

pub enum Output {
    Null,
    Stdout,
    Pipe(PipeWriter),
    File(File),
}

impl From<Input> for Stdio {
    fn from(value: Input) -> Self {
        match value {
            Input::Null => Stdio::null(),
            Input::Stdin => Stdio::inherit(),
            Input::Pipe(reader) => reader.into(),
            Input::File(file) => file.into(),
        }
    }
}

impl From<Output> for Stdio {
    fn from(value: Output) -> Stdio {
        match value {
            Output::Null => Stdio::null(),
            Output::Stdout => Stdio::inherit(),
            Output::Pipe(writer) => writer.into(),
            Output::File(file) => file.into(),
        }
    }
}

impl Input {
    pub fn try_clone(&self) -> io::Result<Self> {
        Ok(match self {
            Input::Null => Input::Null,
            Input::Stdin => Input::Stdin,
            Input::Pipe(pr) => Input::Pipe(pr.try_clone()?),
            Input::File(f) => Input::File(f.try_clone()?),
        })
    }
}

impl Output {
    pub fn try_clone(&self) -> io::Result<Self> {
        Ok(match self {
            Output::Null => Output::Null,
            Output::Stdout => Output::Stdout,
            Output::Pipe(pw) => Output::Pipe(pw.try_clone()?),
            Output::File(f) => Output::File(f.try_clone()?),
        })
    }
}

pub struct Canceler {
    tx: PipeWriter,
}

impl Canceler {
    pub fn cancel(&mut self) {
        let _ = self.tx.write(b".");
    }
}

pub struct InputReader {
    input: Input,
    cancel: PipeReader,
    canceled: Arc<AtomicBool>,
}

impl InputReader {
    pub fn new(input: Input) -> (InputReader, Canceler) {
        let (cancel, tx) = std::io::pipe().unwrap();
        (
            Self {
                input,
                cancel,
                canceled: Arc::new(AtomicBool::new(false)),
            },
            Canceler { tx },
        )
    }

    pub fn try_clone(&self) -> io::Result<Self> {
        let input = self.input.try_clone()?;
        let cancel = self.cancel.try_clone()?;
        let canceled = self.canceled.clone();
        Ok(Self {
            input,
            cancel,
            canceled,
        })
    }
}

const TIMEOUT_MS: u16 = 1000;

enum PollStatus {
    Cancel,
    Ready,
    Wait,
}

fn check<'a>(
    canceled: &AtomicBool,
    cancel: &PipeReader,
    fd: Option<BorrowedFd<'a>>,
    flags: PollFlags,
) -> PollStatus {
    if canceled.load(SeqCst) {
        return PollStatus::Cancel;
    }

    let mut poll_fds = Vec::with_capacity(2);
    poll_fds.push(PollFd::new(cancel.as_fd(), PollFlags::POLLIN));
    if let Some(fd) = fd {
        poll_fds.push(PollFd::new(fd, flags));
    }

    if nix::poll::poll(&mut poll_fds, TIMEOUT_MS).is_err() {
        canceled.store(true, SeqCst);
        return PollStatus::Cancel;
    };

    if let Some(event) = poll_fds[0].revents()
        && event.contains(PollFlags::POLLIN)
    {
        canceled.store(true, SeqCst);
        return PollStatus::Cancel;
    }

    if let Some(event) = poll_fds[1].revents()
        && event.contains(flags)
    {
        return PollStatus::Ready;
    }

    PollStatus::Wait
}

impl InputReader {
    fn poll(&mut self) -> PollStatus {
        let stdin = io::stdin();
        let read_fd = match &self.input {
            Input::Null => None,
            Input::Stdin => Some(stdin.as_fd()),
            Input::Pipe(pipe) => Some(pipe.as_fd()),
            Input::File(file) => Some(file.as_fd()),
        };
        check(&self.canceled, &self.cancel, read_fd, PollFlags::POLLIN)
    }
}

#[derive(Debug, Clone, Copy)]
struct Canceled;

impl fmt::Display for Canceled {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "canceled")
    }
}

impl std::error::Error for Canceled {}

impl Read for InputReader {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        loop {
            match self.poll() {
                PollStatus::Cancel => return Err(io::Error::other(Canceled)),
                PollStatus::Ready => (),
                PollStatus::Wait => continue,
            }
            return match &mut self.input {
                Input::Null => Ok(0),
                Input::Stdin => io::stdin().read(buf),
                Input::Pipe(reader) => reader.read(buf),
                Input::File(file) => file.read(buf),
            };
        }
    }
}

pub struct OutputWriter {
    output: Output,
    cancel: PipeReader,
    canceled: Arc<AtomicBool>,
}

impl OutputWriter {
    pub fn new(output: Output) -> (Self, Canceler) {
        let (cancel, tx) = std::io::pipe().unwrap();
        (
            Self {
                output,
                cancel,
                canceled: Arc::new(AtomicBool::new(false)),
            },
            Canceler { tx },
        )
    }
    fn poll(&mut self) -> PollStatus {
        let stdout = io::stdout();
        let write_fd = match &self.output {
            Output::Null => None,
            Output::Stdout => Some(stdout.as_fd()),
            Output::Pipe(pipe) => Some(pipe.as_fd()),
            Output::File(file) => Some(file.as_fd()),
        };
        check(&self.canceled, &self.cancel, write_fd, PollFlags::POLLOUT)
    }
    pub fn try_clone(&self) -> io::Result<Self> {
        let output = self.output.try_clone()?;
        let cancel = self.cancel.try_clone()?;
        let canceled = self.canceled.clone();
        Ok(Self {
            output,
            cancel,
            canceled,
        })
    }
}

impl Write for OutputWriter {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        loop {
            match self.poll() {
                PollStatus::Cancel => return Err(io::Error::other(Canceled)),
                PollStatus::Ready => (),
                PollStatus::Wait => continue,
            }
            return match &mut self.output {
                Output::Null => Ok(buf.len()),
                Output::Stdout => io::stdout().write(buf),
                Output::Pipe(writer) => writer.write(buf),
                Output::File(file) => file.write(buf),
            };
        }
    }

    fn flush(&mut self) -> io::Result<()> {
        match &mut self.output {
            Output::Null => Ok(()),
            Output::Stdout => io::stdout().flush(),
            Output::Pipe(writer) => writer.flush(),
            Output::File(file) => file.flush(),
        }
    }
}

impl From<InputReader> for Input {
    fn from(value: InputReader) -> Self {
        value.input
    }
}

impl From<OutputWriter> for Output {
    fn from(value: OutputWriter) -> Self {
        value.output
    }
}