use core::fmt;
use std::{
    fs::File,
    io::{self, PipeReader, PipeWriter, Read, Write},
    os::fd::{AsFd, BorrowedFd},
    process::Stdio,
};

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

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

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

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

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: bool,
}

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

const TIMEOUT_MS: u16 = 20;

enum PollStatus {
    Cancel,
    Ready,
    Wait,
}

fn check<'a>(
    canceled: &mut bool,
    cancel: &PipeReader,
    fd: BorrowedFd<'a>,
    flags: PollFlags,
) -> PollStatus {
    if *canceled {
        return PollStatus::Cancel;
    }

    let mut poll_fds = [
        PollFd::new(cancel.as_fd(), PollFlags::POLLIN),
        PollFd::new(fd, flags),
    ];

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

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

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

    PollStatus::Wait
}

impl InputReader {
    fn cancel(&mut self) -> PollStatus {
        self.canceled = true;
        PollStatus::Cancel
    }

    fn poll(&mut self) -> PollStatus {
        let stdin = io::stdin();
        let read_fd = match &self.input {
            Input::Stdin => stdin.as_fd(),
            Input::Pipe(pipe) => pipe.as_fd(),
            Input::File(file) => file.as_fd(),
        };
        check(&mut 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::new(io::ErrorKind::Other, Canceled)),
                PollStatus::Ready => (),
                PollStatus::Wait => continue,
            }
            return match &mut self.input {
                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: bool,
}

impl OutputWriter {
    pub fn new(output: Output) -> (Self, Canceler) {
        let (cancel, tx) = std::io::pipe().unwrap();
        (
            Self {
                output,
                cancel,
                canceled: false,
            },
            Canceler { tx },
        )
    }
    fn poll(&mut self) -> PollStatus {
        let stdout = io::stdout();
        let write_fd = match &self.output {
            Output::Stdout => stdout.as_fd(),
            Output::Pipe(pipe) => pipe.as_fd(),
            Output::File(file) => file.as_fd(),
        };
        check(
            &mut self.canceled,
            &self.cancel,
            write_fd,
            PollFlags::POLLOUT,
        )
    }
}

impl Write for OutputWriter {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        loop {
            match self.poll() {
                PollStatus::Cancel => return Err(io::Error::new(io::ErrorKind::Other, Canceled)),
                PollStatus::Ready => (),
                PollStatus::Wait => continue,
            }
            return match &mut self.output {
                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::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
    }
}