//! `pipe()` related operations
//! The async pipe is kinda broke, but that's fine because we don't really need it anyways.

use super::*;
use errno::Errno;
use std::{
    fmt,
};

/// Represents an error on `pipe()` related operations
#[derive(Debug)]
pub enum Error {

    Create,
    Read,
    Write,
    Broken,
    
    Unknown,
}
impl std::error::Error for Error{}
impl std::fmt::Display for Error
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	match self {
	    Self::Create => write!(f, "failed to create pipe"),
	    Self::Read => write!(f, "failed to read from pipe"),
	    Self::Write => write!(f, "failed to write to pipe"),
	    Self::Broken => write!(f, "broken pipe"),
	    _ => write!(f, "unknown error"),
	}
    }
}

/// Create with `pipe()`
pub(super) fn unix_pipe() -> Result<(i32,i32), Errno<Error>>
{
    use libc::{
	pipe,
    };
    let mut pipe_fd: [libc::c_int; 2] = [0;2];
    if unsafe{pipe(&mut pipe_fd[0] as *mut libc::c_int)} == 0{
	Ok((pipe_fd[0], pipe_fd[1]))
    } else {
	Err(Error::Create.into())
    }
}

/// Write to a pipe
pub(super) fn pipe_write(output: i32, buf: impl AsRef<[u8]>) -> Result<usize, Errno<Error>>
{
    let buf = buf.as_ref();
    let len = buf.len();

    let read = unsafe{libc::write(output, &buf[0] as *const u8 as *const libc::c_void, len)};

    if read < 0 {
	Err(Error::Write.into())
    } else {
	Ok(read as usize)
    }
}


pub(super) fn pipe_read(input: i32, mut buf: impl AsMut<[u8]>) -> Result<usize, Errno<Error>>
{
    let buf = buf.as_mut();
    let len = buf.len();

    let read = unsafe{libc::read(input, &mut buf[0] as *mut u8 as *mut libc::c_void, len)};

    if read < 0 {
	Err(Error::Read.into())
    } else {
	Ok(read as usize)
    }
}

pub(super) unsafe fn pipe_write_value<T: ?Sized>(fd: i32, value: &T) -> Result<(), Errno<Error>>
{
    let sz = std::mem::size_of_val(value);
    
    let write = pipe_write(fd, std::slice::from_raw_parts(value as *const T as *const u8, sz))?;
    if write == sz {
	Ok(())
    } else {
	Err(Error::Broken.into())
    }
}

pub(super) unsafe fn pipe_read_value<T>(fd: i32) -> Result<T, Errno<Error>>
{
    use malloc_array::heap;
    
    let mut buf = heap![unsafe 0u8; std::mem::size_of::<T>()];

    let read = pipe_read(fd, &mut buf)?;

    if read == buf.len() {
	let ptr = buf.reinterpret::<T>();
	Ok(ptr.as_ptr().read())
    } else {
	Err(Error::Broken.into())
    }
}

#[derive(Debug, PartialEq, Eq)]
pub struct WriteHalf(i32);
#[derive(Debug, PartialEq, Eq)]
pub struct ReadHalf(i32);

#[derive(Debug, PartialEq, Eq)]
pub struct Pipe
{
    tx: WriteHalf,
    rx: ReadHalf,
}

impl Pipe
{
    /// Create from a split
    pub fn from_split(tx: WriteHalf, rx: ReadHalf) -> Self
    {
	Self{
	    tx,
	    rx,
	}
    }

    /// Create a new pipe
    pub fn new() -> Result<Self, Error>
    {
	let (tx,rx) = pipe()?;
	Ok(Self::from_split(tx,rx))
    }

    /// Split into write and read half
    pub fn split(self) -> (WriteHalf, ReadHalf)
    {
	(self.tx, self.rx)
    }
}

const GETFL: i32 = 3;
const SETFL: i32 = 4;
const NOBLOCK: i32 = 2048;

fn set_non_blocking(fd: i32)
{
    use libc::fcntl;

    unsafe {
	fcntl(fd, SETFL, fcntl(fd, GETFL, 0) | NOBLOCK);
    }
}

impl WriteHalf
{
    /// Create from a raw file descriptor
    pub unsafe fn from_raw(fd: i32) -> Self
    {
	set_non_blocking(fd);
	Self(fd)
    }
    
    /// Consume and return the output file descriptor
    pub fn into_raw(self) -> i32
    {
	self.0
    }
}

impl ReadHalf
{
    /// Create from a raw file descriptor
    pub unsafe fn from_raw(fd: i32) -> Self
    {
	set_non_blocking(fd);
	Self(fd)
    }

    /// Consume and return the output file descriptor
    pub fn into_raw(self) -> i32
    {
	self.0
    }
}

/// Create a new pipe's `Read` and `Write` halfs
pub fn pipe() -> Result<(WriteHalf, ReadHalf), Error>
{
    let (rx, tx) = unix_pipe().map_err(|x| x.into_inner())?;

    if rx <= 0 || tx <= 0 {
	return Err(Error::Create);
    }
    unsafe {
	Ok((WriteHalf::from_raw(tx), ReadHalf::from_raw(rx)))
    }
}

/// Create 2 linked together pipes.
///
/// # Usage
/// Useful for `fork()`. 1st is parent, 2nd moved to client
pub fn multi() -> Result<(Pipe, Pipe), Error>
{
    let (tx_c, rx_p) = pipe()?;
    let (tx_p, rx_c) = pipe()?;

    Ok((Pipe::from_split(tx_p, rx_p), Pipe::from_split(tx_c, rx_c)))
}

use tokio::{
    io::{
	AsyncWrite,
	AsyncRead,
    },
};
use tokio::io::Error as AsyncError;
use std::{
    pin::Pin,
    task::{
	Context,
	Poll,
    },
};

const POLL_IN: i16 = 1;
const POLL_OUT: i16 = 4;

impl AsyncWrite for WriteHalf
{
    #[inline] fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<Result<(), AsyncError>>
    {
	// as far as i can tell this is a no-op with `write()`?
	Poll::Ready(Ok(()))
    }
    #[inline] fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<Result<(), AsyncError>>
    {
	unsafe {
	    libc::close(self.0);
	}

	Poll::Ready(Ok(()))
    }
    fn poll_write(self: Pin<&mut Self>, cx: &mut Context, buf: &[u8]) -> Poll<Result<usize, AsyncError>>
    {
	use libc::{
	    poll,
	    write,
	    pollfd,
	    c_void,
	};
	use tokio::task::yield_now;

	let future = async {
	    loop {
		let mut fd = pollfd {
		    fd: self.0,
		    revents: 0,
		    events: POLL_OUT,
		};
		let poll = unsafe {
		    poll(&mut fd as *mut pollfd, 1, 0)
		};
		if poll < 0 {
		    break Err(AsyncError::from_raw_os_error(errno::raw()));
		} else if poll > 0 {
		    if fd.revents & POLL_OUT == POLL_OUT {
			// Write ready
			let wr = unsafe{write(self.0, &buf[0] as *const u8 as *const c_void, buf.len())};
			if wr < 0 {
			    break Err(AsyncError::from_raw_os_error(errno::raw()));
			}
			else {
			    break Ok(wr as usize);
			}
		    }
		}
		// Either no poll, or no POLLOUT event
		yield_now().await;
	    }
	};
	tokio::pin!(future);
	future.poll(cx)
    }
}

impl AsyncRead for ReadHalf
{
    fn poll_read(self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, AsyncError>>
    {
	use libc::{
	    poll,
	    read,
	    pollfd,
	    c_void,
	};
	use tokio::task::yield_now;

	let future = async {
	    loop {
		let mut fd = pollfd {
		    fd: self.0,
		    revents: 0,
		    events: POLL_IN,
		};
		let poll = unsafe {
		    poll(&mut fd as *mut pollfd, 1, 0)
		};
		if poll < 0 {
		    break Err(AsyncError::from_raw_os_error(errno::raw()));
		} else if poll > 0 {
		    if fd.revents & POLL_IN == POLL_IN {
			// Read ready
			let wr = unsafe{read(self.0, &mut buf[0] as *mut u8 as *mut c_void, buf.len())};
			if wr < 0 {
			    break Err(AsyncError::from_raw_os_error(errno::raw()));
			}
			else {
			    break Ok(wr as usize);
			}
		    }
		}
		// Either no poll, or no POLLIN event
		yield_now().await;
	    }
	};
	tokio::pin!(future);
	future.poll(cx)
    }
}

use std::ops::Drop;

impl Drop for WriteHalf
{
    fn drop(&mut self)
    {
	unsafe {
	    libc::close(self.0);
	}

    }
}

impl Drop for ReadHalf
{
    fn drop(&mut self)
    {
	unsafe {
	    libc::close(self.0);
	}

    }
}


use tokio::prelude::*;
use futures::Future;
impl AsyncWrite for Pipe
{
    #[inline] fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), AsyncError>>
    {
	let future = async {
	    self.tx.flush().await
	};
	tokio::pin!(future);
	future.poll(cx)
    }
    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), AsyncError>>
    {
	
	let future = async {
	    self.tx.shutdown().await
	};
	tokio::pin!(future);
	future.poll(cx)
    }
    fn poll_write(mut self: Pin<&mut Self>, cx: &mut Context, buf: &[u8]) -> Poll<Result<usize, AsyncError>>
    {
	let future = async {
	    self.tx.write(buf).await
	};
	tokio::pin!(future);
	future.poll(cx)
    }
}

impl AsyncRead for Pipe
{
    fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, AsyncError>>
    {
	let future = async {
	    self.rx.read(buf).await
	};
	tokio::pin!(future);
	future.poll(cx)
    }
}