//! Read both stdout and stderr of child without deadlocks.
//!
//! <https://github.com/rust-lang/cargo/blob/905af549966f23a9288e9993a85d1249a5436556/crates/cargo-util/src/read2.rs>
//! <https://github.com/rust-lang/cargo/blob/58a961314437258065e23cb6316dfc121d96fb71/crates/cargo-util/src/process_builder.rs#L231>

use std::{
    io,
    process::{Command, Output, Stdio},
};

pub fn streaming_output(
    mut cmd: Command,
    on_stdout_line: &mut dyn FnMut(&str),
    on_stderr_line: &mut dyn FnMut(&str),
) -> io::Result<Output> {
    let mut stdout = Vec::new();
    let mut stderr = Vec::new();

    let cmd = cmd.stdout(Stdio::piped()).stderr(Stdio::piped()).stdin(Stdio::null());

    let status = {
        let mut child = cmd.spawn()?;
        let out = child.stdout.take().unwrap();
        let err = child.stderr.take().unwrap();
        imp::read2(out, err, &mut |is_out, data, eof| {
            let idx = if eof {
                data.len()
            } else {
                match data.iter().rposition(|b| *b == b'\n') {
                    Some(i) => i + 1,
                    None => return,
                }
            };
            {
                // scope for new_lines
                let new_lines = {
                    let dst = if is_out { &mut stdout } else { &mut stderr };
                    let start = dst.len();
                    let data = data.drain(..idx);
                    dst.extend(data);
                    &dst[start..]
                };
                for line in String::from_utf8_lossy(new_lines).lines() {
                    if is_out {
                        on_stdout_line(line)
                    } else {
                        on_stderr_line(line)
                    }
                }
            }
        })?;
        child.wait()?
    };

    Ok(Output { status, stdout, stderr })
}

#[cfg(unix)]
mod imp {
    use std::{
        io::{self, prelude::*},
        mem,
        os::unix::prelude::*,
        process::{ChildStderr, ChildStdout},
    };

    pub(crate) fn read2(
        mut out_pipe: ChildStdout,
        mut err_pipe: ChildStderr,
        data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
    ) -> io::Result<()> {
        unsafe {
            libc::fcntl(out_pipe.as_raw_fd(), libc::F_SETFL, libc::O_NONBLOCK);
            libc::fcntl(err_pipe.as_raw_fd(), libc::F_SETFL, libc::O_NONBLOCK);
        }

        let mut out_done = false;
        let mut err_done = false;
        let mut out = Vec::new();
        let mut err = Vec::new();

        let mut fds: [libc::pollfd; 2] = unsafe { mem::zeroed() };
        fds[0].fd = out_pipe.as_raw_fd();
        fds[0].events = libc::POLLIN;
        fds[1].fd = err_pipe.as_raw_fd();
        fds[1].events = libc::POLLIN;
        let mut nfds = 2;
        let mut errfd = 1;

        while nfds > 0 {
            // wait for either pipe to become readable using `select`
            let r = unsafe { libc::poll(fds.as_mut_ptr(), nfds, -1) };
            if r == -1 {
                let err = io::Error::last_os_error();
                if err.kind() == io::ErrorKind::Interrupted {
                    continue;
                }
                return Err(err);
            }

            // Read as much as we can from each pipe, ignoring EWOULDBLOCK or
            // EAGAIN. If we hit EOF, then this will happen because the underlying
            // reader will return Ok(0), in which case we'll see `Ok` ourselves. In
            // this case we flip the other fd back into blocking mode and read
            // whatever's leftover on that file descriptor.
            let handle = |res: io::Result<_>| match res {
                Ok(_) => Ok(true),
                Err(e) => {
                    if e.kind() == io::ErrorKind::WouldBlock {
                        Ok(false)
                    } else {
                        Err(e)
                    }
                }
            };
            if !err_done && fds[errfd].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
                err_done = true;
                nfds -= 1;
            }
            data(false, &mut err, err_done);
            if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? {
                out_done = true;
                fds[0].fd = err_pipe.as_raw_fd();
                errfd = 0;
                nfds -= 1;
            }
            data(true, &mut out, out_done);
        }
        Ok(())
    }
}

#[cfg(windows)]
mod imp {
    use std::{
        io,
        os::windows::prelude::*,
        process::{ChildStderr, ChildStdout},
        slice,
    };

    use miow::{
        iocp::{CompletionPort, CompletionStatus},
        pipe::NamedPipe,
        Overlapped,
    };
    use winapi::shared::winerror::ERROR_BROKEN_PIPE;

    struct Pipe<'a> {
        dst: &'a mut Vec<u8>,
        overlapped: Overlapped,
        pipe: NamedPipe,
        done: bool,
    }

    pub(crate) fn read2(
        out_pipe: ChildStdout,
        err_pipe: ChildStderr,
        data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
    ) -> io::Result<()> {
        let mut out = Vec::new();
        let mut err = Vec::new();

        let port = CompletionPort::new(1)?;
        port.add_handle(0, &out_pipe)?;
        port.add_handle(1, &err_pipe)?;

        unsafe {
            let mut out_pipe = Pipe::new(out_pipe, &mut out);
            let mut err_pipe = Pipe::new(err_pipe, &mut err);

            out_pipe.read()?;
            err_pipe.read()?;

            let mut status = [CompletionStatus::zero(), CompletionStatus::zero()];

            while !out_pipe.done || !err_pipe.done {
                for status in port.get_many(&mut status, None)? {
                    if status.token() == 0 {
                        out_pipe.complete(status);
                        data(true, out_pipe.dst, out_pipe.done);
                        out_pipe.read()?;
                    } else {
                        err_pipe.complete(status);
                        data(false, err_pipe.dst, err_pipe.done);
                        err_pipe.read()?;
                    }
                }
            }

            Ok(())
        }
    }

    impl<'a> Pipe<'a> {
        unsafe fn new<P: IntoRawHandle>(p: P, dst: &'a mut Vec<u8>) -> Pipe<'a> {
            Pipe {
                dst,
                pipe: NamedPipe::from_raw_handle(p.into_raw_handle()),
                overlapped: Overlapped::zero(),
                done: false,
            }
        }

        unsafe fn read(&mut self) -> io::Result<()> {
            let dst = slice_to_end(self.dst);
            match self.pipe.read_overlapped(dst, self.overlapped.raw()) {
                Ok(_) => Ok(()),
                Err(e) => {
                    if e.raw_os_error() == Some(ERROR_BROKEN_PIPE as i32) {
                        self.done = true;
                        Ok(())
                    } else {
                        Err(e)
                    }
                }
            }
        }

        unsafe fn complete(&mut self, status: &CompletionStatus) {
            let prev = self.dst.len();
            self.dst.set_len(prev + status.bytes_transferred() as usize);
            if status.bytes_transferred() == 0 {
                self.done = true;
            }
        }
    }

    unsafe fn slice_to_end(v: &mut Vec<u8>) -> &mut [u8] {
        if v.capacity() == 0 {
            v.reserve(16);
        }
        if v.capacity() == v.len() {
            v.reserve(1);
        }
        slice::from_raw_parts_mut(v.as_mut_ptr().add(v.len()), v.capacity() - v.len())
    }
}

#[cfg(target_arch = "wasm32")]
mod imp {
    use std::{
        io,
        process::{ChildStderr, ChildStdout},
    };

    pub(crate) fn read2(
        _out_pipe: ChildStdout,
        _err_pipe: ChildStderr,
        _data: &mut dyn FnMut(bool, &mut Vec<u8>, bool),
    ) -> io::Result<()> {
        panic!("no processes on wasm")
    }
}
