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    //! Wayland socket manipulation

    use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};

    use nix::sys::socket;
    use nix::sys::uio;
    use nix::Result as NixResult;

    use wire::{ArgumentType, Message, MessageParseError, MessageWriteError};

    /// Maximum number of FD that can be sent in a single socket message
    pub const MAX_FDS_OUT: usize = 28;
    /// Maximum number of bytes that can be sent in a single socket message
    pub const MAX_BYTES_OUT: usize = 4096;

    /*
     * Socket
     */

    /// A wayland socket
    pub struct Socket {
        fd: RawFd,
    }

    impl Socket {
        /// Send a single message to the socket
        ///
        /// A single socket message can contain several wayland messages
        ///
        /// The `fds` slice should not be longer than `MAX_FDS_OUT`, and the `bytes`
        /// slice should not be longer than `MAX_BYTES_OUT` otherwise the receiving
        /// end may lose some data.
        pub fn send_msg(&self, bytes: &[u8], fds: &[RawFd]) -> NixResult<()> {
            let iov = [uio::IoVec::from_slice(bytes)];
            if fds.len() > 0 {
                let cmsgs = [socket::ControlMessage::ScmRights(fds)];
                socket::sendmsg(self.fd, &iov, &cmsgs, socket::MsgFlags::MSG_DONTWAIT, None)?;
            } else {
                socket::sendmsg(self.fd, &iov, &[], socket::MsgFlags::MSG_DONTWAIT, None)?;
            };
            Ok(())
        }

        /// Receive a single message from the socket
        ///
        /// Return the number of bytes received and the number of Fds received.
        ///
        /// Errors with `WouldBlock` is no message is available.
        ///
        /// A single socket message can contain several wayland messages.
        ///
        /// The `buffer` slice should be at least `MAX_BYTES_OUT` long and the `fds`
        /// slice `MAX_FDS_OUT` long, otherwise some data of the received message may
        /// be lost.
        pub fn rcv_msg(&self, buffer: &mut [u8], fds: &mut [RawFd]) -> NixResult<(usize, usize)> {
            let mut cmsg = cmsg_space!([RawFd; MAX_FDS_OUT]);
            let iov = [uio::IoVec::from_mut_slice(buffer)];

            let msg = socket::recvmsg(self.fd, &iov[..], Some(&mut cmsg), socket::MsgFlags::MSG_DONTWAIT)?;

            let mut fd_count = 0;
            let received_fds = msg.cmsgs().flat_map(|cmsg| {
                match cmsg {
                    socket::ControlMessageOwned::ScmRights(s) => s,
                    _ => Vec::new(),
                }
            });
            for (fd, place) in received_fds.zip(fds.iter_mut()) {
                fd_count += 1;
                *place = fd;
            }
            Ok((msg.bytes, fd_count))
        }
    }

    impl FromRawFd for Socket {
        unsafe fn from_raw_fd(fd: RawFd) -> Socket {
            Socket { fd }
        }
    }

    impl AsRawFd for Socket {
        fn as_raw_fd(&self) -> RawFd {
            self.fd
        }
    }

    impl IntoRawFd for Socket {
        fn into_raw_fd(self) -> RawFd {
            self.fd
        }
    }

    impl Drop for Socket {
        fn drop(&mut self) {
            let _ = ::nix::unistd::close(self.fd);
        }
    }

    /*
     * BufferedSocket
     */

    /// An adapter around a raw Socket that directly handles buffering and
    /// conversion from/to wayland messages
    pub struct BufferedSocket {
        socket: Socket,
        in_data: Buffer<u32>,
        in_fds: Buffer<RawFd>,
        out_data: Buffer<u32>,
        out_fds: Buffer<RawFd>,
    }

    impl BufferedSocket {
        /// Wrap a Socket into a Buffered Socket
        pub fn new(socket: Socket) -> BufferedSocket {
            BufferedSocket {
                socket: socket,
                in_data: Buffer::new(2 * MAX_BYTES_OUT / 4), // Incoming buffers are twice as big in order to be
                in_fds: Buffer::new(2 * MAX_FDS_OUT),        // able to store leftover data if needed
                out_data: Buffer::new(MAX_BYTES_OUT / 4),
                out_fds: Buffer::new(MAX_FDS_OUT),
            }
        }

        /// Get direct access to the underlying socket
        pub fn get_socket(&mut self) -> &mut Socket {
            &mut self.socket
        }

        /// Retrieve ownership of the underlying Socket
        ///
        /// Any leftover content in the internal buffers will be lost
        pub fn into_socket(self) -> Socket {
            self.socket
        }

        /// Flush the contents of the outgoing buffer into the socket
        pub fn flush(&mut self) -> NixResult<()> {
            {
                let words = self.out_data.get_contents();
                let bytes = unsafe { ::std::slice::from_raw_parts(words.as_ptr() as *const u8, words.len() * 4) };
                let fds = self.out_fds.get_contents();
                self.socket.send_msg(bytes, fds)?;
            }
            self.out_data.clear();
            self.out_fds.clear();
            Ok(())
        }

        // internal method
        //
        // attempts to write a message in the internal out buffers,
        // returns true if successful
        //
        // if false is returned, it means there is not enough space
        // in the buffer
        fn attempt_write_message(&mut self, msg: &Message) -> NixResult<bool> {
            match msg.write_to_buffers(
                self.out_data.get_writable_storage(),
                self.out_fds.get_writable_storage(),
            ) {
                Ok((bytes_out, fds_out)) => {
                    self.out_data.advance(bytes_out);
                    self.out_fds.advance(fds_out);
                    Ok(true)
                }
                Err(MessageWriteError::BufferTooSmall) => Ok(false),
                Err(MessageWriteError::DupFdFailed(e)) => Err(e),
            }
        }

        /// Write a message to the outgoing buffer
        ///
        /// This method may flush the internal buffer if necessary (if it is full).
        ///
        /// If the message is too big to fit in the buffer, the error `Error::Sys(E2BIG)`
        /// will be returned.
        pub fn write_message(&mut self, msg: &Message) -> NixResult<()> {
            if !self.attempt_write_message(msg)? {
                // the attempt failed, there is not enough space in the buffer
                // we need to flush it
                self.flush()?;
                if !self.attempt_write_message(msg)? {
                    // If this fails again, this means the message is too big
                    // to be transmitted at all
                    return Err(::nix::Error::Sys(::nix::errno::Errno::E2BIG));
                }
            }
            Ok(())
        }

        /// Try to fill the incoming buffers of this socket, to prepare
        /// a new round of parsing.
        pub fn fill_incoming_buffers(&mut self) -> NixResult<()> {
            // clear the buffers if they have no content
            if !self.in_data.has_content() {
                self.in_data.clear();
            }
            if !self.in_fds.has_content() {
                self.in_fds.clear();
            }
            // receive a message
            let (in_bytes, in_fds) = {
                let words = self.in_data.get_writable_storage();
                let bytes =
                    unsafe { ::std::slice::from_raw_parts_mut(words.as_ptr() as *mut u8, words.len() * 4) };
                let fds = self.in_fds.get_writable_storage();
                self.socket.rcv_msg(bytes, fds)?
            };
            if in_bytes == 0 {
                // the other end of the socket was closed
                return Err(::nix::Error::Sys(::nix::errno::Errno::EPIPE));
            }
            // advance the storage
            self.in_data
                .advance(in_bytes / 4 + if in_bytes % 4 > 0 { 1 } else { 0 });
            self.in_fds.advance(in_fds);
            Ok(())
        }

        /// Read and deserialize a single message from the incoming buffers socket
        ///
        /// This method requires one closure that given an object id and an opcode,
        /// must provide the signature of the associated request/event, in the form of
        /// a `&'static [ArgumentType]`. If it returns `None`, meaning that
        /// the couple object/opcode does not exist, an error will be returned.
        ///
        /// There are 3 possibilities of return value:
        ///
        /// - `Ok(Ok(msg))`: no error occurred, this is the message
        /// - `Ok(Err(e))`: either a malformed message was encountered or we need more data,
        ///    in the latter case you need to try calling `fill_incoming_buffers()`.
        /// - `Err(e)`: an I/O error occurred reading from the socked, details are in `e`
        ///   (this can be a "wouldblock" error, which just means that no message is available
        ///   to read)
        pub fn read_one_message<F>(&mut self, mut signature: F) -> Result<Message, MessageParseError>
        where
            F: FnMut(u32, u16) -> Option<&'static [ArgumentType]>,
        {
            let (msg, read_data, read_fd) = {
                let data = self.in_data.get_contents();
                let fds = self.in_fds.get_contents();
                if data.len() < 2 {
                    return Err(MessageParseError::MissingData);
                }
                let object_id = data[0];
                let opcode = (data[1] & 0x0000FFFF) as u16;
                if let Some(sig) = signature(object_id, opcode) {
                    match Message::from_raw(data, sig, fds) {
                        Ok((msg, rest_data, rest_fds)) => {
                            (msg, data.len() - rest_data.len(), fds.len() - rest_fds.len())
                        }
                        // TODO: gracefully handle wayland messages split across unix messages ?
                        Err(e) => return Err(e),
                    }
                } else {
                    // no signature found ?
                    return Err(MessageParseError::Malformed);
                }
            };

            self.in_data.offset(read_data);
            self.in_fds.offset(read_fd);

            Ok(msg)
        }

        /// Read and deserialize messages from the socket
        ///
        /// This method requires two closures:
        ///
        /// - The first one, given an object id and an opcode, must provide
        ///   the signature of the associated request/event, in the form of
        ///   a `&'static [ArgumentType]`. If it returns `None`, meaning that
        ///   the couple object/opcode does not exist, the parsing will be
        ///   prematurely interrupted and this method will return a
        ///   `MessageParseError::Malformed` error.
        /// - The second closure is charged to process the parsed message. If it
        ///   returns `false`, the iteration will be prematurely stopped.
        ///
        /// In both cases of early stopping, the remaining unused data will be left
        /// in the buffers, and will start to be processed at the next call of this
        /// method.
        ///
        /// There are 3 possibilities of return value:
        ///
        /// - `Ok(Ok(n))`: no error occurred, `n` messages where processed
        /// - `Ok(Err(MessageParseError::Malformed))`: a malformed message was encountered
        ///   (this is a protocol error and is supposed to be fatal to the connection).
        /// - `Err(e)`: an I/O error occurred reading from the socked, details are in `e`
        ///   (this can be a "wouldblock" error, which just means that no message is available
        ///   to read)
        pub fn read_messages<F1, F2>(
            &mut self,
            mut signature: F1,
            mut callback: F2,
        ) -> NixResult<Result<usize, MessageParseError>>
        where
            F1: FnMut(u32, u16) -> Option<&'static [ArgumentType]>,
            F2: FnMut(Message) -> bool,
        {
            // message parsing
            let mut dispatched = 0;

            loop {
                let mut err = None;
                // first parse any leftover messages
                loop {
                    match self.read_one_message(&mut signature) {
                        Ok(msg) => {
                            let keep_going = callback(msg);
                            dispatched += 1;
                            if !keep_going {
                                break;
                            }
                        }
                        Err(e) => {
                            err = Some(e);
                            break;
                        }
                    }
                }

                // copy back any leftover content to the front of the buffer
                self.in_data.move_to_front();
                self.in_fds.move_to_front();

                if let Some(MessageParseError::Malformed) = err {
                    // early stop here
                    return Ok(Err(MessageParseError::Malformed));
                }

                if err.is_none() && self.in_data.has_content() {
                    // we stopped reading without error while there is content? That means
                    // the user requested an early stopping
                    return Ok(Ok(dispatched));
                }

                // now, try to get more data
                match self.fill_incoming_buffers() {
                    Ok(()) => (),
                    Err(e @ ::nix::Error::Sys(::nix::errno::Errno::EAGAIN)) => {
                        // stop looping, returning Ok() or EAGAIN depending on whether messages
                        // were dispatched
                        if dispatched == 0 {
                            return Err(e);
                        } else {
                            break;
                        }
                    }
                    Err(e) => return Err(e),
                }
            }

            Ok(Ok(dispatched))
        }
    }

    /*
     * Buffer
     */

    struct Buffer<T: Copy> {
        storage: Vec<T>,
        occupied: usize,
        offset: usize,
    }

    impl<T: Copy + Default> Buffer<T> {
        fn new(size: usize) -> Buffer<T> {
            Buffer {
                storage: vec![T::default(); size],
                occupied: 0,
                offset: 0,
            }
        }

        /// Check if this buffer has content to read
        fn has_content(&self) -> bool {
            self.occupied > self.offset
        }

        /// Advance the internal counter of occupied space
        fn advance(&mut self, bytes: usize) {
            self.occupied += bytes;
        }

        /// Advance the read offset of current occupied space
        fn offset(&mut self, bytes: usize) {
            self.offset += bytes;
        }

        /// Clears the contents of the buffer
        ///
        /// This only sets the counter of occupied space back to zero,
        /// allowing previous content to be overwritten.
        fn clear(&mut self) {
            self.occupied = 0;
            self.offset = 0;
        }

        /// Get the current contents of the occupied space of the buffer
        fn get_contents(&self) -> &[T] {
            &self.storage[(self.offset)..(self.occupied)]
        }

        /// Get mutable access to the unoccupied space of the buffer
        fn get_writable_storage(&mut self) -> &mut [T] {
            &mut self.storage[(self.occupied)..]
        }

        /// Move the unread contents of the buffer to the front, to ensure
        /// maximal write space availability
        fn move_to_front(&mut self) {
            unsafe {
                ::std::ptr::copy(
                    &self.storage[self.offset] as *const T,
                    &mut self.storage[0] as *mut T,
                    self.occupied - self.offset,
                );
            }
            self.occupied -= self.offset;
            self.offset = 0;
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use wire::{Argument, ArgumentType, Message};

        use std::ffi::CString;

        fn same_file(a: RawFd, b: RawFd) -> bool {
            let stat1 = ::nix::sys::stat::fstat(a).unwrap();
            let stat2 = ::nix::sys::stat::fstat(b).unwrap();
            stat1.st_dev == stat2.st_dev && stat1.st_ino == stat2.st_ino
        }

        // check if two messages are equal
        //
        // if arguments contain FDs, check that the fd point to
        // the same file, rather than are the same number.
        fn assert_eq_msgs(msg1: &Message, msg2: &Message) {
            assert_eq!(msg1.sender_id, msg2.sender_id);
            assert_eq!(msg1.opcode, msg2.opcode);
            assert_eq!(msg1.args.len(), msg2.args.len());
            for (arg1, arg2) in msg1.args.iter().zip(msg2.args.iter()) {
                if let (&Argument::Fd(fd1), &Argument::Fd(fd2)) = (arg1, arg2) {
                    assert!(same_file(fd1, fd2));
                } else {
                    assert_eq!(arg1, arg2);
                }
            }
        }

        #[test]
        fn write_read_cycle() {
            let msg = Message {
                sender_id: 42,
                opcode: 7,
                args: vec![
                    Argument::Uint(3),
                    Argument::Fixed(-89),
                    Argument::Str(CString::new(&b"I like trains!"[..]).unwrap()),
                    Argument::Array(vec![1, 2, 3, 4, 5, 6, 7, 8, 9]),
                    Argument::Object(88),
                    Argument::NewId(56),
                    Argument::Int(-25),
                ],
            };

            let (client, server) = ::std::os::unix::net::UnixStream::pair().unwrap();
            let mut client = BufferedSocket::new(unsafe { Socket::from_raw_fd(client.into_raw_fd()) });
            let mut server = BufferedSocket::new(unsafe { Socket::from_raw_fd(server.into_raw_fd()) });

            client.write_message(&msg).unwrap();
            client.flush().unwrap();

            static SIGNATURE: &'static [ArgumentType] = &[
                ArgumentType::Uint,
                ArgumentType::Fixed,
                ArgumentType::Str,
                ArgumentType::Array,
                ArgumentType::Object,
                ArgumentType::NewId,
                ArgumentType::Int,
            ];

            let ret = server
                .read_messages(
                    |sender_id, opcode| {
                        if sender_id == 42 && opcode == 7 {
                            Some(SIGNATURE)
                        } else {
                            None
                        }
                    },
                    |message| {
                        assert_eq_msgs(&message, &msg);
                        true
                    },
                )
                .unwrap()
                .unwrap();

            assert_eq!(ret, 1);
        }

        #[test]
        fn write_read_cycle_fd() {
            let msg = Message {
                sender_id: 42,
                opcode: 7,
                args: vec![
                    Argument::Fd(1), // stdin
                    Argument::Fd(0), // stdout
                ],
            };

            let (client, server) = ::std::os::unix::net::UnixStream::pair().unwrap();
            let mut client = BufferedSocket::new(unsafe { Socket::from_raw_fd(client.into_raw_fd()) });
            let mut server = BufferedSocket::new(unsafe { Socket::from_raw_fd(server.into_raw_fd()) });

            client.write_message(&msg).unwrap();
            client.flush().unwrap();

            static SIGNATURE: &'static [ArgumentType] = &[ArgumentType::Fd, ArgumentType::Fd];

            let ret = server
                .read_messages(
                    |sender_id, opcode| {
                        if sender_id == 42 && opcode == 7 {
                            Some(SIGNATURE)
                        } else {
                            None
                        }
                    },
                    |message| {
                        assert_eq_msgs(&message, &msg);
                        true
                    },
                )
                .unwrap()
                .unwrap();

            assert_eq!(ret, 1);
        }

        #[test]
        fn write_read_cycle_multiple() {
            let messages = [
                Message {
                    sender_id: 42,
                    opcode: 0,
                    args: vec![
                        Argument::Int(42),
                        Argument::Str(CString::new(&b"I like trains"[..]).unwrap()),
                    ],
                },
                Message {
                    sender_id: 42,
                    opcode: 1,
                    args: vec![
                        Argument::Fd(1), // stdin
                        Argument::Fd(0), // stdout
                    ],
                },
                Message {
                    sender_id: 42,
                    opcode: 2,
                    args: vec![
                        Argument::Uint(3),
                        Argument::Fd(2), // stderr
                    ],
                },
            ];

            static SIGNATURES: &'static [&'static [ArgumentType]] = &[
                &[ArgumentType::Int, ArgumentType::Str],
                &[ArgumentType::Fd, ArgumentType::Fd],
                &[ArgumentType::Uint, ArgumentType::Fd],
            ];

            let (client, server) = ::std::os::unix::net::UnixStream::pair().unwrap();
            let mut client = BufferedSocket::new(unsafe { Socket::from_raw_fd(client.into_raw_fd()) });
            let mut server = BufferedSocket::new(unsafe { Socket::from_raw_fd(server.into_raw_fd()) });

            for msg in &messages {
                client.write_message(msg).unwrap();
            }
            client.flush().unwrap();

            let mut recv_msgs = Vec::new();
            let ret = server
                .read_messages(
                    |sender_id, opcode| {
                        if sender_id == 42 {
                            Some(SIGNATURES[opcode as usize])
                        } else {
                            None
                        }
                    },
                    |message| {
                        recv_msgs.push(message);
                        true
                    },
                )
                .unwrap()
                .unwrap();

            assert_eq!(ret, 3);
            assert_eq!(recv_msgs.len(), 3);
            for (msg1, msg2) in messages.iter().zip(recv_msgs.iter()) {
                assert_eq_msgs(msg1, msg2);
            }
        }

        #[test]
        fn parse_with_string_len_multiple_of_4() {
            let msg = Message {
                sender_id: 2,
                opcode: 0,
                args: vec![
                    Argument::Uint(18),
                    Argument::Str(CString::new(&b"wl_shell"[..]).unwrap()),
                    Argument::Uint(1),
                ],
            };

            let (client, server) = ::std::os::unix::net::UnixStream::pair().unwrap();
            let mut client = BufferedSocket::new(unsafe { Socket::from_raw_fd(client.into_raw_fd()) });
            let mut server = BufferedSocket::new(unsafe { Socket::from_raw_fd(server.into_raw_fd()) });

            client.write_message(&msg).unwrap();
            client.flush().unwrap();

            static SIGNATURE: &'static [ArgumentType] =
                &[ArgumentType::Uint, ArgumentType::Str, ArgumentType::Uint];

            let ret = server
                .read_messages(
                    |sender_id, opcode| {
                        if sender_id == 2 && opcode == 0 {
                            Some(SIGNATURE)
                        } else {
                            None
                        }
                    },
                    |message| {
                        assert_eq_msgs(&message, &msg);
                        true
                    },
                )
                .unwrap()
                .unwrap();

            assert_eq!(ret, 1);
        }
    }

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