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    //! Types and routines used to manipulate arguments from the wire format

    use std::ffi::{CStr, CString};
    use std::os::unix::io::RawFd;
    use std::ptr;

    use nix::errno::Errno;
    use nix::{Error as NixError, Result as NixResult};

    /// Wire metadata of a given message
    pub struct MessageDesc {
        /// Name of this message
        pub name: &'static str,
        /// Signature of the message
        pub signature: &'static [ArgumentType],
        /// Minimum required version of the interface
        pub since: u32,
    }

    /// Enum of possible argument types as recognized by the wire
    #[derive(Copy, Clone, PartialEq, Debug)]
    pub enum ArgumentType {
        /// i32
        Int,
        /// u32
        Uint,
        /// fixed point, 1/256 precision
        Fixed,
        /// CString
        Str,
        /// id of a wayland object
        Object,
        /// id of a newly created wayland object
        NewId,
        /// Vec<u8>
        Array,
        /// RawFd
        Fd,
    }

    /// Enum of possible argument as recognized by the wire, including values
    #[derive(Clone, PartialEq, Debug)]
    pub enum Argument {
        /// i32
        Int(i32),
        /// u32
        Uint(u32),
        /// fixed point, 1/256 precision
        Fixed(i32),
        /// CString
        Str(CString),
        /// id of a wayland object
        Object(u32),
        /// id of a newly created wayland object
        NewId(u32),
        /// Vec<u8>
        Array(Vec<u8>),
        /// RawFd
        Fd(RawFd),
    }

    impl Argument {
        /// Retrieve the type of a given argument instance
        pub fn get_type(&self) -> ArgumentType {
            match *self {
                Argument::Int(_) => ArgumentType::Int,
                Argument::Uint(_) => ArgumentType::Uint,
                Argument::Fixed(_) => ArgumentType::Fixed,
                Argument::Str(_) => ArgumentType::Str,
                Argument::Object(_) => ArgumentType::Object,
                Argument::NewId(_) => ArgumentType::NewId,
                Argument::Array(_) => ArgumentType::Array,
                Argument::Fd(_) => ArgumentType::Fd,
            }
        }
    }

    /// A wire message
    #[derive(Debug, Clone, PartialEq)]
    pub struct Message {
        /// ID of the object sending this message
        pub sender_id: u32,
        /// Opcode of the message
        pub opcode: u16,
        /// Arguments of the message
        pub args: Vec<Argument>,
    }

    /// Error generated when trying to serialize a message into buffers
    #[derive(Debug, Clone)]
    pub enum MessageWriteError {
        /// The buffer is too small to hold the message contents
        BufferTooSmall,
        /// The message contains a FD that could not be dup-ed
        DupFdFailed(::nix::Error),
    }

    impl ::std::error::Error for MessageWriteError {
        fn description(&self) -> &str {
            match *self {
                MessageWriteError::BufferTooSmall => "The provided buffer is too small to hold message content.",
                MessageWriteError::DupFdFailed(_) => {
                    "The message contains a file descriptor that could not be dup()-ed."
                }
            }
        }
    }

    impl ::std::fmt::Display for MessageWriteError {
        fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
            f.write_str(::std::error::Error::description(self))
        }
    }

    /// Error generated when trying to deserialize a message from buffers
    #[derive(Debug, Clone)]
    pub enum MessageParseError {
        /// The message references a FD but the buffer FD is empty
        MissingFD,
        /// More data is needed to deserialize the message
        MissingData,
        /// The message is malformed and cannot be parsed
        Malformed,
    }

    impl ::std::error::Error for MessageParseError {
        fn description(&self) -> &str {
            match *self {
                MessageParseError::MissingFD => "The message references a FD but the buffer FD is empty.",
                MessageParseError::MissingData => "More data is needed to deserialize the message",
                MessageParseError::Malformed => "The message is malformed and cannot be parsed",
            }
        }
    }

    impl ::std::fmt::Display for MessageParseError {
        fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
            f.write_str(::std::error::Error::description(self))
        }
    }

    impl Message {
        /// Serialize the contents of this message into provided buffers
        ///
        /// Returns the number of elements written in each buffer
        ///
        /// Any serialized Fd will be `dup()`-ed in the process
        pub fn write_to_buffers<'a, 'b>(
            &self,
            payload: &'a mut [u32],
            mut fds: &'b mut [RawFd],
        ) -> Result<(usize, usize), MessageWriteError> {
            let orig_payload_len = payload.len();
            let orig_fds_len = fds.len();
            // Helper function to write a u32 or a RawFd to its buffer
            fn write_buf<'a, T>(u: T, payload: &'a mut [T]) -> Result<&'a mut [T], MessageWriteError> {
                if let Some((head, tail)) = payload.split_first_mut() {
                    *head = u;
                    Ok(tail)
                } else {
                    Err(MessageWriteError::BufferTooSmall)
                }
            }

            // Helper function to write byte arrays in payload
            fn write_array_to_payload<'a>(
                array: &[u8],
                payload: &'a mut [u32],
            ) -> Result<&'a mut [u32], MessageWriteError> {
                let array_len = array.len();
                let word_len = array_len / 4 + if array_len % 4 != 0 { 1 } else { 0 };
                // need enough space to store the whole array with padding and a size header
                if payload.len() < 1 + word_len {
                    return Err(MessageWriteError::BufferTooSmall);
                }
                // size header
                payload[0] = array_len as u32;
                let (buffer_slice, rest) = payload[1..].split_at_mut(word_len);
                unsafe {
                    ptr::copy(array.as_ptr(), buffer_slice.as_mut_ptr() as *mut u8, array_len);
                }
                Ok(rest)
            }

            let free_size = payload.len();
            if free_size < 2 {
                return Err(MessageWriteError::BufferTooSmall);
            }

            let (header, mut payload) = payload.split_at_mut(2);

            // we store all fds we dup-ed in this, which will auto-close
            // them on drop, if any of the `?` early-returns
            let mut pending_fds = FdStore::new();

            // write the contents in the buffer
            for arg in &self.args {
                // Just to make the borrow checker happy
                let old_payload = payload;
                match *arg {
                    Argument::Int(i) => payload = write_buf(i as u32, old_payload)?,
                    Argument::Uint(u) => payload = write_buf(u, old_payload)?,
                    Argument::Fixed(f) => payload = write_buf(f as u32, old_payload)?,
                    Argument::Str(ref s) => {
                        payload = write_array_to_payload(s.as_bytes_with_nul(), old_payload)?;
                    }
                    Argument::Object(o) => payload = write_buf(o, old_payload)?,
                    Argument::NewId(n) => payload = write_buf(n, old_payload)?,
                    Argument::Array(ref a) => {
                        payload = write_array_to_payload(&a, old_payload)?;
                    }
                    Argument::Fd(fd) => {
                        let old_fds = fds;
                        let dup_fd = dup_fd_cloexec(fd).map_err(MessageWriteError::DupFdFailed)?;
                        pending_fds.push(dup_fd);
                        fds = write_buf(dup_fd, old_fds)?;
                        payload = old_payload;
                    }
                }
            }

            // we reached here, all writing was successful
            // no FD needs to be closed
            pending_fds.clear();

            let wrote_size = (free_size - payload.len()) * 4;
            header[0] = self.sender_id;
            header[1] = ((wrote_size as u32) << 16) | self.opcode as u32;
            Ok((orig_payload_len - payload.len(), orig_fds_len - fds.len()))
        }

        /// Attempts to parse a single wayland message with the given signature.
        ///
        /// If the buffers contains several messages, only the first one will be parsed,
        /// and the unused tail of the buffers is returned. If a single message was present,
        /// the returned slices should thus be empty.
        ///
        /// Errors if the message is malformed.
        pub fn from_raw<'a, 'b>(
            raw: &'a [u32],
            signature: &[ArgumentType],
            fds: &'b [RawFd],
        ) -> Result<(Message, &'a [u32], &'b [RawFd]), MessageParseError> {
            // helper function to read arrays
            fn read_array_from_payload(
                array_len: usize,
                payload: &[u32],
            ) -> Result<(&[u8], &[u32]), MessageParseError> {
                let word_len = array_len / 4 + if array_len % 4 != 0 { 1 } else { 0 };
                if word_len > payload.len() {
                    return Err(MessageParseError::MissingData);
                }
                let (array_contents, rest) = payload.split_at(word_len);
                let array =
                    unsafe { ::std::slice::from_raw_parts(array_contents.as_ptr() as *const u8, array_len) };
                Ok((array, rest))
            }

            if raw.len() < 2 {
                return Err(MessageParseError::MissingData);
            }

            let sender_id = raw[0];
            let word_2 = raw[1];
            let opcode = (word_2 & 0x0000FFFF) as u16;
            let len = (word_2 >> 16) as usize / 4;

            if len < 2 || len > raw.len() {
                return Err(MessageParseError::Malformed);
            }

            let (mut payload, rest) = raw.split_at(len);
            payload = &payload[2..];
            let mut fds = fds;

            let arguments = signature
                .iter()
                .map(|argtype| {
                    if let ArgumentType::Fd = *argtype {
                        // don't consume input but fd
                        if let Some((&front, tail)) = fds.split_first() {
                            fds = tail;
                            Ok(Argument::Fd(front))
                        } else {
                            Err(MessageParseError::MissingFD)
                        }
                    } else if let Some((&front, mut tail)) = payload.split_first() {
                        let arg = match *argtype {
                            ArgumentType::Int => Ok(Argument::Int(front as i32)),
                            ArgumentType::Uint => Ok(Argument::Uint(front)),
                            ArgumentType::Fixed => Ok(Argument::Fixed(front as i32)),
                            ArgumentType::Str => {
                                read_array_from_payload(front as usize, tail).and_then(|(v, rest)| {
                                    tail = rest;
                                    match CStr::from_bytes_with_nul(v) {
                                        Ok(s) => Ok(Argument::Str(s.into())),
                                        Err(_) => Err(MessageParseError::Malformed),
                                    }
                                })
                            }
                            ArgumentType::Object => Ok(Argument::Object(front)),
                            ArgumentType::NewId => Ok(Argument::NewId(front)),
                            ArgumentType::Array => {
                                read_array_from_payload(front as usize, tail).map(|(v, rest)| {
                                    tail = rest;
                                    Argument::Array(v.into())
                                })
                            }
                            ArgumentType::Fd => unreachable!(),
                        };
                        payload = tail;
                        arg
                    } else {
                        Err(MessageParseError::MissingData)
                    }
                })
                .collect::<Result<Vec<_>, MessageParseError>>()?;

            let msg = Message {
                sender_id: sender_id,
                opcode: opcode,
                args: arguments,
            };
            Ok((msg, rest, fds))
        }
    }

    /// Duplicate a `RawFd` and set the CLOEXEC flag on the copy
    pub fn dup_fd_cloexec(fd: RawFd) -> NixResult<RawFd> {
        use nix::fcntl;
        match fcntl::fcntl(fd, fcntl::FcntlArg::F_DUPFD_CLOEXEC(0)) {
            Ok(newfd) => Ok(newfd),
            Err(NixError::Sys(Errno::EINVAL)) => {
                // F_DUPFD_CLOEXEC is not recognized, kernel too old, fallback
                // to setting CLOEXEC manually
                let newfd = fcntl::fcntl(fd, fcntl::FcntlArg::F_DUPFD(0))?;

                let flags = fcntl::fcntl(newfd, fcntl::FcntlArg::F_GETFD);
                let result = flags
                    .map(|f| fcntl::FdFlag::from_bits(f).unwrap() | fcntl::FdFlag::FD_CLOEXEC)
                    .and_then(|f| fcntl::fcntl(newfd, fcntl::FcntlArg::F_SETFD(f)));
                match result {
                    Ok(_) => {
                        // setting the O_CLOEXEC worked
                        return Ok(newfd);
                    }
                    Err(e) => {
                        // something went wrong in F_GETFD or F_SETFD
                        let _ = ::nix::unistd::close(newfd);
                        return Err(e);
                    }
                }
            }
            Err(e) => Err(e),
        }
    }

    /*
     * utility struct that closes every FD it contains on drop
     */

    struct FdStore {
        fds: Vec<RawFd>,
    }

    impl FdStore {
        fn new() -> FdStore {
            FdStore { fds: Vec::new() }
        }
        fn push(&mut self, fd: RawFd) {
            self.fds.push(fd);
        }
        fn clear(&mut self) {
            self.fds.clear();
        }
    }

    impl Drop for FdStore {
        fn drop(&mut self) {
            use nix::unistd::close;
            for fd in self.fds.drain(..) {
                // not much can be done if we can't close that anyway...
                let _ = close(fd);
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn into_from_raw_cycle() {
            let mut bytes_buffer = vec![0; 1024];
            let mut fd_buffer = vec![0; 10];

            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),
                ],
            };
            // write the message to the buffers
            msg.write_to_buffers(&mut bytes_buffer[..], &mut fd_buffer[..])
                .unwrap();
            // read them back
            let (rebuilt, _, _) = Message::from_raw(
                &bytes_buffer[..],
                &[
                    ArgumentType::Uint,
                    ArgumentType::Fixed,
                    ArgumentType::Str,
                    ArgumentType::Array,
                    ArgumentType::Object,
                    ArgumentType::NewId,
                    ArgumentType::Int,
                ],
                &fd_buffer[..],
            )
            .unwrap();
            assert_eq!(rebuilt, msg);
        }
    }

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