use std::ffi::CString;
use std::marker::PhantomData;
use std::mem;
use std::net::{
    IpAddr,
    Ipv4Addr,
    Ipv6Addr,
    SocketAddr,
};
use std::os::raw::{
    c_char,
    c_int,
    c_uchar,
    c_void,
};
use std::ptr;
use std::sync::Arc;

use c_ares_sys;
use c_types;

use a::{
    AResults,
    query_a_callback,
};
use aaaa::{
    AAAAResults,
    query_aaaa_callback,
};
use cname::{
    CNameResults,
    query_cname_callback,
};
use error::{
    Error,
    Result,
};
use flags::Flags;
use host::{
    HostResults,
    get_host_callback,
};
use mx::{
    MXResults,
    query_mx_callback,
};
use nameinfo::{
    NameInfoResult,
    get_name_info_callback,
};
use naptr::{
    NAPTRResults,
    query_naptr_callback,
};
use ni_flags::NIFlags;
use ns::{
    NSResults,
    query_ns_callback,
};
use ptr::{
    PTRResults,
    query_ptr_callback,
};
use query::query_callback;
use soa::{
    SOAResult,
    query_soa_callback,
};
use srv::{
    SRVResults,
    query_srv_callback,
};
use txt::{
    TXTResults,
    query_txt_callback,
};
use types::{
    AddressFamily,
    DnsClass,
    QueryType,
    Socket,
};
use utils::{
  ipv4_as_in_addr,
  ipv6_as_in6_addr,
  socket_addrv4_as_sockaddr_in,
  socket_addrv6_as_sockaddr_in6,
};

/// Used to configure the behaviour of the name resolver.
#[derive(Default)]
pub struct Options {
    ares_options: c_ares_sys::ares_options,
    optmask: c_int,
    domains: Vec<CString>,
    lookups: Option<CString>,
    socket_state_callback: Option<Arc<FnMut(Socket, bool, bool) + Send + 'static>>,
}

impl Options {
    /// Returns a fresh `Options`, on which no values are set.
    pub fn new() -> Self {
        Self::default()
    }

    /// Set flags controlling the behaviour of the resolver.  The available
    /// flags are documented [here](flags/index.html).
    pub fn set_flags(&mut self, flags: Flags) -> &mut Self {
        self.ares_options.flags = flags.bits();
        self.optmask |= c_ares_sys::ARES_OPT_FLAGS;
        self
    }

    /// Set the number of milliseconds each name server is given to respond to
    /// a query on the first try.  (After the first try, the timeout algorithm
    /// becomes more complicated, but scales linearly with the value of
    /// timeout).  The default is 5000ms.
    pub fn set_timeout(&mut self, ms: u32) -> &mut Self {
        self.ares_options.timeout = ms as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_TIMEOUTMS;
        self
    }

    /// Set the number of tries the resolver will try contacting each name
    /// server before giving up.  The default is four tries.
    pub fn set_tries(&mut self, tries: u32) -> &mut Self {
        self.ares_options.tries = tries as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_TRIES;
        self
    }

    /// Set the number of dots which must be present in a domain name for it to
    /// be queried for "as is" prior to querying for it with the default domain
    /// extensions appended.  The default value is 1 unless set otherwise by
    /// resolv.conf or the RES_OPTIONS environment variable.
    pub fn set_ndots(&mut self, ndots: u32) -> &mut Self {
        self.ares_options.ndots = ndots as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_NDOTS;
        self
    }

    /// Set the UDP port to use for queries.  The default value is 53, the
    /// standard name service port.
    pub fn set_udp_port(&mut self, udp_port: u16) -> &mut Self {
        self.ares_options.udp_port = udp_port;
        self.optmask |= c_ares_sys::ARES_OPT_UDP_PORT;
        self
    }

    /// Set the TCP port to use for queries.  The default value is 53, the
    /// standard name service port.
    pub fn set_tcp_port(&mut self, tcp_port: u16) -> &mut Self {
        self.ares_options.tcp_port = tcp_port;
        self.optmask |= c_ares_sys::ARES_OPT_TCP_PORT;
        self
    }

    /// Set the domains to search, instead of the domains specified in
    /// resolv.conf or the domain derived from the kernel hostname variable.
    pub fn set_domains(&mut self, domains: &[&str]) -> &mut Self {
        self.domains = domains
            .iter()
            .map(|&s| CString::new(s).unwrap())
            .collect();
        self.optmask |= c_ares_sys::ARES_OPT_DOMAINS;
        self
    }

    /// Set the lookups to perform for host queries. `lookups` should be set to
    /// a string of the characters "b" or "f", where "b" indicates a DNS lookup
    /// and "f" indicates a lookup in the hosts file.
    pub fn set_lookups(&mut self, lookups: &str) -> &mut Self {
        let c_lookups = CString::new(lookups).unwrap();
        self.lookups = Some(c_lookups);
        self.optmask |= c_ares_sys::ARES_OPT_LOOKUPS;
        self
    }

    /// Set the callback function to be invoked when a socket changes state.
    ///
    /// `callback(socket, read, write)` will be called when a socket changes
    /// state:
    ///
    /// -  `read` is set to true if the socket should listen for read events
    /// -  `write` is set to true if the socket should listen for write events.
    pub fn set_socket_state_callback<F>(&mut self, callback: F) -> &mut Self
        where F: FnMut(Socket, bool, bool) + Send + 'static {
        let boxed_callback = Arc::new(callback);
        self.ares_options.sock_state_cb = Some(socket_state_callback::<F>);
        self.ares_options.sock_state_cb_data =
            &*boxed_callback as *const _ as *mut c_void;
        self.socket_state_callback = Some(boxed_callback);
        self.optmask |= c_ares_sys::ARES_OPT_SOCK_STATE_CB;
        self
    }

    /// Set the socket send buffer size.
    pub fn set_sock_send_buffer_size(&mut self, size: u32) -> &mut Self {
        self.ares_options.socket_send_buffer_size = size as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_SOCK_SNDBUF;
        self
    }

    /// Set the socket receive buffer size.
    pub fn set_sock_receive_buffer_size(&mut self, size: u32) -> &mut Self {
        self.ares_options.socket_receive_buffer_size = size as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_SOCK_RCVBUF;
        self
    }

    /// Configure round robin selection of nameservers.
    pub fn set_rotate(&mut self) -> &mut Self {
        self.optmask |= c_ares_sys::ARES_OPT_ROTATE;
        self
    }

    /// Prevent round robin selection of nameservers.
    pub fn set_no_rotate(&mut self) -> &mut Self {
        self.optmask |= c_ares_sys::ARES_OPT_NOROTATE;
        self
    }

    /// Set the EDNS packet size.
    pub fn set_ednspsz(&mut self, size: u32) -> &mut Self {
        self.ares_options.ednspsz = size as c_int;
        self.optmask |= c_ares_sys::ARES_OPT_EDNSPSZ;
        self
    }
}

/// A channel for name service lookups.
pub struct Channel {
    ares_channel: c_ares_sys::ares_channel,
    phantom: PhantomData<c_ares_sys::ares_channeldata>,

    // For ownership only.
    _socket_state_callback: Option<Arc<FnMut(Socket, bool, bool) + Send + 'static>>,
}

impl Channel {
    /// Create a new channel for name service lookups.
    pub fn new(mut options: Options) -> Result<Channel> {
        // Initialize the library.
        let lib_rc = unsafe {
            c_ares_sys::ares_library_init(c_ares_sys::ARES_LIB_INIT_ALL)
        };
        if lib_rc != c_ares_sys::ARES_SUCCESS {
            return Err(Error::from(lib_rc))
        }

        // We deferred setting up domains in the options - do it now.
        let domains: Vec<_> = options.domains
            .iter()
            .map(|s| s.as_ptr())
            .collect();
        options.ares_options.domains =
            domains.as_ptr() as *mut *mut c_char;
        options.ares_options.ndomains = domains.len() as c_int;

        // Likewise for lookups.
        for c_lookup in &options.lookups {
            options.ares_options.lookups =
                c_lookup.as_ptr() as *mut c_char;
        }

        // Initialize the channel.
        let mut ares_channel = ptr::null_mut();
        let channel_rc = unsafe {
            c_ares_sys::ares_init_options(
                &mut ares_channel,
                &mut options.ares_options,
                options.optmask)
        };
        if channel_rc != c_ares_sys::ARES_SUCCESS {
            unsafe { c_ares_sys::ares_library_cleanup(); }
            return Err(Error::from(channel_rc))
        }

        let channel = Channel {
            ares_channel: ares_channel,
            phantom: PhantomData,
            _socket_state_callback: options.socket_state_callback,
        };
        Ok(channel)
    }

    /// Duplicate a channel.
    pub fn try_clone(&self) -> Result<Channel> {
        let mut ares_channel = ptr::null_mut();
        let rc = unsafe {
            c_ares_sys::ares_dup(&mut ares_channel, self.ares_channel)
        };
        if rc != c_ares_sys::ARES_SUCCESS {
            return Err(Error::from(rc))
        }

        let callback = self._socket_state_callback.as_ref().cloned();
        let channel = Channel {
            ares_channel: ares_channel,
            phantom: PhantomData,
            _socket_state_callback: callback,
        };
        Ok(channel)
    }

    /// Handle input, output, and timeout events associated with the specified
    /// file descriptors (sockets).
    ///
    /// Providing a value for `read_fd` indicates that the identified socket
    /// is readable; likewise providing a value for `write_fd` indicates that
    /// the identified socket is writable.  Use `SOCKET_BAD` for "no action".
    pub fn process_fd(&mut self, read_fd: Socket, write_fd: Socket) {
        unsafe {
            c_ares_sys::ares_process_fd(self.ares_channel, read_fd, write_fd);
        }
    }

    /// Handle input and output events associated with the specified file
    /// descriptors (sockets).  Also handles timeouts associated with the
    /// `Channel`.
    pub fn process(
        &mut self,
        read_fds: &mut c_types::fd_set,
        write_fds: &mut c_types::fd_set) {
        unsafe {
            c_ares_sys::ares_process(self.ares_channel, read_fds, write_fds);
        }
    }

    /// Retrieve the set of socket descriptors which the calling application
    /// should wait on for reading and / or writing.
    pub fn get_sock(&self) -> GetSock {
        let mut socks = [0; c_ares_sys::ARES_GETSOCK_MAXNUM];
        let bitmask = unsafe {
            c_ares_sys::ares_getsock(
                self.ares_channel,
                socks.as_mut_ptr(),
                c_ares_sys::ARES_GETSOCK_MAXNUM as c_int)
        };
        GetSock::new(socks, bitmask as u32)
    }

    /// Retrieve the set of socket descriptors which the calling application
    /// should wait on for reading and / or writing.
    pub fn fds(
        &self,
        read_fds: &mut c_types::fd_set,
        write_fds: &mut c_types::fd_set) -> u32 {
        unsafe {
            c_ares_sys::ares_fds(self.ares_channel, read_fds, write_fds) as u32
        }
    }

    /// Set the list of servers to contact, instead of the servers specified
    /// in resolv.conf or the local named.
    ///
    /// String format is `host[:port]`.  IPv6 addresses with ports require
    /// square brackets eg `[2001:4860:4860::8888]:53`.
    pub fn set_servers(
        &mut self,
        servers: &[&str]) -> Result<&mut Self> {
        let servers_csv = servers.join(",");
        let c_servers = CString::new(servers_csv).unwrap();
        let ares_rc = unsafe {
            c_ares_sys::ares_set_servers_ports_csv(
                self.ares_channel,
                c_servers.as_ptr())
        };
        if ares_rc == c_ares_sys::ARES_SUCCESS {
            Ok(self)
        } else {
            Err(Error::from(ares_rc))
        }
    }

    /// Set the local IPv4 address from which to make queries.
    pub fn set_local_ipv4(&mut self, ipv4: &Ipv4Addr) -> &mut Self {
        unsafe {
            c_ares_sys::ares_set_local_ip4(
                self.ares_channel,
                u32::from(*ipv4));
        }
        self
    }

    /// Set the local IPv6 address from which to make queries.
    pub fn set_local_ipv6(&mut self, ipv6: &Ipv6Addr) -> &mut Self {
        let in6_addr = ipv6_as_in6_addr(ipv6);
        unsafe {
            c_ares_sys::ares_set_local_ip6(
                self.ares_channel,
                &in6_addr as *const _ as *const c_uchar);
        }
        self
    }

    /// Set the local device from which to make queries.
    pub fn set_local_device(&mut self, device: &str) -> &mut Self {
        let c_dev = CString::new(device).unwrap();
        unsafe {
            c_ares_sys::ares_set_local_dev(self.ares_channel, c_dev.as_ptr());
        }
        self
    }

    /// Initiate a single-question DNS query for the A records associated with
    /// `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_a<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<AResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::A as c_int,
                Some(query_a_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the A records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_a<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<AResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::A as c_int,
                Some(query_a_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the AAAA records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_aaaa<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<AAAAResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::AAAA as c_int,
                Some(query_aaaa_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the AAAA records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_aaaa<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<AAAAResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::AAAA as c_int,
                Some(query_aaaa_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the CNAME records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_cname<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<CNameResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::CNAME as c_int,
                Some(query_cname_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the CNAME records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_cname<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<CNameResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::CNAME as c_int,
                Some(query_cname_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the MX records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_mx<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<MXResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::MX as c_int,
                Some(query_mx_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the MX records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_mx<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<MXResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::MX as c_int,
                Some(query_mx_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the NAPTR records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_naptr<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<NAPTRResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::NAPTR as c_int,
                Some(query_naptr_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the NAPTR records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_naptr<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<NAPTRResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::NAPTR as c_int,
                Some(query_naptr_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the NS records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_ns<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<NSResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::NS as c_int,
                Some(query_ns_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the NS records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_ns<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<NSResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::NS as c_int,
                Some(query_ns_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the PTR records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_ptr<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<PTRResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::PTR as c_int,
                Some(query_ptr_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the PTR records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_ptr<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<PTRResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::PTR as c_int,
                Some(query_ptr_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the SOA records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_soa<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<SOAResult>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::SOA as c_int,
                Some(query_soa_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the SOA records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_soa<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<SOAResult>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::SOA as c_int,
                Some(query_soa_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the SRV records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_srv<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<SRVResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::SRV as c_int,
                Some(query_srv_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the SRV records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_srv<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<SRVResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::SRV as c_int,
                Some(query_srv_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for the TXT records associated
    /// with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn query_txt<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<TXTResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::TXT as c_int,
                Some(query_txt_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for the TXT records
    /// associated with `name`.
    ///
    /// On completion, `handler` is called with the result.
    pub fn search_txt<F>(&mut self, name: &str, handler: F)
        where F: FnOnce(Result<TXTResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                DnsClass::IN as c_int,
                QueryType::TXT as c_int,
                Some(query_txt_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Perform a host query by address.
    ///
    /// On completion, `handler` is called with the result.
    pub fn get_host_by_address<F>(
        &mut self,
        address: &IpAddr,
        handler: F) where F: FnOnce(Result<HostResults>) + Send + 'static {
        let in_addr: c_types::in_addr;
        let in6_addr: c_types::in6_addr;
        let c_addr = match *address {
            IpAddr::V4(ref v4) => {
                in_addr = ipv4_as_in_addr(v4);
                &in_addr as *const _ as *const c_void
            },
            IpAddr::V6(ref v6) => {
                in6_addr = ipv6_as_in6_addr(v6);
                &in6_addr as *const _ as *const c_void
            },
        };
        let (family, length) = match *address {
            IpAddr::V4(_) => {
                (AddressFamily::INET, mem::size_of::<c_types::in_addr>())
            },
            IpAddr::V6(_) => {
                (AddressFamily::INET6, mem::size_of::<c_types::in6_addr>())
            },
        };
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_gethostbyaddr(
                self.ares_channel,
                c_addr,
                length as c_int,
                family as c_int,
                Some(get_host_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Perform a host query by name.
    ///
    /// On completion, `handler` is called with the result.
    pub fn get_host_by_name<F>(
        &mut self,
        name: &str,
        family: AddressFamily,
        handler: F) where F: FnOnce(Result<HostResults>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_gethostbyname(
                self.ares_channel,
                c_name.as_ptr(),
                family as c_int,
                Some(get_host_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Address-to-nodename translation in protocol-independent manner.
    ///
    /// The valid values for `flags` are documented
    /// [here](ni_flags/index.html).
    ///
    /// On completion, `handler` is called with the result.
    pub fn get_name_info<F>(
        &mut self,
        address: &SocketAddr,
        flags: NIFlags,
        handler: F)
        where F: FnOnce(Result<NameInfoResult>) + Send + 'static {
        let sockaddr_in: c_types::sockaddr_in;
        let sockaddr_in6: c_types::sockaddr_in6;
        let c_addr = match *address {
            SocketAddr::V4(ref v4) => {
                sockaddr_in = socket_addrv4_as_sockaddr_in(v4);
                &sockaddr_in as *const _ as *const c_types::sockaddr
            },
            SocketAddr::V6(ref v6) => {
                sockaddr_in6 = socket_addrv6_as_sockaddr_in6(v6);
                &sockaddr_in6 as *const _ as *const c_types::sockaddr
            },
        };
        let length = match *address {
            SocketAddr::V4(_) => mem::size_of::<c_types::sockaddr_in>(),
            SocketAddr::V6(_) => mem::size_of::<c_types::sockaddr_in6>(),
        };
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_getnameinfo(
                self.ares_channel,
                c_addr,
                length as c_ares_sys::ares_socklen_t,
                flags.bits(),
                Some(get_name_info_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a single-question DNS query for `name`.  The class and type of
    /// the query are per the provided parameters, taking values as defined in
    /// `arpa/nameser.h`.
    ///
    /// On completion, `handler` is called with the result.
    ///
    /// This method is provided so that users can query DNS types for which
    /// `c-ares` does not provide a parser.  This is expected to be a last
    /// resort; if a suitable `query_xxx()` is available, that should be
    /// preferred.
    pub fn query<F>(
        &mut self,
        name: &str,
        dns_class: u16,
        query_type: u16,
        handler: F)
        where F: FnOnce(Result<&[u8]>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_query(
                self.ares_channel,
                c_name.as_ptr(),
                dns_class as c_int,
                query_type as c_int,
                Some(query_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Initiate a series of single-question DNS queries for `name`.  The class
    /// and type of the query are per the provided parameters, taking values as
    /// defined in `arpa/nameser.h`.
    ///
    /// On completion, `handler` is called with the result.
    ///
    /// This method is provided so that users can query DNS types for which
    /// `c-ares` does not provide a parser.  This is expected to be a last
    /// resort; if a suitable `search_xxx()` is available, that should be
    /// preferred.
    pub fn search<F>(
        &mut self,
        name: &str,
        dns_class: u16,
        query_type: u16,
        handler: F)
        where F: FnOnce(Result<&[u8]>) + Send + 'static {
        let c_name = CString::new(name).unwrap();
        let c_arg = Box::into_raw(Box::new(handler));
        unsafe {
            c_ares_sys::ares_search(
                self.ares_channel,
                c_name.as_ptr(),
                dns_class as c_int,
                query_type as c_int,
                Some(query_callback::<F>),
                c_arg as *mut c_void);
        }
    }

    /// Cancel all requests made on this `Channel`.
    ///
    /// Callbacks will be invoked for each pending query, passing a result
    /// `Err(Error::ECANCELLED)`.
    pub fn cancel(&mut self) {
        unsafe { c_ares_sys::ares_cancel(self.ares_channel); }
    }
}

impl Drop for Channel {
    fn drop(&mut self) {
        unsafe {
            c_ares_sys::ares_destroy(self.ares_channel);
            c_ares_sys::ares_library_cleanup();
        }
    }
}

unsafe impl Send for Channel { }
unsafe impl Sync for Channel { }
unsafe impl Send for Options { }
unsafe impl Sync for Options { }

pub unsafe extern "C" fn socket_state_callback<F>(
    data: *mut c_void,
    socket_fd: c_ares_sys::ares_socket_t,
    readable: c_int,
    writable: c_int)
    where F: FnMut(Socket, bool, bool) + Send + 'static {
    let handler = data as *mut F;
    (*handler)(socket_fd, readable != 0, writable != 0);
}

/// Information about the set of sockets that `c-ares` is interested in, as
/// returned by `get_sock()`.
#[derive(Clone, Copy, Debug)]
pub struct GetSock {
    socks: [c_ares_sys::ares_socket_t; c_ares_sys::ARES_GETSOCK_MAXNUM],
    bitmask: u32,
}

impl GetSock {
    fn new(
        socks: [c_ares_sys::ares_socket_t; c_ares_sys::ARES_GETSOCK_MAXNUM],
        bitmask: u32) -> GetSock {
        GetSock {
            socks: socks,
            bitmask: bitmask,
        }
    }

    /// Returns an iterator over the sockets that `c-ares` is interested in.
    pub fn iter(&self) -> GetSockIter {
        GetSockIter {
            next: 0,
            getsock: self,
        }
    }
}

/// Iterator for sockets of interest to `c-ares`.
///
/// Iterator items are `(socket, readable, writable)`.
#[derive(Clone, Copy, Debug)]
pub struct GetSockIter<'a> {
    next: usize,
    getsock: &'a GetSock,
}

impl<'a> Iterator for GetSockIter<'a> {
    type Item = (Socket, bool, bool);
    fn next(&mut self) -> Option<Self::Item> {
        let index = self.next;
        self.next += 1;
        if index >= c_ares_sys::ARES_GETSOCK_MAXNUM {
            None
        } else {
            let bit = 1 << index;
            let readable = (self.getsock.bitmask & bit) != 0;
            let bit = bit << c_ares_sys::ARES_GETSOCK_MAXNUM;
            let writable = (self.getsock.bitmask & bit) != 0;
            if readable || writable {
                let fd = self.getsock.socks[index];
                Some((fd, readable, writable))
            } else {
                None
            }
        }
    }
}

impl<'a> IntoIterator for &'a GetSock {
    type Item = (Socket, bool, bool);
    type IntoIter = GetSockIter<'a>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}