//! implements the DNS protocol in a transport agnostic fashion

use std::fmt;
use std::hash::{Hash, Hasher};
use std::net::{Ipv4Addr, Ipv6Addr};

use derive_more::{Display, Error, From};
use rand::random;
use serde::{Deserialize, Serialize};

use crate::dns::buffer::{PacketBuffer, VectorPacketBuffer};

#[derive(Debug, Display, From, Error)]
pub enum ProtocolError {
    Buffer(crate::dns::buffer::BufferError),
    Io(std::io::Error)
}

type Result<T> = std::result::Result<T, ProtocolError>;

/// `QueryType` represents the requested Record Type of a query
///
/// The specific type UNKNOWN that an integer parameter in order to retain the
/// id of an unknown query when compiling the reply. An integer can be converted
/// to a querytype using the `from_num` function, and back to an integer using
/// the `to_num` method.
#[derive(PartialEq, Eq, Debug, Clone, Hash, Copy, Serialize, Deserialize)]
pub enum QueryType {
    UNKNOWN(u16),
    A,     // 1
    NS,    // 2
    CNAME, // 5
    SOA,   // 6
    PTR,   // 12
    MX,    // 15
    TXT,   // 16
    AAAA,  // 28
    SRV,   // 33
    OPT,   // 41
    TLSA,  // 52
}

impl QueryType {
    pub fn to_num(&self) -> u16 {
        match *self {
            QueryType::UNKNOWN(x) => x,
            QueryType::A => 1,
            QueryType::NS => 2,
            QueryType::CNAME => 5,
            QueryType::SOA => 6,
            QueryType::PTR => 12,
            QueryType::MX => 15,
            QueryType::TXT => 16,
            QueryType::AAAA => 28,
            QueryType::SRV => 33,
            QueryType::OPT => 41,
            QueryType::TLSA => 52,
        }
    }

    pub fn from_num(num: u16) -> QueryType {
        match num {
            1 => QueryType::A,
            2 => QueryType::NS,
            5 => QueryType::CNAME,
            6 => QueryType::SOA,
            12 => QueryType::PTR,
            15 => QueryType::MX,
            16 => QueryType::TXT,
            28 => QueryType::AAAA,
            33 => QueryType::SRV,
            41 => QueryType::OPT,
            52 => QueryType::TLSA,
            _ => QueryType::UNKNOWN(num),
        }
    }
}

#[derive(Copy, Clone, Debug, Eq, PartialOrd, Ord, Serialize, Deserialize)]
pub struct TransientTtl(pub u32);

impl PartialEq<TransientTtl> for TransientTtl {
    fn eq(&self, other: &TransientTtl) -> bool {
        self.0 == other.0
    }
}

impl Hash for TransientTtl {
    fn hash<H>(&self, _: &mut H) where H: Hasher {
        // purposely left empty
    }
}

/// `DnsRecord` is the primary representation of a DNS record
///
/// This enumeration is used for reading as well as writing records, from network
/// and from disk (for storage of authority data).
#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
#[serde(tag = "type")]
pub enum DnsRecord {
    UNKNOWN {
        domain: String,
        qtype: u16,
        data_len: u16,
        ttl: TransientTtl
    }, // 0
    A {
        domain: String,
        addr: Ipv4Addr,
        ttl: TransientTtl
    }, // 1
    NS {
        domain: String,
        host: String,
        ttl: TransientTtl
    }, // 2
    CNAME {
        domain: String,
        host: String,
        ttl: TransientTtl
    }, // 5
    SOA {
        domain: String,
        m_name: String,
        r_name: String,
        serial: u32,
        refresh: u32,
        retry: u32,
        expire: u32,
        minimum: u32,
        ttl: TransientTtl
    }, // 6
    PTR {
        domain: String,
        data: String,
        ttl: TransientTtl
    }, // 12
    MX {
        domain: String,
        priority: u16,
        host: String,
        ttl: TransientTtl
    }, // 15
    TXT {
        domain: String,
        data: String,
        ttl: TransientTtl
    }, // 16
    AAAA {
        domain: String,
        addr: Ipv6Addr,
        ttl: TransientTtl
    }, // 28
    SRV {
        domain: String,
        priority: u16,
        weight: u16,
        port: u16,
        host: String,
        ttl: TransientTtl
    }, // 33
    OPT {
        packet_len: u16,
        flags: u32,
        data: String
    }, // 41
    TLSA {
        domain: String,
        certificate_usage: u8,
        selector: u8,
        matching_type: u8,
        data: Vec<u8>,
        ttl: TransientTtl
    }, // 52
}

impl DnsRecord {
    pub fn read<T: PacketBuffer>(buffer: &mut T) -> Result<DnsRecord> {
        let mut domain = String::new();
        buffer.read_qname(&mut domain)?;

        let qtype_num = buffer.read_u16()?;
        let qtype = QueryType::from_num(qtype_num);
        let class = buffer.read_u16()?;
        let ttl = buffer.read_u32()?;
        let data_len = buffer.read_u16()?;

        match qtype {
            QueryType::A => {
                let raw_addr = buffer.read_u32()?;
                let addr = Ipv4Addr::new(
                    ((raw_addr >> 24) & 0xFF) as u8,
                    ((raw_addr >> 16) & 0xFF) as u8,
                    ((raw_addr >> 8) & 0xFF) as u8,
                    (raw_addr & 0xFF) as u8
                );

                Ok(DnsRecord::A { domain, addr, ttl: TransientTtl(ttl) })
            }
            QueryType::AAAA => {
                let raw_addr1 = buffer.read_u32()?;
                let raw_addr2 = buffer.read_u32()?;
                let raw_addr3 = buffer.read_u32()?;
                let raw_addr4 = buffer.read_u32()?;
                let addr = Ipv6Addr::new(
                    ((raw_addr1 >> 16) & 0xFFFF) as u16,
                    (raw_addr1 & 0xFFFF) as u16,
                    ((raw_addr2 >> 16) & 0xFFFF) as u16,
                    (raw_addr2 & 0xFFFF) as u16,
                    ((raw_addr3 >> 16) & 0xFFFF) as u16,
                    (raw_addr3 & 0xFFFF) as u16,
                    ((raw_addr4 >> 16) & 0xFFFF) as u16,
                    (raw_addr4 & 0xFFFF) as u16
                );

                Ok(DnsRecord::AAAA { domain, addr, ttl: TransientTtl(ttl) })
            }
            QueryType::NS => {
                let mut ns = String::new();
                buffer.read_qname(&mut ns)?;

                Ok(DnsRecord::NS { domain, host: ns, ttl: TransientTtl(ttl) })
            }
            QueryType::CNAME => {
                let mut cname = String::new();
                buffer.read_qname(&mut cname)?;

                Ok(DnsRecord::CNAME { domain, host: cname, ttl: TransientTtl(ttl) })
            }
            QueryType::SRV => {
                let priority = buffer.read_u16()?;
                let weight = buffer.read_u16()?;
                let port = buffer.read_u16()?;

                let mut srv = String::new();
                buffer.read_qname(&mut srv)?;

                Ok(DnsRecord::SRV { domain, priority, weight, port, host: srv, ttl: TransientTtl(ttl) })
            }
            QueryType::PTR => {
                let mut ptr = String::new();
                buffer.read_qname(&mut ptr)?;

                Ok(DnsRecord::PTR { domain, data: ptr, ttl: TransientTtl(ttl) })
            }
            QueryType::MX => {
                let priority = buffer.read_u16()?;
                let mut mx = String::new();
                buffer.read_qname(&mut mx)?;

                Ok(DnsRecord::MX { domain, priority, host: mx, ttl: TransientTtl(ttl) })
            }
            QueryType::SOA => {
                let mut m_name = String::new();
                buffer.read_qname(&mut m_name)?;

                let mut r_name = String::new();
                buffer.read_qname(&mut r_name)?;

                let serial = buffer.read_u32()?;
                let refresh = buffer.read_u32()?;
                let retry = buffer.read_u32()?;
                let expire = buffer.read_u32()?;
                let minimum = buffer.read_u32()?;

                Ok(DnsRecord::SOA { domain, m_name, r_name, serial, refresh, retry, expire, minimum, ttl: TransientTtl(ttl) })
            }
            QueryType::TXT => {
                let mut txt = String::new();

                let cur_pos = buffer.pos();
                txt.push_str(&String::from_utf8_lossy(buffer.get_range(cur_pos, data_len as usize)?));

                buffer.step(data_len as usize)?;

                Ok(DnsRecord::TXT { domain, data: txt, ttl: TransientTtl(ttl) })
            }
            QueryType::OPT => {
                let mut data = String::new();

                let cur_pos = buffer.pos();
                data.push_str(&String::from_utf8_lossy(buffer.get_range(cur_pos, data_len as usize)?));
                buffer.step(data_len as usize)?;

                Ok(DnsRecord::OPT { packet_len: class, flags: ttl, data })
            }
            QueryType::TLSA => {
                let certificate_usage = buffer.read()?;
                let selector = buffer.read()?;
                let matching_type = buffer.read()?;
                let cur_pos = buffer.pos();
                let data_len = data_len - 3;
                let data = buffer.get_range(cur_pos, data_len as usize)?.to_vec();
                buffer.step(data_len as usize)?;
                Ok(DnsRecord::TLSA { domain, certificate_usage, selector, matching_type, data, ttl: TransientTtl(ttl) })
            }
            QueryType::UNKNOWN(_) => {
                buffer.step(data_len as usize)?;

                Ok(DnsRecord::UNKNOWN { domain, qtype: qtype_num, data_len, ttl: TransientTtl(ttl) })
            }
        }
    }

    pub fn write<T: PacketBuffer>(&self, buffer: &mut T) -> Result<usize> {
        let start_pos = buffer.pos();

        match *self {
            DnsRecord::A { ref domain, ref addr, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::A.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;
                buffer.write_u16(4)?;

                let octets = addr.octets();
                buffer.write_u8(octets[0])?;
                buffer.write_u8(octets[1])?;
                buffer.write_u8(octets[2])?;
                buffer.write_u8(octets[3])?;
            }
            DnsRecord::AAAA { ref domain, ref addr, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::AAAA.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;
                buffer.write_u16(16)?;

                for octet in &addr.segments() {
                    buffer.write_u16(*octet)?;
                }
            }
            DnsRecord::NS { ref domain, ref host, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::NS.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_qname(host)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::CNAME { ref domain, ref host, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::CNAME.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_qname(host)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::SRV { ref domain, priority, weight, port, ref host, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::SRV.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_u16(priority)?;
                buffer.write_u16(weight)?;
                buffer.write_u16(port)?;
                buffer.write_qname(host)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::PTR { ref domain, ref data, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::PTR.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_qname(data)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::MX { ref domain, priority, ref host, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::MX.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_u16(priority)?;
                buffer.write_qname(host)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::SOA { ref domain, ref m_name, ref r_name, serial, refresh, retry, expire, minimum, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::SOA.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let pos = buffer.pos();
                buffer.write_u16(0)?;

                buffer.write_qname(m_name)?;
                buffer.write_qname(r_name)?;
                buffer.write_u32(serial)?;
                buffer.write_u32(refresh)?;
                buffer.write_u32(retry)?;
                buffer.write_u32(expire)?;
                buffer.write_u32(minimum)?;

                let size = buffer.pos() - (pos + 2);
                buffer.set_u16(pos, size as u16)?;
            }
            DnsRecord::TXT { ref domain, ref data, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::TXT.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;

                let bytes = data.as_bytes();
                buffer.write_u16((bytes.len() + 1) as u16)?;
                buffer.write_u8(bytes.len() as u8)?;

                for b in bytes {
                    buffer.write_u8(*b)?;
                }
            }
            DnsRecord::TLSA { ref domain, certificate_usage, selector, matching_type, ref data, ttl: TransientTtl(ttl) } => {
                buffer.write_qname(domain)?;
                buffer.write_u16(QueryType::TLSA.to_num())?;
                buffer.write_u16(1)?;
                buffer.write_u32(ttl)?;
                buffer.write_u16((data.len() + 3) as u16)?;
                buffer.write_u8(certificate_usage)?;
                buffer.write_u8(selector)?;
                buffer.write_u8(matching_type)?;

                for b in data {
                    buffer.write_u8(*b)?;
                }
            }
            DnsRecord::OPT { packet_len, flags, ref data } => {
                buffer.write_u8(0)?;
                buffer.write_u16(QueryType::OPT.to_num())?;
                buffer.write_u16(packet_len)?;
                buffer.write_u32(flags)?;
                buffer.write_u16(data.len() as u16)?;

                for b in data.as_bytes() {
                    buffer.write_u8(*b)?;
                }
            }
            DnsRecord::UNKNOWN { .. } => {
                println!("Skipping record: {:?}", self);
            }
        }

        Ok(buffer.pos() - start_pos)
    }

    pub fn get_querytype(&self) -> QueryType {
        match *self {
            DnsRecord::A { .. } => QueryType::A,
            DnsRecord::AAAA { .. } => QueryType::AAAA,
            DnsRecord::NS { .. } => QueryType::NS,
            DnsRecord::CNAME { .. } => QueryType::CNAME,
            DnsRecord::SRV { .. } => QueryType::SRV,
            DnsRecord::PTR { .. } => QueryType::PTR,
            DnsRecord::MX { .. } => QueryType::MX,
            DnsRecord::UNKNOWN { qtype, .. } => QueryType::UNKNOWN(qtype),
            DnsRecord::SOA { .. } => QueryType::SOA,
            DnsRecord::TXT { .. } => QueryType::TXT,
            DnsRecord::OPT { .. } => QueryType::OPT,
            DnsRecord::TLSA { .. } => QueryType::TLSA,
        }
    }

    pub fn get_domain(&self) -> Option<String> {
        match *self {
            DnsRecord::A { ref domain, .. }
            | DnsRecord::AAAA { ref domain, .. }
            | DnsRecord::NS { ref domain, .. }
            | DnsRecord::CNAME { ref domain, .. }
            | DnsRecord::SRV { ref domain, .. }
            | DnsRecord::PTR { ref domain, .. }
            | DnsRecord::MX { ref domain, .. }
            | DnsRecord::UNKNOWN { ref domain, .. }
            | DnsRecord::SOA { ref domain, .. }
            | DnsRecord::TXT { ref domain, .. }
            | DnsRecord::TLSA { ref domain, .. } => Some(domain.clone()),
            DnsRecord::OPT { .. } => None
        }
    }

    pub fn set_domain(&mut self, new_domain: String) {
        match self {
            DnsRecord::A { ref mut domain, .. }
            | DnsRecord::AAAA { ref mut domain, .. }
            | DnsRecord::NS { ref mut domain, .. }
            | DnsRecord::CNAME { ref mut domain, .. }
            | DnsRecord::SRV { ref mut domain, .. }
            | DnsRecord::PTR { ref mut domain, .. }
            | DnsRecord::MX { ref mut domain, .. }
            | DnsRecord::UNKNOWN { ref mut domain, .. }
            | DnsRecord::SOA { ref mut domain, .. }
            | DnsRecord::TXT { ref mut domain, .. }
            | DnsRecord::TLSA { ref mut domain, .. } => *domain = new_domain,
            DnsRecord::OPT { .. } => {} // OPT records don't have a domain field
        }
    }

    pub fn get_data(&self) -> Option<String> {
        match *self {
            DnsRecord::A { ref addr, .. } => Some(addr.to_string()),
            DnsRecord::AAAA { ref addr, .. } => Some(addr.to_string()),
            DnsRecord::NS { ref host, .. } => Some(host.clone()),
            DnsRecord::CNAME { ref host, .. } => Some(host.clone()),
            DnsRecord::SRV { ref host, .. } => Some(host.clone()),
            DnsRecord::PTR { ref data, .. } => Some(data.clone()),
            DnsRecord::MX { ref host, .. } => Some(host.clone()),
            DnsRecord::TXT { ref data, .. } => Some(data.clone()),
            DnsRecord::SOA { ref m_name, ref r_name, .. } => {
                let mut result = String::from(m_name);
                result.push_str(" @ ");
                result.push_str(r_name);
                Some(result)
            },
            DnsRecord::UNKNOWN { ref domain, .. } => Some(domain.clone()),
            DnsRecord::TLSA { ref domain, certificate_usage, selector, matching_type, ref data, .. } => {
                let data = crate::commons::to_hex(data);
                Some(format!("{} {} {} {} {}", domain, certificate_usage, selector, matching_type, &data))
            },
            DnsRecord::OPT { .. } => None,
        }
    }

    pub fn get_ttl(&self) -> u32 {
        match *self {
            DnsRecord::A { ttl: TransientTtl(ttl), .. }
            | DnsRecord::AAAA { ttl: TransientTtl(ttl), .. }
            | DnsRecord::NS { ttl: TransientTtl(ttl), .. }
            | DnsRecord::CNAME { ttl: TransientTtl(ttl), .. }
            | DnsRecord::SRV { ttl: TransientTtl(ttl), .. }
            | DnsRecord::PTR { ttl: TransientTtl(ttl), .. }
            | DnsRecord::MX { ttl: TransientTtl(ttl), .. }
            | DnsRecord::UNKNOWN { ttl: TransientTtl(ttl), .. }
            | DnsRecord::SOA { ttl: TransientTtl(ttl), .. }
            | DnsRecord::TXT { ttl: TransientTtl(ttl), .. } => ttl,
            | DnsRecord::TLSA { ttl: TransientTtl(ttl), .. } => ttl,
            DnsRecord::OPT { .. } => 0
        }
    }
}

/// The result code for a DNS query, as described in the specification
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum ResultCode {
    NOERROR = 0,
    FORMERR = 1,
    SERVFAIL = 2,
    NXDOMAIN = 3,
    NOTIMP = 4,
    REFUSED = 5
}

impl Default for ResultCode {
    fn default() -> Self {
        ResultCode::NOERROR
    }
}

impl ResultCode {
    pub fn from_num(num: u8) -> ResultCode {
        match num {
            1 => ResultCode::FORMERR,
            2 => ResultCode::SERVFAIL,
            3 => ResultCode::NXDOMAIN,
            4 => ResultCode::NOTIMP,
            5 => ResultCode::REFUSED,
            _ => ResultCode::NOERROR
        }
    }
}

/// Representation of a DNS header
#[derive(Clone, Debug, Default)]
pub struct DnsHeader {
    pub id: u16, // 16 bits

    pub recursion_desired: bool,    // 1 bit
    pub truncated_message: bool,    // 1 bit
    pub authoritative_answer: bool, // 1 bit
    pub opcode: u8,                 // 4 bits
    pub response: bool,             // 1 bit

    pub rescode: ResultCode,       // 4 bits
    pub checking_disabled: bool,   // 1 bit
    pub authed_data: bool,         // 1 bit
    pub z: bool,                   // 1 bit
    pub recursion_available: bool, // 1 bit

    pub questions: u16,             // 16 bits
    pub answers: u16,               // 16 bits
    pub authoritative_entries: u16, // 16 bits
    pub resource_entries: u16       // 16 bits
}

impl DnsHeader {
    pub fn new() -> DnsHeader {
        DnsHeader {
            id: 0,

            recursion_desired: false,
            truncated_message: false,
            authoritative_answer: false,
            opcode: 0,
            response: false,

            rescode: ResultCode::NOERROR,
            checking_disabled: false,
            authed_data: false,
            z: false,
            recursion_available: false,

            questions: 0,
            answers: 0,
            authoritative_entries: 0,
            resource_entries: 0
        }
    }

    pub fn write<T: PacketBuffer>(&self, buffer: &mut T) -> Result<()> {
        buffer.write_u16(self.id)?;

        buffer.write_u8(
            (self.recursion_desired as u8)
                | ((self.truncated_message as u8) << 1)
                | ((self.authoritative_answer as u8) << 2)
                | (self.opcode << 3)
                | ((self.response as u8) << 7) as u8
        )?;

        buffer.write_u8(
            (self.rescode as u8)
                | ((self.checking_disabled as u8) << 4)
                | ((self.authed_data as u8) << 5)
                | ((self.z as u8) << 6)
                | ((self.recursion_available as u8) << 7)
        )?;

        buffer.write_u16(self.questions)?;
        buffer.write_u16(self.answers)?;
        buffer.write_u16(self.authoritative_entries)?;
        buffer.write_u16(self.resource_entries)?;

        Ok(())
    }

    pub fn binary_len(&self) -> usize {
        12
    }

    pub fn read<T: PacketBuffer>(&mut self, buffer: &mut T) -> Result<()> {
        self.id = buffer.read_u16()?;

        let flags = buffer.read_u16()?;
        let a = (flags >> 8) as u8;
        let b = (flags & 0xFF) as u8;
        self.recursion_desired = (a & (1 << 0)) > 0;
        self.truncated_message = (a & (1 << 1)) > 0;
        self.authoritative_answer = (a & (1 << 2)) > 0;
        self.opcode = (a >> 3) & 0x0F;
        self.response = (a & (1 << 7)) > 0;

        self.rescode = ResultCode::from_num(b & 0x0F);
        self.checking_disabled = (b & (1 << 4)) > 0;
        self.authed_data = (b & (1 << 5)) > 0;
        self.z = (b & (1 << 6)) > 0;
        self.recursion_available = (b & (1 << 7)) > 0;

        self.questions = buffer.read_u16()?;
        self.answers = buffer.read_u16()?;
        self.authoritative_entries = buffer.read_u16()?;
        self.resource_entries = buffer.read_u16()?;

        // Return the constant header size
        Ok(())
    }
}

impl fmt::Display for DnsHeader {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(f, "DnsHeader:")?;
        writeln!(f, "\tid: {0}", self.id)?;

        writeln!(f, "\trecursion_desired: {0}", self.recursion_desired)?;
        writeln!(f, "\ttruncated_message: {0}", self.truncated_message)?;
        writeln!(f, "\tauthoritative_answer: {0}", self.authoritative_answer)?;
        writeln!(f, "\topcode: {0}", self.opcode)?;
        writeln!(f, "\tresponse: {0}", self.response)?;

        writeln!(f, "\trescode: {:?}", self.rescode)?;
        writeln!(f, "\tchecking_disabled: {0}", self.checking_disabled)?;
        writeln!(f, "\tauthed_data: {0}", self.authed_data)?;
        writeln!(f, "\tz: {0}", self.z)?;
        writeln!(f, "\trecursion_available: {0}", self.recursion_available)?;

        writeln!(f, "\tquestions: {0}", self.questions)?;
        writeln!(f, "\tanswers: {0}", self.answers)?;
        writeln!(f, "\tauthoritative_entries: {0}", self.authoritative_entries)?;
        writeln!(f, "\tresource_entries: {0}", self.resource_entries)?;

        Ok(())
    }
}

/// Representation of a DNS question
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DnsQuestion {
    pub name: String,
    pub qtype: QueryType
}

impl DnsQuestion {
    pub fn new(name: String, qtype: QueryType) -> DnsQuestion {
        DnsQuestion { name, qtype }
    }

    pub fn binary_len(&self) -> usize {
        self.name.split('.').map(|x| x.len() + 1).fold(1, |x, y| x + y)
    }

    pub fn write<T: PacketBuffer>(&self, buffer: &mut T) -> Result<()> {
        buffer.write_qname(&self.name)?;

        let typenum = self.qtype.to_num();
        buffer.write_u16(typenum)?;
        buffer.write_u16(1)?;

        Ok(())
    }

    pub fn read<T: PacketBuffer>(&mut self, buffer: &mut T) -> Result<()> {
        buffer.read_qname(&mut self.name)?;
        self.qtype = QueryType::from_num(buffer.read_u16()?); // qtype
        let _ = buffer.read_u16()?; // class

        Ok(())
    }
}

impl fmt::Display for DnsQuestion {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(f, "DnsQuestion:")?;
        writeln!(f, "\tname: {0}", self.name)?;
        writeln!(f, "\trecord type: {:?}", self.qtype)?;

        Ok(())
    }
}

/// Representation of a complete DNS packet
///
/// This is the work horse of the server. A DNS packet can be read and written
/// in a single operation, and is used both by the network facing components and
/// internally by the resolver, cache and authority.
#[derive(Clone, Debug, Default)]
pub struct DnsPacket {
    pub header: DnsHeader,
    pub questions: Vec<DnsQuestion>,
    pub answers: Vec<DnsRecord>,
    pub authorities: Vec<DnsRecord>,
    pub resources: Vec<DnsRecord>
}

impl DnsPacket {
    pub fn new() -> DnsPacket {
        DnsPacket { header: DnsHeader::new(), questions: Vec::new(), answers: Vec::new(), authorities: Vec::new(), resources: Vec::new() }
    }

    pub fn from_buffer<T: PacketBuffer>(buffer: &mut T) -> Result<DnsPacket> {
        let mut result = DnsPacket::new();
        result.header.read(buffer)?;

        for _ in 0..result.header.questions {
            let mut question = DnsQuestion::new("".to_string(), QueryType::UNKNOWN(0));
            question.read(buffer)?;
            result.questions.push(question);
        }

        for _ in 0..result.header.answers {
            let rec = DnsRecord::read(buffer)?;
            result.answers.push(rec);
        }
        for _ in 0..result.header.authoritative_entries {
            let rec = DnsRecord::read(buffer)?;
            result.authorities.push(rec);
        }
        for _ in 0..result.header.resource_entries {
            let rec = DnsRecord::read(buffer)?;
            result.resources.push(rec);
        }

        Ok(result)
    }

    #[allow(dead_code)]
    pub fn print(&self) {
        println!("{}", self.header);

        println!("questions:");
        for x in &self.questions {
            println!("\t{:?}", x);
        }

        println!("answers:");
        for x in &self.answers {
            println!("\t{:?}", x);
        }

        println!("authorities:");
        for x in &self.authorities {
            println!("\t{:?}", x);
        }

        println!("resources:");
        for x in &self.resources {
            println!("\t{:?}", x);
        }
    }

    pub fn get_ttl_from_soa(&self) -> Option<u32> {
        for answer in &self.authorities {
            if let DnsRecord::SOA { minimum, .. } = *answer {
                return Some(minimum);
            }
        }

        None
    }

    pub fn get_random_a(&self) -> Option<String> {
        if !self.answers.is_empty() {
            let idx = random::<usize>() % self.answers.len();
            let a_record = &self.answers[idx];
            if let DnsRecord::A { ref addr, .. } = *a_record {
                return Some(addr.to_string());
            }
        }

        None
    }

    pub fn get_unresolved_cnames(&self, qtype: QueryType) -> Vec<DnsRecord> {
        let mut unresolved = Vec::new();
        for answer in &self.answers {
            let mut matched = false;
            if let DnsRecord::CNAME { ref host, .. } = *answer {
                for answer2 in &self.answers {
                    match qtype {
                        QueryType::A => {
                            if let DnsRecord::A { ref domain, .. } = *answer2 {
                                if domain == host {
                                    matched = true;
                                    break;
                                }
                            }
                        }
                        QueryType::AAAA => {
                            if let DnsRecord::AAAA { ref domain, .. } = *answer2 {
                                if domain == host {
                                    matched = true;
                                    break;
                                }
                            }
                        }
                        _ => {}
                    }
                }
            } else {
                continue;
            }

            if !matched {
                unresolved.push(answer.clone());
            }
        }

        unresolved
    }

    pub fn get_resolved_ns(&self, qname: &str) -> Option<String> {
        let mut new_authorities = Vec::new();
        for auth in &self.authorities {
            if let DnsRecord::NS { ref domain, ref host, .. } = *auth {
                if !qname.ends_with(domain) {
                    continue;
                }

                for rsrc in &self.resources {
                    if let DnsRecord::A { ref domain, ref addr, ttl: TransientTtl(ttl) } = *rsrc {
                        if domain != host {
                            continue;
                        }

                        let rec = DnsRecord::A { domain: host.clone(), addr: *addr, ttl: TransientTtl(ttl) };

                        new_authorities.push(rec);
                    }
                }
            }
        }

        if !new_authorities.is_empty() {
            let idx = random::<usize>() % new_authorities.len();
            if let DnsRecord::A { addr, .. } = new_authorities[idx] {
                return Some(addr.to_string());
            }
        }

        None
    }

    pub fn get_unresolved_ns(&self, qname: &str) -> Option<String> {
        let mut new_authorities = Vec::new();
        for auth in &self.authorities {
            if let DnsRecord::NS { ref domain, ref host, .. } = *auth {
                if !qname.ends_with(domain) {
                    continue;
                }

                new_authorities.push(host);
            }
        }

        if !new_authorities.is_empty() {
            let idx = random::<usize>() % new_authorities.len();
            return Some(new_authorities[idx].clone());
        }

        None
    }

    pub fn write<T: PacketBuffer>(&mut self, buffer: &mut T, max_size: usize) -> Result<()> {
        let mut test_buffer = VectorPacketBuffer::new();

        let mut size = self.header.binary_len();
        for question in &self.questions {
            size += question.binary_len();
            question.write(&mut test_buffer)?;
        }

        let mut record_count = self.answers.len() + self.authorities.len() + self.resources.len();

        for (i, rec) in self.answers.iter().chain(self.authorities.iter()).chain(self.resources.iter()).enumerate() {
            size += rec.write(&mut test_buffer)?;
            if size > max_size {
                record_count = i;
                self.header.truncated_message = true;
                break;
            } else if i < self.answers.len() {
                self.header.answers += 1;
            } else if i < self.answers.len() + self.authorities.len() {
                self.header.authoritative_entries += 1;
            } else {
                self.header.resource_entries += 1;
            }
        }

        self.header.questions = self.questions.len() as u16;

        self.header.write(buffer)?;

        for question in &self.questions {
            question.write(buffer)?;
        }

        for rec in self.answers.iter().chain(self.authorities.iter()).chain(self.resources.iter()).take(record_count) {
            rec.write(buffer)?;
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {

    use super::*;
    use crate::dns::buffer::{PacketBuffer, VectorPacketBuffer};

    #[test]
    fn test_packet() {
        let mut packet = DnsPacket::new();
        packet.header.id = 1337;
        packet.header.response = true;

        packet.questions.push(DnsQuestion::new("google.com".to_string(), QueryType::NS));
        //packet.answers.push(DnsRecord::A("ns1.google.com".to_string(), "127.0.0.1".parse::<Ipv4Addr>().unwrap(), 3600));
        packet.answers.push(DnsRecord::NS {
            domain: "google.com".to_string(),
            host: "ns1.google.com".to_string(),
            ttl: TransientTtl(3600)
        });
        packet.answers.push(DnsRecord::NS {
            domain: "google.com".to_string(),
            host: "ns2.google.com".to_string(),
            ttl: TransientTtl(3600)
        });
        packet.answers.push(DnsRecord::NS {
            domain: "google.com".to_string(),
            host: "ns3.google.com".to_string(),
            ttl: TransientTtl(3600)
        });
        packet.answers.push(DnsRecord::NS {
            domain: "google.com".to_string(),
            host: "ns4.google.com".to_string(),
            ttl: TransientTtl(3600)
        });

        let mut buffer = VectorPacketBuffer::new();
        packet.write(&mut buffer, 0xFFFF).unwrap();

        buffer.seek(0).unwrap();

        let parsed_packet = DnsPacket::from_buffer(&mut buffer).unwrap();

        assert_eq!(packet.questions[0], parsed_packet.questions[0]);
        assert_eq!(packet.answers[0], parsed_packet.answers[0]);
        assert_eq!(packet.answers[1], parsed_packet.answers[1]);
        assert_eq!(packet.answers[2], parsed_packet.answers[2]);
        assert_eq!(packet.answers[3], parsed_packet.answers[3]);
    }
}