/*-
 * cdns-rs - a simple sync/async DNS query library
 * Copyright (C) 2020  Aleksandr Morozov
 * 
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 *  file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

use std::{fmt, path::Path, net::{IpAddr, Ipv4Addr, Ipv6Addr}, cmp::Ordering};
use std::borrow::Borrow;
use std::hash::{Hash, Hasher};

use crate::{error::*, query_private::QDnsReq, cfg_resolv_parser::ResolveConfigLookup, cfg_host_parser::HostnameEntry};
use crate::internal_error;

use super::cfg_resolv_parser::ResolveConfig;

/// A location on the disk where resolv.conf is located
pub const RESOLV_CFG_PATH: &'static str = "/etc/resolv.conf";

/// A hosts file location on disk
pub const HOST_CFG_PATH: &'static str = "/etc/hosts";

lazy_static!{
    pub static ref RESOLV_CFG_PATH_P: &'static Path = Path::new(RESOLV_CFG_PATH);
    pub static ref HOST_CFG_PATH_P: &'static Path = Path::new(HOST_CFG_PATH);
}

/// A nsswitch location
pub const NSSWITCH_CFG_PATH: &'static str = "/etc/nsswitch.conf";

const IN_ADDR_ARPA: &[u8] = b"\x07in-addr\x04arpa\x00";
const IN_ADDR6_ARPA: &[u8] = b"\x03ip6\x04arpa\x00";

/// Default BIND for IPv4
pub const IPV4_BIND_ALL: IpAddr = IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0));
/// Default BIND for IPv6
pub const IPV6_BIND_ALL: IpAddr = IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));


/// Converts a part of the octec of IP to printable hex i.e valid range is from
/// 0 up to 15 will be converted to 0x30..0x39 and 'a'..'f'.
/// 
/// # Arguments
/// 
/// * `b` - a part of the octec
/// 
/// # Returns
/// 
/// * u8 an ASCII representation
/// 
/// # Throws
/// 
/// Panic when input b >= 16
pub 
fn byte2hexchar(b: u8) -> u8
{
    match b
    {
        0..=9 => return '0' as u8 + b,
        10..=15 => return 'a' as u8 + (b - 10),
        _ => panic!("out of hex range!")
    }
}

/// Converts [IpAddr] to sequence of bytes coded specially for the payload
/// of package.
/// 
/// # Arguments
/// 
/// * `ip` - the argument with IP address
/// 
/// # Returns
/// 
/// * [CDnsResult] with vector of coded data
pub 
fn ip2pkt(ip: &IpAddr) -> CDnsResult<Vec<u8>>
{    
    match *ip
    {
        IpAddr::V4(ref ipv4) =>
            return ipv4_pkt(ipv4),
        IpAddr::V6(ref ipv6) =>
            return ipv6_pkt(ipv6)
    };
}

const MAX_NAME_LEN: usize = 63;

pub 
fn ipv4_pkt(ip: &Ipv4Addr) -> CDnsResult<Vec<u8>>
{    

    // pre allocate space
    let mut out: Vec<u8> = Vec::with_capacity(16 + IN_ADDR_ARPA.len());
    
    let mut octets = ip.octets();
    octets.reverse();

    for oct in octets
    {
        let str_oct = oct.to_string();

        if str_oct.len() > 3
        {
            internal_error!(
                CDnsErrorType::InternalError, 
                "domain component too long, len: '{}' oct: '{}'", 
                str_oct.len(), str_oct
            );
        }

        let ln: u8 = str_oct.len() as u8;

        out.push(ln);
        out.extend(str_oct.as_bytes());
    }

    out.extend(IN_ADDR_ARPA);

    return Ok(out);
}

pub 
fn ipv6_pkt(ip: &Ipv6Addr) -> CDnsResult<Vec<u8>>
{    
    // pre allocate space
    let mut out: Vec<u8> = Vec::with_capacity(32 + IN_ADDR6_ARPA.len());
    
    let mut octets = ip.octets();
    octets.reverse();

    for oct in octets
    {
        let h_oct = byte2hexchar((oct & 0xF0) >> 4);
        //format!("{:x}", (oct & 0xF0) >> 4);
        let l_oct = byte2hexchar(oct & 0x0F);
        //format!("{:x}", oct & 0x0F);

        //let ln: u8 = str_oct.len() as u8;

        out.push(1);
        out.push(l_oct);
        //out.extend(l_oct.as_bytes());
        out.push(1);
        out.push(h_oct);
    }

    out.extend(IN_ADDR6_ARPA);

    return Ok(out);
}

pub 
fn name2pkt(name: &str) -> CDnsResult<Vec<u8>>
{    
    // pre allocate space
    let mut out: Vec<u8> = Vec::with_capacity(name.len() + 2);
    
    for n in name.split(".")
    {
        if n.len() >= MAX_NAME_LEN
        {
            internal_error!(CDnsErrorType::InternalError, "name too long: '{}' in: '{}'", n.len(), name);
        }

        out.push((n.len() & 0xFF) as u8);
        out.extend(n.as_bytes());
    }

    out.push(0);

    return Ok(out);
}


/// A two octet code which specifies the type of the query.
/// TYPE fields are used in resource records.  Note that these types are a
/// subset of QTYPEs.
/// QTYPE fields appear in the question part of a query.  QTYPES are a
/// superset of TYPEs, hence all TYPEs are valid QTYPEs.
#[repr(u16)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum QType
{
    /// 1 a host address
    A = 1,
    /// 2 an authoritative name server
    NS = 2,
    /// 3 a mail destination (Obsolete - use MX)
    MD = 3,
    /// 4 a mail forwarder (Obsolete - use MX)
    MF = 4,
    /// 5 the canonical name for an alias
    CNAME = 5,
    /// 6 marks the start of a zone of authority
    SOA = 6,
    /// 7 a mailbox domain name (EXPERIMENTAL)
    MB = 7,
    /// 8 a mail group member (EXPERIMENTAL)
    MG = 8,
    /// 9 a mail rename domain name (EXPERIMENTAL)
    MR = 9,
    /// 10 a null RR (EXPERIMENTAL)
    NULL = 10,
    /// 11 a well known service description
    WKS = 11,
    /// 12 a domain name pointer
    PTR = 12,
    /// 13 host information
    HINFO = 13,
    /// 14 mailbox or mail list information
    MINFO = 14,
    /// 15 mail exchange
    MX = 15,
    /// 16 text strings
    TXT = 16,
    /// 18 AFS database record 
    AFSDB = 18,
    /// 25 Key record
    KEY = 25,
    /// 28 IPv6 address record
    AAAA = 28,
    /// 37 Certificate records
    CERT = 37,
    /// 43 Delegation signer
    DS = 43,
    /// 46 DNSSEC signature
    RRSIG = 46,
    /// 47 Next Secure record
    NSEC = 47,
    /// DNS Key record
    DNSKEY = 48,
    /// 50 Next Secure record version 3
    NSEC3 = 50,
    /// 51 NSEC3 parameters
    NSEC3PARAM = 51,
    /// 59 Child DS 
    CDS = 59,
    /// 60 Child copy of DNSKEY record, for transfer to parent
    CDNSKEY = 60,
    /// OpenPGP public key record 
    OPENPGPKEY = 61,
    // ---- QTYPE ----
    /// 252 A request for a transfer of an entire zone
    AXFR = 252,
    /// 253 A request for mailbox-related records (MB, MG or MR)
    MAILB = 253,
    /// 254 A request for mail agent RRs (Obsolete - see MX)
    MAILA = 254,
    /// 257 Certification Authority Authorization 
    CAA = 257,
    /// *
    ALL = 255,
    /// 32769 DNSSEC Lookaside Validation record
    DLV = 32769,
}

impl Default for QType
{
    fn default() -> Self 
    {
        return Self::A;    
    }
}


impl Into<u16> for QType
{
    fn into(self) -> u16 
    {
        return self as u16;
    }
}

impl fmt::Display for QType
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
        match *self
        {
            Self::A          => write!(f, "A"),
            Self::NS         => write!(f, "NS"),
            Self::MD         => write!(f, "MD"),
            Self::MF         => write!(f, "MF"),
            Self::CNAME      => write!(f, "CNAME"),
            Self::SOA        => write!(f, "SOA"),
            Self::MB         => write!(f, "MB"),
            Self::MG         => write!(f, "MG"),
            Self::MR         => write!(f, "MR"),
            Self::NULL       => write!(f, "NULL"),
            Self::WKS        => write!(f, "WKS"),
            Self::PTR        => write!(f, "PTR"),
            Self::HINFO      => write!(f, "HINFO"),
            Self::MINFO      => write!(f, "MINFO"),
            Self::MX         => write!(f, "MX"),
            Self::TXT        => write!(f, "TXT"),
            Self::AFSDB      => write!(f, "AFSDB"),
            Self::KEY        => write!(f, "KEY"),
            Self::AAAA       => write!(f, "AAAA"),
            Self::CERT       => write!(f, "CERT"),
            Self::DS         => write!(f, "DS"),
            Self::RRSIG      => write!(f, "RRSIG"),
            Self::NSEC       => write!(f, "NSEC"),
            Self::DNSKEY     => write!(f, "DNSKEY"),
            Self::NSEC3      => write!(f, "NSEC"),
            Self::NSEC3PARAM => write!(f, "NSEC3PARAM"),
            Self::CDS        => write!(f, "CDS"),
            Self::CDNSKEY    => write!(f, "CDNSKEY"),
            Self::OPENPGPKEY => write!(f, "OPENPGPKEY"),
            Self::AXFR       => write!(f, "AXFR"),
            Self::MAILB      => write!(f, "MAILB"),
            Self::MAILA      => write!(f, "MAILA"),
            Self::CAA        => write!(f, "CAA"),
            Self::ALL        => write!(f, "ALL"),
            Self::DLV        => write!(f, "DLV"),
        }
    }
}


impl QType
{
    pub 
    fn ipaddr_match(&self, ip: &IpAddr) -> bool
    {
        match *self
        {
            Self::A => return ip.is_ipv4(),
            Self::AAAA => return ip.is_ipv6(),
            _ => false,
        }
    }

    pub 
    fn u16_to_qtype(value: u16) -> CDnsResult<QType>
    {
        match value
        {
            x if x == Self::AXFR as u16    => return Ok(Self::AXFR),
            x if x == Self::MAILB as u16   => return Ok(Self::MAILB),
            x if x == Self::MAILA as u16   => return Ok(Self::MAILA),
            x if x == Self::ALL as u16     => return Ok(Self::ALL),
            x if x == Self::DLV as u16     => return Ok(Self::DLV),
            _ => return Self::u16_to_type(value),
        }
    }

    pub 
    fn u16_to_type(value: u16) -> CDnsResult<QType>
    {

        match value
        {
            x if x == Self::A as u16            => return Ok(Self::A),
            x if x == Self::NS as u16           => return Ok(Self::NS),
            x if x == Self::MD as u16           => return Ok(Self::MD),
            x if x == Self::MF as u16           => return Ok(Self::MF),
            x if x == Self::CNAME as u16        => return Ok(Self::CNAME),
            x if x == Self::SOA as u16          => return Ok(Self::SOA),
            x if x == Self::MB as u16           => return Ok(Self::MB),
            x if x == Self::MG as u16           => return Ok(Self::MG),
            x if x == Self::MR as u16           => return Ok(Self::MR),
            x if x == Self::NULL as u16         => return Ok(Self::NULL),
            x if x == Self::WKS as u16          => return Ok(Self::WKS),
            x if x == Self::PTR as u16          => return Ok(Self::PTR),
            x if x == Self::HINFO as u16        => return Ok(Self::HINFO),
            x if x == Self::MINFO as u16        => return Ok(Self::MINFO),
            x if x == Self::MX as u16           => return Ok(Self::MX),
            x if x == Self::TXT as u16          => return Ok(Self::TXT),
            x if x == Self::AFSDB as u16        => return Ok(Self::AFSDB),
            x if x == Self::KEY as u16          => return Ok(Self::KEY),
            x if x == Self::AAAA as u16         => return Ok(Self::AAAA),
            x if x == Self::CERT as u16         => return Ok(Self::CERT),
            x if x == Self::DS as u16           => return Ok(Self::DS),
            x if x == Self::RRSIG as u16        => return Ok(Self::RRSIG),
            x if x == Self::NSEC as u16         => return Ok(Self::NSEC),
            x if x == Self::DNSKEY as u16       => return Ok(Self::DNSKEY),
            x if x == Self::NSEC3 as u16        => return Ok(Self::NSEC3),
            x if x == Self::NSEC3PARAM as u16   => return Ok(Self::NSEC3PARAM),
            x if x == Self::CDS as u16          => return Ok(Self::CDS),
            x if x == Self::CDNSKEY as u16      => return Ok(Self::CDNSKEY),
            x if x == Self::OPENPGPKEY as u16   => return Ok(Self::OPENPGPKEY),
            _ => internal_error!(CDnsErrorType::DnsResponse, "unknown request record type: '{}'", value),
        }
    }
}


/// A two octet code that specifies the class of the query.
/// 
/// 
#[repr(u16)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum QClass
{
    /// the Internet 1
    IN = 1,
    /// the CSNET class (Obsolete) 2
    CS = 2,
    /// the CHAOS class 3
    CH = 3,
    /// Hesiod [Dyer 87] 4
    HS = 4,
    
    //  --- QClass
    /// any class 255
    ALL = 255,
}

impl fmt::Display for QClass
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result 
    {
        match *self
        {
            Self::IN  => write!(f, "IN"),
            Self::CS  => write!(f, "CS"),
            Self::CH  => write!(f, "CH"),
            Self::HS  => write!(f, "HS"),
            Self::ALL => write!(f, "ALL"),
        }
    }
}

impl Default for QClass
{
    fn default() -> Self 
    {
        return Self::IN;    
    }
}

impl Into<u16> for QClass
{
    fn into(self) -> u16 
    {
        return self as u16;
    }
}

impl QClass
{
    /// Converts u16 to enum [QClass].
    /// 
    /// QCLASS fields appear in the question part of a query.  QCLASS are a
    /// superset of CLASSes, hence all CLASSes are valid QCLASSes.
    pub 
    fn u16_to_qclass(value: u16) -> CDnsResult<QClass>
    {
        match value
        {
            x if x == QClass::ALL as u16 => return Ok(QClass::ALL),
            _ => Self::u16_to_class(value),
        }
    }

    /// Converts u16 to enum [QClass], but for the response part of a query.
    pub 
    fn u16_to_class(value: u16) -> CDnsResult<QClass>
    {
        match value
        {
            x if x == QClass::IN as u16 => return Ok(QClass::IN),
            x if x == QClass::CS as u16 => return Ok(QClass::CS),
            x if x == QClass::CH as u16 => return Ok(QClass::CH),
            x if x == QClass::HS as u16 => return Ok(QClass::HS),
            _ => internal_error!(CDnsErrorType::DnsResponse, "unknown QCLASS type: '{}'", value),
        }
    }
}

// (req.status & !StatusBits::OPCODE_STANDARD) | ...
// () 

bitflags! {     
    /// Flags  which control the status of th DNS query    
    #[derive(Default, Debug, Copy, Clone, PartialEq, Eq)] 
    pub struct StatusBits: u16  
    {     
        // Pkt type Request/Result R/W    
        /// A request/response bit, when 1 - response
        const QR_RESP           = 0x8000;

        // Request Type (Write only)
        /// a standard query (QUERY) USE inverse to reset
        const OPCODE_STANDARD   = 0x87FF;
        /// an inverse query (IQUERY)
        const OPCODE_IQUERY     = 0x0040;
        /// a server status request (STATUS)
        const OPCODE_STATUS     = 0x0020;
        // reserved for future use 3-15
        // 0x4000 .. 0x0800

        /// AA  Authoritative Answer (Read only)
        /// Authoritative Answer - this bit is valid in responses,
        /// and specifies that the responding name server is an
        /// authority for the domain name in question section.
        const AUTH_ANSWER       = 0x0400;

        /// TrunCation (Read only)
        /// TrunCation - specifies that this message was truncated
        /// due to length greater than that permitted on the transmission channel.
        const TRUN_CATION       = 0x0200;

        /// RD Recursion desired (write only)
        /// Recursion Desired - this bit may be set in a query and
        /// is copied into the response.  If RD is set, it directs
        /// the name server to pursue the query recursively.
        /// Recursive query support is optional.
        const RECURSION_DESIRED = 0x0100;

        /// RA Recursion available (read only)
        /// Recursion Available - this be is set or cleared in a
        /// response, and denotes whether recursive query support is
        /// available in the name server.
        const RECURSION_AVAIL   = 0x0080;

        /// Z Zero reserver
        /// Reserved for future use.  Must be zero in all queries
        /// and responses.
        const RSERVER0          = 0x0040; 

        const ANSWER_AUTHN      = 0x0020; 
        const NON_AUTH_DATA     = 0x0010; 

        // RCODE response code 

        /// No error condition
        const RESP_NOERROR      = 0x0000; 
        /// Format error - The name server was unable to interpret the query.
        const RESP_FORMERR      = 0x0001; 
        /// Server failure - The name server was unable to process this query due to a
        /// problem with the name server.
        const RESP_SERVFAIL     = 0x0002; 
        /// Name Error - Meaningful only for responses from an authoritative name
        /// server, this code signifies that the domain name referenced in the query does
        /// not exist.
        const RESP_NXDOMAIN     = 0x0003;
        /// Not Implemented - The name server does not support the requested kind of query.
        const RESP_NOT_IMPL     = 0x0004; 
        /// Refused - The name server refuses to perform the specified operation for
        /// policy reasons.
        const RESP_REFUSED      = 0x0005; 
        // ..= 0x000F
    }
}

/// An structure for the target in request.
/// Implements From for [IpAddr], [Ipv4Addr], [Ipv6Addr], [str]
/// In case if IP address is in the human readable 'string' format
/// it will be stored as Name. And later the code will try to convert it
/// to IP address before returing as string.
#[derive(Clone, Debug, Hash)]
pub enum QDnsName<'temp>
{
    //Ip(&'temp IpAddr),
    IpV4(&'temp Ipv4Addr),
    IpV6(&'temp Ipv6Addr),
    Name(&'temp str),
}

impl<'temp> QDnsName<'temp>
{
    /// Answers if current type is IpV4.
    /// But does not performs check if Name is an IP in str format
    pub
    fn is_ipv4(&self) -> bool
    {
        match *self
        {
            Self::IpV4(_) => return true,
            _ => return false,
        }
    }

    /// Answers if current type is IpV6.
    /// But does not performs check if Name is an IP in str format
    pub 
    fn is_ipv6(&self) -> bool
    {
        match *self
        {
            Self::IpV6(_) => return true,
            _ => return false,
        }
    }

    /// Answers if current type is IpV4 or IpV6.
    /// But does not performs check if Name is an IP in str format
    pub 
    fn is_ip(&self) -> bool
    {
        match *self
        {
            Self::IpV4(_) => return true,
            Self::IpV6(_) => return true,
            _ => return false,
        }
    }

    /// Returns the type of the IP address version in [QType] format.
    pub 
    fn get_ip_qtype(&self) -> Option<QType>
    {
        match *self
        {
            Self::IpV4(_) => return Some(QType::A),
            Self::IpV6(_) => return Some(QType::AAAA),
            Self::Name(name) =>
            {
                if let Ok(_) = name.parse::<Ipv4Addr>()
                {   
                    return Some(QType::A);
                }
                else if let Ok(_) = name.parse::<Ipv6Addr>()
                {
                    return Some(QType::AAAA);
                }
                else
                {
                    return None;
                }
            }
        }
    }
}

impl<'temp> Eq for QDnsName<'temp> {}

impl<'temp> PartialEq for QDnsName<'temp> 
{
    fn eq(&self, other: &Self) -> bool 
    {
        return self == other;    
    }
}

impl<'temp> PartialEq<str> for QDnsName<'temp> 
{
    fn eq(&self, other: &str) -> bool 
    {
        match *self
        {
            Self::Name(name) => return name == other,
            Self::IpV4(ip) =>
            {
                if let Ok(other_ip) = other.parse::<Ipv4Addr>()
                {   
                    return &other_ip == ip;
                }
                
                return false;
            },
            Self::IpV6(ip) =>
            {
                if let Ok(other_ip) = other.parse::<Ipv6Addr>()
                {
                    return &other_ip == ip;
                }

                return false;
            }
        }
    }
}

impl<'temp> From<&'temp IpAddr> for QDnsName<'temp>
{
    fn from(ip: &'temp IpAddr) -> Self 
    {
        match *ip
        {
            IpAddr::V4(ref ip) => return Self::IpV4(ip),
            IpAddr::V6(ref ip) => return Self::IpV6(ip),
        }
    }
}

impl<'temp> From<&'temp Ipv4Addr> for QDnsName<'temp>
{
    fn from(ip: &'temp Ipv4Addr) -> Self 
    {
        return Self::IpV4(ip);
    }
}

impl<'temp> From<&'temp Ipv6Addr> for QDnsName<'temp>
{
    fn from(ip: &'temp Ipv6Addr) -> Self 
    {
        return Self::IpV6(ip);
    }
}

impl<'temp> From<&'temp str> for QDnsName<'temp>
{
    fn from(name: &'temp str) -> Self 
    {
        return Self::Name(name);
    }
}

impl<'temp> TryInto<Vec<u8>> for QDnsName<'temp>
{
    type Error = CDnsError;
    fn try_into(self) -> Result<Vec<u8>, Self::Error> 
    {
        match self
        {
            Self::IpV4(ip) =>
            {
                return ipv4_pkt(ip);
            },
            Self::IpV6(ip) =>
            {
                return ipv6_pkt(ip);
            },
            Self::Name(name) =>
            {
                if let Ok(ip) = name.parse::<Ipv4Addr>()
                {   
                    return ipv4_pkt(&ip);
                }
                else if let Ok(ip) = name.parse::<Ipv6Addr>()
                {
                    return ipv6_pkt(&ip);
                }
                else
                {
                    return name2pkt(name);
                }
            }
        }
    }
}

impl<'temp> From<&QDnsName<'temp>> for String
{
    fn from(dnsname: &QDnsName<'temp>) -> Self 
    {
        match *dnsname
        {
            QDnsName::IpV4(ip) =>
            {
                return ip.to_string();
            },
            QDnsName::IpV6(ip) =>
            {
                return ip.to_string();
            },
            QDnsName::Name(name) =>
            {
                return name.to_string();
            }
        }
    }
}


impl<'temp> TryFrom<&QDnsName<'temp>> for IpAddr
{
    type Error = CDnsError;
    fn try_from(value: &QDnsName<'temp>) -> Result<Self, Self::Error> 
    {
        match *value
        {
            QDnsName::IpV4(ip) =>
            {
                return Ok(IpAddr::V4(ip.clone()));
            },
            QDnsName::IpV6(ip) =>
            {
                return Ok(IpAddr::V6(ip.clone()));
            },
            QDnsName::Name(name) =>
            {
                if let Ok(ip) = name.parse::<Ipv4Addr>()
                {   
                    return Ok(IpAddr::V4(ip.clone()));
                }
                else if let Ok(ip) = name.parse::<Ipv6Addr>()
                {
                    return Ok(IpAddr::V6(ip.clone()));
                }
                else
                {
                    internal_error!(CDnsErrorType::InternalError, "not ip address!")
                }
            }
        }
    }
}

impl<'temp> TryFrom<QDnsName<'temp>> for IpAddr
{
    type Error = CDnsError;
    fn try_from(value: QDnsName<'temp>) -> Result<Self, Self::Error> 
    {
        match value
        {
            QDnsName::IpV4(ip) =>
            {
                return Ok(IpAddr::V4(ip.clone()));
            },
            QDnsName::IpV6(ip) =>
            {
                return Ok(IpAddr::V6(ip.clone()));
            },
            QDnsName::Name(name) =>
            {
                if let Ok(ip) = name.parse::<Ipv4Addr>()
                {   
                    return Ok(IpAddr::V4(ip.clone()));
                }
                else if let Ok(ip) = name.parse::<Ipv6Addr>()
                {
                    return Ok(IpAddr::V6(ip.clone()));
                }
                else
                {
                    internal_error!(CDnsErrorType::InternalError, "not ip address!")
                }
            }
        }
    }
}


#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct DnsHeader
{
    /// A 16 bit identifier assigned by the program that
    /// generates any kind of query.
    pub id: u16,

    /// Query control flags
    pub status: StatusBits,

    /// an unsigned 16 bit integer specifying the number of
    /// entries in the question section.
    pub qdcount: u16,

    /// an unsigned 16 bit integer specifying the number of
    /// resource records in the answer section.
    pub ancount: u16,

    /// an unsigned 16 bit integer specifying the number of name
    /// server resource records in the authority records
    /// section.
    pub nscount: u16,

    /// an unsigned 16 bit integer specifying the number of
    /// resource records in the additional records section.
    pub arcount: u16,
}


#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct DnsRequestAnswer
{
    /// request header
    pub header: DnsHeader,
    /// Query content
    pub request: DnsRequestPayload,
    /// Resonse section
    pub response: Vec<DnsResponsePayload>,
    /// Additional RR
    pub additional: Vec<DnsResponsePayload>,
    /// Authortative nameservers
    pub authoratives: Vec<DnsResponsePayload>,
}

impl DnsRequestAnswer
{
    /// Validates the content
    /// 
    /// # Arguments
    /// 
    /// * `req` - a request which was sent 
    pub 
    fn verify(&self, req: &DnsRequestHeader) -> CDnsResult<()>
    {
        if self.header.id != req.header.id
        {
            internal_error!(
                CDnsErrorType::DnsResponse, 
                "request and response ID did not match: '{}' != '{}'", 
                req.header.id, self.header.id
            );
        }

        // check if request matches with what we sent previously
        if self.request != req.payload
        {
            internal_error!(CDnsErrorType::DnsResponse, 
                "received request section is different from sent");
        }
        else if req.payload.qtype != QType::ALL
        {
            // check qtype matches requested. (is it correct?)
            if req.payload.qtype != self.request.qtype
            {
                internal_error!(
                    CDnsErrorType::DnsResponse, 
                    "requested QTYPE differ received TYPE: '{}' != '{}'", 
                    req.payload.qtype, 
                    self.request.qtype
                );
            }
        }
        else if self.header.status.contains(StatusBits::TRUN_CATION) == true
        {
            internal_error!(CDnsErrorType::MessageTruncated, 
                "DNS response was truncated, aborting processing");
        }

        return Ok(());
    }

}

#[derive(Clone, Debug, Default)]
pub struct DnsRequestHeader
{
    /// request header
    pub header: DnsHeader,
    /// Query content
    pub payload: DnsRequestPayload,
}

impl Eq for DnsRequestHeader {}

impl PartialEq for DnsRequestHeader
{
    fn eq(&self, other: &DnsRequestHeader) -> bool 
    {
        return self.header.id == other.header.id;
    }
}

impl Ord for DnsRequestHeader 
{
    fn cmp(&self, other: &Self) -> Ordering 
    {
        // Sort in reverse order
        return self.header.id.cmp(&other.header.id);
    }
}

impl PartialOrd for DnsRequestHeader 
{
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> 
    {
        return Some(self.cmp(other));
    }
}

impl Hash for DnsRequestHeader
{
    fn hash<H: Hasher>(&self, state: &mut H) 
    {
        self.header.id.hash(state);
    }
}

impl Borrow<u16> for DnsRequestHeader
{
    fn borrow(&self) -> &u16 
    {
        return &self.header.id;
    }
}



impl DnsRequestHeader
{
    pub 
    fn regenerate_id(&mut self)
    {
        self.header.id = rand::random();
    }

    pub 
    fn get_id(&self) -> u16
    {
        return self.header.id;
    }

    pub 
    fn from_qdns_req(qrec: &QDnsReq, resolvers: &ResolveConfig) -> CDnsResult<Self>
    {
        if resolvers.lookup.contains(ResolveConfigLookup::BIND) == true
        {
            return DnsRequestHeader::construct_lookup(qrec.get_req_name().clone(), *qrec.get_type());
        }
        else
        {
            panic!("QDnsReq::get_header() misuse!");
        };
    }

    pub 
    fn derive(&self) -> Self
    {
        let header = 
            DnsHeader
            {
                id: rand::random(),
                status: self.header.status,
                qdcount: self.header.qdcount,
                ancount: self.header.ancount,
                nscount: self.header.nscount,
                arcount: self.header.arcount,
            };

        return DnsRequestHeader{ header: header, payload: self.payload.clone() };
    }

    /// Constructs the request from input.
    pub
    fn construct_lookup(name: QDnsName, qtype: QType) -> CDnsResult<DnsRequestHeader>
    {
        //let rng = rand::thread_rng();
        // preparing status register
        let mut status: StatusBits = StatusBits::empty();
        status = (status & !StatusBits::OPCODE_STANDARD) | StatusBits::RECURSION_DESIRED;

        // constructing request structure
        let mut req: DnsRequestHeader = DnsRequestHeader{ ..Default::default() };

        req.header.id = rand::random();
        req.header.status = status;
        req.header.qdcount = 1;

        // creating payload request
        req.payload = DnsRequestPayload::new(name.try_into()?, qtype, QClass::IN);

        
        /*let pkt = req.to_bytes().map_err(|e|
            internal_error_map!(CDnsErrorType::InternalError, "{}", e)
        )?;*/

        return Ok(req);
    }

}

/// A request payload with (request) lines.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct DnsRequestPayload
{
    /// a domain name represented as a sequence of labels
    pub qname: Vec<u8>,

    /// a two octet code which specifies the type of the query.
    pub qtype: QType,
    
    /// a two octet code that specifies the class of the query.
    pub qclass: QClass,
}

impl DnsRequestPayload
{
    pub 
    fn new(qname: Vec<u8>, qtype: QType, qclass: QClass) -> Self
    {
        return DnsRequestPayload{ qname: qname, qtype: qtype.into(), qclass: qclass.into() };
    }
}

/// A response section
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct DnsResponsePayload
{
    // A domain name that was queried, in the same format as the QNAME in the question
    pub name: String,
    /// Two octets containing one of th type codes.
    pub dtype: QType,
    /// Two octets which specify the class of the data in the RDATA field
    pub class: QClass,
    /// specifies the time interval that the resource record may be cached before the source
    /// of the information should again be consulted
    pub ttl: i32,
    /// specifies the length in octets of the RDATA field
    pub rdlength: u16,
    /// a variable length string of octets that describes the resource
    pub rdata: DnsRdata,
}

impl DnsResponsePayload
{
    /// Creates a record from [HostnameEntry], but only for types like
    /// A, AAAA, PTR
    pub(crate)
    fn new_local(dtype: QType, data: &HostnameEntry) -> CDnsResult<Vec<Self>>
    {

        match dtype
        {
            QType::A => 
            {
                let mut out: Vec<Self> = Vec::with_capacity(1);

                let ipv4: Ipv4Addr = 
                    if let IpAddr::V4(ipv4) = data.get_ip() 
                    {
                        ipv4.clone()
                    }
                    else
                    {
                        internal_error!(CDnsErrorType::InternalError, "wrong data type");
                    };

                out.push(
                    DnsResponsePayload
                    {
                        name: [data.get_hostnames()[0].as_str(), ".local"].concat(),
                        dtype: dtype,
                        class: QClass::IN,
                        ttl: i32::MAX,
                        rdlength: 0,
                        rdata: DnsRdata::A{ ip: ipv4 },
                    }
                );

                return Ok(out);
            },
            QType::AAAA => 
            {
                let mut out: Vec<Self> = Vec::with_capacity(1);

                let ipv6: Ipv6Addr = 
                    if let IpAddr::V6(ipv6) = data.get_ip() 
                    {
                        ipv6.clone()
                    }
                    else
                    {
                        internal_error!(CDnsErrorType::InternalError, "wrong data type");
                    };

                out.push(
                    DnsResponsePayload
                    {
                        name: [data.get_hostnames()[0].as_str(), ".local"].concat(),
                        dtype: dtype,
                        class: QClass::IN,
                        ttl: i32::MAX,
                        rdlength: 0,
                        rdata: DnsRdata::AAAA{ ip: ipv6 },
                    }
                );

                return Ok(out);
            },
            QType::PTR => 
            {
                let mut out: Vec<Self> = Vec::with_capacity(data.get_hostnames().len());

                // copy all hostnames from the list
                for h in data.get_hostnames_iter()
                {
                    out.push(
                        DnsResponsePayload
                        {
                            name: [data.get_ip().to_string().as_str(), ".local"].concat(),
                            dtype: dtype,
                            class: QClass::IN,
                            ttl: i32::MAX,
                            rdlength: 0,
                            rdata: DnsRdata::PTR{ fqdn: h.clone() },
                        }
                    );
                }
            
                return Ok(out);
            },
            _ => 
            {
                internal_error!(CDnsErrorType::InternalError, "new_local can not be used for types except A, AAAA, PTR");
            }
        }
        
    }
}

/*impl Default for DnsResponsePayload
{
    fn default() -> Self 
    {
        return Self::Empty;    
    }
}*/

impl fmt::Display for DnsResponsePayload
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result 
    {
        write!(f, "{} {} {} {} {}", 
            self.name, self.dtype, self.class, self.ttl, self.rdata)  
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct DnsSoa
{
    /// primary name server
    pub pnm: String, 
    /// responsible authority mailbox
    pub ram: String,
    /// serial number
    pub serial: u32,
    /// refresh interval
    pub interv_refr: u32,
    /// retry interval
    pub interv_retry: u32,
    /// expire limit
    pub expire_limit: u32,
    /// minimum TTL
    pub min_ttl: u32,
}

impl fmt::Display for DnsSoa
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
        writeln!(f, "{} {} {} {} {} {} {}", 
            self.pnm, self.ram, self.serial, self.interv_refr, 
            self.interv_retry, self.expire_limit, self.min_ttl)
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum DnsRdata
{
    None,
    A{ ip: Ipv4Addr },
    NS{ fqdn: String },
    MD{ data: Vec<u8> },
    MF{ data: Vec<u8> },
    CNAME{ fqdn: String },
    SOA{ soa: DnsSoa },
    MB{ data: Vec<u8> },
    MG{ data: Vec<u8> },
    MR{ data: Vec<u8> },
    NULL{ data: Vec<u8> },
    WKS{ data: Vec<u8> },
    PTR{ fqdn: String },
    HINFO{ data: Vec<u8> },
    MX{ preference: u16, exchange: String },
    TXT{ data: Vec<u8> },
    AFSDB{ data: Vec<u8> },
    KEY{ data: Vec<u8> },
    AAAA{ ip: Ipv6Addr },
    CERT{ data: Vec<u8> },
    DS{ data: Vec<u8> },
    RRSIG{ data: Vec<u8> },
    NSEC{ data: Vec<u8> },
    DNSKEY{ data: Vec<u8> },
    NSEC3{ data: Vec<u8> },
    NSEC3PARAM{ data: Vec<u8> },
    CDS{ data: Vec<u8> },
    CDNSKEY{ data: Vec<u8> },
    OPENPGPKEY{ data: Vec<u8> },    
    UNKNOWN{ data: Vec<u8> },
}

impl fmt::Display for DnsRdata
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result 
    {
        match *self
        {
            Self::None => 
                write!(f, "No record"),
            Self::A{ ref ip } => 
                write!(f, "{}", ip),
            Self::NS{ ref fqdn } => 
                write!(f, "{}", fqdn),
            Self::AAAA{ ref ip} => 
                write!(f, "{}", ip),
            Self::MX{ preference, ref exchange } =>
                write!(f, "{} {}", preference, exchange),
            Self::CNAME{ ref fqdn } => 
                write!(f, "{}", fqdn),
            Self::PTR{ ref fqdn } => 
                write!(f, "{}", fqdn),
            Self::SOA{ ref soa } => 
                write!(f, "{}", soa),
            Self::UNKNOWN{ .. } => 
                write!(f, "UNKNOWN"),
            _ => write!(f, "RAW DATA"),
        }
    }
}

impl Default for DnsRdata
{
    fn default() -> Self 
    {
        return Self::None;   
    }
}

impl DnsRdata
{
    pub 
    fn is_some(&self) -> bool
    {
        return *self != Self::None;
    }
}