use std::convert::TryInto;

#[derive(Debug)]
pub enum DNSOpCode {
    QUERY = 0,
    IQUERY = 1, // obsolete
    STATUS = 2,
    NOTIFY = 4,
    UPDATE = 5,
}

impl From<u16> for DNSOpCode {
    fn from(val: u16) -> Self {
        match val {
            0 => DNSOpCode::QUERY,
            1 => DNSOpCode::IQUERY,
            2 => DNSOpCode::STATUS,
            4 => DNSOpCode::NOTIFY,
            5 => DNSOpCode::UPDATE,
            _ => panic!("KACKE"),
        }
    }
}

// TODO: FIXME: TECHNISCHE SCHULD (alle pubs weg und gucken wie es richtig geht)
#[derive(Debug)]
pub enum DNSRCode {
    NOERROR = 0,
    FORMERR = 1,
    SERVFAIL = 2,
    NXDOMAIN = 3,
    NOTIMP = 4,
    REFUSED = 5,
    XYDOMAIN = 6,
    XYRRSET = 7,
    NXRRSET = 8,
    NOTAUTH = 9,
    NOTINZONE = 10,
}

impl From<u16> for DNSRCode {
    fn from(val: u16) -> Self {
        match val {
            0 => DNSRCode::NOERROR,
            1 => DNSRCode::FORMERR,
            2 => DNSRCode::SERVFAIL,
            3 => DNSRCode::NXDOMAIN,
            4 => DNSRCode::NOTIMP,
            5 => DNSRCode::REFUSED,
            6 => DNSRCode::XYDOMAIN,
            7 => DNSRCode::XYRRSET,
            8 => DNSRCode::NXRRSET,
            9 => DNSRCode::NOTAUTH,
            10 => DNSRCode::NOTINZONE,
            _ => panic!("KACKE"),
        }
    }
}

#[derive(Debug)]
pub struct DNSHeader {
    /// used by the requester to match up replies to outstanding queries
    pub id: u16,
    /// specifies whether this message is a query (false), or a response (true)
    pub qr: bool,
    pub opcode: DNSOpCode,
    /// specifies that the responding name server is an authority for the domain name in question section
    pub aa: bool,
    /// specifies that this message was truncated due to length greater than that permitted on the transmission channel
    pub tc: bool,
    /// it directs the name server to pursue the query recursively
    pub rd: bool,
    /// denotes whether recursive query support is available in the name server
    pub ra: bool,
    /// TODO: add documuentation about this flag
    pub ad: bool,
    /// TODO: add documuentation about this flag
    pub cd: bool,
    pub rcode: DNSRCode,
    /// TODO: add documuentation about this count
    pub qd_zo_count: u16,
    /// TODO: add documuentation about this count
    pub an_pr_count: u16,
    /// TODO: add documuentation about this count
    pub ns_up_count: u16,
    /// TODO: add documuentation about this count
    pub ar_count: u16,
}

#[derive(Debug)]
pub struct DNSQuery {
    pub hdr: DNSHeader,
    pub name: String,
    pub qclass: u16,
    pub qtype: u16,
}

impl DNSHeader {
    const QR_MASK: u16 = 0x0001;
    const OPCODE_MASK: u16 = 0x000e;
    const AA_MASK: u16 = 0x0020;
    const TC_MASK: u16 = 0x0040;
    const RD_MASK: u16 = 0x0080;
    const RA_MASK: u16 = 0x0100;
    const AD_MASK: u16 = 0x0400;
    const CD_MASK: u16 = 0x0800;
    const RCODE_MASK: u16 = 0xf000;

    const OPCODE_OFFSET: u16 = 1;
    const RCODE_OFFSET: u16 = 11;

    pub fn from_udp_datagram(datagram: &[u8]) -> Result<Self, &'static str> {
        if datagram.len() < 11 {
            return Err("Not enough data");
        }

        let id = u16::from_be_bytes((&datagram[..2]).try_into().map_err(|_err| "Invalid id")?);

        let flags = u16::from_be_bytes(
            (&datagram[2..4])
                .try_into()
                .map_err(|_err| "Invalid flags")?,
        );
        let qr = (flags & DNSHeader::QR_MASK) != 0;
        let opcode = DNSOpCode::from((flags & DNSHeader::OPCODE_MASK) >> DNSHeader::OPCODE_OFFSET);
        let aa = (flags & DNSHeader::AA_MASK) != 0;
        let tc = (flags & DNSHeader::TC_MASK) != 0;
        let rd = (flags & DNSHeader::RD_MASK) != 0;
        let ra = (flags & DNSHeader::RA_MASK) != 0;
        let ad = (flags & DNSHeader::AD_MASK) != 0;
        let cd = (flags & DNSHeader::CD_MASK) != 0;
        let rcode = DNSRCode::from((flags & DNSHeader::RCODE_MASK) >> DNSHeader::RCODE_OFFSET);

        let qd_zo_count = u16::from_be_bytes(
            (&datagram[4..6])
                .try_into()
                .map_err(|_err| "Invalid qd_zo_count")?,
        );
        let an_pr_count = u16::from_be_bytes(
            (&datagram[6..8])
                .try_into()
                .map_err(|_err| "Invalid an_pr_count")?,
        );
        let ns_up_count = u16::from_be_bytes(
            (&datagram[8..10])
                .try_into()
                .map_err(|_err| "Invalid ns_up_count")?,
        );
        let ar_count = u16::from_be_bytes(
            (&datagram[10..12])
                .try_into()
                .map_err(|_err| "Invalid ar_count")?,
        );

        Ok(DNSHeader {
            id,
            qr,
            opcode,
            aa,
            tc,
            rd,
            ra,
            ad,
            cd,
            rcode,
            qd_zo_count,
            an_pr_count,
            ns_up_count,
            ar_count,
        })
    }
}