dyns 0.7.2

use std::{
    convert::TryFrom,
    fmt::Display,
    hash::{Hash, Hasher},
    net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6},
    path::Path,
};

use base64::Engine;
use bytes::BufMut;
use dhttp_identity::certificate::{CertificateChainKey, CertificateSequence};
use dquic::qbase::net::addr::EndpointAddr as DquicEndpointAddr;
use nom::{
    IResult, Parser,
    bytes::streaming::take,
    combinator::{flat_map, map},
    error::{ErrorKind, make_error},
    number::streaming::{be_u8, be_u16, be_u32, be_u128},
};
use rustls::{SignatureScheme, pki_types::SubjectPublicKeyInfoDer};
use snafu::{ResultExt, Snafu};

use crate::core::parser::{
    sigin,
    varint::{VarInt, WriteVarInt, be_varint},
};

#[derive(Debug, Snafu)]
#[snafu(module)]
pub enum SignEndpointError {
    #[snafu(display("failed to sign endpoint address"))]
    Sign {
        source: dhttp_identity::identity::SignError,
    },
    #[snafu(display("no supported signature scheme for endpoint address"))]
    NoSupportedScheme,
}

/// EndpointAddress record (Type E = 266)
///
/// Unified endpoint format that encodes address family, routing, clustering and NAT information
/// in a single flags byte, followed by optional fields.
///
/// ## Wire format
///
/// ```text
/// +-------+-----------------+--------------------+----------------+----------------------------+
/// | flags | sequence(varint)| addr               | load(optional) | signature (optional)       |
/// +-------+-----------------+--------------------+----------------+----------------------------+
/// | u8    | QUIC varint     | see addr layout    | f32            | scheme(u16)+len(varint)+N  |
/// +-------+-----------------+--------------------+----------------+----------------------------+
///
/// addr layout:
/// +---------+-----------------------------------------+
/// | kind    | addr fields                             |
/// +---------+-----------------------------------------+
/// | direct  | port(u16) + IP(u32/u128)                |
/// +---------+-----------------------------------------+
/// | nat     | outer_port(u16) + outer_IP(u32/u128)    |
/// |         | + agent_port(u16) + agent_IP(u32/u128)  |
/// +---------+-----------------------------------------+
/// ```
///
/// ## flags (u8) bit layout (bit 1 = MSB)
///
/// - bit 1 (0x80): FAMILY    — address family: 0=IPv4, 1=IPv6
/// - bit 2 (0x40): MAIN      — primary/backup: 1=primary, 0=backup
/// - bit 3 (0x20): CLUSTERED — multiple hosts share this name; record includes a device sequence number
/// - bit 4 (0x10): NAT       — endpoint is behind NAT; record includes the agent endpoint address
/// - bit 5 (0x08): LOAD      — record carries 1-minute load average (f32)
/// - bit 6 (0x04): reserved
/// - bit 7 (0x02): reserved
/// - bit 8 (0x01): SIGNED    — record carries a publisher key signature to prevent DNS poisoning
///
/// ## Field order
///
/// `flags` → `sequence` (if CLUSTERED) → `addr` → `agent addr` (if NAT) → `load` (if LOAD) → `signature` (if SIGNED)
///
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct EndpointSignature {
    scheme: u16,
    signature: Vec<u8>,
}

#[derive(Debug, Clone)]
pub struct EndpointAddr {
    flags: u8,
    /// Certificate-chain sequence used when multiple hosts share a domain (CLUSTERED).
    /// None means no sequence number.
    sequence: Option<CertificateSequence>,
    /// 1-minute load average (present when LOAD flag is set)
    load: Option<f32>,
    signature: Option<EndpointSignature>,
    /// Primary address (the direct address, or the outer/public address for NAT)
    pub primary: SocketAddr,
    /// Agent address used for NAT traversal (present when NAT flag is set)
    pub agent: Option<SocketAddr>,
}

impl PartialEq for EndpointAddr {
    fn eq(&self, other: &Self) -> bool {
        self.flags == other.flags
            && self.sequence == other.sequence
            && self.load.map(f32::to_bits) == other.load.map(f32::to_bits)
            && self.signature == other.signature
            && self.primary == other.primary
            && self.agent == other.agent
    }
}

impl Eq for EndpointAddr {}

impl Hash for EndpointAddr {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.flags.hash(state);
        self.sequence.hash(state);
        self.load.map(f32::to_bits).hash(state);
        self.signature.hash(state);
        self.primary.hash(state);
        self.agent.hash(state);
    }
}

impl EndpointAddr {
    const FLAG_FAMILY: u8 = 0b1000_0000; // bit 1: 0=IPv4, 1=IPv6
    const FLAG_MAIN: u8 = 0b0100_0000; // bit 2: 1=primary, 0=backup
    const FLAG_CLUSTERED: u8 = 0b0010_0000; // bit 3: multiple hosts share this domain
    const FLAG_NAT: u8 = 0b0001_0000; // bit 4: endpoint is behind NAT, agent address present
    const FLAG_LOAD: u8 = 0b0000_1000; // bit 5: record carries load average
    // bit 6 (0x04): reserved
    // bit 7 (0x02): reserved
    const FLAG_SIGNED: u8 = 0b0000_0001; // bit 8: record carries publisher signature

    pub fn direct_v4(addr: SocketAddrV4) -> Self {
        Self {
            flags: 0, // IPv4 direct: FAMILY=0, NAT=0
            sequence: None,
            load: None,
            signature: None,
            primary: addr.into(),
            agent: None,
        }
    }

    pub fn direct_v6(addr: SocketAddrV6) -> Self {
        Self {
            flags: Self::FLAG_FAMILY, // IPv6 direct: FAMILY=1, NAT=0
            sequence: None,
            load: None,
            signature: None,
            primary: addr.into(),
            agent: None,
        }
    }

    /// Create an IPv4 endpoint that requires NAT traversal.
    /// `outer` is the public address; `agent` is the NAT helper address.
    pub fn nat_v4(outer: SocketAddrV4, agent: SocketAddrV4) -> Self {
        Self {
            flags: Self::FLAG_NAT, // IPv4 NAT: FAMILY=0, NAT=1
            sequence: None,
            load: None,
            signature: None,
            primary: outer.into(),
            agent: Some(agent.into()),
        }
    }

    /// Create an IPv6 endpoint that requires NAT traversal.
    /// `outer` is the public address; `agent` is the NAT helper address.
    pub fn nat_v6(outer: SocketAddrV6, agent: SocketAddrV6) -> Self {
        Self {
            flags: Self::FLAG_FAMILY | Self::FLAG_NAT, // IPv6 NAT: FAMILY=1, NAT=1
            sequence: None,
            load: None,
            signature: None,
            primary: outer.into(),
            agent: Some(agent.into()),
        }
    }

    /// Returns true if the address family is IPv6.
    pub fn is_ipv6(&self) -> bool {
        self.flags & Self::FLAG_FAMILY != 0
    }

    /// Returns true if NAT traversal is required (agent address is present).
    pub fn is_nat(&self) -> bool {
        self.flags & Self::FLAG_NAT != 0
    }

    /// Returns true if this domain maps to a cluster of hosts (sequence number is present).
    pub fn is_clustered(&self) -> bool {
        self.flags & Self::FLAG_CLUSTERED != 0
    }

    /// Returns true if the record carries a load average value.
    pub fn is_load(&self) -> bool {
        self.flags & Self::FLAG_LOAD != 0
    }

    pub fn set_clustered(&mut self, clustered: bool) {
        if clustered {
            self.flags |= Self::FLAG_CLUSTERED;
        } else {
            self.flags &= !Self::FLAG_CLUSTERED;
            self.sequence = None; // clear sequence number
        }
    }

    pub fn set_load(&mut self, load: Option<f32>) {
        self.load = load;
        if self.load.is_some() {
            self.flags |= Self::FLAG_LOAD;
        } else {
            self.flags &= !Self::FLAG_LOAD;
        }
    }

    pub async fn sign_with_authority(
        &mut self,
        authority: &(impl dhttp_identity::identity::LocalAuthority + ?Sized),
    ) -> Result<(), SignEndpointError> {
        self.set_signed(true);
        let data = self.signed_data();

        let scheme = authority
            .cert_chain()
            .first()
            .and_then(|_| sigin::canonical_scheme_for_spki(authority.public_key()))
            .ok_or(SignEndpointError::NoSupportedScheme)?;
        let signature = authority
            .sign(&data)
            .await
            .context(sign_endpoint_error::SignSnafu)?;

        self.signature = Some(EndpointSignature {
            scheme: u16::from(scheme),
            signature,
        });
        Ok(())
    }

    pub fn verify_signature(
        &self,
        spki: SubjectPublicKeyInfoDer<'_>,
    ) -> Result<bool, sigin::VerifyError> {
        let Some(sig) = &self.signature else {
            return Ok(false);
        };
        let data = self.signed_data();
        sigin::verify(
            spki,
            SignatureScheme::from(sig.scheme),
            &data,
            &sig.signature,
        )
    }

    pub fn verify_signature_from_der(&self, cert_der: &[u8]) -> Result<bool, sigin::VerifyError> {
        let (_, cert) = x509_parser::parse_x509_certificate(cert_der).map_err(|e| {
            sigin::VerifyError::InvalidCertificate {
                details: e.to_string(),
            }
        })?;

        let spki = SubjectPublicKeyInfoDer::from(cert.tbs_certificate.subject_pki.raw);
        self.verify_signature(spki)
    }

    pub fn verify_signature_from_pem(&self, cert_pem: &[u8]) -> Result<bool, sigin::VerifyError> {
        let mut reader = std::io::Cursor::new(cert_pem);
        if let Some(item) = rustls_pemfile::certs(&mut reader).next() {
            let cert_der = item.map_err(|e| sigin::VerifyError::InvalidPem { source: e })?;
            return self.verify_signature_from_der(&cert_der);
        }
        Err(sigin::VerifyError::InvalidCertificate {
            details: "No certificate found in PEM".to_string(),
        })
    }

    pub fn verify_signature_from_base64(
        &self,
        cert_base64: &str,
    ) -> Result<bool, sigin::VerifyError> {
        let cert_base64 = cert_base64.trim();
        let cert_der = base64::engine::general_purpose::STANDARD
            .decode(cert_base64)
            .map_err(|e| sigin::VerifyError::InvalidBase64 { source: e })?;
        self.verify_signature_from_der(&cert_der)
    }

    pub fn verify_signature_from_file(
        &self,
        path: impl AsRef<Path>,
    ) -> Result<bool, sigin::VerifyError> {
        let contents = std::fs::read(path).map_err(|e| sigin::VerifyError::Io { source: e })?;
        // Try PEM first
        if let Ok(res) = self.verify_signature_from_pem(&contents) {
            return Ok(res);
        }
        // If PEM failed, try DER
        self.verify_signature_from_der(&contents)
    }

    pub fn is_main(&self) -> bool {
        self.flags() & Self::FLAG_MAIN == Self::FLAG_MAIN
    }

    pub fn set_main(&mut self, is_main: bool) {
        let flags = self.flags_mut();
        if is_main {
            *flags |= Self::FLAG_MAIN;
        } else {
            *flags &= !Self::FLAG_MAIN;
        }
    }

    pub fn is_signed(&self) -> bool {
        self.flags() & Self::FLAG_SIGNED == Self::FLAG_SIGNED
    }

    pub fn set_signed(&mut self, is_signed: bool) {
        let flags = self.flags_mut();
        if is_signed {
            *flags |= Self::FLAG_SIGNED;
        } else {
            *flags &= !Self::FLAG_SIGNED;
        }
    }

    pub fn encpding_size(&self) -> usize {
        let mut meta_len = 1; // flags

        // sequence is only encoded when CLUSTERED flag is set
        if let Some(seq) = &self.sequence {
            meta_len += VarInt::from_u32(seq.get()).encoding_size();
        }

        if self.load.is_some() {
            meta_len += 4; // f32
        }

        if self.is_signed()
            && let Some(sig) = &self.signature
        {
            let sig_len =
                VarInt::try_from(sig.signature.len() as u64).unwrap_or(VarInt::from_u32(0));
            meta_len += 2 + sig_len.encoding_size() + sig.signature.len();
        }

        let addr_len = match (self.is_ipv6(), self.is_nat()) {
            (false, false) => 2 + 4,      // IPv4 direct: port + ipv4
            (false, true) => (2 + 4) * 2, // IPv4 NAT: (port + ipv4) * 2
            (true, false) => 2 + 16,      // IPv6 direct: port + ipv6
            (true, true) => (2 + 16) * 2, // IPv6 NAT: (port + ipv6) * 2
        };

        meta_len + addr_len
    }

    pub fn addr(&self) -> SocketAddr {
        self.primary
    }

    pub fn agent_addr(&self) -> Option<SocketAddr> {
        self.agent
    }

    pub fn sequence(&self) -> Option<CertificateSequence> {
        self.sequence
    }

    pub fn normalized_sequence(&self) -> CertificateSequence {
        self.sequence
            .unwrap_or_else(|| CertificateSequence::from(0u8))
    }

    pub fn set_sequence(&mut self, sequence: CertificateSequence) {
        if sequence.get() > 0 {
            self.sequence = Some(sequence);
            self.set_clustered(true);
        } else {
            self.sequence = None;
            self.set_clustered(false);
        }
    }

    pub fn certificate_chain_key(&self) -> CertificateChainKey {
        if self.is_main() {
            crate::core::certificate::primary_chain_key(self.normalized_sequence())
        } else {
            crate::core::certificate::secondary_chain_key(self.normalized_sequence())
        }
    }

    pub fn load(&self) -> Option<f32> {
        self.load
    }

    fn flags(&self) -> u8 {
        self.flags
    }

    fn flags_mut(&mut self) -> &mut u8 {
        &mut self.flags
    }

    pub fn signature(&self) -> Option<&EndpointSignature> {
        self.signature.as_ref()
    }

    pub fn signature_base64(&self) -> Option<String> {
        self.signature
            .as_ref()
            .map(|sig| base64::engine::general_purpose::STANDARD.encode(&sig.signature))
    }

    fn write_base<B: BufMut>(&self, buf: &mut B) {
        buf.put_u8(self.flags);

        // Sequence is only written when CLUSTERED is set
        if let Some(seq) = &self.sequence {
            buf.put_varint(VarInt::from_u32(seq.get()));
        }

        // Write primary address
        match self.primary {
            SocketAddr::V4(addr) => buf.put_socket_addr_v4(&addr),
            SocketAddr::V6(addr) => buf.put_socket_addr_v6(&addr),
        }

        // Write agent address when NAT traversal is required
        if let Some(agent_addr) = &self.agent {
            match agent_addr {
                SocketAddr::V4(addr) => buf.put_socket_addr_v4(addr),
                SocketAddr::V6(addr) => buf.put_socket_addr_v6(addr),
            }
        }

        if let Some(load) = self.load {
            buf.put_u32(load.to_bits());
        }
    }

    fn signed_data(&self) -> Vec<u8> {
        let mut unsigned = self.clone();
        unsigned.set_signed(true);
        unsigned.signature = None;
        let mut buf = bytes::BytesMut::with_capacity(unsigned.encpding_size());
        unsigned.write_base(&mut buf);
        buf.to_vec()
    }
}

pub(crate) trait WriteEndpointAddr {
    fn put_endpoint_addr(&mut self, endpoint: &EndpointAddr);
}

impl<B: BufMut> WriteEndpointAddr for B {
    fn put_endpoint_addr(&mut self, endpoint: &EndpointAddr) {
        endpoint.write_base(self);
        if endpoint.is_signed()
            && let Some(sig) = endpoint.signature()
        {
            self.put_u16(sig.scheme);
            let len = VarInt::try_from(sig.signature.len() as u64).unwrap_or(VarInt::from_u32(0));
            self.put_varint(len);
            self.put_slice(&sig.signature);
        }
    }
}

pub fn be_endpoint_addr(input: &[u8]) -> nom::IResult<&[u8], EndpointAddr> {
    let (remain, flags) = be_u8(input)?;

    let is_clustered = flags & EndpointAddr::FLAG_CLUSTERED != 0;
    let is_ipv6 = flags & EndpointAddr::FLAG_FAMILY != 0;
    let is_nat = flags & EndpointAddr::FLAG_NAT != 0;
    let has_load = flags & EndpointAddr::FLAG_LOAD != 0;

    // Sequence number is only present when CLUSTERED is set
    let (remain, sequence) = if is_clustered {
        let (remain, seq) = be_varint(remain)?;
        let sequence = match CertificateSequence::try_from(seq.into_inner()) {
            Ok(sequence) => sequence,
            Err(_error) => {
                return Err(nom::Err::Failure(make_error(remain, ErrorKind::TooLarge)));
            }
        };
        (remain, Some(sequence))
    } else {
        (remain, None)
    };

    let (remain, primary) = if is_ipv6 {
        let (remain, addr) = be_socket_addr_v6(remain)?;
        (remain, SocketAddr::V6(addr))
    } else {
        let (remain, addr) = be_socket_addr_v4(remain)?;
        (remain, SocketAddr::V4(addr))
    };

    let (remain, agent) = if is_nat {
        let agent_addr = if is_ipv6 {
            let (remain, addr) = be_socket_addr_v6(remain)?;
            (remain, SocketAddr::V6(addr))
        } else {
            let (remain, addr) = be_socket_addr_v4(remain)?;
            (remain, SocketAddr::V4(addr))
        };
        let (remain, addr) = agent_addr;
        (remain, Some(addr))
    } else {
        (remain, None)
    };

    let (remain, load) = if has_load {
        let (remain, load) = be_u32(remain)?;
        (remain, Some(f32::from_bits(load)))
    } else {
        (remain, None)
    };

    let (remain, signature) = be_endpoint_signature(remain, flags)?;

    Ok((
        remain,
        EndpointAddr {
            flags,
            sequence,
            load,
            signature,
            primary,
            agent,
        },
    ))
}

/// Parse an EndpointAddr with backward compatibility.
///
/// - If `rdlen` matches a legacy fixed length, parse as address-only and fill in default flags.
/// - Otherwise parse as the modern format (with `flags` + optional fields).
///
/// Note: Legacy and modern records differ in their leading bytes.
/// Disambiguation is done via `RDLENGTH` to avoid misinterpreting the port's high byte as `flags`.
pub(crate) fn be_endpoint_addr_compat(
    input: &[u8],
    rdlen: u16,
) -> nom::IResult<&[u8], EndpointAddr> {
    // Check for legacy fixed lengths
    let legacy_lengths = [
        6,  // IPv4 direct: port(2) + ip(4)
        12, // IPv4 NAT:    (port(2) + ip(4)) * 2
        18, // IPv6 direct: port(2) + ip(16)
        36, // IPv6 NAT:    (port(2) + ip(16)) * 2
    ];

    if legacy_lengths.contains(&(rdlen as usize)) {
        // Modern records have variable length, so a valid modern encoding can
        // legitimately be 12, 18, or 36 bytes as well. Prefer a complete
        // modern parse and only fall back to the legacy layout when it fails.
        if let Ok((remaining, endpoint)) = be_endpoint_addr(input)
            && remaining.is_empty()
        {
            return Ok((remaining, endpoint));
        }
        return be_legacy_endpoint_addr_by_length(input, rdlen);
    }

    // Modern format
    be_endpoint_addr(input)
}

/// Parse a legacy EndpointAddr record, identified by its fixed RDLENGTH.
fn be_legacy_endpoint_addr_by_length(
    input: &[u8],
    rdlen: u16,
) -> nom::IResult<&[u8], EndpointAddr> {
    match rdlen {
        6 => {
            // IPv4 direct
            let (remain, addr) = be_socket_addr_v4(input)?;
            Ok((
                remain,
                EndpointAddr {
                    flags: 0,
                    sequence: None,
                    load: None,
                    signature: None,
                    primary: addr.into(),
                    agent: None,
                },
            ))
        }
        12 => {
            // IPv4 NAT
            let (remain, primary) = be_socket_addr_v4(input)?;
            let (remain, agent) = be_socket_addr_v4(remain)?;
            Ok((
                remain,
                EndpointAddr {
                    flags: EndpointAddr::FLAG_NAT,
                    sequence: None,
                    load: None,
                    signature: None,
                    primary: primary.into(),
                    agent: Some(agent.into()),
                },
            ))
        }
        18 => {
            // IPv6 direct
            let (remain, addr) = be_socket_addr_v6(input)?;
            Ok((
                remain,
                EndpointAddr {
                    flags: EndpointAddr::FLAG_FAMILY,
                    sequence: None,
                    load: None,
                    signature: None,
                    primary: addr.into(),
                    agent: None,
                },
            ))
        }
        36 => {
            // IPv6 NAT
            let (remain, primary) = be_socket_addr_v6(input)?;
            let (remain, agent) = be_socket_addr_v6(remain)?;
            Ok((
                remain,
                EndpointAddr {
                    flags: EndpointAddr::FLAG_FAMILY | EndpointAddr::FLAG_NAT,
                    sequence: None,
                    load: None,
                    signature: None,
                    primary: primary.into(),
                    agent: Some(agent.into()),
                },
            ))
        }
        _ => Err(nom::Err::Error(nom::error::make_error(
            input,
            nom::error::ErrorKind::LengthValue,
        ))),
    }
}

fn be_endpoint_signature(input: &[u8], flags: u8) -> IResult<&[u8], Option<EndpointSignature>> {
    if (flags & EndpointAddr::FLAG_SIGNED) != EndpointAddr::FLAG_SIGNED {
        if !input.is_empty() {
            return Err(nom::Err::Error(make_error(input, ErrorKind::Eof)));
        }
        return Ok((input, None));
    }

    let (remain, scheme_u16) = be_u16(input)?;
    let (remain, sig_len) = be_varint(remain)?;
    let sig_len = usize::try_from(sig_len.into_inner())
        .map_err(|_| nom::Err::Error(make_error(remain, ErrorKind::TooLarge)))?;
    let (remain, sig) = take(sig_len)(remain)?;
    Ok((
        remain,
        Some(EndpointSignature {
            scheme: scheme_u16,
            signature: sig.to_vec(),
        }),
    ))
}

pub trait WriteSocketAddr {
    fn put_socket_addr_v4(&mut self, addr: &SocketAddrV4);

    fn put_socket_addr_v6(&mut self, addr: &SocketAddrV6);

    fn put_socket_addr(&mut self, addr: &SocketAddr) {
        match addr {
            SocketAddr::V4(v4) => self.put_socket_addr_v4(v4),
            SocketAddr::V6(v6) => self.put_socket_addr_v6(v6),
        }
    }
}

impl<T: BufMut> WriteSocketAddr for T {
    fn put_socket_addr_v4(&mut self, addr: &SocketAddrV4) {
        self.put_u16(addr.port());
        self.put_u32(u32::from(*addr.ip()));
    }

    fn put_socket_addr_v6(&mut self, addr: &SocketAddrV6) {
        self.put_u16(addr.port());
        self.put_u128(u128::from(*addr.ip()));
    }
}

pub fn be_socket_addr_v4(input: &[u8]) -> IResult<&[u8], SocketAddrV4> {
    flat_map(be_u16, |port| {
        map(be_ipv4_addr, move |ip| SocketAddrV4::new(ip, port))
    })
    .parse(input)
}

pub fn be_socket_addr_v6(input: &[u8]) -> IResult<&[u8], SocketAddrV6> {
    flat_map(be_u16, |port| {
        map(be_ipv6_addr, move |ip| SocketAddrV6::new(ip, port, 0, 0))
    })
    .parse(input)
}

pub fn be_ipv4_addr(input: &[u8]) -> IResult<&[u8], Ipv4Addr> {
    map(be_u32, Ipv4Addr::from).parse(input)
}

pub fn be_ipv6_addr(input: &[u8]) -> IResult<&[u8], Ipv6Addr> {
    map(be_u128, Ipv6Addr::from).parse(input)
}

pub fn be_ip_addr(is_v6: bool) -> impl Fn(&[u8]) -> IResult<&[u8], IpAddr> {
    move |input| match is_v6 {
        true => map(be_u128, |ip| IpAddr::V6(Ipv6Addr::from(ip))).parse(input),
        false => map(be_u32, |ip| IpAddr::V4(Ipv4Addr::from(ip))).parse(input),
    }
}

impl Display for EndpointAddr {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        if let Some(agent_addr) = &self.agent {
            write!(f, "{}-{agent_addr}", self.primary)
        } else {
            write!(f, "{}", self.primary)
        }
    }
}

impl TryFrom<DquicEndpointAddr> for EndpointAddr {
    type Error = ();

    fn try_from(value: DquicEndpointAddr) -> Result<Self, Self::Error> {
        match value {
            DquicEndpointAddr::Direct {
                addr: SocketAddr::V4(addr),
            } => Ok(Self::direct_v4(addr)),
            DquicEndpointAddr::Direct {
                addr: SocketAddr::V6(addr),
            } => Ok(Self::direct_v6(addr)),
            DquicEndpointAddr::Mediate {
                agent: SocketAddr::V4(agent),
                outer: SocketAddr::V4(outer),
            } => Ok(Self::nat_v4(outer, agent)),
            DquicEndpointAddr::Mediate {
                agent: SocketAddr::V6(agent),
                outer: SocketAddr::V6(outer),
            } => Ok(Self::nat_v6(outer, agent)),
            _ => Err(()),
        }
    }
}

impl TryFrom<EndpointAddr> for DquicEndpointAddr {
    type Error = ();

    fn try_from(value: EndpointAddr) -> Result<Self, Self::Error> {
        if let Some(agent_addr) = value.agent {
            match (value.primary, agent_addr) {
                (SocketAddr::V4(outer), SocketAddr::V4(agent)) => Ok(DquicEndpointAddr::Mediate {
                    outer: SocketAddr::V4(outer),
                    agent: SocketAddr::V4(agent),
                }),
                (SocketAddr::V6(outer), SocketAddr::V6(agent)) => Ok(DquicEndpointAddr::Mediate {
                    outer: SocketAddr::V6(outer),
                    agent: SocketAddr::V6(agent),
                }),
                _ => Err(()),
            }
        } else {
            match value.primary {
                SocketAddr::V4(addr) => Ok(DquicEndpointAddr::Direct {
                    addr: SocketAddr::V4(addr),
                }),
                SocketAddr::V6(addr) => Ok(DquicEndpointAddr::Direct {
                    addr: SocketAddr::V6(addr),
                }),
            }
        }
    }
}

pub async fn sign_endponit_address(
    server_id: u8,
    authority: Option<&(impl dhttp_identity::identity::LocalAuthority + ?Sized)>,
    endpoint: DquicEndpointAddr,
) -> Option<EndpointAddr> {
    let mut ep: EndpointAddr = endpoint.try_into().ok()?;
    ep.set_main(server_id == 0);
    ep.set_sequence(CertificateSequence::from(server_id));
    if let Some(authority) = authority {
        let _ = ep.sign_with_authority(authority).await;
    }
    Some(ep)
}

#[cfg(test)]
mod tests {
    use std::{
        net::{Ipv4Addr, Ipv6Addr},
        sync::Arc,
    };

    use bytes::BytesMut;
    use futures::future::BoxFuture;
    use ring::signature::KeyPair;
    use rustls::sign::{Signer, SigningKey};

    use super::*;

    fn v4_outer() -> SocketAddrV4 {
        SocketAddrV4::new(Ipv4Addr::new(203, 0, 113, 10), 4433)
    }

    #[test]
    fn endpoint_certificate_chain_key_normalizes_missing_sequence() {
        let mut endpoint = EndpointAddr::direct_v4(v4_outer());
        endpoint.set_main(true);

        let key = endpoint.certificate_chain_key();

        assert_eq!(key.usage().kind_flag(), "0");
        assert_eq!(key.sequence().get(), 0);
    }

    #[test]
    fn endpoint_certificate_chain_key_uses_present_sequence() {
        let mut endpoint = EndpointAddr::direct_v4(v4_outer());
        endpoint.set_main(false);
        endpoint.set_sequence(
            dhttp_identity::certificate::CertificateSequence::try_from(7u32).unwrap(),
        );

        let key = endpoint.certificate_chain_key();

        assert_eq!(key.usage().kind_flag(), "1");
        assert_eq!(key.sequence().get(), 7);
    }

    #[test]
    fn endpoint_parser_rejects_over_range_certificate_sequence() {
        let sequence = crate::core::parser::varint::VarInt::from_u64(
            dhttp_identity::certificate::CertificateSequence::MAX as u64 + 1,
        )
        .unwrap();
        let mut packet = BytesMut::new();
        packet.put_u8(EndpointAddr::FLAG_MAIN | EndpointAddr::FLAG_CLUSTERED);
        packet.put_varint(sequence);
        packet.put_u16(v4_outer().port());
        packet.put_slice(&v4_outer().ip().octets());

        assert!(be_endpoint_addr(&packet).is_err());
    }

    #[test]
    fn legacy_endpoint_v4_direct_without_meta() {
        let port = 5353u16;
        let ip = Ipv4Addr::new(10, 0, 0, 1);
        let mut buf = BytesMut::new();
        buf.extend_from_slice(&port.to_be_bytes());
        buf.extend_from_slice(&u32::from(ip).to_be_bytes());
        let (remain, decoded) = be_endpoint_addr_compat(&buf, 6).unwrap();
        assert!(remain.is_empty());
        assert_eq!(
            decoded,
            EndpointAddr::direct_v4(SocketAddrV4::new(ip, port))
        );
    }

    #[test]
    fn legacy_endpoint_v4_nat_without_meta() {
        let outer = SocketAddrV4::new(Ipv4Addr::new(10, 0, 0, 1), 1000);
        let agent = SocketAddrV4::new(Ipv4Addr::new(10, 0, 0, 2), 2000);
        let mut buf = BytesMut::new();
        buf.extend_from_slice(&outer.port().to_be_bytes());
        buf.extend_from_slice(&u32::from(*outer.ip()).to_be_bytes());
        buf.extend_from_slice(&agent.port().to_be_bytes());
        buf.extend_from_slice(&u32::from(*agent.ip()).to_be_bytes());
        let (remain, decoded) = be_endpoint_addr_compat(&buf, 12).unwrap();
        assert!(remain.is_empty());
        assert_eq!(decoded, EndpointAddr::nat_v4(outer, agent));
    }

    #[test]
    fn flag_bit_ops_work() {
        let addr = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 5353);
        let mut ep = EndpointAddr {
            flags: 0b0011_0000,
            sequence: None,
            load: None,
            signature: None,
            primary: addr.into(),
            agent: None,
        };

        assert!(!ep.is_main());
        assert!(!ep.is_signed());

        ep.set_main(true);
        assert!(ep.is_main());
        assert_eq!(ep.flags, 0b0111_0000);

        ep.set_signed(true);
        assert!(ep.is_signed());
        assert_eq!(ep.flags, 0b0111_0001);

        ep.set_main(false);
        assert!(!ep.is_main());
        assert!(ep.is_signed());
        assert_eq!(ep.flags, 0b0011_0001);

        ep.set_signed(false);
        assert!(!ep.is_signed());
        assert_eq!(ep.flags, 0b0011_0000);
    }

    #[test]
    fn varint_roundtrip_and_len() {
        fn roundtrip(v: u64) {
            let v = VarInt::from_u64(v).unwrap();
            let mut buf = BytesMut::new();
            buf.put_varint(v);
            assert_eq!(buf.len(), v.encoding_size());
            let (remain, decoded) = be_varint(&buf).unwrap();
            assert!(remain.is_empty());
            assert_eq!(decoded, v);
        }

        for v in [
            0u64,
            1,
            63,
            64,
            16383,
            16384,
            (1 << 30) - 1,
            1 << 30,
            (1 << 62) - 1,
        ] {
            roundtrip(v);
        }
    }

    #[test]
    fn varint_rejects_overflow_and_incomplete() {
        assert!(VarInt::from_u64((1 << 62) + 1).is_err());

        let incomplete = [0b01_000000u8];
        match be_varint(&incomplete) {
            Err(nom::Err::Incomplete(_)) => {}
            other => panic!("expected Incomplete, got {other:?}"),
        }
    }

    #[test]
    fn endpoint_encode_decode_roundtrip() {
        let v4_outer = SocketAddrV4::new(Ipv4Addr::new(10, 0, 0, 1), 1000);
        let v4_agent = SocketAddrV4::new(Ipv4Addr::new(10, 0, 0, 2), 2000);
        let v6_outer = SocketAddrV6::new(Ipv6Addr::LOCALHOST, 3000, 0, 0);
        let v6_agent = SocketAddrV6::new(Ipv6Addr::LOCALHOST, 4000, 0, 0);

        let mut with_load = EndpointAddr::direct_v4(v4_outer);
        with_load.set_load(Some(0.42_f32));

        let cases = vec![
            // IPv4 direct, MAIN + CLUSTERED flags
            EndpointAddr {
                flags: EndpointAddr::FLAG_MAIN | EndpointAddr::FLAG_CLUSTERED,
                sequence: Some(CertificateSequence::from(0u8)),
                load: None,
                signature: None,
                primary: v4_outer.into(),
                agent: None,
            },
            // IPv4 NAT, CLUSTERED flag
            EndpointAddr {
                flags: EndpointAddr::FLAG_NAT | EndpointAddr::FLAG_CLUSTERED,
                sequence: Some(CertificateSequence::try_from(127u32).unwrap()),
                load: None,
                signature: None,
                primary: v4_outer.into(),
                agent: Some(v4_agent.into()),
            },
            // IPv6 direct, MAIN + CLUSTERED flags
            EndpointAddr {
                flags: EndpointAddr::FLAG_FAMILY
                    | EndpointAddr::FLAG_MAIN
                    | EndpointAddr::FLAG_CLUSTERED,
                sequence: Some(CertificateSequence::try_from(128u32).unwrap()),
                load: None,
                signature: None,
                primary: v6_outer.into(),
                agent: None,
            },
            // IPv6 NAT, CLUSTERED flag
            EndpointAddr {
                flags: EndpointAddr::FLAG_FAMILY
                    | EndpointAddr::FLAG_NAT
                    | EndpointAddr::FLAG_CLUSTERED,
                sequence: Some(CertificateSequence::try_from(16_384u32).unwrap()),
                load: None,
                signature: None,
                primary: v6_outer.into(),
                agent: Some(v6_agent.into()),
            },
            // IPv4 direct with LOAD
            with_load,
        ];

        for ep in cases {
            let mut buf = BytesMut::new();
            buf.put_endpoint_addr(&ep);
            assert_eq!(buf.len(), ep.encpding_size());

            let (remain, decoded) = be_endpoint_addr(&buf).unwrap();
            assert!(remain.is_empty());
            assert_eq!(decoded, ep);
        }
    }

    #[test]
    fn compat_parser_does_not_misclassify_modern_lengths_as_legacy() {
        let mut direct = EndpointAddr::direct_v4("203.0.113.10:4433".parse().unwrap());
        direct.set_main(true);
        direct.set_sequence(CertificateSequence::try_from(10u32).unwrap());
        direct.set_load(Some(1.0));

        let mut nat = EndpointAddr::nat_v4(
            "198.51.100.10:4433".parse().unwrap(),
            "192.0.2.10:4433".parse().unwrap(),
        );
        nat.set_main(true);
        nat.set_sequence(CertificateSequence::from(1u8));
        nat.set_load(Some(2.0));

        for endpoint in [direct, nat] {
            let mut buf = BytesMut::new();
            buf.put_endpoint_addr(&endpoint);
            assert!([12, 18].contains(&buf.len()));

            let (remaining, decoded) =
                be_endpoint_addr_compat(&buf, u16::try_from(buf.len()).unwrap()).unwrap();
            assert!(remaining.is_empty());
            assert_eq!(decoded, endpoint);
        }
    }

    #[test]
    fn endpoint_signature_roundtrip_and_verify() {
        #[derive(Debug)]
        struct Ed25519Key {
            keypair: Arc<ring::signature::Ed25519KeyPair>,
            cert_chain: Vec<rustls::pki_types::CertificateDer<'static>>,
        }

        #[derive(Debug)]
        struct Ed25519Signer(Arc<ring::signature::Ed25519KeyPair>);

        impl Signer for Ed25519Signer {
            fn sign(&self, message: &[u8]) -> Result<Vec<u8>, rustls::Error> {
                Ok(self.0.sign(message).as_ref().to_vec())
            }

            fn scheme(&self) -> SignatureScheme {
                SignatureScheme::ED25519
            }
        }

        impl SigningKey for Ed25519Key {
            fn choose_scheme(&self, offered: &[SignatureScheme]) -> Option<Box<dyn Signer>> {
                offered
                    .contains(&SignatureScheme::ED25519)
                    .then(|| Box::new(Ed25519Signer(self.keypair.clone())) as Box<dyn Signer>)
            }

            fn algorithm(&self) -> rustls::SignatureAlgorithm {
                rustls::SignatureAlgorithm::ED25519
            }
        }

        impl dhttp_identity::identity::LocalAuthority for Ed25519Key {
            fn name(&self) -> &str {
                "authority.example"
            }

            fn cert_chain(&self) -> &[rustls::pki_types::CertificateDer<'static>] {
                &self.cert_chain
            }

            fn sign(
                &self,
                data: &[u8],
            ) -> BoxFuture<'_, Result<Vec<u8>, dhttp_identity::identity::SignError>> {
                let result = dhttp_identity::identity::sign_with_key(self, data);
                Box::pin(std::future::ready(result))
            }
        }

        let rng = ring::rand::SystemRandom::new();
        let pkcs8 = ring::signature::Ed25519KeyPair::generate_pkcs8(&rng).unwrap();
        let keypair =
            Arc::new(ring::signature::Ed25519KeyPair::from_pkcs8(pkcs8.as_ref()).unwrap());
        let mut spki = Vec::with_capacity(44);
        spki.extend_from_slice(&[
            0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x70, 0x03, 0x21, 0x00,
        ]);
        spki.extend_from_slice(keypair.public_key().as_ref());
        let key = Ed25519Key {
            keypair: keypair.clone(),
            cert_chain: vec![rustls::pki_types::CertificateDer::from(spki.clone())],
        };

        let addr = SocketAddrV4::new(Ipv4Addr::new(10, 0, 0, 1), 5353);
        let mut ep = EndpointAddr::direct_v4(addr);
        ep.set_main(true);
        futures::executor::block_on(ep.sign_with_authority(&key)).unwrap();

        let mut buf = BytesMut::new();
        buf.put_endpoint_addr(&ep);
        assert_eq!(buf.len(), ep.encpding_size());

        let (remain, decoded) = be_endpoint_addr(&buf).unwrap();
        assert!(remain.is_empty());
        assert!(decoded.is_signed());
        assert!(decoded.signature().is_some());
        assert!(
            decoded
                .verify_signature(SubjectPublicKeyInfoDer::from(spki.as_slice()))
                .unwrap()
        );

        let mut tampered = decoded.clone();
        tampered.set_main(false);
        assert!(
            !tampered
                .verify_signature(SubjectPublicKeyInfoDer::from(spki.as_slice()))
                .unwrap()
        );
    }

    #[test]
    fn sign_with_authority_uses_canonical_scheme_from_public_key() {
        #[derive(Debug)]
        struct Ed25519Authority {
            cert_chain: Vec<rustls::pki_types::CertificateDer<'static>>,
        }

        impl dhttp_identity::identity::LocalAuthority for Ed25519Authority {
            fn name(&self) -> &str {
                "authority.example"
            }

            fn cert_chain(&self) -> &[rustls::pki_types::CertificateDer<'static>] {
                &self.cert_chain
            }

            fn sign(
                &self,
                _data: &[u8],
            ) -> BoxFuture<'_, Result<Vec<u8>, dhttp_identity::identity::SignError>> {
                Box::pin(async move { Ok(vec![1, 2, 3]) })
            }
        }

        let cert_chain = vec![rustls::pki_types::CertificateDer::from(vec![
            0x30, 0x2a, 0x30, 0x05, 0x06, 0x03, 0x2b, 0x65, 0x70, 0x03, 0x21, 0x00, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        ])];
        let mut ep = EndpointAddr::direct_v4(SocketAddrV4::new(Ipv4Addr::LOCALHOST, 5353));
        futures::executor::block_on(ep.sign_with_authority(&Ed25519Authority { cert_chain }))
            .unwrap();

        let signature = ep.signature().unwrap();
        assert_eq!(
            SignatureScheme::from(signature.scheme),
            SignatureScheme::ED25519
        );
        assert_eq!(signature.signature, vec![1, 2, 3]);
    }

    #[test]
    fn optional_fields_flags_follow_values() {
        let addr = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 5353);
        let mut ep = EndpointAddr::direct_v4(addr);

        assert!(!ep.is_load());

        ep.set_load(Some(0.5_f32));

        assert!(ep.is_load());
        assert_eq!(ep.load(), Some(0.5_f32));

        ep.set_load(None);

        assert!(!ep.is_load());
        assert_eq!(ep.load(), None);
    }
}