use std::{any::Any, convert::TryInto, io, str, sync::Arc};

use bytes::BytesMut;
use ring::aead;
pub use rustls::Error;
use rustls::{
    self,
    quic::{
        ClientQuicExt, HeaderProtectionKey, KeyChange, PacketKey, QuicExt, Secrets, ServerQuicExt,
        Version,
    },
    Connection,
};

use crate::{
    crypto::{
        self, CryptoError, ExportKeyingMaterialError, HeaderKey, KeyPair, Keys, UnsupportedVersion,
    },
    transport_parameters::TransportParameters,
    ConnectError, ConnectionId, Side, TransportError, TransportErrorCode,
};

/// A rustls TLS session
pub struct TlsSession {
    version: Version,
    got_handshake_data: bool,
    next_secrets: Option<Secrets>,
    inner: Connection,
}

impl TlsSession {
    fn side(&self) -> Side {
        match self.inner {
            Connection::Client(_) => Side::Client,
            Connection::Server(_) => Side::Server,
        }
    }
}

impl crypto::Session for TlsSession {
    fn initial_keys(&self, dst_cid: &ConnectionId, side: Side) -> Keys {
        initial_keys(self.version, dst_cid, side)
    }

    fn handshake_data(&self) -> Option<Box<dyn Any>> {
        if !self.got_handshake_data {
            return None;
        }
        Some(Box::new(HandshakeData {
            protocol: self.inner.alpn_protocol().map(|x| x.into()),
            server_name: match self.inner {
                Connection::Client(_) => None,
                Connection::Server(ref session) => session.sni_hostname().map(|x| x.into()),
            },
        }))
    }

    fn peer_identity(&self) -> Option<Box<dyn Any>> {
        self.inner
            .peer_certificates()
            .map(|v| -> Box<dyn Any> { Box::new(v.to_vec()) })
    }

    fn early_crypto(&self) -> Option<(Box<dyn HeaderKey>, Box<dyn crypto::PacketKey>)> {
        let keys = self.inner.zero_rtt_keys()?;
        Some((Box::new(keys.header), Box::new(keys.packet)))
    }

    fn early_data_accepted(&self) -> Option<bool> {
        match self.inner {
            Connection::Client(ref session) => Some(session.is_early_data_accepted()),
            _ => None,
        }
    }

    fn is_handshaking(&self) -> bool {
        self.inner.is_handshaking()
    }

    fn read_handshake(&mut self, buf: &[u8]) -> Result<bool, TransportError> {
        self.inner.read_hs(buf).map_err(|e| {
            if let Some(alert) = self.inner.alert() {
                TransportError {
                    code: TransportErrorCode::crypto(alert.get_u8()),
                    frame: None,
                    reason: e.to_string(),
                }
            } else {
                TransportError::PROTOCOL_VIOLATION(format!("TLS error: {}", e))
            }
        })?;
        if !self.got_handshake_data {
            // Hack around the lack of an explicit signal from rustls to reflect ClientHello being
            // ready on incoming connections, or ALPN negotiation completing on outgoing
            // connections.
            let have_server_name = match self.inner {
                Connection::Client(_) => false,
                Connection::Server(ref session) => session.sni_hostname().is_some(),
            };
            if self.inner.alpn_protocol().is_some() || have_server_name || !self.is_handshaking() {
                self.got_handshake_data = true;
                return Ok(true);
            }
        }
        Ok(false)
    }

    fn transport_parameters(&self) -> Result<Option<TransportParameters>, TransportError> {
        match self.inner.quic_transport_parameters() {
            None => Ok(None),
            Some(buf) => match TransportParameters::read(self.side(), &mut io::Cursor::new(buf)) {
                Ok(params) => Ok(Some(params)),
                Err(e) => Err(e.into()),
            },
        }
    }

    fn write_handshake(&mut self, buf: &mut Vec<u8>) -> Option<Keys> {
        let keys = match self.inner.write_hs(buf)? {
            KeyChange::Handshake { keys } => keys,
            KeyChange::OneRtt { keys, next } => {
                self.next_secrets = Some(next);
                keys
            }
        };

        Some(Keys {
            header: KeyPair {
                local: Box::new(keys.local.header),
                remote: Box::new(keys.remote.header),
            },
            packet: KeyPair {
                local: Box::new(keys.local.packet),
                remote: Box::new(keys.remote.packet),
            },
        })
    }

    fn next_1rtt_keys(&mut self) -> Option<KeyPair<Box<dyn crypto::PacketKey>>> {
        let secrets = self.next_secrets.as_mut()?;
        let keys = secrets.next_packet_keys();
        Some(KeyPair {
            local: Box::new(keys.local),
            remote: Box::new(keys.remote),
        })
    }

    fn is_valid_retry(&self, orig_dst_cid: &ConnectionId, header: &[u8], payload: &[u8]) -> bool {
        let tag_start = match payload.len().checked_sub(16) {
            Some(x) => x,
            None => return false,
        };

        let mut pseudo_packet =
            Vec::with_capacity(header.len() + payload.len() + orig_dst_cid.len() + 1);
        pseudo_packet.push(orig_dst_cid.len() as u8);
        pseudo_packet.extend_from_slice(orig_dst_cid);
        pseudo_packet.extend_from_slice(header);
        let tag_start = tag_start + pseudo_packet.len();
        pseudo_packet.extend_from_slice(payload);

        let (nonce, key) = match self.version {
            Version::V1 => (RETRY_INTEGRITY_NONCE_V1, RETRY_INTEGRITY_KEY_V1),
            Version::V1Draft => (RETRY_INTEGRITY_NONCE_DRAFT, RETRY_INTEGRITY_KEY_DRAFT),
            _ => unreachable!(),
        };

        let nonce = aead::Nonce::assume_unique_for_key(nonce);
        let key = aead::LessSafeKey::new(aead::UnboundKey::new(&aead::AES_128_GCM, &key).unwrap());

        let (aad, tag) = pseudo_packet.split_at_mut(tag_start);
        key.open_in_place(nonce, aead::Aad::from(aad), tag).is_ok()
    }

    fn export_keying_material(
        &self,
        output: &mut [u8],
        label: &[u8],
        context: &[u8],
    ) -> Result<(), ExportKeyingMaterialError> {
        self.inner
            .export_keying_material(output, label, Some(context))
            .map_err(|_| ExportKeyingMaterialError)
    }
}

const RETRY_INTEGRITY_KEY_DRAFT: [u8; 16] = [
    0xcc, 0xce, 0x18, 0x7e, 0xd0, 0x9a, 0x09, 0xd0, 0x57, 0x28, 0x15, 0x5a, 0x6c, 0xb9, 0x6b, 0xe1,
];
const RETRY_INTEGRITY_NONCE_DRAFT: [u8; 12] = [
    0xe5, 0x49, 0x30, 0xf9, 0x7f, 0x21, 0x36, 0xf0, 0x53, 0x0a, 0x8c, 0x1c,
];

const RETRY_INTEGRITY_KEY_V1: [u8; 16] = [
    0xbe, 0x0c, 0x69, 0x0b, 0x9f, 0x66, 0x57, 0x5a, 0x1d, 0x76, 0x6b, 0x54, 0xe3, 0x68, 0xc8, 0x4e,
];
const RETRY_INTEGRITY_NONCE_V1: [u8; 12] = [
    0x46, 0x15, 0x99, 0xd3, 0x5d, 0x63, 0x2b, 0xf2, 0x23, 0x98, 0x25, 0xbb,
];

impl crypto::HeaderKey for HeaderProtectionKey {
    fn decrypt(&self, pn_offset: usize, packet: &mut [u8]) {
        let (header, sample) = packet.split_at_mut(pn_offset + 4);
        let (first, rest) = header.split_at_mut(1);
        let pn_end = Ord::min(pn_offset + 3, rest.len());
        self.decrypt_in_place(
            &sample[..self.sample_size()],
            &mut first[0],
            &mut rest[pn_offset - 1..pn_end],
        )
        .unwrap();
    }

    fn encrypt(&self, pn_offset: usize, packet: &mut [u8]) {
        let (header, sample) = packet.split_at_mut(pn_offset + 4);
        let (first, rest) = header.split_at_mut(1);
        let pn_end = Ord::min(pn_offset + 3, rest.len());
        self.encrypt_in_place(
            &sample[..self.sample_size()],
            &mut first[0],
            &mut rest[pn_offset - 1..pn_end],
        )
        .unwrap();
    }

    fn sample_size(&self) -> usize {
        self.sample_len()
    }
}

/// Authentication data for (rustls) TLS session
pub struct HandshakeData {
    /// The negotiated application protocol, if ALPN is in use
    ///
    /// Guaranteed to be set if a nonempty list of protocols was specified for this connection.
    pub protocol: Option<Vec<u8>>,
    /// The server name specified by the client, if any
    ///
    /// Always `None` for outgoing connections
    pub server_name: Option<String>,
}

impl crypto::ClientConfig for rustls::ClientConfig {
    fn start_session(
        self: Arc<Self>,
        version: u32,
        server_name: &str,
        params: &TransportParameters,
    ) -> Result<Box<dyn crypto::Session>, ConnectError> {
        let version = interpret_version(version)?;
        Ok(Box::new(TlsSession {
            version,
            got_handshake_data: false,
            next_secrets: None,
            inner: Connection::Client(
                rustls::ClientConnection::new_quic(
                    self,
                    version,
                    server_name
                        .try_into()
                        .map_err(|_| ConnectError::InvalidDnsName(server_name.into()))?,
                    to_vec(params),
                )
                .unwrap(),
            ),
        }))
    }
}

impl crypto::ServerConfig for rustls::ServerConfig {
    fn start_session(
        self: Arc<Self>,
        version: u32,
        params: &TransportParameters,
    ) -> Box<dyn crypto::Session> {
        let version = interpret_version(version).unwrap();
        Box::new(TlsSession {
            version,
            got_handshake_data: false,
            next_secrets: None,
            inner: Connection::Server(
                rustls::ServerConnection::new_quic(self, version, to_vec(params)).unwrap(),
            ),
        })
    }

    fn initial_keys(
        &self,
        version: u32,
        dst_cid: &ConnectionId,
        side: Side,
    ) -> Result<Keys, UnsupportedVersion> {
        let version = interpret_version(version)?;
        Ok(initial_keys(version, dst_cid, side))
    }

    fn retry_tag(&self, version: u32, orig_dst_cid: &ConnectionId, packet: &[u8]) -> [u8; 16] {
        let version = interpret_version(version).unwrap();
        let (nonce, key) = match version {
            Version::V1 => (RETRY_INTEGRITY_NONCE_V1, RETRY_INTEGRITY_KEY_V1),
            Version::V1Draft => (RETRY_INTEGRITY_NONCE_DRAFT, RETRY_INTEGRITY_KEY_DRAFT),
            _ => unreachable!(),
        };

        let mut pseudo_packet = Vec::with_capacity(packet.len() + orig_dst_cid.len() + 1);
        pseudo_packet.push(orig_dst_cid.len() as u8);
        pseudo_packet.extend_from_slice(orig_dst_cid);
        pseudo_packet.extend_from_slice(packet);

        let nonce = aead::Nonce::assume_unique_for_key(nonce);
        let key = aead::LessSafeKey::new(aead::UnboundKey::new(&aead::AES_128_GCM, &key).unwrap());

        let tag = key
            .seal_in_place_separate_tag(nonce, aead::Aad::from(pseudo_packet), &mut [])
            .unwrap();
        let mut result = [0; 16];
        result.copy_from_slice(tag.as_ref());
        result
    }
}

fn to_vec(params: &TransportParameters) -> Vec<u8> {
    let mut bytes = Vec::new();
    params.write(&mut bytes);
    bytes
}

pub(crate) fn initial_keys(version: Version, dst_cid: &ConnectionId, side: Side) -> Keys {
    let keys = rustls::quic::Keys::initial(version, dst_cid, side.is_client());
    Keys {
        header: KeyPair {
            local: Box::new(keys.local.header),
            remote: Box::new(keys.remote.header),
        },
        packet: KeyPair {
            local: Box::new(keys.local.packet),
            remote: Box::new(keys.remote.packet),
        },
    }
}

impl crypto::PacketKey for PacketKey {
    fn encrypt(&self, packet: u64, buf: &mut [u8], header_len: usize) {
        let (header, payload_tag) = buf.split_at_mut(header_len);
        let (payload, tag_storage) = payload_tag.split_at_mut(payload_tag.len() - self.tag_len());
        let tag = self.encrypt_in_place(packet, &*header, payload).unwrap();
        tag_storage.copy_from_slice(tag.as_ref());
    }

    fn decrypt(
        &self,
        packet: u64,
        header: &[u8],
        payload: &mut BytesMut,
    ) -> Result<(), CryptoError> {
        let plain = self
            .decrypt_in_place(packet, header, payload.as_mut())
            .map_err(|_| CryptoError)?;
        let plain_len = plain.len();
        payload.truncate(plain_len);
        Ok(())
    }

    fn tag_len(&self) -> usize {
        self.tag_len()
    }

    fn confidentiality_limit(&self) -> u64 {
        self.confidentiality_limit()
    }

    fn integrity_limit(&self) -> u64 {
        self.integrity_limit()
    }
}

/// Initialize a sane QUIC-compatible TLS client configuration
///
/// QUIC requires that TLS 1.3 be enabled. Advanced users can use any [`rustls::ClientConfig`] that
/// satisfies this requirement.
pub(crate) fn client_config(roots: rustls::RootCertStore) -> rustls::ClientConfig {
    let mut cfg = rustls::ClientConfig::builder()
        .with_safe_default_cipher_suites()
        .with_safe_default_kx_groups()
        .with_protocol_versions(&[&rustls::version::TLS13])
        .unwrap()
        .with_root_certificates(roots)
        .with_no_client_auth();
    cfg.enable_early_data = true;
    cfg
}

/// Initialize a sane QUIC-compatible TLS server configuration
///
/// QUIC requires that TLS 1.3 be enabled, and that the maximum early data size is either 0 or
/// `u32::MAX`. Advanced users can use any [`rustls::ServerConfig`] that satisfies these
/// requirements.
pub(crate) fn server_config(
    cert_chain: Vec<rustls::Certificate>,
    key: rustls::PrivateKey,
) -> Result<rustls::ServerConfig, Error> {
    let mut cfg = rustls::ServerConfig::builder()
        .with_safe_default_cipher_suites()
        .with_safe_default_kx_groups()
        .with_protocol_versions(&[&rustls::version::TLS13])
        .unwrap()
        .with_no_client_auth()
        .with_single_cert(cert_chain, key)?;
    cfg.max_early_data_size = u32::MAX;
    Ok(cfg)
}

fn interpret_version(version: u32) -> Result<Version, UnsupportedVersion> {
    match version {
        0xff00_001d..=0xff00_0020 => Ok(Version::V1Draft),
        0x0000_0001 | 0xff00_0021..=0xff00_0022 => Ok(Version::V1),
        _ => Err(UnsupportedVersion),
    }
}