use session::{Session, SessionCommon};
use keylog::{KeyLog, NoKeyLog};
use suites::{SupportedCipherSuite, ALL_CIPHERSUITES};
use msgs::enums::{ContentType, SignatureScheme};
use msgs::enums::{AlertDescription, HandshakeType, ProtocolVersion};
use msgs::handshake::{ServerExtension, SessionID};
use msgs::message::Message;
use error::TLSError;
use sign;
use verify;
use key;
use vecbuf::WriteV;

use webpki;

use std::sync::Arc;
use std::io;
use std::fmt;

mod hs;
mod common;
pub mod handy;

/// A trait for the ability to generate Session IDs, and store
/// server session data. The keys and values are opaque.
///
/// Both the keys and values should be treated as
/// **highly sensitive data**, containing enough key material
/// to break all security of the corresponding session.
///
/// `put` is a mutating operation; this isn't expressed
/// in the type system to allow implementations freedom in
/// how to achieve interior mutability.  `Mutex` is a common
/// choice.
pub trait StoresServerSessions : Send + Sync {
    /// Generate a session ID.
    fn generate(&self) -> SessionID;

    /// Store session secrets encoded in `value` against key `id`,
    /// overwrites any existing value against `id`.  Returns `true`
    /// if the value was stored.
    fn put(&self, key: Vec<u8>, value: Vec<u8>) -> bool;

    /// Find a session with the given `id`.  Return it, or None
    /// if it doesn't exist.
    fn get(&self, key: &[u8]) -> Option<Vec<u8>>;
}

/// A trait for the ability to encrypt and decrypt tickets.
pub trait ProducesTickets : Send + Sync {
    /// Returns true if this implementation will encrypt/decrypt
    /// tickets.  Should return false if this is a dummy
    /// implementation: the server will not send the SessionTicket
    /// extension and will not call the other functions.
    fn enabled(&self) -> bool;

    /// Returns the lifetime in seconds of tickets produced now.
    /// The lifetime is provided as a hint to clients that the
    /// ticket will not be useful after the given time.
    ///
    /// This lifetime must be implemented by key rolling and
    /// erasure, *not* by storing a lifetime in the ticket.
    ///
    /// The objective is to limit damage to forward secrecy caused
    /// by tickets, not just limiting their lifetime.
    fn get_lifetime(&self) -> u32;

    /// Encrypt and authenticate `plain`, returning the resulting
    /// ticket.  Return None if `plain` cannot be encrypted for
    /// some reason: an empty ticket will be sent and the connection
    /// will continue.
    fn encrypt(&self, plain: &[u8]) -> Option<Vec<u8>>;

    /// Decrypt `cipher`, validating its authenticity protection
    /// and recovering the plaintext.  `cipher` is fully attacker
    /// controlled, so this decryption must be side-channel free,
    /// panic-proof, and otherwise bullet-proof.  If the decryption
    /// fails, return None.
    fn decrypt(&self, cipher: &[u8]) -> Option<Vec<u8>>;
}

/// How to choose a certificate chain and signing key for use
/// in server authentication.
pub trait ResolvesServerCert : Send + Sync {
    /// Choose a certificate chain and matching key given any server DNS
    /// name provided via SNI, and signature schemes.
    ///
    /// The certificate chain is returned as a vec of `Certificate`s,
    /// the key is inside a `SigningKey`.
    fn resolve(&self,
               server_name: Option<webpki::DNSNameRef>,
               sigschemes: &[SignatureScheme])
               -> Option<sign::CertifiedKey>;
}

/// Common configuration for a set of server sessions.
///
/// Making one of these can be expensive, and should be
/// once per process rather than once per connection.
#[derive(Clone)]
pub struct ServerConfig {
    /// List of ciphersuites, in preference order.
    pub ciphersuites: Vec<&'static SupportedCipherSuite>,

    /// Ignore the client's ciphersuite order. Instead,
    /// choose the top ciphersuite in the server list
    /// which is supported by the client.
    pub ignore_client_order: bool,

    /// Our MTU.  If None, we don't limit TLS message sizes.
    pub mtu: Option<usize>,

    /// How to store client sessions.
    pub session_storage: Arc<StoresServerSessions + Send + Sync>,

    /// How to produce tickets.
    pub ticketer: Arc<ProducesTickets>,

    /// How to choose a server cert and key.
    pub cert_resolver: Arc<ResolvesServerCert>,

    /// Protocol names we support, most preferred first.
    /// If empty we don't do ALPN at all.
    pub alpn_protocols: Vec<String>,

    /// Supported protocol versions, in no particular order.
    /// The default is all supported versions.
    pub versions: Vec<ProtocolVersion>,

    /// How to verify client certificates.
    verifier: Arc<verify::ClientCertVerifier>,

    /// How to output key material for debugging.  The default
    /// does nothing.
    pub key_log: Arc<KeyLog>,
}

impl ServerConfig {
    /// Make a `ServerConfig` with a default set of ciphersuites,
    /// no keys/certificates, and no ALPN protocols.  Session resumption
    /// is enabled by storing up to 256 recent sessions in memory. Tickets are
    /// disabled.
    ///
    /// Publicly-available web servers on the internet generally don't do client
    /// authentication; for this use case, `client_cert_verifier` should be a
    /// `NoClientAuth`. Otherwise, use `AllowAnyAuthenticatedClient` or another
    /// implementation to enforce client authentication.
    ///
    /// We don't provide a default for `client_cert_verifier` because the safest
    /// default, requiring client authentication, requires additional
    /// configuration that we cannot provide reasonable defaults for.
    pub fn new(client_cert_verifier: Arc<verify::ClientCertVerifier>) -> ServerConfig {
        ServerConfig {
            ciphersuites: ALL_CIPHERSUITES.to_vec(),
            ignore_client_order: false,
            mtu: None,
            session_storage: handy::ServerSessionMemoryCache::new(256),
            ticketer: Arc::new(handy::NeverProducesTickets {}),
            alpn_protocols: Vec::new(),
            cert_resolver: Arc::new(handy::FailResolveChain {}),
            versions: vec![ ProtocolVersion::TLSv1_3, ProtocolVersion::TLSv1_2 ],
            verifier: client_cert_verifier,
            key_log: Arc::new(NoKeyLog {}),
        }
    }

    #[doc(hidden)]
    pub fn get_verifier(&self) -> &verify::ClientCertVerifier {
        self.verifier.as_ref()
    }

    /// Sets the session persistence layer to `persist`.
    pub fn set_persistence(&mut self, persist: Arc<StoresServerSessions + Send + Sync>) {
        self.session_storage = persist;
    }

    /// Sets a single certificate chain and matching private key.  This
    /// certificate and key is used for all subsequent connections,
    /// irrespective of things like SNI hostname.
    ///
    /// Note that the end-entity certificate must have the 
    /// [Subject Alternative Name](https://tools.ietf.org/html/rfc6125#section-4.1) 
    /// extension to describe, e.g., the valid DNS name. The `commonName` field is 
    /// disregarded.
    ///
    /// `cert_chain` is a vector of DER-encoded certificates.
    /// `key_der` is a DER-encoded RSA or ECDSA private key.
    ///
    /// This function fails if `key_der` is invalid.
    pub fn set_single_cert(&mut self,
                           cert_chain: Vec<key::Certificate>,
                           key_der: key::PrivateKey) -> Result<(), TLSError> {
        let resolver = handy::AlwaysResolvesChain::new(cert_chain, &key_der)?;
        self.cert_resolver = Arc::new(resolver);
        Ok(())
    }

    /// Sets a single certificate chain, matching private key and OCSP
    /// response.  This certificate and key is used for all subsequent
    /// connections, irrespective of things like SNI hostname.
    ///
    /// `cert_chain` is a vector of DER-encoded certificates.
    /// `key_der` is a DER-encoded RSA or ECDSA private key.
    /// `ocsp` is a DER-encoded OCSP response.  Ignored if zero length.
    /// `scts` is an `SignedCertificateTimestampList` encoding (see RFC6962)
    /// and is ignored if empty.
    ///
    /// This function fails if `key_der` is invalid.
    pub fn set_single_cert_with_ocsp_and_sct(&mut self,
                                             cert_chain: Vec<key::Certificate>,
                                             key_der: key::PrivateKey,
                                             ocsp: Vec<u8>,
                                             scts: Vec<u8>) -> Result<(), TLSError> {
        let resolver = handy::AlwaysResolvesChain::new_with_extras(cert_chain,
                                                                   &key_der,
                                                                   ocsp,
                                                                   scts)?;
        self.cert_resolver = Arc::new(resolver);
        Ok(())
    }

    /// Set the ALPN protocol list to the given protocol names.
    /// Overwrites any existing configured protocols.
    ///
    /// The first element in the `protocols` list is the most
    /// preferred, the last is the least preferred.
    pub fn set_protocols(&mut self, protocols: &[String]) {
        self.alpn_protocols.clear();
        self.alpn_protocols.extend_from_slice(protocols);
    }
}

pub struct ServerSessionImpl {
    pub config: Arc<ServerConfig>,
    pub common: SessionCommon,
    sni: Option<webpki::DNSName>,
    pub alpn_protocol: Option<String>,
    pub quic_params: Option<Vec<u8>>,
    pub error: Option<TLSError>,
    pub state: Option<Box<hs::State + Send + Sync>>,
    pub client_cert_chain: Option<Vec<key::Certificate>>,
}

impl fmt::Debug for ServerSessionImpl {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("ServerSessionImpl").finish()
    }
}

impl ServerSessionImpl {
    pub fn new(server_config: &Arc<ServerConfig>, extra_exts: Vec<ServerExtension>)
               -> ServerSessionImpl {
        let perhaps_client_auth = server_config.verifier.offer_client_auth();

        ServerSessionImpl {
            config: server_config.clone(),
            common: SessionCommon::new(server_config.mtu, false),
            sni: None,
            alpn_protocol: None,
            quic_params: None,
            error: None,
            state: Some(Box::new(hs::ExpectClientHello::new(perhaps_client_auth, extra_exts))),
            client_cert_chain: None,
        }
    }

    pub fn wants_read(&self) -> bool {
        // We want to read more data all the time, except when we
        // have unprocessed plaintext.  This provides back-pressure
        // to the TCP buffers.
        //
        // This also covers the handshake case, because we don't have
        // readable plaintext before handshake has completed.
        !self.common.has_readable_plaintext()
    }

    pub fn wants_write(&self) -> bool {
        !self.common.sendable_tls.is_empty()
    }

    pub fn is_handshaking(&self) -> bool {
        !self.common.traffic
    }

    pub fn set_buffer_limit(&mut self, len: usize) {
        self.common.set_buffer_limit(len)
    }

    pub fn process_msg(&mut self, mut msg: Message) -> Result<(), TLSError> {
        // TLS1.3: drop CCS at any time during handshaking
        if self.common.is_tls13()
            && msg.is_content_type(ContentType::ChangeCipherSpec)
            && self.is_handshaking() {
            trace!("Dropping CCS");
            return Ok(());
        }

        // Decrypt if demanded by current state.
        if self.common.peer_encrypting {
            let dm = self.common.decrypt_incoming(msg)?;
            msg = dm;
        }

        // For handshake messages, we need to join them before parsing
        // and processing.
        if self.common.handshake_joiner.want_message(&msg) {
            self.common.handshake_joiner.take_message(msg)
                .ok_or_else(|| {
                            self.common.send_fatal_alert(AlertDescription::DecodeError);
                            TLSError::CorruptMessagePayload(ContentType::Handshake)
                            })?;
            return self.process_new_handshake_messages();
        }

        // Now we can fully parse the message payload.
        msg.decode_payload();

        if msg.is_content_type(ContentType::Alert) {
            return self.common.process_alert(msg);
        }

        self.process_main_protocol(msg)
    }

    fn process_new_handshake_messages(&mut self) -> Result<(), TLSError> {
        while let Some(msg) = self.common.handshake_joiner.frames.pop_front() {
            self.process_main_protocol(msg)?;
        }

        Ok(())
    }

    fn queue_unexpected_alert(&mut self) {
        self.common.send_fatal_alert(AlertDescription::UnexpectedMessage);
    }

    pub fn process_main_protocol(&mut self, msg: Message) -> Result<(), TLSError> {
        if self.common.traffic && !self.common.is_tls13() &&
           msg.is_handshake_type(HandshakeType::ClientHello) {
            self.common.send_warning_alert(AlertDescription::NoRenegotiation);
            return Ok(());
        }

        let st = self.state.take().unwrap();
        st.check_message(&msg)
            .map_err(|err| { self.queue_unexpected_alert(); err })?;

        self.state = Some(st.handle(self, msg)?);

        Ok(())
    }

    pub fn process_new_packets(&mut self) -> Result<(), TLSError> {
        if let Some(ref err) = self.error {
            return Err(err.clone());
        }

        if self.common.message_deframer.desynced {
            return Err(TLSError::CorruptMessage);
        }

        while let Some(msg) = self.common.message_deframer.frames.pop_front() {
            match self.process_msg(msg) {
                Ok(_) => {}
                Err(err) => {
                    self.error = Some(err.clone());
                    return Err(err);
                }
            }

        }

        Ok(())
    }

    pub fn get_peer_certificates(&self) -> Option<Vec<key::Certificate>> {
        if self.client_cert_chain.is_none() {
            return None;
        }

        let mut r = Vec::new();

        for cert in self.client_cert_chain.as_ref().unwrap() {
            r.push(cert.clone());
        }

        Some(r)
    }

    pub fn get_alpn_protocol(&self) -> Option<&str> {
        self.alpn_protocol.as_ref().map(|s| s.as_ref())
    }

    pub fn get_protocol_version(&self) -> Option<ProtocolVersion> {
        self.common.negotiated_version
    }

    pub fn get_negotiated_ciphersuite(&self) -> Option<&'static SupportedCipherSuite> {
        self.common.get_suite()
    }

    pub fn get_sni(&self)-> Option<&webpki::DNSName> {
        self.sni.as_ref()
    }

    pub fn set_sni(&mut self, value: webpki::DNSName) {
        // The SNI hostname is immutable once set.
        assert!(self.sni.is_none());
        self.sni = Some(value)
    }
}

/// This represents a single TLS server session.
///
/// Send TLS-protected data to the peer using the `io::Write` trait implementation.
/// Read data from the peer using the `io::Read` trait implementation.
#[derive(Debug)]
pub struct ServerSession {
    // We use the pimpl idiom to hide unimportant details.
    pub(crate) imp: ServerSessionImpl,
}

impl ServerSession {
    /// Make a new ServerSession.  `config` controls how
    /// we behave in the TLS protocol.
    pub fn new(config: &Arc<ServerConfig>) -> ServerSession {
        ServerSession { imp: ServerSessionImpl::new(config, vec![]) }
    }

    /// Retrieves the SNI hostname, if any, used to select the certificate and
    /// private key.
    ///
    /// This returns `None` until some time after the client's SNI extension
    /// value is processed during the handshake. It will never be `None` when
    /// the connection is ready to send or process application data, unless the
    /// client does not support SNI.
    ///
    /// This is useful for application protocols that need to enforce that the
    /// SNI hostname matches an application layer protocol hostname. For
    /// example, HTTP/1.1 servers commonly expect the `Host:` header field of
    /// every request on a connection to match the hostname in the SNI extension
    /// when the client provides the SNI extension.
    ///
    /// The SNI hostname is also used to match sessions during session
    /// resumption.
    pub fn get_sni_hostname(&self)-> Option<&str> {
        self.imp.get_sni().map(|s| s.as_ref().into())
    }
}

impl Session for ServerSession {
    fn read_tls(&mut self, rd: &mut io::Read) -> io::Result<usize> {
        self.imp.common.read_tls(rd)
    }

    /// Writes TLS messages to `wr`.
    fn write_tls(&mut self, wr: &mut io::Write) -> io::Result<usize> {
        self.imp.common.write_tls(wr)
    }

    fn writev_tls(&mut self, wr: &mut WriteV) -> io::Result<usize> {
        self.imp.common.writev_tls(wr)
    }

    fn process_new_packets(&mut self) -> Result<(), TLSError> {
        self.imp.process_new_packets()
    }

    fn wants_read(&self) -> bool {
        self.imp.wants_read()
    }

    fn wants_write(&self) -> bool {
        self.imp.wants_write()
    }

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

    fn set_buffer_limit(&mut self, len: usize) {
        self.imp.set_buffer_limit(len)
    }

    fn send_close_notify(&mut self) {
        self.imp.common.send_close_notify()
    }

    fn get_peer_certificates(&self) -> Option<Vec<key::Certificate>> {
        self.imp.get_peer_certificates()
    }

    fn get_alpn_protocol(&self) -> Option<&str> {
        self.imp.get_alpn_protocol()
    }

    fn get_protocol_version(&self) -> Option<ProtocolVersion> {
        self.imp.get_protocol_version()
    }

    fn export_keying_material(&self,
                              output: &mut [u8],
                              label: &[u8],
                              context: Option<&[u8]>) -> Result<(), TLSError> {
        self.imp.common.export_keying_material(output, label, context)
    }

    fn get_negotiated_ciphersuite(&self) -> Option<&'static SupportedCipherSuite> {
        self.imp.get_negotiated_ciphersuite()
    }
}

impl io::Read for ServerSession {
    /// Obtain plaintext data received from the peer over
    /// this TLS connection.
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.imp.common.read(buf)
    }
}

impl io::Write for ServerSession {
    /// Send the plaintext `buf` to the peer, encrypting
    /// and authenticating it.  Once this function succeeds
    /// you should call `write_tls` which will output the
    /// corresponding TLS records.
    ///
    /// This function buffers plaintext sent before the
    /// TLS handshake completes, and sends it as soon
    /// as it can.  This buffer is of *unlimited size* so
    /// writing much data before it can be sent will
    /// cause excess memory usage.
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.imp.common.send_some_plaintext(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.imp.common.flush_plaintext();
        Ok(())
    }
}