// Copyright 2017-2019 int08h LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//!
//! Implements the Roughenough server functionality.
//!

use hex;
use std::io::ErrorKind;
use std::net::SocketAddr;
use std::process;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::Duration;
use time;

use byteorder::{LittleEndian, WriteBytesExt};

use mio::net::{TcpListener, UdpSocket};
use mio::{Events, Poll, PollOpt, Ready, Token};
use mio_extras::timer::Timer;

use crate::config::ServerConfig;
use crate::key::{LongTermKey, OnlineKey};
use crate::kms;
use crate::merkle::MerkleTree;
use mio::tcp::Shutdown;
use std::io::Write;
use crate::{Error, RtMessage, Tag, MIN_REQUEST_LENGTH};

macro_rules! check_ctrlc {
    ($keep_running:expr) => {
        if !$keep_running.load(Ordering::Acquire) {
            warn!("Ctrl-C caught, exiting...");
            return true;
        }
    };
}

// mio event registrations
const MESSAGE: Token = Token(0);
const STATUS: Token = Token(1);
const HEALTH_CHECK: Token = Token(2);

// Canned response to health check request
const HTTP_RESPONSE: &str = "HTTP/1.1 200 OK\nContent-Length: 0\nConnection: close\n\n";

/// The main Roughenough server instance.
///
/// The [ServerConfig](../config/trait.ServerConfig.html) trait specifies the required and optional
/// parameters available for configuring a Roughenoguh server instance.
///
/// Implementations of `ServerConfig` obtain configurations from different back-end sources
/// such as files or environment variables.
///
/// See [the config module](../config/index.html) for more information.
///
pub struct Server {
    config: Box<ServerConfig>,
    online_key: OnlineKey,
    cert_bytes: Vec<u8>,

    response_counter: u64,
    num_bad_requests: u64,

    socket: UdpSocket,
    health_listener: Option<TcpListener>,
    keep_running: Arc<AtomicBool>,
    poll_duration: Option<Duration>,
    timer: Timer<()>,
    poll: Poll,
    events: Events,
    merkle: MerkleTree,
    requests: Vec<(Vec<u8>, SocketAddr)>,
    buf: [u8; 65_536],

    public_key: String,

    // Used to send requests to ourselves in fuzzing mode
    #[cfg(fuzzing)]
    fake_client_socket: UdpSocket,
}

impl Server {
    ///
    /// Create a new server instance from the provided
    /// [`ServerConfig`](../config/trait.ServerConfig.html) trait object instance.
    ///
    pub fn new(config: Box<ServerConfig>) -> Server {
        let online_key = OnlineKey::new();
        let public_key: String;

        let cert_bytes = {
            let seed = match kms::load_seed(&config) {
                Ok(seed) => seed,
                Err(e) => {
                    error!("Failed to load seed: {:#?}", e);
                    process::exit(1);
                }
            };
            let mut long_term_key = LongTermKey::new(&seed);
            public_key = hex::encode(long_term_key.public_key());

            long_term_key.make_cert(&online_key).encode().unwrap()
        };

        let keep_running = Arc::new(AtomicBool::new(true));

        let sock_addr = config.udp_socket_addr().expect("udp sock addr");
        let socket = UdpSocket::bind(&sock_addr).expect("failed to bind to socket");

        let poll_duration = Some(Duration::from_millis(100));

        let mut timer: Timer<()> = Timer::default();
        timer.set_timeout(config.status_interval(), ());

        let poll = Poll::new().unwrap();
        poll.register(&socket, MESSAGE, Ready::readable(), PollOpt::edge())
            .unwrap();
        poll.register(&timer, STATUS, Ready::readable(), PollOpt::edge())
            .unwrap();

        let health_listener = if let Some(hc_port) = config.health_check_port() {
            let hc_sock_addr: SocketAddr = format!("{}:{}", config.interface(), hc_port)
                .parse()
                .unwrap();

            let tcp_listener = TcpListener::bind(&hc_sock_addr)
                .expect("failed to bind TCP listener for health check");

            poll.register(&tcp_listener, HEALTH_CHECK, Ready::readable(), PollOpt::edge())
                .unwrap();

            Some(tcp_listener)
        } else {
            None
        };

        let merkle = MerkleTree::new();
        let requests = Vec::with_capacity(config.batch_size() as usize);

        Server {
            config,
            online_key,
            cert_bytes,

            response_counter: 0,
            num_bad_requests: 0,
            socket,
            health_listener,

            keep_running,
            poll_duration,
            timer,
            poll,
            events: Events::with_capacity(32),
            merkle,
            requests,
            buf: [0u8; 65_536],

            public_key,

            #[cfg(fuzzing)]
            fake_client_socket: UdpSocket::bind(&"127.0.0.1:0".parse().unwrap()).unwrap(),
        }
    }

    /// Returns a reference counted pointer the this server's `keep_running` value.
    pub fn get_keep_running(&self) -> Arc<AtomicBool> {
        self.keep_running.clone()
    }

    // extract the client's nonce from its request
    fn nonce_from_request<'a>(&self, buf: &'a [u8], num_bytes: usize) -> Result<&'a [u8], Error> {
        if num_bytes < MIN_REQUEST_LENGTH as usize {
            return Err(Error::RequestTooShort);
        }

        let tag_count = &buf[..4];
        let expected_nonc = &buf[8..12];
        let expected_pad = &buf[12..16];

        let tag_count_is_2 = tag_count == [0x02, 0x00, 0x00, 0x00];
        let tag1_is_nonc = expected_nonc == Tag::NONC.wire_value();
        let tag2_is_pad = expected_pad == Tag::PAD.wire_value();

        if tag_count_is_2 && tag1_is_nonc && tag2_is_pad {
            Ok(&buf[0x10..0x50])
        } else {
            Err(Error::InvalidRequest)
        }
    }

    fn make_response(
        &self,
        srep: &RtMessage,
        cert_bytes: &[u8],
        path: &[u8],
        idx: u32,
    ) -> RtMessage {
        let mut index = [0; 4];
        (&mut index as &mut [u8])
            .write_u32::<LittleEndian>(idx)
            .unwrap();

        let sig_bytes = srep.get_field(Tag::SIG).unwrap();
        let srep_bytes = srep.get_field(Tag::SREP).unwrap();

        let mut response = RtMessage::new(5);
        response.add_field(Tag::SIG, sig_bytes).unwrap();
        response.add_field(Tag::PATH, path).unwrap();
        response.add_field(Tag::SREP, srep_bytes).unwrap();
        response.add_field(Tag::CERT, cert_bytes).unwrap();
        response.add_field(Tag::INDX, &index).unwrap();

        response
    }

    /// The main processing function for incoming connections. This method should be
    /// called repeatedly in a loop to process requests. It returns 'true' when the
    /// server has shutdown (due to keep_running being set to 'false').
    ///
    pub fn process_events(&mut self) -> bool {
        self.poll
            .poll(&mut self.events, self.poll_duration)
            .expect("poll failed");

        for event in self.events.iter() {
            match event.token() {
                MESSAGE => {
                    let mut done = false;

                    'process_batch: loop {
                        check_ctrlc!(self.keep_running);

                        let resp_start = self.response_counter;

                        for i in 0..self.config.batch_size() {
                            match self.socket.recv_from(&mut self.buf) {
                                Ok((num_bytes, src_addr)) => {
                                    match self.nonce_from_request(&self.buf, num_bytes) {
                                        Ok(nonce) => {
                                            self.requests.push((Vec::from(nonce), src_addr));
                                            self.merkle.push_leaf(nonce);
                                        }
                                        Err(e) => {
                                            self.num_bad_requests += 1;

                                            info!(
                                                "Invalid request: '{:?}' ({} bytes) from {} (#{} in batch, resp #{})",
                                                e, num_bytes, src_addr, i, resp_start + i as u64
                                            );
                                        }
                                    }
                                }
                                Err(e) => match e.kind() {
                                    ErrorKind::WouldBlock => {
                                        done = true;
                                        break;
                                    }
                                    _ => {
                                        error!(
                                            "Error receiving from socket: {:?}: {:?}",
                                            e.kind(),
                                            e
                                        );
                                        break;
                                    }
                                },
                            };
                        }

                        if self.requests.is_empty() {
                            break 'process_batch;
                        }

                        let merkle_root = self.merkle.compute_root();
                        let srep = self.online_key.make_srep(time::get_time(), &merkle_root);

                        for (i, &(ref nonce, ref src_addr)) in self.requests.iter().enumerate() {
                            let paths = self.merkle.get_paths(i);

                            let resp =
                                self.make_response(&srep, &self.cert_bytes, &paths, i as u32);
                            let resp_bytes = resp.encode().unwrap();

                            let bytes_sent = self
                                .socket
                                .send_to(&resp_bytes, &src_addr)
                                .expect("send_to failed");

                            self.response_counter += 1;

                            info!(
                                "Responded {} bytes to {} for '{}..' (#{} in batch, resp #{})",
                                bytes_sent,
                                src_addr,
                                hex::encode(&nonce[0..4]),
                                i,
                                self.response_counter
                            );
                        }

                        self.merkle.reset();
                        self.requests.clear();

                        if done {
                            break 'process_batch;
                        }
                    }
                }

                HEALTH_CHECK => {
                    let listener = self.health_listener.as_ref().unwrap();

                    match listener.accept() {
                        Ok((ref mut stream, src_addr)) => {
                            info!("health check from {}", src_addr);

                            match stream.write(HTTP_RESPONSE.as_bytes()) {
                                Ok(_) => (),
                                Err(e) => warn!("error writing health check {}", e),
                            }

                            match stream.shutdown(Shutdown::Both) {
                                Ok(_) => (),
                                Err(e) => warn!("error in health check socket shutdown {}", e),
                            }
                        }
                        Err(ref e) if e.kind() == ErrorKind::WouldBlock => {
                            debug!("blocking in TCP health check");
                        }
                        Err(e) => {
                            warn!("unexpected health check error {}", e);
                        }
                    }
                }

                STATUS => {
                    info!(
                        "responses {}, invalid requests {}",
                        self.response_counter, self.num_bad_requests
                    );

                    self.timer.set_timeout(self.config.status_interval(), ());
                }

                _ => unreachable!(),
            }
        }
        false
    }

    /// Returns a reference to the server's long-term public key
    pub fn get_public_key(&self) -> &str {
        &self.public_key
    }

    /// Returns a reference to the server's on-line (delegated) key
    pub fn get_online_key(&self) -> &OnlineKey {
        &self.online_key
    }

    /// Returns a reference to the `ServerConfig` this server was configured with
    pub fn get_config(&self) -> &Box<ServerConfig> {
        &self.config
    }

    #[cfg(fuzzing)]
    pub fn send_to_self(&mut self, data: &[u8]) {
        self.response_counter = 0;
        self.num_bad_requests = 0;
        let res = self
            .fake_client_socket
            .send_to(data, &self.socket.local_addr().unwrap());
        info!("Sent to self: {:?}", res);
    }
}