use std::collections::BTreeMap;
use std::hash::Hash;
use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
use std::sync::atomic::AtomicUsize;
use std::sync::Arc;
use std::time::Instant;

use crossbeam_channel::Sender;

use aquatic_common::access_list::{create_access_list_cache, AccessListArcSwap};
use aquatic_common::AHashIndexMap;
use aquatic_common::ValidUntil;
use aquatic_udp_protocol::*;

use crate::config::Config;

pub const MAX_PACKET_SIZE: usize = 8192;

pub trait Ip: Hash + PartialEq + Eq + Clone + Copy {
    fn ip_addr(self) -> IpAddr;
}

impl Ip for Ipv4Addr {
    fn ip_addr(self) -> IpAddr {
        IpAddr::V4(self)
    }
}

impl Ip for Ipv6Addr {
    fn ip_addr(self) -> IpAddr {
        IpAddr::V6(self)
    }
}

#[derive(Debug)]
pub struct PendingScrapeRequest {
    pub transaction_id: TransactionId,
    pub info_hashes: BTreeMap<usize, InfoHash>,
}

#[derive(Debug)]
pub struct PendingScrapeResponse {
    pub transaction_id: TransactionId,
    pub torrent_stats: BTreeMap<usize, TorrentScrapeStatistics>,
}

#[derive(Debug)]
pub enum ConnectedRequest {
    Announce(AnnounceRequest),
    Scrape(PendingScrapeRequest),
}

#[derive(Debug)]
pub enum ConnectedResponse {
    AnnounceIpv4(AnnounceResponseIpv4),
    AnnounceIpv6(AnnounceResponseIpv6),
    Scrape(PendingScrapeResponse),
}

#[derive(Clone, Copy, Debug)]
pub struct SocketWorkerIndex(pub usize);

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub struct RequestWorkerIndex(pub usize);

impl RequestWorkerIndex {
    pub fn from_info_hash(config: &Config, info_hash: InfoHash) -> Self {
        Self(info_hash.0[0] as usize % config.request_workers)
    }
}

pub struct ConnectedRequestSender {
    index: SocketWorkerIndex,
    senders: Vec<Sender<(SocketWorkerIndex, ConnectedRequest, SocketAddr)>>,
}

impl ConnectedRequestSender {
    pub fn new(
        index: SocketWorkerIndex,
        senders: Vec<Sender<(SocketWorkerIndex, ConnectedRequest, SocketAddr)>>,
    ) -> Self {
        Self { index, senders }
    }

    pub fn try_send_to(
        &self,
        index: RequestWorkerIndex,
        request: ConnectedRequest,
        addr: SocketAddr,
    ) {
        if let Err(err) = self.senders[index.0].try_send((self.index, request, addr)) {
            ::log::warn!("request_sender.try_send failed: {:?}", err)
        }
    }
}

pub struct ConnectedResponseSender {
    senders: Vec<Sender<(ConnectedResponse, SocketAddr)>>,
}

impl ConnectedResponseSender {
    pub fn new(senders: Vec<Sender<(ConnectedResponse, SocketAddr)>>) -> Self {
        Self { senders }
    }

    pub fn try_send_to(
        &self,
        index: SocketWorkerIndex,
        response: ConnectedResponse,
        addr: SocketAddr,
    ) {
        if let Err(err) = self.senders[index.0].try_send((response, addr)) {
            ::log::warn!("request_sender.try_send failed: {:?}", err)
        }
    }
}

#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
pub enum PeerStatus {
    Seeding,
    Leeching,
    Stopped,
}

impl PeerStatus {
    /// Determine peer status from announce event and number of bytes left.
    ///
    /// Likely, the last branch will be taken most of the time.
    #[inline]
    pub fn from_event_and_bytes_left(event: AnnounceEvent, bytes_left: NumberOfBytes) -> Self {
        if event == AnnounceEvent::Stopped {
            Self::Stopped
        } else if bytes_left.0 == 0 {
            Self::Seeding
        } else {
            Self::Leeching
        }
    }
}

#[derive(Clone, Debug)]
pub struct Peer<I: Ip> {
    pub ip_address: I,
    pub port: Port,
    pub status: PeerStatus,
    pub valid_until: ValidUntil,
}

pub type PeerMap<I> = AHashIndexMap<PeerId, Peer<I>>;

pub struct TorrentData<I: Ip> {
    pub peers: PeerMap<I>,
    pub num_seeders: usize,
    pub num_leechers: usize,
}

impl<I: Ip> Default for TorrentData<I> {
    fn default() -> Self {
        Self {
            peers: Default::default(),
            num_seeders: 0,
            num_leechers: 0,
        }
    }
}

pub type TorrentMap<I> = AHashIndexMap<InfoHash, TorrentData<I>>;

#[derive(Default)]
pub struct TorrentMaps {
    pub ipv4: TorrentMap<Ipv4Addr>,
    pub ipv6: TorrentMap<Ipv6Addr>,
}

impl TorrentMaps {
    /// Remove disallowed and inactive torrents
    pub fn clean(&mut self, config: &Config, access_list: &Arc<AccessListArcSwap>) {
        let now = Instant::now();
        let access_list_mode = config.access_list.mode;

        let mut access_list_cache = create_access_list_cache(access_list);

        self.ipv4.retain(|info_hash, torrent| {
            access_list_cache
                .load()
                .allows(access_list_mode, &info_hash.0)
                && Self::clean_torrent_and_peers(now, torrent)
        });
        self.ipv4.shrink_to_fit();

        self.ipv6.retain(|info_hash, torrent| {
            access_list_cache
                .load()
                .allows(access_list_mode, &info_hash.0)
                && Self::clean_torrent_and_peers(now, torrent)
        });
        self.ipv6.shrink_to_fit();
    }

    /// Returns true if torrent is to be kept
    #[inline]
    fn clean_torrent_and_peers<I: Ip>(now: Instant, torrent: &mut TorrentData<I>) -> bool {
        let num_seeders = &mut torrent.num_seeders;
        let num_leechers = &mut torrent.num_leechers;

        torrent.peers.retain(|_, peer| {
            let keep = peer.valid_until.0 > now;

            if !keep {
                match peer.status {
                    PeerStatus::Seeding => {
                        *num_seeders -= 1;
                    }
                    PeerStatus::Leeching => {
                        *num_leechers -= 1;
                    }
                    _ => (),
                };
            }

            keep
        });

        torrent.peers.shrink_to_fit();

        !torrent.peers.is_empty()
    }
}

pub struct Statistics {
    pub requests_received: AtomicUsize,
    pub responses_sent: AtomicUsize,
    pub bytes_received: AtomicUsize,
    pub bytes_sent: AtomicUsize,
    pub torrents: Vec<AtomicUsize>,
    pub peers: Vec<AtomicUsize>,
}

impl Statistics {
    pub fn new(num_request_workers: usize) -> Self {
        Self {
            requests_received: Default::default(),
            responses_sent: Default::default(),
            bytes_received: Default::default(),
            bytes_sent: Default::default(),
            torrents: Self::create_atomic_usize_vec(num_request_workers),
            peers: Self::create_atomic_usize_vec(num_request_workers),
        }
    }

    fn create_atomic_usize_vec(len: usize) -> Vec<AtomicUsize> {
        ::std::iter::repeat_with(|| AtomicUsize::default())
            .take(len)
            .collect()
    }
}

#[derive(Clone)]
pub struct State {
    pub access_list: Arc<AccessListArcSwap>,
    pub statistics_ipv4: Arc<Statistics>,
    pub statistics_ipv6: Arc<Statistics>,
}

impl State {
    pub fn new(num_request_workers: usize) -> Self {
        Self {
            access_list: Arc::new(AccessListArcSwap::default()),
            statistics_ipv4: Arc::new(Statistics::new(num_request_workers)),
            statistics_ipv6: Arc::new(Statistics::new(num_request_workers)),
        }
    }
}

#[cfg(test)]
mod tests {
    use std::net::Ipv6Addr;

    use crate::{common::MAX_PACKET_SIZE, config::Config};

    #[test]
    fn test_peer_status_from_event_and_bytes_left() {
        use crate::common::*;

        use PeerStatus::*;

        let f = PeerStatus::from_event_and_bytes_left;

        assert_eq!(Stopped, f(AnnounceEvent::Stopped, NumberOfBytes(0)));
        assert_eq!(Stopped, f(AnnounceEvent::Stopped, NumberOfBytes(1)));

        assert_eq!(Seeding, f(AnnounceEvent::Started, NumberOfBytes(0)));
        assert_eq!(Leeching, f(AnnounceEvent::Started, NumberOfBytes(1)));

        assert_eq!(Seeding, f(AnnounceEvent::Completed, NumberOfBytes(0)));
        assert_eq!(Leeching, f(AnnounceEvent::Completed, NumberOfBytes(1)));

        assert_eq!(Seeding, f(AnnounceEvent::None, NumberOfBytes(0)));
        assert_eq!(Leeching, f(AnnounceEvent::None, NumberOfBytes(1)));
    }

    // Assumes that announce response with maximum amount of ipv6 peers will
    // be the longest
    #[test]
    fn test_max_package_size() {
        use aquatic_udp_protocol::*;

        let config = Config::default();

        let peers = ::std::iter::repeat(ResponsePeerIpv6 {
            ip_address: Ipv6Addr::new(1, 1, 1, 1, 1, 1, 1, 1),
            port: Port(1),
        })
        .take(config.protocol.max_response_peers)
        .collect();

        let response = Response::AnnounceIpv6(AnnounceResponseIpv6 {
            transaction_id: TransactionId(1),
            announce_interval: AnnounceInterval(1),
            seeders: NumberOfPeers(1),
            leechers: NumberOfPeers(1),
            peers,
        });

        let mut buf = Vec::new();

        response.write(&mut buf).unwrap();

        println!("Buffer len: {}", buf.len());

        assert!(buf.len() <= MAX_PACKET_SIZE);
    }
}