#![allow(dead_code)]

use std::cmp::min;
use std::collections::{BTreeMap, VecDeque};
use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
use std::time::{Duration, Instant};
use torment_core::infohash::v1::U160;
use torment_core::ContactInfo;

use std::mem;
use std::ops::Add;
use std::ops::Bound::Included;
use std::option::Option::Some;

pub mod host_node;
pub mod krpc;

const DHT_K: usize = 8;

#[derive(Debug)]
pub struct Table {
    id: U160,
    buckets: BTreeMap<U160, Bucket>,
}

type NodeHandle = (U160, IpAddr, u16);

impl Default for Table {
    fn default() -> Self {
        Table::new()
    }
}

impl Table {
    pub fn new_with_id(id: U160) -> Table {
        Table {
            id,
            buckets: {
                let mut tree = BTreeMap::new();
                tree.insert(U160::MAX, Bucket::new(U160::MIN, U160::MAX));
                tree
            },
        }
    }

    pub fn new() -> Table {
        Self::new_with_id(U160::random())
    }

    fn get_bucket_index(&self, id: U160) -> U160 {
        *self.buckets.range(id..).next().unwrap().0
    }

    fn get_bucket(&self, id: U160) -> &Bucket {
        self.buckets
            .get(&self.get_bucket_index(id))
            .expect("DHT corrupt")
    }

    fn get_bucket_mut(&mut self, id: U160) -> &mut Bucket {
        self.buckets
            .get_mut(&self.get_bucket_index(id))
            .expect("DHT corrupt")
    }

    pub fn has_node(&self, contact_info: &ContactInfo) -> bool {
        self.get_node(
            contact_info.id,
            contact_info.contact.ip(),
            contact_info.contact.port(),
        )
        .is_some()
    }

    fn get_node(&self, id: U160, address: IpAddr, port: u16) -> Option<&Node> {
        self.get_bucket(id).nodes.get(&(id, address, port))
    }

    pub fn find_node(&self, id: U160) -> Option<ContactInfo> {
        self.get_bucket(id)
            .nodes
            .range((
                Included(&(id, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0)), 0)),
                Included(&(
                    id,
                    IpAddr::V6(Ipv6Addr::new(
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                        u16::MAX,
                    )),
                    u16::MAX,
                )),
            ))
            .next()
            .map(|(_, node)| node.to_contact_info())
    }

    fn get_node_mut(&mut self, id: U160, address: IpAddr, port: u16) -> Option<&mut Node> {
        self.get_bucket_mut(id).nodes.get_mut(&(id, address, port))
    }

    pub fn find_k_closest_nodes(
        &self,
        target: U160,
        excluding: Option<(U160, IpAddr, u16)>,
    ) -> Vec<ContactInfo> {
        let mut nodes = vec![];
        let mut found_before = 0;
        let mut found_after = 0;

        let mut before_range = self.buckets.range(..target);
        while let Some((_, bucket)) = before_range.next_back() {
            let info = bucket.get_contact_info();
            found_before += info.len();
            nodes.extend(info);

            if found_before >= DHT_K {
                break;
            }
        }

        let mut after_range = self.buckets.range(target..);
        while let Some((_, bucket)) = after_range.next() {
            let info = bucket.get_contact_info();
            found_after += info.len();
            nodes.extend(info);

            if found_after >= DHT_K {
                break;
            }
        }

        nodes.sort_by_key(|x| x.id ^ target);
        let nodes = if let Some(exclude) = excluding {
            nodes
                .iter()
                .filter(|x| {
                    x.id != exclude.0
                        || x.contact.ip() != exclude.1
                        || x.contact.port() != exclude.2
                })
                .copied()
                .collect()
        } else {
            nodes
        };

        nodes[..min(8, nodes.len())].to_vec()
    }

    pub fn handle_activity(&mut self, id: U160, address: IpAddr, port: u16) {
        let bucket_has_activity = if let Some(node) = self.get_node_mut(id, address, port) {
            node.handle_activity();

            true
        } else {
            self.add_node(id, address, port)
        };

        if bucket_has_activity {
            self.get_bucket_mut(id).last_activity = Some(Instant::now());
        }
    }

    pub fn handle_outgoing_activity(&mut self, id: U160, address: IpAddr, port: u16) {
        if let Some(node) = self.get_node_mut(id, address, port) {
            node.handle_outgoing_activity();
        }
    }

    pub fn add_incoming_node(&mut self, id: U160, address: IpAddr, port: u16) {
        self.add_node(id, address, port);
        self.handle_activity(id, address, port);
    }

    pub fn add_node(&mut self, id: U160, address: IpAddr, port: u16) -> bool {
        let own_id = self.id;
        if own_id == id {
            return false;
        }

        let bucket = self.get_bucket_mut(id);
        if bucket.add_node(id, address, port) {
            return true;
        }

        if !(bucket.start <= own_id
            && own_id <= bucket.end
            && (bucket.end - bucket.start) > U160::ONE)
        {
            return false;
        }

        let low_end = bucket.start + (bucket.end - bucket.start).half();

        fn split_node_map(
            nodes: &mut BTreeMap<NodeHandle, Node>,
            split_at: U160,
        ) -> (BTreeMap<NodeHandle, Node>, BTreeMap<NodeHandle, Node>) {
            let mut high = BTreeMap::new();
            let mut low = BTreeMap::new();
            let keys = nodes.keys().copied().collect::<Vec<_>>();
            for key in keys {
                let node = nodes.remove(&key).unwrap();
                if node.id <= split_at {
                    low.insert(key, node);
                } else {
                    high.insert(key, node);
                }
            }

            (low, high)
        }

        fn recount_nodes_per_id(nodes: &BTreeMap<NodeHandle, Node>) -> BTreeMap<U160, usize> {
            nodes
                .values()
                .map(|x| x.id)
                .fold(BTreeMap::new(), |mut c, i| {
                    c.entry(i).and_modify(|x| *x += 1).or_insert(1);
                    c
                })
        }

        fn get_last_activity(nodes: &BTreeMap<NodeHandle, Node>) -> Option<Instant> {
            nodes.values().filter_map(|x| x.last_activity).max()
        }

        let (low, high) = split_node_map(&mut bucket.nodes, low_end);
        let (low_q, high_q) = split_node_map(&mut bucket.queue, low_end);

        bucket.last_activity = get_last_activity(&high);
        bucket.nodes_per_id = recount_nodes_per_id(&high);
        bucket.nodes = high;
        bucket.queue = high_q;
        let low_start = bucket.start;
        bucket.start = low_end + U160::ONE;

        let mut new_bucket = Bucket::new(low_start, low_end);
        new_bucket.last_activity = get_last_activity(&low);
        new_bucket.nodes_per_id = recount_nodes_per_id(&low);
        new_bucket.nodes = low;
        new_bucket.queue = low_q;
        self.buckets.insert(low_end, new_bucket);
        self.add_node(id, address, port)
    }

    pub fn get_silent_nodes(&self) -> Vec<ContactInfo> {
        self.iter()
            .filter(|node| {
                if let Some(last_activity) = node.last_activity {
                    if last_activity.add(Duration::from_secs(60 * 15)) < Instant::now() {
                        return true;
                    }
                }

                if let Some(last_outgoing_activity) = node.last_activity {
                    if node.last_activity.is_none()
                        && last_outgoing_activity.add(Duration::from_secs(60)) < Instant::now()
                    {
                        return true;
                    }
                }

                false
            })
            .map(|node| node.to_contact_info())
            .collect()
    }

    pub fn update_nodes(&mut self) {
        for node in self.iter_mut() {
            if node
                .last_activity
                .map(|x| x.add(Duration::from_secs(15 * 60)) < Instant::now())
                .unwrap_or(false)
            {
                if let NodeState::Questioning(n) = node.state {
                    if n > 3 {
                        #[cfg(debug_assertions)]
                        {
                            if node.state != NodeState::Bad {
                                println!(
                                    "Node[id={},addr={}] went from {:?} to {:?}",
                                    node.id,
                                    node.sock_addr(),
                                    node.state,
                                    NodeState::Bad
                                );
                            }
                        }

                        node.state = NodeState::Bad;
                    }

                    if node
                        .last_outgoing_activity
                        .map(|x| x.add(Duration::from_secs(3 * 60)) < Instant::now())
                        .unwrap_or(false)
                    {
                        #[cfg(debug_assertions)]
                        {
                            if node.state != NodeState::Bad {
                                println!(
                                    "Node[id={},addr={}] went from {:?} to {:?}",
                                    node.id,
                                    node.sock_addr(),
                                    node.state,
                                    NodeState::Bad
                                );
                            }
                        }

                        node.state = NodeState::Bad;
                    }
                } else {
                    #[cfg(debug_assertions)]
                    {
                        if node.state != NodeState::Questioning(0) {
                            println!(
                                "Node[id={},addr={}] went from {:?} to {:?}",
                                node.id,
                                node.sock_addr(),
                                node.state,
                                NodeState::Questioning(0)
                            );
                        }
                    }

                    node.state = NodeState::Questioning(0);
                }
            }
        }

        for (_, bucket) in &mut self.buckets {
            if !bucket.queue.is_empty() {
                let old_nodes = mem::replace(&mut bucket.nodes, BTreeMap::new());
                let mut keys = bucket
                    .queue
                    .iter()
                    .map(|(key, node)| (key.clone(), node.first_activity))
                    .collect::<Vec<_>>();
                keys.sort_by_key(|(_, first_activity)| *first_activity);
                let mut keys = VecDeque::from(keys);

                for (key, old_node) in old_nodes {
                    if bucket.queue.is_empty() {
                        bucket.nodes.insert(key, old_node);
                        continue;
                    }

                    if old_node.state == NodeState::Bad {
                        if let Some((key, _)) = keys.pop_front() {
                            if let Some(node) = bucket.queue.remove(&key) {
                                bucket.nodes.insert(key, node);
                                continue;
                            }
                        }
                    }

                    bucket.nodes.insert(key, old_node);
                }
            }
        }
    }

    pub fn count_nodes(&self) -> usize {
        self.buckets.values().map(|x| x.nodes.len()).sum()
    }

    fn iter(&self) -> impl Iterator<Item = &Node> {
        self.buckets
            .iter()
            .flat_map(|(_, bucket)| bucket.nodes.iter().map(|(_, node)| node))
    }

    fn iter_mut(&mut self) -> impl Iterator<Item = &mut Node> {
        self.buckets
            .iter_mut()
            .flat_map(|(_, bucket)| bucket.nodes.iter_mut().map(|(_, node)| node))
    }
}

#[derive(Debug)]
struct Bucket {
    start: U160,
    end: U160,
    last_activity: Option<Instant>,
    nodes: BTreeMap<(U160, IpAddr, u16), Node>,
    nodes_per_id: BTreeMap<U160, usize>,
    queue: BTreeMap<(U160, IpAddr, u16), Node>,
}

impl Bucket {
    fn new(start: U160, end: U160) -> Bucket {
        Bucket {
            start,
            end,
            last_activity: None,
            nodes: BTreeMap::new(),
            nodes_per_id: Default::default(),
            queue: BTreeMap::new(),
        }
    }

    fn get_contact_info(&self) -> Vec<ContactInfo> {
        self.nodes
            .iter()
            .map(|(_, node)| ContactInfo {
                id: node.id,
                contact: SocketAddr::new(node.address, node.port),
            })
            .collect()
    }

    fn internal_add_node(&mut self, id: U160, address: IpAddr, port: u16) {
        self.nodes_per_id
            .entry(id)
            .and_modify(|x| *x += 1)
            .or_insert(1);
        self.nodes
            .insert((id, address, port), Node::new(id, address, port));

        self.last_activity = None;
    }

    fn add_node(&mut self, id: U160, address: IpAddr, port: u16) -> bool {
        // Discard after 4 nodes with the same id
        if self.nodes_per_id.get(&id).unwrap_or(&0) >= &4 {
            return true;
        }

        if self.nodes.len() < DHT_K {
            self.internal_add_node(id, address, port);

            true
        } else {
            let mut replace = None;
            let mut has_questionable = false;
            for (key, node) in &self.nodes {
                if node.state == NodeState::Bad {
                    replace = Some(*key);
                    break;
                }

                if let NodeState::Questioning(_) = node.state {
                    has_questionable = true;
                }
            }

            if let Some(key) = replace {
                self.nodes.remove(&key);
                self.nodes_per_id.entry(key.0).and_modify(|x| *x -= 1);
                if Some(&0usize) == self.nodes_per_id.get(&key.0) {
                    self.nodes_per_id.remove(&key.0);
                }

                self.internal_add_node(id, address, port);
                true
            } else {
                if has_questionable {
                    let len = self.queue.len();
                    let entry = self
                        .queue
                        .entry((id, address, port))
                        .and_modify(|node| node.handle_activity());

                    if len < DHT_K {
                        entry.or_insert_with(|| {
                            let mut queued_node = Node::new(id, address, port);
                            queued_node.set_queued();
                            queued_node
                        });
                    }
                }

                false
            }
        }
    }
}

#[derive(Debug)]
struct Node {
    id: U160,
    address: IpAddr,
    port: u16,
    first_activity: Instant,
    last_outgoing_activity: Option<Instant>,
    last_activity: Option<Instant>,
    is_queued: bool,
    state: NodeState,
}

#[derive(Debug, Ord, PartialOrd, Eq, PartialEq, Copy, Clone)]
enum NodeState {
    Good,
    Bad,
    Questioning(u16),
}

impl Node {
    fn new(id: U160, address: IpAddr, port: u16) -> Self {
        Node {
            id,
            address,
            port,
            first_activity: Instant::now(),
            last_outgoing_activity: None,
            last_activity: None,
            is_queued: false,
            state: NodeState::Questioning(0),
        }
    }

    fn sock_addr(&self) -> SocketAddr {
        SocketAddr::new(self.address, self.port)
    }

    fn handle_activity(&mut self) {
        self.last_activity = Some(Instant::now());
        #[cfg(debug_assertions)]
        {
            if self.state != NodeState::Good {
                println!(
                    "Node[id={},addr={}] went from {:?} to {:?}",
                    self.id,
                    self.sock_addr(),
                    self.state,
                    NodeState::Good
                );
            }
        }
        self.state = NodeState::Good;
    }

    fn handle_outgoing_activity(&mut self) {
        self.last_outgoing_activity = Some(Instant::now());

        if let NodeState::Questioning(nr) = self.state {
            #[cfg(debug_assertions)]
            {
                if self.state != NodeState::Questioning(nr + 1) {
                    println!(
                        "Node[id={},addr={}] went from {:?} to {:?}",
                        self.id,
                        self.sock_addr(),
                        self.state,
                        NodeState::Questioning(nr + 1)
                    );
                }
            }

            self.state = NodeState::Questioning(nr + 1);
        }
    }

    fn set_queued(&mut self) {
        self.is_queued = true;
    }

    fn set_live(&mut self) {
        self.is_queued = false;
    }

    fn is_queued(&self) -> bool {
        self.is_queued
    }

    fn to_contact_info(&self) -> ContactInfo {
        ContactInfo {
            id: self.id,
            contact: SocketAddr::new(self.address, self.port),
        }
    }
}

#[cfg(test)]
mod test {
    use crate::Table;
    use std::net::{IpAddr, Ipv4Addr};
    use torment_core::infohash::v1::U160;

    #[test]
    fn test_table_fulfillment() {
        let mut table = Table::new_with_id(U160::ZERO);
        table.add_node(U160::ONE, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 1);
        table.add_node(U160::ONE, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 2);
        table.add_node(U160::ONE, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 3);
        table.add_node(U160::ONE, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 4);
        assert_eq!(4, table.count_nodes());
        // Shouldn't be added anymore since we already have 4 nodes with the same id
        table.add_node(U160::ONE, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 5);
        assert_eq!(4, table.count_nodes());

        // Don't add self
        table.add_node(U160::ZERO, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 5);
        assert_eq!(4, table.count_nodes());

        let two = U160::ONE + U160::ONE;

        table.add_node(two, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 5);
        assert_eq!(5, table.count_nodes());

        table.add_node(two, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 6);
        table.add_node(two, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 7);
        table.add_node(two, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 8);
        // node_id: MAX
        table.add_node(U160::MAX, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 9);
        table.add_node(U160::MAX, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 10);
        table.add_node(U160::MAX, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 11);
        table.add_node(U160::MAX, IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)), 12);
        table.add_node(
            U160::MAX - U160::ONE,
            IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)),
            13,
        );
        table.add_node(
            U160::MAX - U160::ONE,
            IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)),
            14,
        );
        table.add_node(
            U160::MAX - U160::ONE,
            IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)),
            15,
        );
        table.add_node(
            U160::MAX - U160::ONE,
            IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)),
            16,
        );

        // This one however should too, since we already know 8 nodes with U160::MIN as id
        table.add_node(
            U160::MAX - (U160::ONE + U160::ONE),
            IpAddr::V4(Ipv4Addr::new(0, 0, 0, 1)),
            17,
        );
        assert_eq!(16, table.count_nodes());
    }
}