use std::collections::{HashMap, HashSet};
use std::fmt;
use std::sync::Arc;
use std::{cmp, time::Duration};

use anyhow::Result;

use futures::future::BoxFuture;
use futures::stream::{FuturesUnordered, StreamExt};

use tokio::{select, sync::watch, time::sleep};
use tracing::*;

use df_consul::*;

const IPV4_TARGET_METADATA_TAG: &str = "public_ipv4";
const IPV6_TARGET_METADATA_TAG: &str = "public_ipv6";
const CNAME_TARGET_METADATA_TAG: &str = "cname_target";

// ---- Extract DNS config from Consul catalog ----

#[derive(Debug)]
pub struct DnsConfig {
    pub entries: HashMap<DnsEntryKey, DnsEntryValue>,
}

#[derive(Debug, Hash, PartialEq, Eq)]
pub struct DnsEntryKey {
    pub dns_path: String,
    pub record_type: DnsRecordType,
}

#[derive(Debug, PartialEq, Eq)]
pub struct DnsEntryValue {
    pub targets: HashSet<String>,
}

#[derive(Debug, Hash, PartialEq, Eq)]
#[allow(clippy::upper_case_acronyms)]
pub enum DnsRecordType {
    A,
    AAAA,
    CNAME,
}

impl DnsConfig {
    pub fn new() -> Self {
        Self {
            entries: HashMap::new(),
        }
    }

    fn add(&mut self, k: DnsEntryKey, v: DnsEntryValue) {
        if let Some(ent) = self.entries.get_mut(&k) {
            ent.targets.extend(v.targets);
        } else {
            self.entries.insert(k, v);
        }
    }
}

fn parse_d53_tag(tag: &str, node: &ConsulNode) -> Option<(DnsEntryKey, DnsEntryValue)> {
    let splits = tag.split(' ').collect::<Vec<_>>();
    if splits.len() != 2 {
        return None;
    }

    let (record_type, targets) = match splits[0] {
        "d53-a" => match node.meta.get(IPV4_TARGET_METADATA_TAG) {
            Some(tgt) => (DnsRecordType::A, [tgt.to_string()].into_iter().collect()),
            None => {
                warn!("Got d53-a tag `{}` but node {} does not have a {} metadata value. Tag is ignored.", tag, node.node, IPV4_TARGET_METADATA_TAG);
                return None;
            }
        },
        "d53-aaaa" => match node.meta.get(IPV6_TARGET_METADATA_TAG) {
            Some(tgt) => (DnsRecordType::AAAA, [tgt.to_string()].into_iter().collect()),
            None => {
                warn!("Got d53-aaaa tag `{}` but node {} does not have a {} metadata value. Tag is ignored.", tag, node.node, IPV6_TARGET_METADATA_TAG);
                return None;
            }
        },
        "d53-cname" => match node.meta.get(CNAME_TARGET_METADATA_TAG) {
            Some(tgt) => (
                DnsRecordType::CNAME,
                [tgt.to_string()].into_iter().collect(),
            ),
            None => {
                warn!("Got d53-cname tag `{}` but node {} does not have a {} metadata value. Tag is ignored.", tag, node.node, CNAME_TARGET_METADATA_TAG);
                return None;
            }
        },
        _ => return None,
    };

    Some((
        DnsEntryKey {
            dns_path: splits[1].to_string(),
            record_type,
        },
        DnsEntryValue { targets },
    ))
}

fn parse_consul_catalog(catalog: &ConsulNodeCatalog, dns_config: &mut DnsConfig) {
    trace!("Parsing node catalog: {:#?}", catalog);

    for (_, svc) in catalog.services.iter() {
        for tag in svc.tags.iter() {
            if let Some((k, v)) = parse_d53_tag(tag, &catalog.node) {
                dns_config.add(k, v);
            }
        }
    }
}

#[derive(Default)]
struct NodeWatchState {
    last_idx: Option<usize>,
    last_catalog: Option<ConsulNodeCatalog>,
    retries: u32,
}

pub fn spawn_dns_config_task(
    consul: Consul,
    mut must_exit: watch::Receiver<bool>,
) -> watch::Receiver<Arc<DnsConfig>> {
    let (tx, rx) = watch::channel(Arc::new(DnsConfig::new()));

    let consul = Arc::new(consul);

    tokio::spawn(async move {
        let mut nodes = HashMap::new();
        let mut watches = FuturesUnordered::<BoxFuture<'static, (String, Result<_>)>>::new();

        let mut node_site = HashMap::new();

        while !*must_exit.borrow() {
            let list_nodes = select! {
                ln = consul.list_nodes() => ln,
                _ = must_exit.changed() => continue,
            };

            match list_nodes {
                Ok(consul_nodes) => {
                    debug!("Watched consul nodes: {:?}", consul_nodes);
                    for consul_node in consul_nodes {
                        let node = &consul_node.node;
                        if !nodes.contains_key(node) {
                            nodes.insert(node.clone(), NodeWatchState::default());

                            let node = node.to_string();
                            let consul = consul.clone();

                            watches.push(Box::pin(async move {
                                let res = consul.watch_node(&node, None).await;
                                (node, res)
                            }));
                        }
                        if let Some(site) = consul_node.meta.get("site") {
                            node_site.insert(node.clone(), site.clone());
                        }
                    }
                }
                Err(e) => {
                    error!("Could not get Consul node list: {}", e);
                }
            }

            let next_watch = select! {
                nw = watches.next() => nw,
                _ = must_exit.changed() => continue,
            };

            let (node, res): (String, Result<_>) = match next_watch {
                Some(v) => v,
                None => {
                    warn!("No nodes currently watched in dns_config.rs");
                    sleep(Duration::from_secs(10)).await;
                    continue;
                }
            };

            match res {
                Ok((catalog, new_idx)) => {
                    let mut watch_state = nodes.get_mut(&node).unwrap();
                    watch_state.last_idx = Some(new_idx);
                    watch_state.last_catalog = Some(catalog);
                    watch_state.retries = 0;

                    let idx = watch_state.last_idx;
                    let consul = consul.clone();
                    watches.push(Box::pin(async move {
                        let res = consul.watch_node(&node, idx).await;
                        (node, res)
                    }));
                }
                Err(e) => {
                    let mut watch_state = nodes.get_mut(&node).unwrap();
                    watch_state.retries += 1;
                    watch_state.last_idx = None;

                    let will_retry_in =
                        retry_to_time(watch_state.retries, Duration::from_secs(600));
                    error!(
                        "Failed to query consul for node {}. Will retry in {}s. {}",
                        node,
                        will_retry_in.as_secs(),
                        e
                    );

                    let consul = consul.clone();
                    watches.push(Box::pin(async move {
                        sleep(will_retry_in).await;
                        let res = consul.watch_node(&node, None).await;
                        (node, res)
                    }));
                    continue;
                }
            }

            let mut dns_config = DnsConfig::new();
            for (_, watch_state) in nodes.iter() {
                if let Some(catalog) = &watch_state.last_catalog {
                    parse_consul_catalog(catalog, &mut dns_config);
                }
            }

            tx.send(Arc::new(dns_config)).expect("Internal error");
        }
    });

    rx
}

fn retry_to_time(retries: u32, max_time: Duration) -> Duration {
    // 1.2^x seems to be a good value to exponentially increase time at a good pace
    // eg. 1.2^32 = 341 seconds ~= 5 minutes - ie. after 32 retries we wait 5
    // minutes
    Duration::from_secs(cmp::min(
        max_time.as_secs(),
        1.2f64.powf(retries as f64) as u64,
    ))
}

// ---- Display impls ----

impl std::fmt::Display for DnsRecordType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            DnsRecordType::A => write!(f, "A"),
            DnsRecordType::AAAA => write!(f, "AAAA"),
            DnsRecordType::CNAME => write!(f, "CNAME"),
        }
    }
}

impl std::fmt::Display for DnsEntryKey {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{} IN {}", self.dns_path, self.record_type)
    }
}

impl std::fmt::Display for DnsEntryValue {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "[")?;
        for (i, tgt) in self.targets.iter().enumerate() {
            if i > 0 {
                write!(f, " ")?;
            }
            write!(f, "{}", tgt)?;
        }
        write!(f, "]")
    }
}