use std::net::SocketAddr;
use std::sync::{atomic, Arc};
use std::collections::HashMap;
use std::{cmp, time::Duration};

use anyhow::Result;

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

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

use crate::consul::*;

// ---- Extract proxy config from Consul catalog ----

#[derive(Debug)]
pub struct ProxyEntry {
	pub target_addr: SocketAddr,

	pub host: String,
	pub path_prefix: Option<String>,
	pub priority: u32,
	pub add_headers: Vec<(String, String)>,

	// Counts the number of times this proxy server has been called to
	// This implements a round-robin load balancer if there are multiple
	// entries for the same host and same path prefix.
	pub calls: atomic::AtomicU64,
}

#[derive(Debug)]
pub struct ProxyConfig {
	pub entries: Vec<ProxyEntry>,
}

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
	return Duration::from_secs(cmp::min(
		max_time.as_secs(),
		1.2f64.powf(retries as f64) as u64,
	));
}

fn parse_tricot_tag(tag: &str, target_addr: SocketAddr, add_headers: &[(String, String)]) -> Option<ProxyEntry> {
	let splits = tag.split(' ').collect::<Vec<_>>();
	if (splits.len() != 2 && splits.len() != 3) || splits[0] != "tricot" {
		return None;
	}

	let (host, path_prefix) = match splits[1].split_once('/') {
		Some((h, p)) => (h, Some(p.to_string())),
		None => (splits[1], None),
	};

	let priority = match splits.len() {
		3 => splits[2].parse().ok()?,
		_ => 100,
	};

	Some(ProxyEntry {
		target_addr,
		host: host.to_string(),
		path_prefix,
		priority,
		add_headers: add_headers.to_vec(),
		calls: atomic::AtomicU64::from(0),
	})
}

fn parse_tricot_add_header_tag(tag: &str) -> Option<(String, String)> {
	let splits = tag.split(' ').collect::<Vec<_>>();
	if splits.len() == 3 && splits[0] == "tricot-add-header" {
		Some((splits[1].to_string(), splits[2].to_string()))
	} else {
		None
	}
}

fn parse_consul_catalog(catalog: &ConsulNodeCatalog) -> Vec<ProxyEntry> {
	let mut entries = vec![];

	for (_, svc) in catalog.services.iter() {
		let ip_addr = match svc.address.parse() {
			Ok(ip) => ip,
			_ => continue,
		};
		let addr = SocketAddr::new(ip_addr, svc.port);

		let mut add_headers = vec![];
		for tag in svc.tags.iter() {
			if let Some(pair) = parse_tricot_add_header_tag(tag) {
				add_headers.push(pair);
			}
		}

		for tag in svc.tags.iter() {
			if let Some(ent) = parse_tricot_tag(tag, addr, &add_headers[..]) {
				entries.push(ent);
			}
		}
	}

	entries
}

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

pub fn spawn_proxy_config_task(consul: Consul) -> watch::Receiver<Arc<ProxyConfig>> {
	let (tx, rx) = watch::channel(Arc::new(ProxyConfig {
		entries: Vec::new(),
	}));
	
	let consul = Arc::new(consul);

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

		loop {
			match consul.list_nodes().await {
				Ok(consul_nodes) => {
					info!("Watched consul nodes: {:?}", consul_nodes);
					for node in consul_nodes {
						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)
							}));
						}
					}
				}
				Err(e) => {
					warn!("Could not get Consul node list: {}", e);
				}
			}

			let (node, res): (String, Result<_>) = match watches.next().await {
				Some(v) => v,
				None => {
					warn!("No nodes currently watched in proxy_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. Will retry in {}s. {}",
						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 entries = vec![];
			for (_, watch_state) in nodes.iter() {
				if let Some(catalog) = &watch_state.last_catalog {
					entries.extend(parse_consul_catalog(catalog));
				}
			}
			let config = ProxyConfig { entries };

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

	rx
}