use std::path::PathBuf;
use std::sync::Arc;
use std::time::Duration;

use arc_swap::ArcSwapOption;
use futures::future::*;
use futures::stream::*;
use serde::{Deserialize, Serialize};
use tokio::fs;
use tokio::prelude::*;
use tokio::sync::{watch, Mutex};

use crate::data;
use crate::data::*;
use crate::error::Error;
use crate::membership::System;
use crate::rpc_client::*;
use crate::rpc_server::*;

use crate::server::Garage;

pub const INLINE_THRESHOLD: usize = 3072;

const BLOCK_RW_TIMEOUT: Duration = Duration::from_secs(42);
const NEED_BLOCK_QUERY_TIMEOUT: Duration = Duration::from_secs(5);
const RESYNC_RETRY_TIMEOUT: Duration = Duration::from_secs(10);

#[derive(Debug, Serialize, Deserialize)]
pub enum Message {
	Ok,
	GetBlock(Hash),
	PutBlock(PutBlockMessage),
	NeedBlockQuery(Hash),
	NeedBlockReply(bool),
}

#[derive(Debug, Serialize, Deserialize)]
pub struct PutBlockMessage {
	pub hash: Hash,

	#[serde(with = "serde_bytes")]
	pub data: Vec<u8>,
}

impl RpcMessage for Message {}

pub struct BlockManager {
	pub data_dir: PathBuf,
	pub rc: sled::Tree,
	pub resync_queue: sled::Tree,
	pub lock: Mutex<()>,
	pub system: Arc<System>,
	rpc_client: Arc<RpcClient<Message>>,
	pub garage: ArcSwapOption<Garage>,
}

impl BlockManager {
	pub fn new(
		db: &sled::Db,
		data_dir: PathBuf,
		system: Arc<System>,
		rpc_server: &mut RpcServer,
	) -> Arc<Self> {
		let rc = db
			.open_tree("block_local_rc")
			.expect("Unable to open block_local_rc tree");
		rc.set_merge_operator(rc_merge);

		let resync_queue = db
			.open_tree("block_local_resync_queue")
			.expect("Unable to open block_local_resync_queue tree");

		let rpc_path = "block_manager";
		let rpc_client = system.rpc_client::<Message>(rpc_path);

		let block_manager = Arc::new(Self {
			rc,
			resync_queue,
			data_dir,
			lock: Mutex::new(()),
			system,
			rpc_client,
			garage: ArcSwapOption::from(None),
		});
		block_manager
			.clone()
			.register_handler(rpc_server, rpc_path.into());
		block_manager
	}

	fn register_handler(self: Arc<Self>, rpc_server: &mut RpcServer, path: String) {
		rpc_server.add_handler::<Message, _, _>(path, move |msg, _addr| {
			let self2 = self.clone();
			async move {
				match msg {
					Message::PutBlock(m) => self2.write_block(&m.hash, &m.data).await,
					Message::GetBlock(h) => self2.read_block(&h).await,
					Message::NeedBlockQuery(h) => {
						self2.need_block(&h).await.map(Message::NeedBlockReply)
					}
					_ => Err(Error::BadRequest(format!("Unexpected RPC message"))),
				}
			}
		});
	}

	pub async fn spawn_background_worker(self: Arc<Self>) {
		// Launch 2 simultaneous workers for background resync loop preprocessing
		for _i in 0..2usize {
			let bm2 = self.clone();
			self.system
				.background
				.spawn_worker(move |must_exit| bm2.resync_loop(must_exit))
				.await;
		}
	}

	pub async fn write_block(&self, hash: &Hash, data: &[u8]) -> Result<Message, Error> {
		let _lock = self.lock.lock().await;

		let mut path = self.block_dir(hash);
		fs::create_dir_all(&path).await?;

		path.push(hex::encode(hash));
		if fs::metadata(&path).await.is_ok() {
			return Ok(Message::Ok);
		}

		let mut f = fs::File::create(path).await?;
		f.write_all(data).await?;
		drop(f);

		Ok(Message::Ok)
	}

	pub async fn read_block(&self, hash: &Hash) -> Result<Message, Error> {
		let path = self.block_path(hash);

		let mut f = match fs::File::open(&path).await {
			Ok(f) => f,
			Err(e) => {
				// Not found but maybe we should have had it ??
				self.put_to_resync(hash, 0)?;
				return Err(Into::into(e));
			}
		};
		let mut data = vec![];
		f.read_to_end(&mut data).await?;
		drop(f);

		if data::hash(&data[..]) != *hash {
			let _lock = self.lock.lock().await;
			eprintln!("Block {:?} is corrupted. Deleting and resyncing.", hash);
			fs::remove_file(path).await?;
			self.put_to_resync(&hash, 0)?;
			return Err(Error::CorruptData(hash.clone()));
		}

		Ok(Message::PutBlock(PutBlockMessage {
			hash: hash.clone(),
			data,
		}))
	}

	pub async fn need_block(&self, hash: &Hash) -> Result<bool, Error> {
		let needed = self
			.rc
			.get(hash.as_ref())?
			.map(|x| u64_from_bytes(x.as_ref()) > 0)
			.unwrap_or(false);
		if needed {
			let path = self.block_path(hash);
			let exists = fs::metadata(&path).await.is_ok();
			Ok(!exists)
		} else {
			Ok(false)
		}
	}

	fn block_dir(&self, hash: &Hash) -> PathBuf {
		let mut path = self.data_dir.clone();
		path.push(hex::encode(&hash.as_slice()[0..1]));
		path.push(hex::encode(&hash.as_slice()[1..2]));
		path
	}
	fn block_path(&self, hash: &Hash) -> PathBuf {
		let mut path = self.block_dir(hash);
		path.push(hex::encode(hash.as_ref()));
		path
	}

	pub fn block_incref(&self, hash: &Hash) -> Result<(), Error> {
		let old_rc = self.rc.get(&hash)?;
		self.rc.merge(&hash, vec![1])?;
		if old_rc.map(|x| u64_from_bytes(&x[..]) == 0).unwrap_or(true) {
			self.put_to_resync(&hash, BLOCK_RW_TIMEOUT.as_millis() as u64)?;
		}
		Ok(())
	}

	pub fn block_decref(&self, hash: &Hash) -> Result<(), Error> {
		let new_rc = self.rc.merge(&hash, vec![0])?;
		if new_rc.map(|x| u64_from_bytes(&x[..]) == 0).unwrap_or(true) {
			self.put_to_resync(&hash, 0)?;
		}
		Ok(())
	}

	fn put_to_resync(&self, hash: &Hash, delay_millis: u64) -> Result<(), Error> {
		let when = now_msec() + delay_millis;
		eprintln!("Put resync_queue: {} {:?}", when, hash);
		let mut key = u64::to_be_bytes(when).to_vec();
		key.extend(hash.as_ref());
		self.resync_queue.insert(key, hash.as_ref())?;
		Ok(())
	}

	async fn resync_loop(self: Arc<Self>, must_exit: watch::Receiver<bool>) -> Result<(), Error> {
		while !*must_exit.borrow() {
			if let Some((time_bytes, hash_bytes)) = self.resync_queue.pop_min()? {
				let time_msec = u64_from_bytes(&time_bytes[0..8]);
				eprintln!(
					"First in resync queue: {} (now = {})",
					time_msec,
					now_msec()
				);
				if now_msec() >= time_msec {
					let mut hash = [0u8; 32];
					hash.copy_from_slice(hash_bytes.as_ref());
					let hash = Hash::from(hash);

					if let Err(e) = self.resync_iter(&hash).await {
						eprintln!("Failed to resync block {:?}, retrying later: {}", hash, e);
						self.put_to_resync(&hash, RESYNC_RETRY_TIMEOUT.as_millis() as u64)?;
					}
					continue;
				} else {
					self.resync_queue.insert(time_bytes, hash_bytes)?;
				}
			}
			tokio::time::delay_for(Duration::from_secs(1)).await;
		}
		Ok(())
	}

	async fn resync_iter(&self, hash: &Hash) -> Result<(), Error> {
		let path = self.block_path(hash);

		let exists = fs::metadata(&path).await.is_ok();
		let needed = self
			.rc
			.get(hash.as_ref())?
			.map(|x| u64_from_bytes(x.as_ref()) > 0)
			.unwrap_or(false);

		eprintln!(
			"Resync block {:?}: exists {}, needed {}",
			hash, exists, needed
		);

		if exists && !needed {
			let garage = self.garage.load_full().unwrap();
			let active_refs = garage
				.block_ref_table
				.get_range(&hash, None, Some(()), 1)
				.await?;
			let needed_by_others = !active_refs.is_empty();
			if needed_by_others {
				let ring = garage.system.ring.borrow().clone();
				let who = ring.walk_ring(&hash, garage.system.config.data_replication_factor);
				let msg = Arc::new(Message::NeedBlockQuery(hash.clone()));
				let who_needs_fut = who.iter().map(|to| {
					self.rpc_client
						.call(to, msg.clone(), NEED_BLOCK_QUERY_TIMEOUT)
				});
				let who_needs = join_all(who_needs_fut).await;

				let mut need_nodes = vec![];
				let mut errors = 0;
				for (node, needed) in who.into_iter().zip(who_needs.iter()) {
					match needed {
						Ok(Message::NeedBlockReply(true)) => {
							need_nodes.push(node);
						}
						Err(_) => {
							errors += 1;
						}
						_ => (),
					}
				}

				if errors > (garage.system.config.data_replication_factor - 1) / 2 {
					return Err(Error::Message(format!(
						"Should delete block, but not enough nodes confirm that they have it."
					)));
				}

				if need_nodes.len() > 0 {
					let put_block_message = self.read_block(hash).await?;
					let put_responses = self
						.rpc_client
						.call_many(&need_nodes[..], put_block_message, BLOCK_RW_TIMEOUT)
						.await;
					for resp in put_responses {
						resp?;
					}
				}
			}
			fs::remove_file(path).await?;
			self.resync_queue.remove(&hash)?;
		}

		if needed && !exists {
			// TODO find a way to not do this if they are sending it to us
			// Let's suppose this isn't an issue for now with the BLOCK_RW_TIMEOUT delay
			// between the RC being incremented and this part being called.
			let block_data = self.rpc_get_block(&hash).await?;
			self.write_block(hash, &block_data[..]).await?;
		}

		Ok(())
	}

	pub async fn rpc_get_block(&self, hash: &Hash) -> Result<Vec<u8>, Error> {
		let ring = self.system.ring.borrow().clone();
		let who = ring.walk_ring(&hash, self.system.config.data_replication_factor);
		let msg = Arc::new(Message::GetBlock(hash.clone()));
		let mut resp_stream = who
			.iter()
			.map(|to| self.rpc_client.call(to, msg.clone(), BLOCK_RW_TIMEOUT))
			.collect::<FuturesUnordered<_>>();

		while let Some(resp) = resp_stream.next().await {
			if let Ok(Message::PutBlock(msg)) = resp {
				if data::hash(&msg.data[..]) == *hash {
					return Ok(msg.data);
				}
			}
		}
		Err(Error::Message(format!(
			"Unable to read block {:?}: no valid blocks returned",
			hash
		)))
	}

	pub async fn rpc_put_block(&self, hash: Hash, data: Vec<u8>) -> Result<(), Error> {
		let ring = self.system.ring.borrow().clone();
		let who = ring.walk_ring(&hash, self.system.config.data_replication_factor);
		self.rpc_client
			.try_call_many(
				&who[..],
				Message::PutBlock(PutBlockMessage { hash, data }),
				(self.system.config.data_replication_factor + 1) / 2,
				BLOCK_RW_TIMEOUT,
			)
			.await?;
		Ok(())
	}
}

fn u64_from_bytes(bytes: &[u8]) -> u64 {
	assert!(bytes.len() == 8);
	let mut x8 = [0u8; 8];
	x8.copy_from_slice(bytes);
	u64::from_be_bytes(x8)
}

fn rc_merge(_key: &[u8], old: Option<&[u8]>, new: &[u8]) -> Option<Vec<u8>> {
	let old = old.map(u64_from_bytes).unwrap_or(0);
	assert!(new.len() == 1);
	let new = match new[0] {
		0 => {
			if old > 0 {
				old - 1
			} else {
				0
			}
		}
		1 => old + 1,
		_ => unreachable!(),
	};
	if new == 0 {
		None
	} else {
		Some(u64::to_be_bytes(new).to_vec())
	}
}