// Copyright 2015-2018 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

use std::sync::Arc;
use std::slice;
use std::collections::{hash_map, HashMap, BTreeSet};

use error;
use listener::{Listener, NoopListener};
use options::Options;
use ready::{Ready, Readiness};
use scoring::{self, Scoring, ScoreWithRef};
use status::{LightStatus, Status};
use transactions::{AddResult, Transactions};

use {VerifiedTransaction};

/// Internal representation of transaction.
///
/// Includes unique insertion id that can be used for scoring explictly,
/// but internally is used to resolve conflicts in case of equal scoring
/// (newer transactionsa are preferred).
#[derive(Debug)]
pub struct Transaction<T> {
	/// Sequential id of the transaction
	pub insertion_id: u64,
	/// Shared transaction
	pub transaction: Arc<T>,
}

impl<T> Clone for Transaction<T> {
	fn clone(&self) -> Self {
		Transaction {
			insertion_id: self.insertion_id,
			transaction: self.transaction.clone(),
		}
	}
}

impl<T> ::std::ops::Deref for Transaction<T> {
	type Target = Arc<T>;

	fn deref(&self) -> &Self::Target {
		&self.transaction
	}
}

/// A transaction pool.
#[derive(Debug)]
pub struct Pool<T: VerifiedTransaction, S: Scoring<T>, L = NoopListener> {
	listener: L,
	scoring: S,
	options: Options,
	mem_usage: usize,

	transactions: HashMap<T::Sender, Transactions<T, S>>,
	by_hash: HashMap<T::Hash, Transaction<T>>,

	best_transactions: BTreeSet<ScoreWithRef<T, S::Score>>,
	worst_transactions: BTreeSet<ScoreWithRef<T, S::Score>>,

	insertion_id: u64,
}

impl<T: VerifiedTransaction, S: Scoring<T> + Default> Default for Pool<T, S> {
	fn default() -> Self {
		Self::with_scoring(S::default(), Options::default())
	}
}

impl<T: VerifiedTransaction, S: Scoring<T> + Default> Pool<T, S> {
	/// Creates a new `Pool` with given options
	/// and default `Scoring` and `Listener`.
	pub fn with_options(options: Options) -> Self {
		Self::with_scoring(S::default(), options)
	}
}

impl<T: VerifiedTransaction, S: Scoring<T>> Pool<T, S> {
	/// Creates a new `Pool` with given `Scoring` and options.
	pub fn with_scoring(scoring: S, options: Options) -> Self {
		Self::new(NoopListener, scoring, options)
	}
}

const INITIAL_NUMBER_OF_SENDERS: usize = 16;

impl<T, S, L> Pool<T, S, L> where
	T: VerifiedTransaction,
	S: Scoring<T>,
	L: Listener<T>,
{
	/// Creates new `Pool` with given `Scoring`, `Listener` and options.
	pub fn new(listener: L, scoring: S, options: Options) -> Self {
		let transactions = HashMap::with_capacity(INITIAL_NUMBER_OF_SENDERS);
		let by_hash = HashMap::with_capacity(options.max_count / 16);

		Pool {
			listener,
			scoring,
			options,
			mem_usage: 0,
			transactions,
			by_hash,
			best_transactions: Default::default(),
			worst_transactions: Default::default(),
			insertion_id: 0,
		}

	}

	/// Attempts to import new transaction to the pool, returns a `Arc<T>` or an `Error`.
	///
	/// NOTE: Since `Ready`ness is separate from the pool it's possible to import stalled transactions.
	/// It's the caller responsibility to make sure that's not the case.
	///
	/// NOTE: The transaction may push out some other transactions from the pool
	/// either because of limits (see `Options`) or because `Scoring` decides that the transaction
	/// replaces an existing transaction from that sender.
	/// If any limit is reached the transaction with the lowest `Score` is evicted to make room.
	///
	/// The `Listener` will be informed on any drops or rejections.
	pub fn import(&mut self, transaction: T) -> error::Result<Arc<T>> {
		let mem_usage = transaction.mem_usage();

		ensure!(!self.by_hash.contains_key(transaction.hash()), error::ErrorKind::AlreadyImported(format!("{:?}", transaction.hash())));

		self.insertion_id += 1;
		let transaction = Transaction {
			insertion_id: self.insertion_id,
			transaction: Arc::new(transaction),
		};

		// TODO [ToDr] Most likely move this after the transaction is inserted.
		// Avoid using should_replace, but rather use scoring for that.
		{
			let remove_worst = |s: &mut Self, transaction| {
				match s.remove_worst(transaction) {
					Err(err) => {
						s.listener.rejected(transaction, err.kind());
						Err(err)
					},
					Ok(None) => Ok(false),
					Ok(Some(removed)) => {
						s.listener.dropped(&removed, Some(transaction));
						s.finalize_remove(removed.hash());
						Ok(true)
					},
				}
			};

			while self.by_hash.len() + 1 > self.options.max_count {
				trace!("Count limit reached: {} > {}", self.by_hash.len() + 1, self.options.max_count);
				if !remove_worst(self, &transaction)? {
					break;
				}
			}

			while self.mem_usage + mem_usage > self.options.max_mem_usage {
				trace!("Mem limit reached: {} > {}", self.mem_usage + mem_usage, self.options.max_mem_usage);
				if !remove_worst(self, &transaction)? {
					break;
				}
			}
		}

		let (result, prev_state, current_state) = {
			let transactions = self.transactions.entry(transaction.sender().clone()).or_insert_with(Transactions::default);
			// get worst and best transactions for comparison
			let prev = transactions.worst_and_best();
			let result = transactions.add(transaction, &self.scoring, self.options.max_per_sender);
			let current = transactions.worst_and_best();
			(result, prev, current)
		};

		// update best and worst transactions from this sender (if required)
		self.update_senders_worst_and_best(prev_state, current_state);

		match result {
			AddResult::Ok(tx) => {
				self.listener.added(&tx, None);
				self.finalize_insert(&tx, None);
				Ok(tx.transaction)
			},
			AddResult::PushedOut { new, old } |
			AddResult::Replaced { new, old } => {
				self.listener.added(&new, Some(&old));
				self.finalize_insert(&new, Some(&old));
				Ok(new.transaction)
			},
			AddResult::TooCheap { new, old } => {
				let error = error::ErrorKind::TooCheapToReplace(format!("{:x}", old.hash()), format!("{:x}", new.hash()));
				self.listener.rejected(&new, &error);
				bail!(error)
			},
			AddResult::TooCheapToEnter(new, score) => {
				let error = error::ErrorKind::TooCheapToEnter(format!("{:x}", new.hash()), format!("{:?}", score));
				self.listener.rejected(&new, &error);
				bail!(error)
			}
		}
	}

	/// Updates state of the pool statistics if the transaction was added to a set.
	fn finalize_insert(&mut self, new: &Transaction<T>, old: Option<&Transaction<T>>) {
		self.mem_usage += new.mem_usage();
		self.by_hash.insert(new.hash().clone(), new.clone());

		if let Some(old) = old {
			self.finalize_remove(old.hash());
		}
	}

	/// Updates the pool statistics if transaction was removed.
	fn finalize_remove(&mut self, hash: &T::Hash) -> Option<Arc<T>> {
		self.by_hash.remove(hash).map(|old| {
			self.mem_usage -= old.transaction.mem_usage();
			old.transaction
		})
	}

	/// Updates best and worst transactions from a sender.
	fn update_senders_worst_and_best(
		&mut self,
		previous: Option<((S::Score, Transaction<T>), (S::Score, Transaction<T>))>,
		current: Option<((S::Score, Transaction<T>), (S::Score, Transaction<T>))>,
	) {
		let worst_collection = &mut self.worst_transactions;
		let best_collection = &mut self.best_transactions;

		let is_same = |a: &(S::Score, Transaction<T>), b: &(S::Score, Transaction<T>)| {
			a.0 == b.0 && a.1.hash() == b.1.hash()
		};

		let update = |collection: &mut BTreeSet<_>, (score, tx), remove| if remove {
			collection.remove(&ScoreWithRef::new(score, tx));
		} else {
			collection.insert(ScoreWithRef::new(score, tx));
		};

		match (previous, current) {
			(None, Some((worst, best))) => {
				update(worst_collection, worst, false);
				update(best_collection, best, false);
			},
			(Some((worst, best)), None) => {
				// all transactions from that sender has been removed.
				// We can clear a hashmap entry.
				self.transactions.remove(worst.1.sender());
				update(worst_collection, worst, true);
				update(best_collection, best, true);
			},
			(Some((w1, b1)), Some((w2, b2))) => {
				if !is_same(&w1, &w2) {
					update(worst_collection, w1, true);
					update(worst_collection, w2, false);
				}
				if !is_same(&b1, &b2) {
					update(best_collection, b1, true);
					update(best_collection, b2, false);
				}
			},
			(None, None) => {},
		}
	}

	/// Attempts to remove the worst transaction from the pool if it's worse than the given one.
	///
	/// Returns `None` in case we couldn't decide if the transaction should replace the worst transaction or not.
	/// In such case we will accept the transaction even though it is going to exceed the limit.
	fn remove_worst(&mut self, transaction: &Transaction<T>) -> error::Result<Option<Transaction<T>>> {
		let to_remove = match self.worst_transactions.iter().next_back() {
			// No elements to remove? and the pool is still full?
			None => {
				warn!("The pool is full but there are no transactions to remove.");
				return Err(error::ErrorKind::TooCheapToEnter(format!("{:?}", transaction.hash()), "unknown".into()).into());
			},
			Some(old) => match self.scoring.should_replace(&old.transaction, transaction) {
				// We can't decide which of them should be removed, so accept both.
				scoring::Choice::InsertNew => None,
				// New transaction is better than the worst one so we can replace it.
				scoring::Choice::ReplaceOld => Some(old.clone()),
				// otherwise fail
				scoring::Choice::RejectNew => {
					return Err(error::ErrorKind::TooCheapToEnter(format!("{:?}", transaction.hash()), format!("{:?}", old.score)).into())
				},
			},
		};

		if let Some(to_remove) = to_remove {
			// Remove from transaction set
			self.remove_from_set(to_remove.transaction.sender(), |set, scoring| {
				set.remove(&to_remove.transaction, scoring)
			});

			Ok(Some(to_remove.transaction))
		} else {
			Ok(None)
		}
	}

	/// Removes transaction from sender's transaction `HashMap`.
	fn remove_from_set<R, F: FnOnce(&mut Transactions<T, S>, &S) -> R>(&mut self, sender: &T::Sender, f: F) -> Option<R> {
		let (prev, next, result) = if let Some(set) = self.transactions.get_mut(sender) {
			let prev = set.worst_and_best();
			let result = f(set, &self.scoring);
			(prev, set.worst_and_best(), result)
		} else {
			return None;
		};

		self.update_senders_worst_and_best(prev, next);
		Some(result)
	}

	/// Clears pool from all transactions.
	/// This causes a listener notification that all transactions were dropped.
	/// NOTE: the drop-notification order will be arbitrary.
	pub fn clear(&mut self) {
		self.mem_usage = 0;
		self.transactions.clear();
		self.best_transactions.clear();
		self.worst_transactions.clear();

		for (_hash, tx) in self.by_hash.drain() {
			self.listener.dropped(&tx.transaction, None)
		}
	}

	/// Removes single transaction from the pool.
	/// Depending on the `is_invalid` flag the listener
	/// will either get a `cancelled` or `invalid` notification.
	pub fn remove(&mut self, hash: &T::Hash, is_invalid: bool) -> Option<Arc<T>> {
		if let Some(tx) = self.finalize_remove(hash) {
			self.remove_from_set(tx.sender(), |set, scoring| {
				set.remove(&tx, scoring)
			});
			if is_invalid {
				self.listener.invalid(&tx);
			} else {
				self.listener.canceled(&tx);
			}
			Some(tx)
		} else {
			None
		}
	}

	/// Removes all stalled transactions from given sender.
	fn remove_stalled<R: Ready<T>>(&mut self, sender: &T::Sender, ready: &mut R) -> usize {
		let removed_from_set = self.remove_from_set(sender, |transactions, scoring| {
			transactions.cull(ready, scoring)
		});

		match removed_from_set {
			Some(removed) => {
				let len = removed.len();
				for tx in removed {
					self.finalize_remove(tx.hash());
					self.listener.culled(&tx);
				}
				len
			},
			None => 0,
		}
	}

	/// Removes all stalled transactions from given sender list (or from all senders).
	pub fn cull<R: Ready<T>>(&mut self, senders: Option<&[T::Sender]>, mut ready: R) -> usize {
		let mut removed = 0;
		match senders {
			Some(senders) => {
				for sender in senders {
					removed += self.remove_stalled(sender, &mut ready);
				}
			},
			None => {
				let senders = self.transactions.keys().cloned().collect::<Vec<_>>();
				for sender in senders {
					removed += self.remove_stalled(&sender, &mut ready);
				}
			},
		}

		removed
	}

	/// Returns a transaction if it's part of the pool or `None` otherwise.
	pub fn find(&self, hash: &T::Hash) -> Option<Arc<T>> {
		self.by_hash.get(hash).map(|t| t.transaction.clone())
	}

	/// Returns worst transaction in the queue (if any).
	pub fn worst_transaction(&self) -> Option<Arc<T>> {
		self.worst_transactions.iter().next_back().map(|x| x.transaction.transaction.clone())
	}

	/// Returns true if the pool is at it's capacity.
	pub fn is_full(&self) -> bool {
		self.by_hash.len() >= self.options.max_count
			|| self.mem_usage >= self.options.max_mem_usage
	}

	/// Returns senders ordered by priority of their transactions.
	pub fn senders(&self) -> impl Iterator<Item=&T::Sender> {
		self.best_transactions.iter().map(|tx| tx.transaction.sender())
	}

	/// Returns an iterator of pending (ready) transactions.
	pub fn pending<R: Ready<T>>(&self, ready: R) -> PendingIterator<T, R, S, L> {
		PendingIterator {
			ready,
			best_transactions: self.best_transactions.clone(),
			pool: self,
		}
	}

	/// Returns pending (ready) transactions from given sender.
	pub fn pending_from_sender<R: Ready<T>>(&self, ready: R, sender: &T::Sender) -> PendingIterator<T, R, S, L> {
		let best_transactions = self.transactions.get(sender)
			.and_then(|transactions| transactions.worst_and_best())
			.map(|(_, best)| ScoreWithRef::new(best.0, best.1))
			.map(|s| {
				let mut set = BTreeSet::new();
				set.insert(s);
				set
			})
			.unwrap_or_default();

		PendingIterator {
			ready,
			best_transactions,
			pool: self,
		}
	}

	/// Returns unprioritized list of ready transactions.
	pub fn unordered_pending<R: Ready<T>>(&self, ready: R) -> UnorderedIterator<T, R, S> {
		UnorderedIterator {
			ready,
			senders: self.transactions.iter(),
			transactions: None,
		}
	}

	/// Update score of transactions of a particular sender.
	pub fn update_scores(&mut self, sender: &T::Sender, event: S::Event) {
		let res = if let Some(set) = self.transactions.get_mut(sender) {
			let prev = set.worst_and_best();
			set.update_scores(&self.scoring, event);
			let current = set.worst_and_best();
			Some((prev, current))
		} else {
			None
		};

		if let Some((prev, current)) = res {
			self.update_senders_worst_and_best(prev, current);
		}
	}

	/// Computes the full status of the pool (including readiness).
	pub fn status<R: Ready<T>>(&self, mut ready: R) -> Status {
		let mut status = Status::default();

		for (_sender, transactions) in &self.transactions {
			let len = transactions.len();
			for (idx, tx) in transactions.iter().enumerate() {
				match ready.is_ready(tx) {
					Readiness::Stale => status.stalled += 1,
					Readiness::Ready => status.pending += 1,
					Readiness::Future => {
						status.future += len - idx;
						break;
					}
				}
			}
		}

		status
	}

	/// Returns light status of the pool.
	pub fn light_status(&self) -> LightStatus {
		LightStatus {
			mem_usage: self.mem_usage,
			transaction_count: self.by_hash.len(),
			senders: self.transactions.len(),
		}
	}

	/// Returns current pool options.
	pub fn options(&self) -> Options {
		self.options.clone()
	}

	/// Borrows listener instance.
	pub fn listener(&self) -> &L {
		&self.listener
	}

	/// Borrows scoring instance.
	pub fn scoring(&self) -> &S {
		&self.scoring
	}

	/// Borrows listener mutably.
	pub fn listener_mut(&mut self) -> &mut L {
		&mut self.listener
	}
}

/// An iterator over all pending (ready) transactions in unoredered fashion.
///
/// NOTE: Current implementation will iterate over all transactions from particular sender
/// ordered by nonce, but that might change in the future.
///
/// NOTE: the transactions are not removed from the queue.
/// You might remove them later by calling `cull`.
pub struct UnorderedIterator<'a, T, R, S> where
	T: VerifiedTransaction + 'a,
	S: Scoring<T> + 'a,
{
	ready: R,
	senders: hash_map::Iter<'a, T::Sender, Transactions<T, S>>,
	transactions: Option<slice::Iter<'a, Transaction<T>>>,
}

impl<'a, T, R, S> Iterator for UnorderedIterator<'a, T, R, S> where
	T: VerifiedTransaction,
	R: Ready<T>,
	S: Scoring<T>,
{
	type Item = Arc<T>;

	fn next(&mut self) -> Option<Self::Item> {
		loop {
			if let Some(transactions) = self.transactions.as_mut() {
				if let Some(tx) = transactions.next() {
					match self.ready.is_ready(&tx) {
						Readiness::Ready => {
							return Some(tx.transaction.clone());
						},
						state => trace!("[{:?}] Ignoring {:?} transaction.", tx.hash(), state),
					}
				}
			}

			// otherwise fallback and try next sender
			let next_sender = self.senders.next()?;
			self.transactions = Some(next_sender.1.iter());
		}
	}
}


/// An iterator over all pending (ready) transactions.
/// NOTE: the transactions are not removed from the queue.
/// You might remove them later by calling `cull`.
pub struct PendingIterator<'a, T, R, S, L> where
	T: VerifiedTransaction + 'a,
	S: Scoring<T> + 'a,
	L: 'a,
{
	ready: R,
	best_transactions: BTreeSet<ScoreWithRef<T, S::Score>>,
	pool: &'a Pool<T, S, L>,
}

impl<'a, T, R, S, L> Iterator for PendingIterator<'a, T, R, S, L> where
	T: VerifiedTransaction,
	R: Ready<T>,
	S: Scoring<T>,
{
	type Item = Arc<T>;

	fn next(&mut self) -> Option<Self::Item> {
		while !self.best_transactions.is_empty() {
			let best = {
				let best = self.best_transactions.iter().next().expect("current_best is not empty; qed").clone();
				self.best_transactions.take(&best).expect("Just taken from iterator; qed")
			};

			match self.ready.is_ready(&best.transaction) {
				Readiness::Ready => {
					// retrieve next one from that sender.
					let next = self.pool.transactions
						.get(best.transaction.sender())
						.and_then(|s| s.find_next(&best.transaction, &self.pool.scoring));
					if let Some((score, tx)) = next {
						self.best_transactions.insert(ScoreWithRef::new(score, tx));
					}

					return Some(best.transaction.transaction)
				},
				state => trace!("[{:?}] Ignoring {:?} transaction.", best.transaction.hash(), state),
			}
		}

		None
	}
}