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    use std::collections::{HashMap, HashSet, VecDeque};
    use std::collections::hash_map::Entry;
    use linked_hash_map::LinkedHashMap;
    use time;
    use chain::IndexedTransaction;
    use primitives::hash::H256;

    #[derive(Debug)]
    /// Storage for transactions, for which we have no parent transactions yet.
    /// Transactions from this storage are either moved to verification queue, or removed at all.
    pub struct OrphanTransactionsPool {
    	/// Orphan transactions by hash.
    	by_hash: LinkedHashMap<H256, OrphanTransaction>,
    	/// Orphan transactions by parent' transaction hash
    	by_parent: HashMap<H256, HashSet<H256>>,
    }

    #[derive(Debug)]
    /// Orphan transaction representation.
    pub struct OrphanTransaction {
    	/// Time when this transaction was inserted to the pool
    	pub insertion_time: f64,
    	/// Transaction itself
    	pub transaction: IndexedTransaction,
    	/// Parent transactions, which are still unknown to us
    	pub unknown_parents: HashSet<H256>,
    }

    impl OrphanTransactionsPool {
    	/// Create new pool
    	pub fn new() -> Self {
    		OrphanTransactionsPool {
    			by_hash: LinkedHashMap::new(),
    			by_parent: HashMap::new(),
    		}
    	}

    	#[cfg(test)]
    	/// Get total number of transactions in pool
    	pub fn len(&self) -> usize {
    		self.by_hash.len()
    	}

    	/// Get unknown transactions in the insertion order
    	pub fn transactions(&self) -> &LinkedHashMap<H256, OrphanTransaction> {
    		&self.by_hash
    	}

    	/// Check if pool contains this transaction
    	pub fn contains(&self, hash: &H256) -> bool {
    		self.by_hash.contains_key(hash)
    	}

    	/// Insert orphan transaction
    	pub fn insert(&mut self, transaction: IndexedTransaction, unknown_parents: HashSet<H256>) {
    		assert!(!self.by_hash.contains_key(&transaction.hash));
    		assert!(unknown_parents.iter().all(|h| transaction.raw.inputs.iter().any(|i| &i.previous_output.hash == h)));

    		for unknown_parent in &unknown_parents {
    			self.by_parent.entry(unknown_parent.clone())
    				.or_insert_with(HashSet::new)
    				.insert(transaction.hash.clone());
    		}

    		let hash = transaction.hash.clone();
    		self.by_hash.insert(hash, OrphanTransaction::new(transaction, unknown_parents));
    	}

    	/// Remove all transactions, depending on this parent
    	pub fn remove_transactions_for_parent(&mut self, hash: &H256) -> Vec<IndexedTransaction> {
    		assert!(!self.by_hash.contains_key(hash));

    		let mut removal_queue: VecDeque<H256> = VecDeque::new();
    		removal_queue.push_back(hash.clone());

    		let mut removed_orphans: Vec<IndexedTransaction> = Vec::new();
    		while let Some(hash) = removal_queue.pop_front() {
    			// remove direct children of hash
    			let mut removed_orphans_hashes: Vec<H256> = Vec::new();
    			if let Entry::Occupied(children_entry) = self.by_parent.entry(hash.clone()) {
    				for child in children_entry.get() {
    					let all_parents_are_known = match self.by_hash.get_mut(child) {
    						Some(child_entry) => child_entry.remove_known_parent(&hash),
    						None => false,
    					};

    					if all_parents_are_known {
    						removed_orphans_hashes.push(child.clone());
    						removed_orphans.push(self.by_hash.remove(child).expect("checked couple of lines above").transaction);
    					}
    				}

    				children_entry.remove_entry();
    			}

    			// then also remove grandchildren of hash & so on
    			removal_queue.extend(removed_orphans_hashes);
    		}

    		removed_orphans
    	}

    	/// Remove transactions with given hashes + all dependent blocks
    	pub fn remove_transactions(&mut self, hashes: &[H256]) -> Vec<IndexedTransaction> {
    		let mut removed: Vec<IndexedTransaction> = Vec::new();
    		for hash in hashes {
    			if let Some(transaction) = self.by_hash.remove(hash) {
    				removed.push(transaction.transaction);
    			}
    			removed.extend(self.remove_transactions_for_parent(hash));
    		}
    		removed
    	}
    }

    impl OrphanTransaction {
    	/// Create new orphaned transaction
    	pub fn new(transaction: IndexedTransaction, unknown_parents: HashSet<H256>) -> Self {
    		OrphanTransaction {
    			insertion_time: time::precise_time_s(),
    			transaction: transaction,
    			unknown_parents: unknown_parents,
    		}
    	}

    	/// Remove parent, which is now known. Return true if all parents all now known
    	pub fn remove_known_parent(&mut self, parent_hash: &H256) -> bool {
    		self.unknown_parents.remove(parent_hash);
    		self.unknown_parents.is_empty()
    	}
    }

    #[cfg(test)]
    mod tests {
    	extern crate test_data;

    	use std::collections::HashSet;
    	use self::test_data::{TransactionBuilder, ChainBuilder};
    	use primitives::hash::H256;
    	use super::OrphanTransactionsPool;

    	#[test]
    	fn orphan_transaction_pool_empty_on_start() {
    		let pool = OrphanTransactionsPool::new();
    		assert_eq!(pool.len(), 0);
    	}

    	#[test]
    	fn orphan_transaction_pool_insert_dependent_transactions() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)			// t1
    			.into_input(0).add_output(200).store(chain)				// t1 -> t2
    			.into_input(0).add_output(300).store(chain)				// t1 -> t2 -> t3
    			.set_default_input(0).set_output(400).store(chain)		// t4
    			.into_input(0).set_output(500).store(chain);			// t4 -> t5
    		let t2_unknown: HashSet<H256> = chain.at(1).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t3_unknown: HashSet<H256> = chain.at(2).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t5_unknown: HashSet<H256> = chain.at(4).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();

    		let mut pool = OrphanTransactionsPool::new();
    		pool.insert(chain.at(1).into(), t2_unknown); // t2
    		pool.insert(chain.at(2).into(), t3_unknown); // t3
    		pool.insert(chain.at(4).into(), t5_unknown); // t5
    		assert_eq!(pool.len(), 3);

    		let removed = pool.remove_transactions_for_parent(&chain.at(0).hash());
    		assert_eq!(pool.len(), 1);
    		let removed: Vec<H256> = removed.into_iter().map(|tx| tx.hash).collect();
    		assert_eq!(removed, vec![chain.at(1).hash(), chain.at(2).hash()]);

    		let removed = pool.remove_transactions_for_parent(&chain.at(3).hash());
    		assert_eq!(pool.len(), 0);
    		let removed: Vec<H256> = removed.into_iter().map(|tx| tx.hash).collect();
    		assert_eq!(removed, vec![chain.at(4).hash()]);
    	}

    	#[test]
    	fn orphan_transaction_pool_remove_transactions() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)			// t1
    			.into_input(0).add_output(200).store(chain)				// t1 -> t2
    			.into_input(0).add_output(300).store(chain)				// t1 -> t2 -> t3
    			.set_default_input(0).set_output(400).store(chain)		// t4
    			.into_input(0).set_output(500).store(chain)				// t4 -> t5
    			.set_default_input(0).set_output(600).store(chain)		// t6
    			.into_input(0).set_output(700).store(chain);			// t6 -> t7
    		let t2_unknown: HashSet<H256> = chain.at(1).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t3_unknown: HashSet<H256> = chain.at(2).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t5_unknown: HashSet<H256> = chain.at(4).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t7_unknown: HashSet<H256> = chain.at(6).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();

    		let mut pool = OrphanTransactionsPool::new();
    		pool.insert(chain.at(1).into(), t2_unknown); // t2
    		pool.insert(chain.at(2).into(), t3_unknown); // t3
    		pool.insert(chain.at(4).into(), t5_unknown); // t5
    		pool.insert(chain.at(6).into(), t7_unknown); // t7
    		assert_eq!(pool.len(), 4);

    		let removed = pool.remove_transactions(&vec![chain.at(1).hash(), chain.at(3).hash()]);
    		assert_eq!(pool.len(), 1);
    		let removed: Vec<H256> = removed.into_iter().map(|tx| tx.hash).collect();
    		assert_eq!(removed, vec![chain.at(1).hash(), chain.at(2).hash(), chain.at(4).hash()]);

    		let removed = pool.remove_transactions(&vec![chain.at(6).hash()]);
    		assert_eq!(pool.len(), 0);
    		let removed: Vec<H256> = removed.into_iter().map(|tx| tx.hash).collect();
    		assert_eq!(removed, vec![chain.at(6).hash()]);
    	}

    	#[test]
    	fn orphan_transaction_pool_remove_transactions_child_before_parent() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)			// t1
    			.into_input(0).add_output(200).store(chain)				// t1 -> t2
    			.into_input(0).add_output(300).store(chain);			// t1 -> t2 -> t3
    		let t2_unknown: HashSet<H256> = chain.at(1).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();
    		let t3_unknown: HashSet<H256> = chain.at(2).inputs.iter().map(|i| i.previous_output.hash.clone()).collect();

    		let mut pool = OrphanTransactionsPool::new();
    		pool.insert(chain.at(1).into(), t2_unknown); // t2
    		pool.insert(chain.at(2).into(), t3_unknown); // t3

    		pool.remove_transactions(&[chain.at(2).hash(), chain.at(1).hash()]);
    	}
    }

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