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    1126

    use std::collections::{VecDeque, HashSet};
    use std::fmt;
    use linked_hash_map::LinkedHashMap;
    use chain::{BlockHeader, Transaction, IndexedBlockHeader, IndexedBlock, IndexedTransaction};
    use storage;
    use miner::{MemoryPoolOrderingStrategy, MemoryPoolInformation};
    use network::ConsensusParams;
    use primitives::bytes::Bytes;
    use primitives::hash::H256;
    use utils::{BestHeadersChain, BestHeadersChainInformation, HashQueueChain, HashPosition};
    use types::{BlockHeight, StorageRef, MemoryPoolRef};

    /// Index of 'verifying' queue
    const VERIFYING_QUEUE: usize = 0;
    /// Index of 'requested' queue
    const REQUESTED_QUEUE: usize = 1;
    /// Index of 'scheduled' queue
    const SCHEDULED_QUEUE: usize = 2;
    /// Number of hash queues
    const NUMBER_OF_QUEUES: usize = 3;

    /// Block insertion result
    #[derive(Default, PartialEq)]
    pub struct BlockInsertionResult {
    	/// Hashes of blocks, which were canonized during this insertion procedure. Order matters
    	pub canonized_blocks_hashes: Vec<H256>,
    	/// Transaction to 'reverify'. Order matters
    	pub transactions_to_reverify: Vec<IndexedTransaction>,
    }

    impl fmt::Debug for BlockInsertionResult {
    	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    		f.debug_struct("BlockInsertionResult")
    			.field("canonized_blocks_hashes", &self.canonized_blocks_hashes.iter().map(H256::reversed).collect::<Vec<_>>())
    			.field("transactions_to_reverify", &self.transactions_to_reverify)
    			.finish()
    	}
    }

    impl BlockInsertionResult {
    	#[cfg(test)]
    	pub fn with_canonized_blocks(canonized_blocks_hashes: Vec<H256>) -> Self {
    		BlockInsertionResult {
    			canonized_blocks_hashes: canonized_blocks_hashes,
    			transactions_to_reverify: Vec::new(),
    		}
    	}
    }

    /// Block synchronization state
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub enum BlockState {
    	/// Block is unknown
    	Unknown,
    	/// Scheduled for requesting
    	Scheduled,
    	/// Requested from peers
    	Requested,
    	/// Currently verifying
    	Verifying,
    	/// In storage
    	Stored,
    	/// This block has been marked as dead-end block
    	DeadEnd,
    }

    /// Transactions synchronization state
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub enum TransactionState {
    	/// Transaction is unknown
    	Unknown,
    	/// Currently verifying
    	Verifying,
    	/// In memory pool
    	InMemory,
    	/// In storage
    	Stored,
    }

    /// Synchronization chain information
    pub struct Information {
    	/// Number of blocks hashes currently scheduled for requesting
    	pub scheduled: BlockHeight,
    	/// Number of blocks hashes currently requested from peers
    	pub requested: BlockHeight,
    	/// Number of blocks currently verifying
    	pub verifying: BlockHeight,
    	/// Number of blocks in the storage
    	pub stored: BlockHeight,
    	/// Information on memory pool
    	pub transactions: MemoryPoolInformation,
    	/// Information on headers chain
    	pub headers: BestHeadersChainInformation,
    }

    /// Blockchain from synchroniation point of view, consisting of:
    /// 1) all blocks from the `storage` [oldest blocks]
    /// 2) all blocks currently verifying by `verification_queue`
    /// 3) all blocks currently requested from peers
    /// 4) all blocks currently scheduled for requesting [newest blocks]
    pub struct Chain {
    	/// Genesis block hash (stored for optimizations)
    	genesis_block_hash: H256,
    	/// Best storage block (stored for optimizations)
    	best_storage_block: storage::BestBlock,
    	/// Local blocks storage
    	storage: StorageRef,
    	/// In-memory queue of blocks hashes
    	hash_chain: HashQueueChain,
    	/// In-memory queue of blocks headers
    	headers_chain: BestHeadersChain,
    	/// Currently verifying transactions
    	verifying_transactions: LinkedHashMap<H256, IndexedTransaction>,
    	/// Transactions memory pool
    	memory_pool: MemoryPoolRef,
    	/// Blocks that have been marked as dead-ends
    	dead_end_blocks: HashSet<H256>,
    	/// Is SegWit is possible on this chain? SegWit inventory types are used when block/tx-es are
    	/// requested and this flag is true.
    	is_segwit_possible: bool,
    }

    impl BlockState {
    	pub fn from_queue_index(queue_index: usize) -> BlockState {
    		match queue_index {
    			SCHEDULED_QUEUE => BlockState::Scheduled,
    			REQUESTED_QUEUE => BlockState::Requested,
    			VERIFYING_QUEUE => BlockState::Verifying,
    			_ => panic!("Unsupported queue_index: {}", queue_index),
    		}
    	}

    	pub fn to_queue_index(&self) -> usize {
    		match *self {
    			BlockState::Scheduled => SCHEDULED_QUEUE,
    			BlockState::Requested => REQUESTED_QUEUE,
    			BlockState::Verifying => VERIFYING_QUEUE,
    			_ => panic!("Unsupported queue: {:?}", self),
    		}
    	}
    }

    impl Chain {
    	/// Create new `Chain` with given storage
    	pub fn new(storage: StorageRef, consensus: ConsensusParams, memory_pool: MemoryPoolRef) -> Self {
    		// we only work with storages with genesis block
    		let genesis_block_hash = storage.block_hash(0)
    			.expect("storage with genesis block is required");
    		let best_storage_block = storage.best_block();
    		let best_storage_block_hash = best_storage_block.hash.clone();
    		let is_segwit_possible = consensus.is_segwit_possible();

    		Chain {
    			genesis_block_hash: genesis_block_hash,
    			best_storage_block: best_storage_block,
    			storage: storage,
    			hash_chain: HashQueueChain::with_number_of_queues(NUMBER_OF_QUEUES),
    			headers_chain: BestHeadersChain::new(best_storage_block_hash),
    			verifying_transactions: LinkedHashMap::new(),
    			memory_pool: memory_pool,
    			dead_end_blocks: HashSet::new(),
    			is_segwit_possible,
    		}
    	}

    	/// Get information on current blockchain state
    	pub fn information(&self) -> Information {
    		Information {
    			scheduled: self.hash_chain.len_of(SCHEDULED_QUEUE),
    			requested: self.hash_chain.len_of(REQUESTED_QUEUE),
    			verifying: self.hash_chain.len_of(VERIFYING_QUEUE),
    			stored: self.best_storage_block.number + 1,
    			transactions: self.memory_pool.read().information(),
    			headers: self.headers_chain.information(),
    		}
    	}

    	/// Get storage
    	pub fn storage(&self) -> StorageRef {
    		self.storage.clone()
    	}

    	/// Get memory pool
    	pub fn memory_pool(&self) -> MemoryPoolRef {
    		self.memory_pool.clone()
    	}

    	/// Is segwit active
    	pub fn is_segwit_possible(&self) -> bool {
    		self.is_segwit_possible
    	}

    	/// Get number of blocks in given state
    	pub fn length_of_blocks_state(&self, state: BlockState) -> BlockHeight {
    		match state {
    			BlockState::Stored => self.best_storage_block.number + 1,
    			_ => self.hash_chain.len_of(state.to_queue_index()),
    		}
    	}

    	/// Get n best blocks of given state
    	pub fn best_n_of_blocks_state(&self, state: BlockState, n: BlockHeight) -> Vec<H256> {
    		match state {
    			BlockState::Scheduled | BlockState::Requested | BlockState::Verifying => self.hash_chain.front_n_at(state.to_queue_index(), n),
    			_ => unreachable!("must be checked by caller"),
    		}
    	}

    	/// Get best block
    	pub fn best_block(&self) -> storage::BestBlock {
    		match self.hash_chain.back() {
    			Some(hash) => storage::BestBlock {
    				number: self.best_storage_block.number + self.hash_chain.len(),
    				hash: hash.clone(),
    			},
    			None => self.best_storage_block.clone(),
    		}
    	}

    	/// Get best storage block
    	pub fn best_storage_block(&self) -> storage::BestBlock {
    		self.best_storage_block.clone()
    	}

    	/// Get best block header
    	pub fn best_block_header(&self) -> storage::BestBlock {
    		let headers_chain_information = self.headers_chain.information();
    		if headers_chain_information.best == 0 {
    			return self.best_storage_block()
    		}
    		storage::BestBlock {
    			number: self.best_storage_block.number + headers_chain_information.best,
    			hash: self.headers_chain.at(headers_chain_information.best - 1)
    				.expect("got this index above; qed")
    				.hash,
    		}
    	}

    	/// Get block header by hash
    	pub fn block_hash(&self, number: BlockHeight) -> Option<H256> {
    		if number <= self.best_storage_block.number {
    			self.storage.block_hash(number)
    		} else {
    			// we try to keep these in order, but they are probably not
    			self.hash_chain.at(number - self.best_storage_block.number)
    		}
    	}

    	/// Get block number by hash
    	pub fn block_number(&self, hash: &H256) -> Option<BlockHeight> {
    		if let Some(number) = self.storage.block_number(hash) {
    			return Some(number);
    		}
    		self.headers_chain.height(hash).map(|p| self.best_storage_block.number + p + 1)
    	}

    	/// Get block header by number
    	pub fn block_header_by_number(&self, number: BlockHeight) -> Option<IndexedBlockHeader> {
    		if number <= self.best_storage_block.number {
    			self.storage.block_header(storage::BlockRef::Number(number)).map(Into::into)
    		} else {
    			self.headers_chain.at(number - self.best_storage_block.number)
    		}
    	}

    	/// Get block header by hash
    	pub fn block_header_by_hash(&self, hash: &H256) -> Option<IndexedBlockHeader> {
    		if let Some(block) = self.storage.block(storage::BlockRef::Hash(hash.clone())) {
    			return Some(block.block_header.into());
    		}
    		self.headers_chain.by_hash(hash)
    	}

    	/// Get block state
    	pub fn block_state(&self, hash: &H256) -> BlockState {
    		match self.hash_chain.contains_in(hash) {
    			Some(queue_index) => BlockState::from_queue_index(queue_index),
    			None => if self.storage.contains_block(storage::BlockRef::Hash(hash.clone())) {
    				BlockState::Stored
    			} else if self.dead_end_blocks.contains(hash) {
    				BlockState::DeadEnd
    			} else {
    				BlockState::Unknown
    			},
    		}
    	}

    	/// Prepare block locator hashes, as described in protocol documentation:
    	/// https://en.bitcoin.it/wiki/Protocol_documentation#getblocks
    	/// When there are forked blocks in the queue, this method can result in
    	/// mixed block locator hashes ([0 - from fork1, 1 - from fork2, 2 - from fork1]).
    	/// Peer will respond with blocks of fork1 || fork2 => we could end up in some side fork
    	/// To resolve this, after switching to saturated state, we will also ask all peers for inventory.
    	pub fn block_locator_hashes(&self) -> Vec<H256> {
    		let mut block_locator_hashes: Vec<H256> = Vec::new();

    		// calculate for hash_queue
    		let (local_index, step) = self.block_locator_hashes_for_queue(&mut block_locator_hashes);

    		// calculate for storage
    		let storage_index = if self.best_storage_block.number < local_index { 0 } else { self.best_storage_block.number - local_index };
    		self.block_locator_hashes_for_storage(storage_index, step, &mut block_locator_hashes);
    		block_locator_hashes
    	}

    	/// Schedule blocks hashes for requesting
    	pub fn schedule_blocks_headers(&mut self, headers: Vec<IndexedBlockHeader>) {
    		self.hash_chain.push_back_n_at(SCHEDULED_QUEUE, headers.iter().map(|h| h.hash.clone()).collect());
    		self.headers_chain.insert_n(headers);
    	}

    	/// Moves n blocks from scheduled queue to requested queue
    	pub fn request_blocks_hashes(&mut self, n: BlockHeight) -> Vec<H256> {
    		let scheduled = self.hash_chain.pop_front_n_at(SCHEDULED_QUEUE, n);
    		self.hash_chain.push_back_n_at(REQUESTED_QUEUE, scheduled.clone());
    		scheduled
    	}

    	/// Add block to verifying queue
    	pub fn verify_block(&mut self, header: IndexedBlockHeader) {
    		// insert header to the in-memory chain in case when it is not already there (non-headers-first sync)
    		self.hash_chain.push_back_at(VERIFYING_QUEUE, header.hash.clone());
    		self.headers_chain.insert(header);
    	}

    	/// Add blocks to verifying queue
    	pub fn verify_blocks(&mut self, blocks: Vec<IndexedBlockHeader>) {
    		for block in blocks {
    			self.verify_block(block);
    		}
    	}

    	/// Moves n blocks from requested queue to verifying queue
    	#[cfg(test)]
    	pub fn verify_blocks_hashes(&mut self, n: BlockHeight) -> Vec<H256> {
    		let requested = self.hash_chain.pop_front_n_at(REQUESTED_QUEUE, n);
    		self.hash_chain.push_back_n_at(VERIFYING_QUEUE, requested.clone());
    		requested
    	}

    	/// Mark this block as dead end, so these tasks won't be synchronized
    	pub fn mark_dead_end_block(&mut self, hash: &H256) {
    		self.dead_end_blocks.insert(hash.clone());
    	}

    	/// Insert new best block to storage
    	pub fn insert_best_block(&mut self, block: IndexedBlock) -> Result<BlockInsertionResult, storage::Error> {
    		assert_eq!(Some(self.storage.best_block().hash), self.storage.block_hash(self.storage.best_block().number));
    		let block_origin = self.storage.block_origin(&block.header)?;
    		trace!(target: "sync", "insert_best_block {:?} origin: {:?}", block.hash().reversed(), block_origin);
    		match block_origin {
    			storage::BlockOrigin::KnownBlock => {
    				// there should be no known blocks at this point
    				unreachable!();
    			},
    			// case 1: block has been added to the main branch
    			storage::BlockOrigin::CanonChain { .. } => {
    				self.storage.insert(block.clone())?;
    				self.storage.canonize(block.hash())?;

    				// remember new best block hash
    				self.best_storage_block = self.storage.as_store().best_block();

    				// remove inserted block + handle possible reorganization in headers chain
    				// TODO: mk, not sure if we need both of those params
    				self.headers_chain.block_inserted_to_storage(block.hash(), &self.best_storage_block.hash);

    				// double check
    				assert_eq!(self.best_storage_block.hash, block.hash().clone());

    				// all transactions from this block were accepted
    				// => delete accepted transactions from verification queue and from the memory pool
    				// + also remove transactions which spent outputs which have been spent by transactions from the block
    				let mut memory_pool = self.memory_pool.write();
    				for tx in &block.transactions {
    					memory_pool.remove_by_hash(&tx.hash);
    					self.verifying_transactions.remove(&tx.hash);
    					for tx_input in &tx.raw.inputs {
    						memory_pool.remove_by_prevout(&tx_input.previous_output);
    					}
    				}
    				// no transactions to reverify, because we have just appended new transactions to the blockchain

    				Ok(BlockInsertionResult {
    					canonized_blocks_hashes: vec![block.hash().clone()],
    					transactions_to_reverify: Vec::new(),
    				})
    			},
    			// case 2: block has been added to the side branch with reorganization to this branch
    			storage::BlockOrigin::SideChainBecomingCanonChain(origin) => {
    				let fork = self.storage.fork(origin.clone())?;
    				fork.store().insert(block.clone())?;
    				fork.store().canonize(block.hash())?;
    				self.storage.switch_to_fork(fork)?;

    				// remember new best block hash
    				self.best_storage_block = self.storage.best_block();

    				// remove inserted block + handle possible reorganization in headers chain
    				// TODO: mk, not sure if we need both of those params
    				self.headers_chain.block_inserted_to_storage(block.hash(), &self.best_storage_block.hash);

    				// all transactions from this block were accepted
    				// + all transactions from previous blocks of this fork were accepted
    				// => delete accepted transactions from verification queue and from the memory pool
    				let this_block_transactions_hashes = block.transactions.iter().map(|tx| tx.hash.clone()).collect::<Vec<_>>();
    				let mut canonized_blocks_hashes = origin.canonized_route.clone();
    				let new_main_blocks_transactions_hashes = origin.canonized_route.into_iter()
    					.flat_map(|block_hash| self.storage.block_transaction_hashes(block_hash.into()))
    					.collect::<Vec<_>>();

    				let mut memory_pool = self.memory_pool.write();
    				for transaction_accepted in this_block_transactions_hashes.into_iter().chain(new_main_blocks_transactions_hashes.into_iter()) {
    					memory_pool.remove_by_hash(&transaction_accepted);
    					self.verifying_transactions.remove(&transaction_accepted);
    				}

    				// reverify all transactions from old main branch' blocks
    				let old_main_blocks_transactions = origin.decanonized_route.into_iter()
    					.flat_map(|block_hash| self.storage.indexed_block_transactions(block_hash.into()))
    					.collect::<Vec<_>>();

    				trace!(target: "sync", "insert_best_block, old_main_blocks_transactions: {:?}",
    					   old_main_blocks_transactions.iter().map(|tx| tx.hash.reversed()).collect::<Vec<H256>>());

    				// reverify memory pool transactions, sorted by timestamp
    				let memory_pool_transactions_count = memory_pool.information().transactions_count;
    				let memory_pool_transactions: Vec<IndexedTransaction> = memory_pool
    					.remove_n_with_strategy(memory_pool_transactions_count, MemoryPoolOrderingStrategy::ByTimestamp)
    					.into_iter()
    					.map(|t| t.into())
    					.collect();

    				// reverify verifying transactions
    				let verifying_transactions: Vec<IndexedTransaction> = self.verifying_transactions
    					.iter()
    					.map(|(_, t)| t.clone())
    					.collect();
    				self.verifying_transactions.clear();

    				canonized_blocks_hashes.push(block.hash().clone());

    				let result = BlockInsertionResult {
    					canonized_blocks_hashes: canonized_blocks_hashes,
    					// order matters: db transactions, then ordered mempool transactions, then ordered verifying transactions
    					transactions_to_reverify: old_main_blocks_transactions.into_iter()
    						.chain(memory_pool_transactions.into_iter())
    						.chain(verifying_transactions.into_iter())
    						.collect(),
    				};

    				trace!(target: "sync", "result: {:?}", result);

    				Ok(result)
    			},
    			// case 3: block has been added to the side branch without reorganization to this branch
    			storage::BlockOrigin::SideChain(_origin) => {
    				let block_hash = block.hash().clone();
    				self.storage.insert(block)?;

    				// remove inserted block + handle possible reorganization in headers chain
    				// TODO: mk, not sure if it's needed here at all
    				self.headers_chain.block_inserted_to_storage(&block_hash, &self.best_storage_block.hash);

    				// no transactions were accepted
    				// no transactions to reverify
    				Ok(BlockInsertionResult::default())
    			},
    		}
    	}

    	/// Forget in-memory block
    	pub fn forget_block(&mut self, hash: &H256) -> HashPosition {
    		self.headers_chain.remove(hash);
    		self.forget_block_leave_header(hash)
    	}

    	/// Forget in-memory blocks
    	pub fn forget_blocks(&mut self, hashes: &[H256]) {
    		for hash in hashes {
    			self.forget_block(hash);
    		}
    	}

    	/// Forget in-memory block, but leave its header in the headers_chain (orphan queue)
    	pub fn forget_block_leave_header(&mut self, hash: &H256) -> HashPosition {
    		match self.hash_chain.remove_at(VERIFYING_QUEUE, hash) {
    			HashPosition::Missing => match self.hash_chain.remove_at(REQUESTED_QUEUE, hash) {
    				HashPosition::Missing => self.hash_chain.remove_at(SCHEDULED_QUEUE, hash),
    				position => position,
    			},
    			position => position,
    		}
    	}

    	/// Forget in-memory blocks, but leave their headers in the headers_chain (orphan queue)
    	pub fn forget_blocks_leave_header(&mut self, hashes: &[H256]) {
    		for hash in hashes {
    			self.forget_block_leave_header(hash);
    		}
    	}

    	/// Forget in-memory block by hash if it is currently in given state
    	#[cfg(test)]
    	pub fn forget_block_with_state(&mut self, hash: &H256, state: BlockState) -> HashPosition {
    		self.headers_chain.remove(hash);
    		self.forget_block_with_state_leave_header(hash, state)
    	}

    	/// Forget in-memory block by hash if it is currently in given state
    	pub fn forget_block_with_state_leave_header(&mut self, hash: &H256, state: BlockState) -> HashPosition {
    		self.hash_chain.remove_at(state.to_queue_index(), hash)
    	}

    	/// Forget in-memory block by hash.
    	/// Also forget all its known children.
    	pub fn forget_block_with_children(&mut self, hash: &H256) {
    		let mut removal_stack: VecDeque<H256> = VecDeque::new();
    		let mut removal_queue: VecDeque<H256> = VecDeque::new();
    		removal_queue.push_back(hash.clone());

    		// remove in reverse order to minimize headers operations
    		while let Some(hash) = removal_queue.pop_front() {
    			removal_queue.extend(self.headers_chain.children(&hash));
    			removal_stack.push_back(hash);
    		}
    		while let Some(hash) = removal_stack.pop_back() {
    			self.forget_block(&hash);
    		}
    	}

    	/// Forget all blocks with given state
    	pub fn forget_all_blocks_with_state(&mut self, state: BlockState) {
    		let hashes = self.hash_chain.remove_all_at(state.to_queue_index());
    		self.headers_chain.remove_n(hashes);
    	}

    	/// Get transaction state
    	pub fn transaction_state(&self, hash: &H256) -> TransactionState {
    		if self.verifying_transactions.contains_key(hash) {
    			return TransactionState::Verifying;
    		}
    		if self.storage.contains_transaction(hash) {
    			return TransactionState::Stored;
    		}
    		if self.memory_pool.read().contains(hash) {
    			return TransactionState::InMemory;
    		}
    		TransactionState::Unknown
    	}

    	/// Get transactions hashes with given state
    	pub fn transactions_hashes_with_state(&self, state: TransactionState) -> Vec<H256> {
    		match state {
    			TransactionState::InMemory => self.memory_pool.read().get_transactions_ids(),
    			TransactionState::Verifying => self.verifying_transactions.keys().cloned().collect(),
    			_ => panic!("wrong argument"),
    		}
    	}

    	/// Add transaction to verifying queue
    	pub fn verify_transaction(&mut self, tx: IndexedTransaction) {
    		self.verifying_transactions.insert(tx.hash.clone(), tx);
    	}

    	/// Remove verifying trasaction
    	pub fn forget_verifying_transaction(&mut self, hash: &H256) -> bool {
    		self.verifying_transactions.remove(hash).is_some()
    	}

    	/// Remove verifying trasaction + all dependent transactions currently verifying
    	pub fn forget_verifying_transaction_with_children(&mut self, hash: &H256) {
    		self.forget_verifying_transaction(hash);

    		// TODO: suboptimal
    		let mut queue: VecDeque<H256> = VecDeque::new();
    		queue.push_back(hash.clone());
    		while let Some(hash) = queue.pop_front() {
    			let all_keys: Vec<_> = self.verifying_transactions.keys().cloned().collect();
    			for h in all_keys {
    				let remove_verifying_transaction = {
    					if let Some(entry) = self.verifying_transactions.get(&h) {
    						if entry.raw.inputs.iter().any(|i| i.previous_output.hash == hash) {
    							queue.push_back(h.clone());
    							true
    						} else {
    							false
    						}
    					} else {
    						// iterating by previously read keys
    						unreachable!()
    					}
    				};

    				if remove_verifying_transaction {
    					self.verifying_transactions.remove(&h);
    				}
    			}
    		}
    	}

    	/// Get transaction by hash (if it's in memory pool or verifying)
    	pub fn transaction_by_hash(&self, hash: &H256) -> Option<IndexedTransaction> {
    		self.verifying_transactions.get(hash).cloned()
    			.or_else(|| self.memory_pool.read().read_by_hash(hash).cloned().map(|t| t.into()))
    	}

    	/// Insert transaction to memory pool
    	pub fn insert_verified_transaction(&mut self, transaction: IndexedTransaction) {
    		// we have verified transaction, but possibly this transaction replaces
    		// existing transaction from memory pool
    		// => remove previous transactions before
    		let mut memory_pool = self.memory_pool.write();
    		for input in &transaction.raw.inputs {
    			memory_pool.remove_by_prevout(&input.previous_output);
    		}
    		// now insert transaction itself
    		memory_pool.insert_verified(transaction);
    	}

    	/// Calculate block locator hashes for hash queue
    	fn block_locator_hashes_for_queue(&self, hashes: &mut Vec<H256>) -> (BlockHeight, BlockHeight) {
    		let queue_len = self.hash_chain.len();
    		if queue_len == 0 {
    			return (0, 1);
    		}

    		let mut index = queue_len - 1;
    		let mut step = 1u32;
    		loop {
    			let block_hash = self.hash_chain[index].clone();
    			hashes.push(block_hash);

    			if hashes.len() >= 10 {
    				step <<= 1;
    			}
    			if index < step {
    				return (step - index - 1, step);
    			}
    			index -= step;
    		}
    	}

    	/// Calculate block locator hashes for storage
    	fn block_locator_hashes_for_storage(&self, mut index: BlockHeight, mut step: BlockHeight, hashes: &mut Vec<H256>) {
    		loop {
    			let block_hash = self.storage.block_hash(index)
    				.expect("private function; index calculated in `block_locator_hashes`; qed");
    			hashes.push(block_hash);

    			if hashes.len() >= 10 {
    				step <<= 1;
    			}
    			if index < step {
    				// always include genesis hash
    				if index != 0 {
    					hashes.push(self.genesis_block_hash.clone())
    				}

    				break;
    			}
    			index -= step;
    		}
    	}
    }

    impl storage::TransactionProvider for Chain {
    	fn transaction_bytes(&self, hash: &H256) -> Option<Bytes> {
    		self.memory_pool.read().transaction_bytes(hash)
    			.or_else(|| self.storage.transaction_bytes(hash))
    	}

    	fn transaction(&self, hash: &H256) -> Option<Transaction> {
    		self.memory_pool.read().transaction(hash)
    			.or_else(|| self.storage.transaction(hash))
    	}
    }

    impl storage::BlockHeaderProvider for Chain {
    	fn block_header_bytes(&self, block_ref: storage::BlockRef) -> Option<Bytes> {
    		use ser::serialize;
    		self.block_header(block_ref).map(|h| serialize(&h))
    	}

    	fn block_header(&self, block_ref: storage::BlockRef) -> Option<BlockHeader> {
    		match block_ref {
    			storage::BlockRef::Hash(hash) => self.block_header_by_hash(&hash).map(|h| h.raw),
    			storage::BlockRef::Number(n) => self.block_header_by_number(n).map(|h| h.raw),
    		}
    	}
    }

    impl fmt::Debug for Information {
    	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    		write!(f, "[sch:{} -> req:{} -> vfy:{} -> stored: {}]", self.scheduled, self.requested, self.verifying, self.stored)
    	}
    }

    impl fmt::Debug for Chain {
    	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    		try!(writeln!(f, "chain: ["));
    		{
    			let mut num = self.best_storage_block.number;
    			try!(writeln!(f, "\tworse(stored): {} {:?}", 0, self.storage.block_hash(0)));
    			try!(writeln!(f, "\tbest(stored): {} {:?}", num, self.storage.block_hash(num)));

    			let queues = vec![
    				("verifying", VERIFYING_QUEUE),
    				("requested", REQUESTED_QUEUE),
    				("scheduled", SCHEDULED_QUEUE),
    			];
    			for (state, queue) in queues {
    				let queue_len = self.hash_chain.len_of(queue);
    				if queue_len != 0 {
    					try!(writeln!(f, "\tworse({}): {} {:?}", state, num + 1, self.hash_chain.front_at(queue)));
    					num += queue_len;
    					if let Some(pre_best) = self.hash_chain.pre_back_at(queue) {
    						try!(writeln!(f, "\tpre-best({}): {} {:?}", state, num - 1, pre_best));
    					}
    					try!(writeln!(f, "\tbest({}): {} {:?}", state, num, self.hash_chain.back_at(queue)));
    				}
    			}
    		}
    		writeln!(f, "]")
    	}
    }

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

    	use std::sync::Arc;
    	use parking_lot::RwLock;
    	use chain::{Transaction, IndexedBlockHeader};
    	use db::BlockChainDatabase;
    	use miner::MemoryPool;
    	use network::{Network, ConsensusParams, ConsensusFork};
    	use primitives::hash::H256;
    	use super::{Chain, BlockState, TransactionState, BlockInsertionResult};
    	use utils::HashPosition;

    	#[test]
    	fn chain_empty() {
    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let db_best_block = db.best_block();
    		let chain = Chain::new(db.clone(), ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		assert_eq!(chain.information().scheduled, 0);
    		assert_eq!(chain.information().requested, 0);
    		assert_eq!(chain.information().verifying, 0);
    		assert_eq!(chain.information().stored, 1);
    		assert_eq!(chain.length_of_blocks_state(BlockState::Scheduled), 0);
    		assert_eq!(chain.length_of_blocks_state(BlockState::Requested), 0);
    		assert_eq!(chain.length_of_blocks_state(BlockState::Verifying), 0);
    		assert_eq!(chain.length_of_blocks_state(BlockState::Stored), 1);
    		assert_eq!(&chain.best_block(), &db_best_block);
    		assert_eq!(chain.block_state(&db_best_block.hash), BlockState::Stored);
    		assert_eq!(chain.block_state(&H256::from(0)), BlockState::Unknown);
    	}

    	#[test]
    	fn chain_block_path() {
    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db.clone(), ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));

    		// add 6 blocks to scheduled queue
    		let blocks = test_data::build_n_empty_blocks_from_genesis(6, 0);
    		let headers: Vec<IndexedBlockHeader> = blocks.into_iter().map(|b| b.block_header.into()).collect();
    		let hashes: Vec<_> = headers.iter().map(|h| h.hash.clone()).collect();
    		chain.schedule_blocks_headers(headers.clone());
    		assert!(chain.information().scheduled == 6 && chain.information().requested == 0
    			&& chain.information().verifying == 0 && chain.information().stored == 1);

    		// move 2 best blocks to requested queue
    		chain.request_blocks_hashes(2);
    		assert!(chain.information().scheduled == 4 && chain.information().requested == 2
    			&& chain.information().verifying == 0 && chain.information().stored == 1);
    		// move 0 best blocks to requested queue
    		chain.request_blocks_hashes(0);
    		assert!(chain.information().scheduled == 4 && chain.information().requested == 2
    			&& chain.information().verifying == 0 && chain.information().stored == 1);
    		// move 1 best blocks to requested queue
    		chain.request_blocks_hashes(1);
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 3
    			&& chain.information().verifying == 0 && chain.information().stored == 1);

    		// try to remove block 0 from scheduled queue => missing
    		assert_eq!(chain.forget_block_with_state(&hashes[0], BlockState::Scheduled), HashPosition::Missing);
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 3
    			&& chain.information().verifying == 0 && chain.information().stored == 1);
    		// remove blocks 0 & 1 from requested queue
    		assert_eq!(chain.forget_block_with_state(&hashes[1], BlockState::Requested), HashPosition::Inside(1));
    		assert_eq!(chain.forget_block_with_state(&hashes[0], BlockState::Requested), HashPosition::Front);
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 1
    			&& chain.information().verifying == 0 && chain.information().stored == 1);
    		// mark 0 & 1 as verifying
    		chain.verify_block(headers[0].clone().into());
    		chain.verify_block(headers[1].clone().into());
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 1
    			&& chain.information().verifying == 2 && chain.information().stored == 1);

    		// mark block 0 as verified
    		assert_eq!(chain.forget_block_with_state(&hashes[0], BlockState::Verifying), HashPosition::Front);
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 1
    			&& chain.information().verifying == 1 && chain.information().stored == 1);
    		// insert new best block to the chain
    		chain.insert_best_block(test_data::block_h1().into()).expect("Db error");
    		assert!(chain.information().scheduled == 3 && chain.information().requested == 1
    			&& chain.information().verifying == 1 && chain.information().stored == 2);
    		assert_eq!(db.best_block().number, 1);
    	}

    	#[test]
    	fn chain_block_locator_hashes() {
    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		let genesis_hash = chain.best_block().hash;
    		assert_eq!(chain.block_locator_hashes(), vec![genesis_hash.clone()]);

    		let block1 = test_data::block_h1();
    		let block1_hash = block1.hash();

    		chain.insert_best_block(block1.into()).expect("Error inserting new block");
    		assert_eq!(chain.block_locator_hashes(), vec![block1_hash.clone(), genesis_hash.clone()]);

    		let block2 = test_data::block_h2();
    		let block2_hash = block2.hash();

    		chain.insert_best_block(block2.into()).expect("Error inserting new block");
    		assert_eq!(chain.block_locator_hashes(), vec![block2_hash.clone(), block1_hash.clone(), genesis_hash.clone()]);

    		let blocks0 = test_data::build_n_empty_blocks_from_genesis(11, 0);
    		let headers0: Vec<IndexedBlockHeader> = blocks0.into_iter().map(|b| b.block_header.into()).collect();
    		let hashes0: Vec<_> = headers0.iter().map(|h| h.hash.clone()).collect();
    		chain.schedule_blocks_headers(headers0.clone());
    		chain.request_blocks_hashes(10);
    		chain.verify_blocks_hashes(10);

    		assert_eq!(chain.block_locator_hashes(), vec![
    			hashes0[10].clone(),
    			hashes0[9].clone(),
    			hashes0[8].clone(),
    			hashes0[7].clone(),
    			hashes0[6].clone(),
    			hashes0[5].clone(),
    			hashes0[4].clone(),
    			hashes0[3].clone(),
    			hashes0[2].clone(),
    			hashes0[1].clone(),
    			block2_hash.clone(),
    			genesis_hash.clone(),
    		]);

    		let blocks1 = test_data::build_n_empty_blocks_from(6, 0, &headers0[10].raw);
    		let headers1: Vec<IndexedBlockHeader> = blocks1.into_iter().map(|b| b.block_header.into()).collect();
    		let hashes1: Vec<_> = headers1.iter().map(|h| h.hash.clone()).collect();
    		chain.schedule_blocks_headers(headers1.clone());
    		chain.request_blocks_hashes(10);

    		assert_eq!(chain.block_locator_hashes(), vec![
    			hashes1[5].clone(),
    			hashes1[4].clone(),
    			hashes1[3].clone(),
    			hashes1[2].clone(),
    			hashes1[1].clone(),
    			hashes1[0].clone(),
    			hashes0[10].clone(),
    			hashes0[9].clone(),
    			hashes0[8].clone(),
    			hashes0[7].clone(),
    			hashes0[5].clone(),
    			hashes0[1].clone(),
    			genesis_hash.clone(),
    		]);

    		let blocks2 = test_data::build_n_empty_blocks_from(3, 0, &headers1[5].raw);
    		let headers2: Vec<IndexedBlockHeader> = blocks2.into_iter().map(|b| b.block_header.into()).collect();
    		let hashes2: Vec<_> = headers2.iter().map(|h| h.hash.clone()).collect();
    		chain.schedule_blocks_headers(headers2);

    		assert_eq!(chain.block_locator_hashes(), vec![
    			hashes2[2].clone(),
    			hashes2[1].clone(),
    			hashes2[0].clone(),
    			hashes1[5].clone(),
    			hashes1[4].clone(),
    			hashes1[3].clone(),
    			hashes1[2].clone(),
    			hashes1[1].clone(),
    			hashes1[0].clone(),
    			hashes0[10].clone(),
    			hashes0[8].clone(),
    			hashes0[4].clone(),
    			genesis_hash.clone(),
    		]);
    	}

    	#[test]
    	fn chain_transaction_state() {
    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		let genesis_block = test_data::genesis();
    		let block1 = test_data::block_h1();
    		let tx1: Transaction = test_data::TransactionBuilder::with_version(1).into();
    		let tx2: Transaction = test_data::TransactionBuilder::with_version(2).into();
    		let tx1_hash = tx1.hash();
    		let tx2_hash = tx2.hash();
    		chain.verify_transaction(tx1.into());
    		chain.insert_verified_transaction(tx2.into());

    		assert_eq!(chain.transaction_state(&genesis_block.transactions[0].hash()), TransactionState::Stored);
    		assert_eq!(chain.transaction_state(&block1.transactions[0].hash()), TransactionState::Unknown);
    		assert_eq!(chain.transaction_state(&tx1_hash), TransactionState::Verifying);
    		assert_eq!(chain.transaction_state(&tx2_hash), TransactionState::InMemory);
    	}

    	#[test]
    	fn chain_block_transaction_is_removed_from_on_block_insert() {
    		let b0 = test_data::block_builder().header().build()
    			.transaction().coinbase()
    				.output().value(10).build()
    				.build()
    			.build();
    		let b1 = test_data::block_builder().header().parent(b0.hash()).build()
    			.transaction().coinbase()
    				.output().value(10).build()
    				.build()
    			.transaction()
    				.input().hash(b0.transactions[0].hash()).index(0).build()
    				.build()
    			.build();
    		let tx1 = b1.transactions[0].clone();
    		let tx1_hash = tx1.hash();
    		let tx2 = b1.transactions[1].clone();
    		let tx2_hash = tx2.hash();

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![b0.into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.verify_transaction(tx1.into());
    		chain.insert_verified_transaction(tx2.into());

    		// only one transaction is in the memory pool
    		assert_eq!(chain.information().transactions.transactions_count, 1);

    		// when block is inserted to the database => all accepted transactions are removed from mempool && verifying queue
    		chain.insert_best_block(b1.into()).expect("block accepted");

    		assert_eq!(chain.information().transactions.transactions_count, 0);
    		assert!(!chain.forget_verifying_transaction(&tx1_hash));
    		assert!(!chain.forget_verifying_transaction(&tx2_hash));
    	}

    	#[test]
    	fn chain_forget_verifying_transaction_with_children() {
    		let test_chain = &mut test_data::ChainBuilder::new();
    		test_data::TransactionBuilder::with_output(100).store(test_chain)	// t1
    			.into_input(0).add_output(200).store(test_chain)				// t1 -> t2
    			.into_input(0).add_output(300).store(test_chain)				// t1 -> t2 -> t3
    			.set_default_input(0).set_output(400).store(test_chain);		// t4

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.verify_transaction(test_chain.at(0).into());
    		chain.verify_transaction(test_chain.at(1).into());
    		chain.verify_transaction(test_chain.at(2).into());
    		chain.verify_transaction(test_chain.at(3).into());

    		chain.forget_verifying_transaction_with_children(&test_chain.at(0).hash());
    		assert!(!chain.forget_verifying_transaction(&test_chain.at(0).hash()));
    		assert!(!chain.forget_verifying_transaction(&test_chain.at(1).hash()));
    		assert!(!chain.forget_verifying_transaction(&test_chain.at(2).hash()));
    		assert!(chain.forget_verifying_transaction(&test_chain.at(3).hash()));
    	}

    	#[test]
    	fn chain_transactions_hashes_with_state() {
    		let test_chain = &mut test_data::ChainBuilder::new();
    		test_data::TransactionBuilder::with_output(100).store(test_chain)	// t1
    			.into_input(0).add_output(200).store(test_chain)				// t1 -> t2
    			.into_input(0).add_output(300).store(test_chain)				// t1 -> t2 -> t3
    			.set_default_input(0).set_output(400).store(test_chain);		// t4

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.insert_verified_transaction(test_chain.at(0).into());
    		chain.insert_verified_transaction(test_chain.at(1).into());
    		chain.insert_verified_transaction(test_chain.at(2).into());
    		chain.insert_verified_transaction(test_chain.at(3).into());

    		let chain_transactions = chain.transactions_hashes_with_state(TransactionState::InMemory);
    		assert!(chain_transactions.contains(&test_chain.at(0).hash()));
    		assert!(chain_transactions.contains(&test_chain.at(1).hash()));
    		assert!(chain_transactions.contains(&test_chain.at(2).hash()));
    		assert!(chain_transactions.contains(&test_chain.at(3).hash()));
    	}

    	#[test]
    	fn memory_pool_transactions_are_reverified_after_reorganization() {
    		let b0 = test_data::block_builder().header().build().build();
    		let b1 = test_data::block_builder().header().nonce(1).parent(b0.hash()).build().build();
    		let b2 = test_data::block_builder().header().nonce(2).parent(b0.hash()).build().build();
    		let b3 = test_data::block_builder().header().parent(b2.hash()).build().build();

    		let tx1: Transaction = test_data::TransactionBuilder::with_version(1).into();
    		let tx1_hash = tx1.hash();
    		let tx2: Transaction = test_data::TransactionBuilder::with_version(2).into();
    		let tx2_hash = tx2.hash();

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![b0.into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.verify_transaction(tx1.into());
    		chain.insert_verified_transaction(tx2.into());

    		// no reorg
    		let result = chain.insert_best_block(b1.into()).expect("no error");
    		assert_eq!(result.transactions_to_reverify.len(), 0);

    		// no reorg
    		let result = chain.insert_best_block(b2.into()).expect("no error");
    		assert_eq!(result.transactions_to_reverify.len(), 0);

    		// reorg
    		let result = chain.insert_best_block(b3.into()).expect("no error");
    		assert_eq!(result.transactions_to_reverify.len(), 2);
    		assert!(result.transactions_to_reverify.iter().any(|ref tx| &tx.hash == &tx1_hash));
    		assert!(result.transactions_to_reverify.iter().any(|ref tx| &tx.hash == &tx2_hash));
    	}

    	#[test]
    	fn fork_chain_block_transaction_is_removed_from_on_block_insert() {
    		let genesis = test_data::genesis();
    		let b0 = test_data::block_builder().header().parent(genesis.hash()).build().build(); // genesis -> b0
    		let b1 = test_data::block_builder().header().nonce(1).parent(b0.hash()).build()
    			.transaction().output().value(10).build().build()
    			.build(); // genesis -> b0 -> b1[tx1]
    		let b2 = test_data::block_builder().header().parent(b1.hash()).build()
    			.transaction().output().value(20).build().build()
    			.build(); // genesis -> b0 -> b1[tx1] -> b2[tx2]
    		let b3 = test_data::block_builder().header().nonce(2).parent(b0.hash()).build()
    			.transaction().output().value(30).build().build()
    			.build(); // genesis -> b0 -> b3[tx3]
    		let b4 = test_data::block_builder().header().parent(b3.hash()).build()
    			.transaction().output().value(40).build().build()
    			.build(); // genesis -> b0 -> b3[tx3] -> b4[tx4]
    		let b5 = test_data::block_builder().header().parent(b4.hash()).build()
    			.transaction().output().value(50).build().build()
    			.build(); // genesis -> b0 -> b3[tx3] -> b4[tx4] -> b5[tx5]

    		let tx1 = b1.transactions[0].clone();
    		let tx1_hash = tx1.hash();
    		let tx2 = b2.transactions[0].clone();
    		let tx2_hash = tx2.hash();
    		let tx3 = b3.transactions[0].clone();
    		let tx4 = b4.transactions[0].clone();
    		let tx5 = b5.transactions[0].clone();

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![genesis.into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));

    		chain.insert_verified_transaction(tx3.into());
    		chain.insert_verified_transaction(tx4.into());
    		chain.insert_verified_transaction(tx5.into());

    		assert_eq!(chain.insert_best_block(b0.clone().into()).expect("block accepted"), BlockInsertionResult::with_canonized_blocks(vec![b0.hash()]));
    		assert_eq!(chain.information().transactions.transactions_count, 3);
    		assert_eq!(chain.insert_best_block(b1.clone().into()).expect("block accepted"), BlockInsertionResult::with_canonized_blocks(vec![b1.hash()]));
    		assert_eq!(chain.information().transactions.transactions_count, 3);
    		assert_eq!(chain.insert_best_block(b2.clone().into()).expect("block accepted"), BlockInsertionResult::with_canonized_blocks(vec![b2.hash()]));
    		assert_eq!(chain.information().transactions.transactions_count, 3);
    		assert_eq!(chain.insert_best_block(b3.clone().into()).expect("block accepted"), BlockInsertionResult::default());
    		assert_eq!(chain.information().transactions.transactions_count, 3);
    		assert_eq!(chain.insert_best_block(b4.clone().into()).expect("block accepted"), BlockInsertionResult::default());
    		assert_eq!(chain.information().transactions.transactions_count, 3);
    		// order matters
    		let insert_result = chain.insert_best_block(b5.clone().into()).expect("block accepted");
    		let transactions_to_reverify_hashes: Vec<_> = insert_result
    			.transactions_to_reverify
    			.into_iter()
    			.map(|tx| tx.hash)
    			.collect();
    		assert_eq!(transactions_to_reverify_hashes, vec![tx1_hash, tx2_hash]);
    		assert_eq!(insert_result.canonized_blocks_hashes, vec![b3.hash(), b4.hash(), b5.hash()]);
    		assert_eq!(chain.information().transactions.transactions_count, 0); // tx3, tx4, tx5 are added to the database
    	}

    	#[test]
    	fn double_spend_transaction_is_removed_from_memory_pool_when_output_is_spent_in_block_transaction() {
    		let genesis = test_data::genesis();
    		let tx0 = genesis.transactions[0].clone();
    		let b0 = test_data::block_builder().header().nonce(1).parent(genesis.hash()).build()
    			.transaction()
    				.lock_time(1)
    				.input().hash(tx0.hash()).index(0).build()
    				.build()
    			.build(); // genesis -> b0[tx1]
    		// tx1 && tx2 are spending same output
    		let tx2: Transaction = test_data::TransactionBuilder::with_output(20).add_input(&tx0, 0).into();
    		let tx3: Transaction = test_data::TransactionBuilder::with_output(20).add_input(&tx0, 1).into();

    		// insert tx2 to memory pool
    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.insert_verified_transaction(tx2.clone().into());
    		chain.insert_verified_transaction(tx3.clone().into());
    		// insert verified block with tx1
    		chain.insert_best_block(b0.into()).expect("no error");
    		// => tx2 is removed from memory pool, but tx3 remains
    		assert_eq!(chain.information().transactions.transactions_count, 1);
    	}

    	#[test]
    	fn update_memory_pool_transaction() {
    		use self::test_data::{ChainBuilder, TransactionBuilder};

    		let data_chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(10).add_output(10).add_output(10).store(data_chain)		// transaction0
    			.reset().set_input(&data_chain.at(0), 0).add_output(20).lock().store(data_chain)	// transaction0 -> transaction1
    			.reset().set_input(&data_chain.at(0), 0).add_output(30).store(data_chain);			// transaction0 -> transaction2

    		let db = Arc::new(BlockChainDatabase::init_test_chain(vec![test_data::genesis().into()]));
    		let mut chain = Chain::new(db, ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore), Arc::new(RwLock::new(MemoryPool::new())));
    		chain.insert_verified_transaction(data_chain.at(1).into());
    		assert_eq!(chain.information().transactions.transactions_count, 1);
    		chain.insert_verified_transaction(data_chain.at(2).into());
    		assert_eq!(chain.information().transactions.transactions_count, 1); // tx was replaces
    	}
    }

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