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    // Copyright 2015-2017 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::collections::{HashSet, HashMap, BTreeMap, VecDeque};
    use std::str::FromStr;
    use std::sync::{Arc, Weak};
    use std::path::{Path};
    use std::fmt;
    use std::sync::atomic::{AtomicUsize, AtomicBool, Ordering as AtomicOrdering};
    use std::time::{Instant};
    use time::precise_time_ns;

    // util
    use util::{Bytes, PerfTimer, Itertools, Mutex, RwLock, MutexGuard, Hashable};
    use util::{journaldb, TrieFactory, Trie};
    use util::{U256, H256, Address, H2048, Uint, FixedHash};
    use util::trie::TrieSpec;
    use util::kvdb::*;

    // other
    use io::*;
    use views::BlockView;
    use error::{ImportError, ExecutionError, CallError, BlockError, ImportResult, Error as EthcoreError};
    use header::BlockNumber;
    use state::{State, CleanupMode};
    use spec::Spec;
    use basic_types::Seal;
    use engines::Engine;
    use service::ClientIoMessage;
    use env_info::LastHashes;
    use verification;
    use verification::{PreverifiedBlock, Verifier};
    use block::*;
    use transaction::{LocalizedTransaction, UnverifiedTransaction, SignedTransaction, Transaction, PendingTransaction, Action};
    use blockchain::extras::TransactionAddress;
    use types::filter::Filter;
    use types::mode::Mode as IpcMode;
    use log_entry::LocalizedLogEntry;
    use verification::queue::BlockQueue;
    use blockchain::{BlockChain, BlockProvider, TreeRoute, ImportRoute};
    use client::{
    	BlockId, TransactionId, UncleId, TraceId, ClientConfig, BlockChainClient,
    	MiningBlockChainClient, EngineClient, TraceFilter, CallAnalytics, BlockImportError, Mode,
    	ChainNotify, PruningInfo,
    };
    use client::Error as ClientError;
    use env_info::EnvInfo;
    use executive::{Executive, Executed, TransactOptions, contract_address};
    use receipt::{Receipt, LocalizedReceipt};
    use trace::{TraceDB, ImportRequest as TraceImportRequest, LocalizedTrace, Database as TraceDatabase};
    use trace;
    use trace::FlatTransactionTraces;
    use evm::{Factory as EvmFactory, Schedule};
    use miner::{Miner, MinerService, TransactionImportResult};
    use snapshot::{self, io as snapshot_io};
    use factory::Factories;
    use rlp::{View, UntrustedRlp};
    use state_db::StateDB;
    use rand::OsRng;
    use client::registry::Registry;
    use encoded;

    // re-export
    pub use types::blockchain_info::BlockChainInfo;
    pub use types::block_status::BlockStatus;
    pub use blockchain::CacheSize as BlockChainCacheSize;
    pub use verification::queue::QueueInfo as BlockQueueInfo;

    const MAX_TX_QUEUE_SIZE: usize = 4096;
    const MAX_QUEUE_SIZE_TO_SLEEP_ON: usize = 2;
    const MIN_HISTORY_SIZE: u64 = 8;

    impl fmt::Display for BlockChainInfo {
    	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    		write!(f, "#{}.{}", self.best_block_number, self.best_block_hash)
    	}
    }

    /// Report on the status of a client.
    #[derive(Default, Clone, Debug, Eq, PartialEq)]
    pub struct ClientReport {
    	/// How many blocks have been imported so far.
    	pub blocks_imported: usize,
    	/// How many transactions have been applied so far.
    	pub transactions_applied: usize,
    	/// How much gas has been processed so far.
    	pub gas_processed: U256,
    	/// Memory used by state DB
    	pub state_db_mem: usize,
    }

    impl ClientReport {
    	/// Alter internal reporting to reflect the additional `block` has been processed.
    	pub fn accrue_block(&mut self, block: &PreverifiedBlock) {
    		self.blocks_imported += 1;
    		self.transactions_applied += block.transactions.len();
    		self.gas_processed = self.gas_processed + block.header.gas_used().clone();
    	}
    }

    struct SleepState {
    	last_activity: Option<Instant>,
    	last_autosleep: Option<Instant>,
    }

    impl SleepState {
    	fn new(awake: bool) -> Self {
    		SleepState {
    			last_activity: match awake { false => None, true => Some(Instant::now()) },
    			last_autosleep: match awake { false => Some(Instant::now()), true => None },
    		}
    	}
    }

    /// Blockchain database client backed by a persistent database. Owns and manages a blockchain and a block queue.
    /// Call `import_block()` to import a block asynchronously; `flush_queue()` flushes the queue.
    pub struct Client {
    	enabled: AtomicBool,
    	mode: Mutex<Mode>,
    	chain: RwLock<Arc<BlockChain>>,
    	tracedb: RwLock<TraceDB<BlockChain>>,
    	engine: Arc<Engine>,
    	config: ClientConfig,
    	pruning: journaldb::Algorithm,
    	db: RwLock<Arc<Database>>,
    	state_db: Mutex<StateDB>,
    	block_queue: BlockQueue,
    	report: RwLock<ClientReport>,
    	import_lock: Mutex<()>,
    	panic_handler: Arc<PanicHandler>,
    	verifier: Box<Verifier>,
    	miner: Arc<Miner>,
    	sleep_state: Mutex<SleepState>,
    	liveness: AtomicBool,
    	io_channel: Mutex<IoChannel<ClientIoMessage>>,
    	notify: RwLock<Vec<Weak<ChainNotify>>>,
    	queue_transactions: AtomicUsize,
    	last_hashes: RwLock<VecDeque<H256>>,
    	factories: Factories,
    	history: u64,
    	rng: Mutex<OsRng>,
    	on_mode_change: Mutex<Option<Box<FnMut(&Mode) + 'static + Send>>>,
    	registrar: Mutex<Option<Registry>>,
    }

    impl Client {
    	/// Create a new client with given spec and DB path and custom verifier.
    	pub fn new(
    		config: ClientConfig,
    		spec: &Spec,
    		path: &Path,
    		miner: Arc<Miner>,
    		message_channel: IoChannel<ClientIoMessage>,
    		db_config: &DatabaseConfig,
    	) -> Result<Arc<Client>, ClientError> {

    		let path = path.to_path_buf();
    		let db = Arc::new(Database::open(&db_config, &path.to_str().expect("DB path could not be converted to string.")).map_err(ClientError::Database)?);
    		let trie_spec = match config.fat_db {
    			true => TrieSpec::Fat,
    			false => TrieSpec::Secure,
    		};

    		let trie_factory = TrieFactory::new(trie_spec);
    		let factories = Factories {
    			vm: EvmFactory::new(config.vm_type.clone(), config.jump_table_size),
    			trie: trie_factory,
    			accountdb: Default::default(),
    		};

    		let journal_db = journaldb::new(db.clone(), config.pruning, ::db::COL_STATE);
    		let mut state_db = StateDB::new(journal_db, config.state_cache_size);
    		if state_db.journal_db().is_empty() {
    			// Sets the correct state root.
    			state_db = spec.ensure_db_good(state_db, &factories)?;
    			let mut batch = DBTransaction::new(&db);
    			state_db.journal_under(&mut batch, 0, &spec.genesis_header().hash())?;
    			db.write(batch).map_err(ClientError::Database)?;
    		}

    		let gb = spec.genesis_block();
    		let chain = Arc::new(BlockChain::new(config.blockchain.clone(), &gb, db.clone()));
    		let tracedb = RwLock::new(TraceDB::new(config.tracing.clone(), db.clone(), chain.clone()));

    		trace!("Cleanup journal: DB Earliest = {:?}, Latest = {:?}", state_db.journal_db().earliest_era(), state_db.journal_db().latest_era());

    		let history = if config.history < MIN_HISTORY_SIZE {
    			info!(target: "client", "Ignoring pruning history parameter of {}\
    				, falling back to minimum of {}",
    				config.history, MIN_HISTORY_SIZE);
    			MIN_HISTORY_SIZE
    		} else {
    			config.history
    		};

    		if !chain.block_header(&chain.best_block_hash()).map_or(true, |h| state_db.journal_db().contains(h.state_root())) {
    			warn!("State root not found for block #{} ({})", chain.best_block_number(), chain.best_block_hash().hex());
    		}

    		let engine = spec.engine.clone();

    		let block_queue = BlockQueue::new(config.queue.clone(), engine.clone(), message_channel.clone(), config.verifier_type.verifying_seal());
    		let panic_handler = PanicHandler::new_in_arc();
    		panic_handler.forward_from(&block_queue);

    		let awake = match config.mode { Mode::Dark(..) | Mode::Off => false, _ => true };

    		let client = Arc::new(Client {
    			enabled: AtomicBool::new(true),
    			sleep_state: Mutex::new(SleepState::new(awake)),
    			liveness: AtomicBool::new(awake),
    			mode: Mutex::new(config.mode.clone()),
    			chain: RwLock::new(chain),
    			tracedb: tracedb,
    			engine: engine,
    			pruning: config.pruning.clone(),
    			verifier: verification::new(config.verifier_type.clone()),
    			config: config,
    			db: RwLock::new(db),
    			state_db: Mutex::new(state_db),
    			block_queue: block_queue,
    			report: RwLock::new(Default::default()),
    			import_lock: Mutex::new(()),
    			panic_handler: panic_handler,
    			miner: miner,
    			io_channel: Mutex::new(message_channel),
    			notify: RwLock::new(Vec::new()),
    			queue_transactions: AtomicUsize::new(0),
    			last_hashes: RwLock::new(VecDeque::new()),
    			factories: factories,
    			history: history,
    			rng: Mutex::new(OsRng::new().map_err(::util::UtilError::StdIo)?),
    			on_mode_change: Mutex::new(None),
    			registrar: Mutex::new(None),
    		});

    		{
    			let state_db = client.state_db.lock().boxed_clone();
    			let chain = client.chain.read();
    			client.prune_ancient(state_db, &chain)?;
    		}

    		if let Some(reg_addr) = client.additional_params().get("registrar").and_then(|s| Address::from_str(s).ok()) {
    			trace!(target: "client", "Found registrar at {}", reg_addr);
    			let weak = Arc::downgrade(&client);
    			let registrar = Registry::new(reg_addr, move |a, d| weak.upgrade().ok_or("No client!".into()).and_then(|c| c.call_contract(a, d)));
    			*client.registrar.lock() = Some(registrar);
    		}
    		Ok(client)
    	}

    	/// Adds an actor to be notified on certain events
    	pub fn add_notify(&self, target: Arc<ChainNotify>) {
    		self.notify.write().push(Arc::downgrade(&target));
    	}

    	/// Returns engine reference.
    	pub fn engine(&self) -> &Engine {
    		&*self.engine
    	}

    	fn notify<F>(&self, f: F) where F: Fn(&ChainNotify) {
    		for np in self.notify.read().iter() {
    			if let Some(n) = np.upgrade() {
    				f(&*n);
    			}
    		}
    	}

    	/// Get the Registry object - useful for looking up names.
    	pub fn registrar(&self) -> MutexGuard<Option<Registry>> {
    		self.registrar.lock()
    	}

    	/// Register an action to be done if a mode change happens.
    	pub fn on_mode_change<F>(&self, f: F) where F: 'static + FnMut(&Mode) + Send {
    		*self.on_mode_change.lock() = Some(Box::new(f));
    	}

    	/// Flush the block import queue.
    	pub fn flush_queue(&self) {
    		self.block_queue.flush();
    		while !self.block_queue.queue_info().is_empty() {
    			self.import_verified_blocks();
    		}
    	}

    	/// The env info as of the best block.
    	fn latest_env_info(&self) -> EnvInfo {
    		let header = self.best_block_header();

    		EnvInfo {
    			number: header.number(),
    			author: header.author(),
    			timestamp: header.timestamp(),
    			difficulty: header.difficulty(),
    			last_hashes: self.build_last_hashes(header.hash()),
    			gas_used: U256::default(),
    			gas_limit: header.gas_limit(),
    		}
    	}

    	fn build_last_hashes(&self, parent_hash: H256) -> Arc<LastHashes> {
    		{
    			let hashes = self.last_hashes.read();
    			if hashes.front().map_or(false, |h| h == &parent_hash) {
    				let mut res = Vec::from(hashes.clone());
    				res.resize(256, H256::default());
    				return Arc::new(res);
    			}
    		}
    		let mut last_hashes = LastHashes::new();
    		last_hashes.resize(256, H256::default());
    		last_hashes[0] = parent_hash;
    		let chain = self.chain.read();
    		for i in 0..255 {
    			match chain.block_details(&last_hashes[i]) {
    				Some(details) => {
    					last_hashes[i + 1] = details.parent.clone();
    				},
    				None => break,
    			}
    		}
    		let mut cached_hashes = self.last_hashes.write();
    		*cached_hashes = VecDeque::from(last_hashes.clone());
    		Arc::new(last_hashes)
    	}

    	fn check_and_close_block(&self, block: &PreverifiedBlock) -> Result<LockedBlock, ()> {
    		let engine = &*self.engine;
    		let header = &block.header;

    		let chain = self.chain.read();
    		// Check the block isn't so old we won't be able to enact it.
    		let best_block_number = chain.best_block_number();
    		if best_block_number >= self.history && header.number() <= best_block_number - self.history {
    			warn!(target: "client", "Block import failed for #{} ({})\nBlock is ancient (current best block: #{}).", header.number(), header.hash(), best_block_number);
    			return Err(());
    		}

    		// Verify Block Family
    		let verify_family_result = self.verifier.verify_block_family(header, &block.bytes, engine, &**chain);
    		if let Err(e) = verify_family_result {
    			warn!(target: "client", "Stage 3 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
    			return Err(());
    		};

    		// Check if Parent is in chain
    		let chain_has_parent = chain.block_header(header.parent_hash());
    		if let Some(parent) = chain_has_parent {
    			// Enact Verified Block
    			let last_hashes = self.build_last_hashes(header.parent_hash().clone());
    			let db = self.state_db.lock().boxed_clone_canon(header.parent_hash());

    			let enact_result = enact_verified(block, engine, self.tracedb.read().tracing_enabled(), db, &parent, last_hashes, self.factories.clone());
    			let locked_block = enact_result.map_err(|e| {
    				warn!(target: "client", "Block import failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
    			})?;

    			// Final Verification
    			if let Err(e) = self.verifier.verify_block_final(header, locked_block.block().header()) {
    				warn!(target: "client", "Stage 4 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
    				return Err(());
    			}

    			Ok(locked_block)
    		} else {
    			warn!(target: "client", "Block import failed for #{} ({}): Parent not found ({}) ", header.number(), header.hash(), header.parent_hash());
    			Err(())
    		}
    	}

    	fn calculate_enacted_retracted(&self, import_results: &[ImportRoute]) -> (Vec<H256>, Vec<H256>) {
    		fn map_to_vec(map: Vec<(H256, bool)>) -> Vec<H256> {
    			map.into_iter().map(|(k, _v)| k).collect()
    		}

    		// In ImportRoute we get all the blocks that have been enacted and retracted by single insert.
    		// Because we are doing multiple inserts some of the blocks that were enacted in import `k`
    		// could be retracted in import `k+1`. This is why to understand if after all inserts
    		// the block is enacted or retracted we iterate over all routes and at the end final state
    		// will be in the hashmap
    		let map = import_results.iter().fold(HashMap::new(), |mut map, route| {
    			for hash in &route.enacted {
    				map.insert(hash.clone(), true);
    			}
    			for hash in &route.retracted {
    				map.insert(hash.clone(), false);
    			}
    			map
    		});

    		// Split to enacted retracted (using hashmap value)
    		let (enacted, retracted) = map.into_iter().partition(|&(_k, v)| v);
    		// And convert tuples to keys
    		(map_to_vec(enacted), map_to_vec(retracted))
    	}

    	/// This is triggered by a message coming from a block queue when the block is ready for insertion
    	pub fn import_verified_blocks(&self) -> usize {

    		// Shortcut out if we know we're incapable of syncing the chain.
    		if !self.enabled.load(AtomicOrdering::Relaxed) {
    			return 0;
    		}

    		let max_blocks_to_import = 4;
    		let (imported_blocks, import_results, invalid_blocks, imported, proposed_blocks, duration, is_empty) = {
    			let mut imported_blocks = Vec::with_capacity(max_blocks_to_import);
    			let mut invalid_blocks = HashSet::new();
    			let mut proposed_blocks = Vec::with_capacity(max_blocks_to_import);
    			let mut import_results = Vec::with_capacity(max_blocks_to_import);

    			let _import_lock = self.import_lock.lock();
    			let blocks = self.block_queue.drain(max_blocks_to_import);
    			if blocks.is_empty() {
    				return 0;
    			}
    			let _timer = PerfTimer::new("import_verified_blocks");
    			let start = precise_time_ns();

    			for block in blocks {
    				let header = &block.header;
    				let is_invalid = invalid_blocks.contains(header.parent_hash());
    				if is_invalid {
    					invalid_blocks.insert(header.hash());
    					continue;
    				}
    				if let Ok(closed_block) = self.check_and_close_block(&block) {
    					if self.engine.is_proposal(&block.header) {
    						self.block_queue.mark_as_good(&[header.hash()]);
    						proposed_blocks.push(block.bytes);
    					} else {
    						imported_blocks.push(header.hash());

    						let route = self.commit_block(closed_block, &header.hash(), &block.bytes);
    						import_results.push(route);

    						self.report.write().accrue_block(&block);
    					}
    				} else {
    					invalid_blocks.insert(header.hash());
    				}
    			}

    			let imported = imported_blocks.len();
    			let invalid_blocks = invalid_blocks.into_iter().collect::<Vec<H256>>();

    			if !invalid_blocks.is_empty() {
    				self.block_queue.mark_as_bad(&invalid_blocks);
    			}
    			let is_empty = self.block_queue.mark_as_good(&imported_blocks);
    			let duration_ns = precise_time_ns() - start;
    			(imported_blocks, import_results, invalid_blocks, imported, proposed_blocks, duration_ns, is_empty)
    		};

    		{
    			if !imported_blocks.is_empty() && is_empty {
    				let (enacted, retracted) = self.calculate_enacted_retracted(&import_results);

    				if is_empty {
    					self.miner.chain_new_blocks(self, &imported_blocks, &invalid_blocks, &enacted, &retracted);
    				}

    				self.notify(|notify| {
    					notify.new_blocks(
    						imported_blocks.clone(),
    						invalid_blocks.clone(),
    						enacted.clone(),
    						retracted.clone(),
    						Vec::new(),
    						proposed_blocks.clone(),
    						duration,
    					);
    				});
    			}
    		}

    		self.db.read().flush().expect("DB flush failed.");
    		imported
    	}

    	/// Import a block with transaction receipts.
    	/// The block is guaranteed to be the next best blocks in the first block sequence.
    	/// Does no sealing or transaction validation.
    	fn import_old_block(&self, block_bytes: Bytes, receipts_bytes: Bytes) -> Result<H256, ::error::Error> {
    		let block = BlockView::new(&block_bytes);
    		let header = block.header();
    		let hash = header.hash();
    		let _import_lock = self.import_lock.lock();
    		{
    			let _timer = PerfTimer::new("import_old_block");
    			let mut rng = self.rng.lock();
    			let chain = self.chain.read();

    			// verify block.
    			::snapshot::verify_old_block(
    				&mut *rng,
    				&header,
    				&*self.engine,
    				&*chain,
    				Some(&block_bytes),
    				false,
    			)?;

    			// Commit results
    			let receipts = ::rlp::decode(&receipts_bytes);
    			let mut batch = DBTransaction::new(&self.db.read());
    			chain.insert_unordered_block(&mut batch, &block_bytes, receipts, None, false, true);
    			// Final commit to the DB
    			self.db.read().write_buffered(batch);
    			chain.commit();
    		}
    		self.db.read().flush().expect("DB flush failed.");
    		Ok(hash)
    	}

    	fn commit_block<B>(&self, block: B, hash: &H256, block_data: &[u8]) -> ImportRoute where B: IsBlock + Drain {
    		let number = block.header().number();
    		let parent = block.header().parent_hash().clone();
    		let chain = self.chain.read();

    		// Commit results
    		let receipts = block.receipts().to_owned();
    		let traces = block.traces().clone().unwrap_or_else(Vec::new);
    		let traces: Vec<FlatTransactionTraces> = traces.into_iter()
    			.map(Into::into)
    			.collect();

    		//let traces = From::from(block.traces().clone().unwrap_or_else(Vec::new));

    		let mut batch = DBTransaction::new(&self.db.read());
    		// CHECK! I *think* this is fine, even if the state_root is equal to another
    		// already-imported block of the same number.
    		// TODO: Prove it with a test.
    		let mut state = block.drain();

    		state.journal_under(&mut batch, number, hash).expect("DB commit failed");
    		let route = chain.insert_block(&mut batch, block_data, receipts);
    		self.tracedb.read().import(&mut batch, TraceImportRequest {
    			traces: traces.into(),
    			block_hash: hash.clone(),
    			block_number: number,
    			enacted: route.enacted.clone(),
    			retracted: route.retracted.len()
    		});

    		let is_canon = route.enacted.last().map_or(false, |h| h == hash);
    		state.sync_cache(&route.enacted, &route.retracted, is_canon);
    		// Final commit to the DB
    		self.db.read().write_buffered(batch);
    		chain.commit();
    		self.update_last_hashes(&parent, hash);

    		if let Err(e) = self.prune_ancient(state, &chain) {
    			warn!("Failed to prune ancient state data: {}", e);
    		}

    		route
    	}

    	// prune ancient states until below the memory limit or only the minimum amount remain.
    	fn prune_ancient(&self, mut state_db: StateDB, chain: &BlockChain) -> Result<(), ClientError> {
    		let number = match state_db.journal_db().latest_era() {
    			Some(n) => n,
    			None => return Ok(()),
    		};

    		// prune all ancient eras until we're below the memory target,
    		// but have at least the minimum number of states.
    		loop {
    			let needs_pruning = state_db.journal_db().is_pruned() &&
    				state_db.journal_db().journal_size() >= self.config.history_mem;

    			if !needs_pruning { break }
    			match state_db.journal_db().earliest_era() {
    				Some(era) if era + self.history <= number => {
    					trace!(target: "client", "Pruning state for ancient era {}", era);
    					match chain.block_hash(era) {
    						Some(ancient_hash) => {
    							let mut batch = DBTransaction::new(&self.db.read());
    							state_db.mark_canonical(&mut batch, era, &ancient_hash)?;
    							self.db.read().write_buffered(batch);
    							state_db.journal_db().flush();
    						}
    						None =>
    							debug!(target: "client", "Missing expected hash for block {}", era),
    					}
    				}
    				_ => break, // means that every era is kept, no pruning necessary.
    			}
    		}

    		Ok(())
    	}

    	fn update_last_hashes(&self, parent: &H256, hash: &H256) {
    		let mut hashes = self.last_hashes.write();
    		if hashes.front().map_or(false, |h| h == parent) {
    			if hashes.len() > 255 {
    				hashes.pop_back();
    			}
    			hashes.push_front(hash.clone());
    		}
    	}

    	/// Import transactions from the IO queue
    	pub fn import_queued_transactions(&self, transactions: &[Bytes], peer_id: usize) -> usize {
    		trace!(target: "external_tx", "Importing queued");
    		let _timer = PerfTimer::new("import_queued_transactions");
    		self.queue_transactions.fetch_sub(transactions.len(), AtomicOrdering::SeqCst);
    		let txs: Vec<UnverifiedTransaction> = transactions.iter().filter_map(|bytes| UntrustedRlp::new(bytes).as_val().ok()).collect();
    		let hashes: Vec<_> = txs.iter().map(|tx| tx.hash()).collect();
    		self.notify(|notify| {
    			notify.transactions_received(hashes.clone(), peer_id);
    		});
    		let results = self.miner.import_external_transactions(self, txs);
    		results.len()
    	}

    	/// Get shared miner reference.
    	pub fn miner(&self) -> Arc<Miner> {
    		self.miner.clone()
    	}

    	/// Replace io channel. Useful for testing.
    	pub fn set_io_channel(&self, io_channel: IoChannel<ClientIoMessage>) {
    		*self.io_channel.lock() = io_channel;
    	}

    	/// Attempt to get a copy of a specific block's final state.
    	///
    	/// This will not fail if given BlockId::Latest.
    	/// Otherwise, this can fail (but may not) if the DB prunes state or the block
    	/// is unknown.
    	pub fn state_at(&self, id: BlockId) -> Option<State> {
    		// fast path for latest state.
    		match id.clone() {
    			BlockId::Pending => return self.miner.pending_state().or_else(|| Some(self.state())),
    			BlockId::Latest => return Some(self.state()),
    			_ => {},
    		}

    		let block_number = match self.block_number(id.clone()) {
    			Some(num) => num,
    			None => return None,
    		};

    		self.block_header(id).and_then(|header| {
    			let db = self.state_db.lock().boxed_clone();

    			// early exit for pruned blocks
    			if db.is_pruned() && self.chain.read().best_block_number() >= block_number + self.history {
    				return None;
    			}

    			let root = header.state_root();
    			State::from_existing(db, root, self.engine.account_start_nonce(), self.factories.clone()).ok()
    		})
    	}

    	/// Attempt to get a copy of a specific block's beginning state.
    	///
    	/// This will not fail if given BlockId::Latest.
    	/// Otherwise, this can fail (but may not) if the DB prunes state.
    	pub fn state_at_beginning(&self, id: BlockId) -> Option<State> {
    		// fast path for latest state.
    		match id {
    			BlockId::Pending => self.state_at(BlockId::Latest),
    			id => match self.block_number(id) {
    				None | Some(0) => None,
    				Some(n) => self.state_at(BlockId::Number(n - 1)),
    			}
    		}
    	}

    	/// Get a copy of the best block's state.
    	pub fn state(&self) -> State {
    		let header = self.best_block_header();
    		State::from_existing(
    			self.state_db.lock().boxed_clone_canon(&header.hash()),
    			header.state_root(),
    			self.engine.account_start_nonce(),
    			self.factories.clone())
    		.expect("State root of best block header always valid.")
    	}

    	/// Get info on the cache.
    	pub fn blockchain_cache_info(&self) -> BlockChainCacheSize {
    		self.chain.read().cache_size()
    	}

    	/// Get the report.
    	pub fn report(&self) -> ClientReport {
    		let mut report = self.report.read().clone();
    		report.state_db_mem = self.state_db.lock().mem_used();
    		report
    	}

    	/// Tick the client.
    	// TODO: manage by real events.
    	pub fn tick(&self) {
    		self.check_garbage();
    		self.check_snooze();
    	}

    	fn check_garbage(&self) {
    		self.chain.read().collect_garbage();
    		self.block_queue.collect_garbage();
    		self.tracedb.read().collect_garbage();
    	}

    	fn check_snooze(&self) {
    		let mode = self.mode.lock().clone();
    		match mode {
    			Mode::Dark(timeout) => {
    				let mut ss = self.sleep_state.lock();
    				if let Some(t) = ss.last_activity {
    					if Instant::now() > t + timeout {
    						self.sleep();
    						ss.last_activity = None;
    					}
    				}
    			}
    			Mode::Passive(timeout, wakeup_after) => {
    				let mut ss = self.sleep_state.lock();
    				let now = Instant::now();
    				if let Some(t) = ss.last_activity {
    					if now > t + timeout {
    						self.sleep();
    						ss.last_activity = None;
    						ss.last_autosleep = Some(now);
    					}
    				}
    				if let Some(t) = ss.last_autosleep {
    					if now > t + wakeup_after {
    						self.wake_up();
    						ss.last_activity = Some(now);
    						ss.last_autosleep = None;
    					}
    				}
    			}
    			_ => {}
    		}
    	}

    	/// Take a snapshot at the given block.
    	/// If the ID given is "latest", this will default to 1000 blocks behind.
    	pub fn take_snapshot<W: snapshot_io::SnapshotWriter + Send>(&self, writer: W, at: BlockId, p: &snapshot::Progress) -> Result<(), EthcoreError> {
    		let db = self.state_db.lock().journal_db().boxed_clone();
    		let best_block_number = self.chain_info().best_block_number;
    		let block_number = self.block_number(at).ok_or(snapshot::Error::InvalidStartingBlock(at))?;

    		if best_block_number > self.history + block_number && db.is_pruned() {
    			return Err(snapshot::Error::OldBlockPrunedDB.into());
    		}

    		let history = ::std::cmp::min(self.history, 1000);

    		let start_hash = match at {
    			BlockId::Latest => {
    				let start_num = match db.earliest_era() {
    					Some(era) => ::std::cmp::max(era, best_block_number - history),
    					None => best_block_number - history,
    				};

    				match self.block_hash(BlockId::Number(start_num)) {
    					Some(h) => h,
    					None => return Err(snapshot::Error::InvalidStartingBlock(at).into()),
    				}
    			}
    			_ => match self.block_hash(at) {
    				Some(hash) => hash,
    				None => return Err(snapshot::Error::InvalidStartingBlock(at).into()),
    			},
    		};

    		snapshot::take_snapshot(&self.chain.read(), start_hash, db.as_hashdb(), writer, p)?;

    		Ok(())
    	}

    	/// Ask the client what the history parameter is.
    	pub fn pruning_history(&self) -> u64 {
    		self.history
    	}

    	fn block_hash(chain: &BlockChain, id: BlockId) -> Option<H256> {
    		match id {
    			BlockId::Hash(hash) => Some(hash),
    			BlockId::Number(number) => chain.block_hash(number),
    			BlockId::Earliest => chain.block_hash(0),
    			BlockId::Latest | BlockId::Pending => Some(chain.best_block_hash()),
    		}
    	}

    	fn transaction_address(&self, id: TransactionId) -> Option<TransactionAddress> {
    		match id {
    			TransactionId::Hash(ref hash) => self.chain.read().transaction_address(hash),
    			TransactionId::Location(id, index) => Self::block_hash(&self.chain.read(), id).map(|hash| TransactionAddress {
    				block_hash: hash,
    				index: index,
    			})
    		}
    	}

    	fn wake_up(&self) {
    		if !self.liveness.load(AtomicOrdering::Relaxed) {
    			self.liveness.store(true, AtomicOrdering::Relaxed);
    			self.notify(|n| n.start());
    			trace!(target: "mode", "wake_up: Waking.");
    		}
    	}

    	fn sleep(&self) {
    		if self.liveness.load(AtomicOrdering::Relaxed) {
    			// only sleep if the import queue is mostly empty.
    			if self.queue_info().total_queue_size() <= MAX_QUEUE_SIZE_TO_SLEEP_ON {
    				self.liveness.store(false, AtomicOrdering::Relaxed);
    				self.notify(|n| n.stop());
    				trace!(target: "mode", "sleep: Sleeping.");
    			} else {
    				trace!(target: "mode", "sleep: Cannot sleep - syncing ongoing.");
    				// TODO: Consider uncommenting.
    				//*self.last_activity.lock() = Some(Instant::now());
    			}
    		}
    	}
    }

    impl snapshot::DatabaseRestore for Client {
    	/// Restart the client with a new backend
    	fn restore_db(&self, new_db: &str) -> Result<(), EthcoreError> {
    		trace!(target: "snapshot", "Replacing client database with {:?}", new_db);

    		let _import_lock = self.import_lock.lock();
    		let mut state_db = self.state_db.lock();
    		let mut chain = self.chain.write();
    		let mut tracedb = self.tracedb.write();
    		self.miner.clear();
    		let db = self.db.write();
    		db.restore(new_db)?;

    		let cache_size = state_db.cache_size();
    		*state_db = StateDB::new(journaldb::new(db.clone(), self.pruning, ::db::COL_STATE), cache_size);
    		*chain = Arc::new(BlockChain::new(self.config.blockchain.clone(), &[], db.clone()));
    		*tracedb = TraceDB::new(self.config.tracing.clone(), db.clone(), chain.clone());
    		Ok(())
    	}
    }

    impl BlockChainClient for Client {
    	fn call(&self, t: &SignedTransaction, block: BlockId, analytics: CallAnalytics) -> Result<Executed, CallError> {
    		let header = self.block_header(block).ok_or(CallError::StatePruned)?;
    		let last_hashes = self.build_last_hashes(header.parent_hash());
    		let env_info = EnvInfo {
    			number: header.number(),
    			author: header.author(),
    			timestamp: header.timestamp(),
    			difficulty: header.difficulty(),
    			last_hashes: last_hashes,
    			gas_used: U256::zero(),
    			gas_limit: U256::max_value(),
    		};
    		// that's just a copy of the state.
    		let mut state = self.state_at(block).ok_or(CallError::StatePruned)?;
    		let original_state = if analytics.state_diffing { Some(state.clone()) } else { None };

    		let sender = t.sender();
    		let balance = state.balance(&sender);
    		let needed_balance = t.value + t.gas * t.gas_price;
    		if balance < needed_balance {
    			// give the sender a sufficient balance
    			state.add_balance(&sender, &(needed_balance - balance), CleanupMode::NoEmpty);
    		}
    		let options = TransactOptions { tracing: analytics.transaction_tracing, vm_tracing: analytics.vm_tracing, check_nonce: false };
    		let mut ret = Executive::new(&mut state, &env_info, &*self.engine, &self.factories.vm).transact(t, options)?;

    		// TODO gav move this into Executive.
    		ret.state_diff = original_state.map(|original| state.diff_from(original));

    		Ok(ret)
    	}

    	fn estimate_gas(&self, t: &SignedTransaction, block: BlockId) -> Result<U256, CallError> {
    		const UPPER_CEILING: u64 = 1_000_000_000_000u64;
    		let header = self.block_header(block).ok_or(CallError::StatePruned)?;
    		let last_hashes = self.build_last_hashes(header.parent_hash());
    		let env_info = EnvInfo {
    			number: header.number(),
    			author: header.author(),
    			timestamp: header.timestamp(),
    			difficulty: header.difficulty(),
    			last_hashes: last_hashes,
    			gas_used: U256::zero(),
    			gas_limit: UPPER_CEILING.into(),
    		};
    		// that's just a copy of the state.
    		let original_state = self.state_at(block).ok_or(CallError::StatePruned)?;
    		let sender = t.sender();
    		let balance = original_state.balance(&sender);
    		let options = TransactOptions { tracing: true, vm_tracing: false, check_nonce: false };

    		let cond = |gas| {
    			let mut tx = t.as_unsigned().clone();
    			tx.gas = gas;
    			let tx = tx.fake_sign(sender);

    			let mut state = original_state.clone();
    			let needed_balance = tx.value + tx.gas * tx.gas_price;
    			if balance < needed_balance {
    				// give the sender a sufficient balance
    				state.add_balance(&sender, &(needed_balance - balance), CleanupMode::NoEmpty);
    			}

    			Executive::new(&mut state, &env_info, &*self.engine, &self.factories.vm)
    				.transact(&tx, options.clone())
    				.map(|r| r.exception.is_none())
    				.unwrap_or(false)
    		};

    		let mut upper = header.gas_limit();
    		if !cond(upper) {
    			// impossible at block gas limit - try `UPPER_CEILING` instead.
    			// TODO: consider raising limit by powers of two.
    			upper = UPPER_CEILING.into();
    			if !cond(upper) {
    				trace!(target: "estimate_gas", "estimate_gas failed with {}", upper);
    				return Err(CallError::Execution(ExecutionError::Internal))
    			}
    		}
    		let lower = t.gas_required(&self.engine.schedule(&env_info)).into();
    		if cond(lower) {
    			trace!(target: "estimate_gas", "estimate_gas succeeded with {}", lower);
    			return Ok(lower)
    		}

    		/// Find transition point between `lower` and `upper` where `cond` changes from `false` to `true`.
    		/// Returns the lowest value between `lower` and `upper` for which `cond` returns true.
    		/// We assert: `cond(lower) = false`, `cond(upper) = true`
    		fn binary_chop<F>(mut lower: U256, mut upper: U256, mut cond: F) -> U256 where F: FnMut(U256) -> bool {
    			while upper - lower > 1.into() {
    				let mid = (lower + upper) / 2.into();
    				trace!(target: "estimate_gas", "{} .. {} .. {}", lower, mid, upper);
    				let c = cond(mid);
    				match c {
    					true => upper = mid,
    					false => lower = mid,
    				};
    				trace!(target: "estimate_gas", "{} => {} .. {}", c, lower, upper);
    			}
    			upper
    		}

    		// binary chop to non-excepting call with gas somewhere between 21000 and block gas limit
    		trace!(target: "estimate_gas", "estimate_gas chopping {} .. {}", lower, upper);
    		Ok(binary_chop(lower, upper, cond))
    	}

    	fn replay(&self, id: TransactionId, analytics: CallAnalytics) -> Result<Executed, CallError> {
    		let address = self.transaction_address(id).ok_or(CallError::TransactionNotFound)?;
    		let header = self.block_header(BlockId::Hash(address.block_hash)).ok_or(CallError::StatePruned)?;
    		let body = self.block_body(BlockId::Hash(address.block_hash)).ok_or(CallError::StatePruned)?;
    		let mut state = self.state_at_beginning(BlockId::Hash(address.block_hash)).ok_or(CallError::StatePruned)?;
    		let mut txs = body.transactions();

    		if address.index >= txs.len() {
    			return Err(CallError::TransactionNotFound);
    		}

    		let options = TransactOptions { tracing: analytics.transaction_tracing, vm_tracing: analytics.vm_tracing, check_nonce: false };
    		let last_hashes = self.build_last_hashes(header.hash());
    		let mut env_info = EnvInfo {
    			number: header.number(),
    			author: header.author(),
    			timestamp: header.timestamp(),
    			difficulty: header.difficulty(),
    			last_hashes: last_hashes,
    			gas_used: U256::default(),
    			gas_limit: header.gas_limit(),
    		};
    		const PROOF: &'static str = "Transactions fetched from blockchain; blockchain transactions are valid; qed";
    		let rest = txs.split_off(address.index);
    		for t in txs {
    			let t = SignedTransaction::new(t).expect(PROOF);
    			match Executive::new(&mut state, &env_info, &*self.engine, &self.factories.vm).transact(&t, Default::default()) {
    				Ok(x) => { env_info.gas_used = env_info.gas_used + x.gas_used; }
    				Err(ee) => { return Err(CallError::Execution(ee)) }
    			}
    		}
    		let first = rest.into_iter().next().expect("We split off < `address.index`; Length is checked earlier; qed");
    		let t = SignedTransaction::new(first).expect(PROOF);
    		let original_state = if analytics.state_diffing { Some(state.clone()) } else { None };
    		let mut ret = Executive::new(&mut state, &env_info, &*self.engine, &self.factories.vm).transact(&t, options)?;
    		ret.state_diff = original_state.map(|original| state.diff_from(original));

    		Ok(ret)
    	}

    	fn keep_alive(&self) {
    		let should_wake = match *self.mode.lock() {
    			Mode::Dark(..) | Mode::Passive(..) => true,
    			_ => false,
    		};
    		if should_wake {
    			self.wake_up();
    			(*self.sleep_state.lock()).last_activity = Some(Instant::now());
    		}
    	}

    	fn mode(&self) -> IpcMode {
    		let r = self.mode.lock().clone().into();
    		trace!(target: "mode", "Asked for mode = {:?}. returning {:?}", &*self.mode.lock(), r);
    		r
    	}

    	fn disable(&self) {
    		self.set_mode(IpcMode::Off);
    		self.enabled.store(false, AtomicOrdering::Relaxed);
    		self.clear_queue();
    	}

    	fn set_mode(&self, new_mode: IpcMode) {
    		trace!(target: "mode", "Client::set_mode({:?})", new_mode);
    		if !self.enabled.load(AtomicOrdering::Relaxed) {
    			return;
    		}
    		{
    			let mut mode = self.mode.lock();
    			*mode = new_mode.clone().into();
    			trace!(target: "mode", "Mode now {:?}", &*mode);
    			if let Some(ref mut f) = *self.on_mode_change.lock() {
    				trace!(target: "mode", "Making callback...");
    				f(&*mode)
    			}
    		}
    		match new_mode {
    			IpcMode::Active => self.wake_up(),
    			IpcMode::Off => self.sleep(),
    			_ => {(*self.sleep_state.lock()).last_activity = Some(Instant::now()); }
    		}
    	}

    	fn best_block_header(&self) -> encoded::Header {
    		self.chain.read().best_block_header()
    	}

    	fn block_header(&self, id: BlockId) -> Option<::encoded::Header> {
    		let chain = self.chain.read();
    		Self::block_hash(&chain, id).and_then(|hash| chain.block_header_data(&hash))
    	}

    	fn block_number(&self, id: BlockId) -> Option<BlockNumber> {
    		match id {
    			BlockId::Number(number) => Some(number),
    			BlockId::Hash(ref hash) => self.chain.read().block_number(hash),
    			BlockId::Earliest => Some(0),
    			BlockId::Latest | BlockId::Pending => Some(self.chain.read().best_block_number()),
    		}
    	}

    	fn block_body(&self, id: BlockId) -> Option<encoded::Body> {
    		let chain = self.chain.read();
    		Self::block_hash(&chain, id).and_then(|hash| chain.block_body(&hash))
    	}

    	fn block(&self, id: BlockId) -> Option<encoded::Block> {
    		if let BlockId::Pending = id {
    			if let Some(block) = self.miner.pending_block() {
    				return Some(encoded::Block::new(block.rlp_bytes(Seal::Without)));
    			}
    		}
    		let chain = self.chain.read();
    		Self::block_hash(&chain, id).and_then(|hash| {
    			chain.block(&hash)
    		})
    	}

    	fn block_status(&self, id: BlockId) -> BlockStatus {
    		let chain = self.chain.read();
    		match Self::block_hash(&chain, id) {
    			Some(ref hash) if chain.is_known(hash) => BlockStatus::InChain,
    			Some(hash) => self.block_queue.status(&hash).into(),
    			None => BlockStatus::Unknown
    		}
    	}

    	fn block_total_difficulty(&self, id: BlockId) -> Option<U256> {
    		if let BlockId::Pending = id {
    			if let Some(block) = self.miner.pending_block() {
    				return Some(*block.header.difficulty() + self.block_total_difficulty(BlockId::Latest).expect("blocks in chain have details; qed"));
    			}
    		}
    		let chain = self.chain.read();
    		Self::block_hash(&chain, id).and_then(|hash| chain.block_details(&hash)).map(|d| d.total_difficulty)
    	}

    	fn nonce(&self, address: &Address, id: BlockId) -> Option<U256> {
    		self.state_at(id).map(|s| s.nonce(address))
    	}

    	fn storage_root(&self, address: &Address, id: BlockId) -> Option<H256> {
    		self.state_at(id).and_then(|s| s.storage_root(address))
    	}

    	fn block_hash(&self, id: BlockId) -> Option<H256> {
    		let chain = self.chain.read();
    		Self::block_hash(&chain, id)
    	}

    	fn code(&self, address: &Address, id: BlockId) -> Option<Option<Bytes>> {
    		self.state_at(id).map(|s| s.code(address).map(|c| (*c).clone()))
    	}

    	fn balance(&self, address: &Address, id: BlockId) -> Option<U256> {
    		self.state_at(id).map(|s| s.balance(address))
    	}

    	fn storage_at(&self, address: &Address, position: &H256, id: BlockId) -> Option<H256> {
    		self.state_at(id).map(|s| s.storage_at(address, position))
    	}

    	fn list_accounts(&self, id: BlockId, after: Option<&Address>, count: u64) -> Option<Vec<Address>> {
    		if !self.factories.trie.is_fat() {
    			trace!(target: "fatdb", "list_accounts: Not a fat DB");
    			return None;
    		}

    		let state = match self.state_at(id) {
    			Some(state) => state,
    			_ => return None,
    		};

    		let (root, db) = state.drop();
    		let trie = match self.factories.trie.readonly(db.as_hashdb(), &root) {
    			Ok(trie) => trie,
    			_ => {
    				trace!(target: "fatdb", "list_accounts: Couldn't open the DB");
    				return None;
    			}
    		};

    		let mut iter = match trie.iter() {
    			Ok(iter) => iter,
    			_ => return None,
    		};

    		if let Some(after) = after {
    			if let Err(e) = iter.seek(after) {
    				trace!(target: "fatdb", "list_accounts: Couldn't seek the DB: {:?}", e);
    			}
    		}

    		let accounts = iter.filter_map(|item| {
    			item.ok().map(|(addr, _)| Address::from_slice(&addr))
    		}).take(count as usize).collect();

    		Some(accounts)
    	}

    	fn list_storage(&self, id: BlockId, account: &Address, after: Option<&H256>, count: u64) -> Option<Vec<H256>> {
    		if !self.factories.trie.is_fat() {
    			trace!(target: "fatdb", "list_stroage: Not a fat DB");
    			return None;
    		}

    		let state = match self.state_at(id) {
    			Some(state) => state,
    			_ => return None,
    		};

    		let root = match state.storage_root(account) {
    			Some(root) => root,
    			_ => return None,
    		};

    		let (_, db) = state.drop();
    		let account_db = self.factories.accountdb.readonly(db.as_hashdb(), account.sha3());
    		let trie = match self.factories.trie.readonly(account_db.as_hashdb(), &root) {
    			Ok(trie) => trie,
    			_ => {
    				trace!(target: "fatdb", "list_storage: Couldn't open the DB");
    				return None;
    			}
    		};

    		let mut iter = match trie.iter() {
    			Ok(iter) => iter,
    			_ => return None,
    		};

    		if let Some(after) = after {
    			if let Err(e) = iter.seek(after) {
    				trace!(target: "fatdb", "list_accounts: Couldn't seek the DB: {:?}", e);
    			}
    		}

    		let keys = iter.filter_map(|item| {
    			item.ok().map(|(key, _)| H256::from_slice(&key))
    		}).take(count as usize).collect();

    		Some(keys)
    	}

    	fn transaction(&self, id: TransactionId) -> Option<LocalizedTransaction> {
    		self.transaction_address(id).and_then(|address| self.chain.read().transaction(&address))
    	}

    	fn transaction_block(&self, id: TransactionId) -> Option<H256> {
    		self.transaction_address(id).map(|addr| addr.block_hash)
    	}

    	fn uncle(&self, id: UncleId) -> Option<encoded::Header> {
    		let index = id.position;
    		self.block_body(id.block).and_then(|body| body.view().uncle_rlp_at(index))
    			.map(encoded::Header::new)
    	}

    	fn transaction_receipt(&self, id: TransactionId) -> Option<LocalizedReceipt> {
    		let chain = self.chain.read();
    		self.transaction_address(id)
    			.and_then(|address| chain.block_number(&address.block_hash).and_then(|block_number| {
    				let transaction = chain.block_body(&address.block_hash)
    					.and_then(|body| body.view().localized_transaction_at(&address.block_hash, block_number, address.index));

    				let previous_receipts = (0..address.index + 1)
    					.map(|index| {
    						let mut address = address.clone();
    						address.index = index;
    						chain.transaction_receipt(&address)
    					})
    					.collect();
    				match (transaction, previous_receipts) {
    					(Some(transaction), Some(previous_receipts)) => {
    						Some(transaction_receipt(transaction, previous_receipts))
    					},
    					_ => None,
    				}
    			}))
    	}

    	fn tree_route(&self, from: &H256, to: &H256) -> Option<TreeRoute> {
    		let chain = self.chain.read();
    		match chain.is_known(from) && chain.is_known(to) {
    			true => Some(chain.tree_route(from.clone(), to.clone())),
    			false => None
    		}
    	}

    	fn find_uncles(&self, hash: &H256) -> Option<Vec<H256>> {
    		self.chain.read().find_uncle_hashes(hash, self.engine.maximum_uncle_age())
    	}

    	fn state_data(&self, hash: &H256) -> Option<Bytes> {
    		self.state_db.lock().journal_db().state(hash)
    	}

    	fn block_receipts(&self, hash: &H256) -> Option<Bytes> {
    		self.chain.read().block_receipts(hash).map(|receipts| ::rlp::encode(&receipts).to_vec())
    	}

    	fn import_block(&self, bytes: Bytes) -> Result<H256, BlockImportError> {
    		use verification::queue::kind::BlockLike;
    		use verification::queue::kind::blocks::Unverified;

    		// create unverified block here so the `sha3` calculation can be cached.
    		let unverified = Unverified::new(bytes);

    		{
    			if self.chain.read().is_known(&unverified.hash()) {
    				return Err(BlockImportError::Import(ImportError::AlreadyInChain));
    			}
    			if self.block_status(BlockId::Hash(unverified.parent_hash())) == BlockStatus::Unknown {
    				return Err(BlockImportError::Block(BlockError::UnknownParent(unverified.parent_hash())));
    			}
    		}
    		Ok(self.block_queue.import(unverified)?)
    	}

    	fn import_block_with_receipts(&self, block_bytes: Bytes, receipts_bytes: Bytes) -> Result<H256, BlockImportError> {
    		{
    			// check block order
    			let header = BlockView::new(&block_bytes).header_view();
    			if self.chain.read().is_known(&header.hash()) {
    				return Err(BlockImportError::Import(ImportError::AlreadyInChain));
    			}
    			if self.block_status(BlockId::Hash(header.parent_hash())) == BlockStatus::Unknown {
    				return Err(BlockImportError::Block(BlockError::UnknownParent(header.parent_hash())));
    			}
    		}
    		self.import_old_block(block_bytes, receipts_bytes).map_err(Into::into)
    	}

    	fn queue_info(&self) -> BlockQueueInfo {
    		self.block_queue.queue_info()
    	}

    	fn clear_queue(&self) {
    		self.block_queue.clear();
    	}

    	fn chain_info(&self) -> BlockChainInfo {
    		let mut chain_info = self.chain.read().chain_info();
    		chain_info.pending_total_difficulty = chain_info.total_difficulty + self.block_queue.total_difficulty();
    		chain_info
    	}

    	fn additional_params(&self) -> BTreeMap<String, String> {
    		self.engine.additional_params().into_iter().collect()
    	}

    	fn blocks_with_bloom(&self, bloom: &H2048, from_block: BlockId, to_block: BlockId) -> Option<Vec<BlockNumber>> {
    		match (self.block_number(from_block), self.block_number(to_block)) {
    			(Some(from), Some(to)) => Some(self.chain.read().blocks_with_bloom(bloom, from, to)),
    			_ => None
    		}
    	}

    	fn logs(&self, filter: Filter) -> Vec<LocalizedLogEntry> {
    		let blocks = filter.bloom_possibilities().iter()
    			.filter_map(|bloom| self.blocks_with_bloom(bloom, filter.from_block.clone(), filter.to_block.clone()))
    			.flat_map(|m| m)
    			// remove duplicate elements
    			.collect::<HashSet<u64>>()
    			.into_iter()
    			.collect::<Vec<u64>>();

    		self.chain.read().logs(blocks, |entry| filter.matches(entry), filter.limit)
    	}

    	fn filter_traces(&self, filter: TraceFilter) -> Option<Vec<LocalizedTrace>> {
    		let start = self.block_number(filter.range.start);
    		let end = self.block_number(filter.range.end);

    		match (start, end) {
    			(Some(s), Some(e)) => {
    				let filter = trace::Filter {
    					range: s as usize..e as usize,
    					from_address: From::from(filter.from_address),
    					to_address: From::from(filter.to_address),
    				};

    				let traces = self.tracedb.read().filter(&filter);
    				Some(traces)
    			},
    			_ => None,
    		}
    	}

    	fn trace(&self, trace: TraceId) -> Option<LocalizedTrace> {
    		let trace_address = trace.address;
    		self.transaction_address(trace.transaction)
    			.and_then(|tx_address| {
    				self.block_number(BlockId::Hash(tx_address.block_hash))
    					.and_then(|number| self.tracedb.read().trace(number, tx_address.index, trace_address))
    			})
    	}

    	fn transaction_traces(&self, transaction: TransactionId) -> Option<Vec<LocalizedTrace>> {
    		self.transaction_address(transaction)
    			.and_then(|tx_address| {
    				self.block_number(BlockId::Hash(tx_address.block_hash))
    					.and_then(|number| self.tracedb.read().transaction_traces(number, tx_address.index))
    			})
    	}

    	fn block_traces(&self, block: BlockId) -> Option<Vec<LocalizedTrace>> {
    		self.block_number(block)
    			.and_then(|number| self.tracedb.read().block_traces(number))
    	}

    	fn last_hashes(&self) -> LastHashes {
    		(*self.build_last_hashes(self.chain.read().best_block_hash())).clone()
    	}

    	fn queue_transactions(&self, transactions: Vec<Bytes>, peer_id: usize) {
    		let queue_size = self.queue_transactions.load(AtomicOrdering::Relaxed);
    		trace!(target: "external_tx", "Queue size: {}", queue_size);
    		if queue_size > MAX_TX_QUEUE_SIZE {
    			debug!("Ignoring {} transactions: queue is full", transactions.len());
    		} else {
    			let len = transactions.len();
    			match self.io_channel.lock().send(ClientIoMessage::NewTransactions(transactions, peer_id)) {
    				Ok(_) => {
    					self.queue_transactions.fetch_add(len, AtomicOrdering::SeqCst);
    				}
    				Err(e) => {
    					debug!("Ignoring {} transactions: error queueing: {}", len, e);
    				}
    			}
    		}
    	}

    	fn ready_transactions(&self) -> Vec<PendingTransaction> {
    		self.miner.ready_transactions(self.chain.read().best_block_number())
    	}

    	fn queue_consensus_message(&self, message: Bytes) {
    		let channel = self.io_channel.lock().clone();
    		if let Err(e) = channel.send(ClientIoMessage::NewMessage(message)) {
    			debug!("Ignoring the message, error queueing: {}", e);
    		}
    	}

    	fn signing_network_id(&self) -> Option<u64> {
    		self.engine.signing_network_id(&self.latest_env_info())
    	}

    	fn block_extra_info(&self, id: BlockId) -> Option<BTreeMap<String, String>> {
    		self.block_header(id)
    			.map(|header| self.engine.extra_info(&header.decode()))
    	}

    	fn uncle_extra_info(&self, id: UncleId) -> Option<BTreeMap<String, String>> {
    		self.uncle(id)
    			.map(|header| self.engine.extra_info(&header.decode()))
    	}

    	fn pruning_info(&self) -> PruningInfo {
    		PruningInfo {
    			earliest_chain: self.chain.read().first_block_number().unwrap_or(1),
    			earliest_state: self.state_db.lock().journal_db().earliest_era().unwrap_or(0),
    		}
    	}

    	fn call_contract(&self, address: Address, data: Bytes) -> Result<Bytes, String> {
    		let from = Address::default();
    		let transaction = Transaction {
    			nonce: self.latest_nonce(&from),
    			action: Action::Call(address),
    			gas: U256::from(50_000_000),
    			gas_price: U256::default(),
    			value: U256::default(),
    			data: data,
    		}.fake_sign(from);

    		self.call(&transaction, BlockId::Latest, Default::default())
    			.map_err(|e| format!("{:?}", e))
    			.map(|executed| {
    				executed.output
    			})
    	}

    	fn transact_contract(&self, address: Address, data: Bytes) -> Result<TransactionImportResult, EthcoreError> {
    		let transaction = Transaction {
    			nonce: self.latest_nonce(&self.miner.author()),
    			action: Action::Call(address),
    			gas: self.miner.gas_floor_target(),
    			gas_price: self.miner.sensible_gas_price(),
    			value: U256::zero(),
    			data: data,
    		};
    		let network_id = self.engine.signing_network_id(&self.latest_env_info());
    		let signature = self.engine.sign(transaction.hash(network_id))?;
    		let signed = SignedTransaction::new(transaction.with_signature(signature, network_id))?;
    		self.miner.import_own_transaction(self, signed.into())
    	}

    	fn registrar_address(&self) -> Option<Address> {
    		self.registrar.lock().as_ref().map(|r| r.address.clone())
    	}

    	fn registry_address(&self, name: String) -> Option<Address> {
    		self.registrar.lock().as_ref()
    			.and_then(|r| r.get_address(&(name.as_bytes().sha3()), "A").ok())
    			.and_then(|a| if a.is_zero() { None } else { Some(a) })
    	}
    }

    impl MiningBlockChainClient for Client {
    	fn latest_schedule(&self) -> Schedule {
    		self.engine.schedule(&self.latest_env_info())
    	}

    	fn prepare_open_block(&self, author: Address, gas_range_target: (U256, U256), extra_data: Bytes) -> OpenBlock {
    		let engine = &*self.engine;
    		let chain = self.chain.read();
    		let h = chain.best_block_hash();

    		let mut open_block = OpenBlock::new(
    			engine,
    			self.factories.clone(),
    			false,	// TODO: this will need to be parameterised once we want to do immediate mining insertion.
    			self.state_db.lock().boxed_clone_canon(&h),
    			&chain.block_header(&h).expect("h is best block hash: so its header must exist: qed"),
    			self.build_last_hashes(h.clone()),
    			author,
    			gas_range_target,
    			extra_data,
    		).expect("OpenBlock::new only fails if parent state root invalid; state root of best block's header is never invalid; qed");

    		// Add uncles
    		chain
    			.find_uncle_headers(&h, engine.maximum_uncle_age())
    			.unwrap_or_else(Vec::new)
    			.into_iter()
    			.take(engine.maximum_uncle_count())
    			.foreach(|h| {
    				open_block.push_uncle(h).expect("pushing maximum_uncle_count;
    												open_block was just created;
    												push_uncle is not ok only if more than maximum_uncle_count is pushed;
    												so all push_uncle are Ok;
    												qed");
    			});

    		open_block
    	}

    	fn vm_factory(&self) -> &EvmFactory {
    		&self.factories.vm
    	}

    	fn broadcast_proposal_block(&self, block: SealedBlock) {
    		self.notify(|notify| {
    			notify.new_blocks(
    				vec![],
    				vec![],
    				vec![],
    				vec![],
    				vec![],
    				vec![block.rlp_bytes()],
    				0,
    			);
    		});
    	}

    	fn import_sealed_block(&self, block: SealedBlock) -> ImportResult {
    		let h = block.header().hash();
    		let start = precise_time_ns();
    		let route = {
    			// scope for self.import_lock
    			let _import_lock = self.import_lock.lock();
    			let _timer = PerfTimer::new("import_sealed_block");

    			let number = block.header().number();
    			let block_data = block.rlp_bytes();
    			let route = self.commit_block(block, &h, &block_data);
    			trace!(target: "client", "Imported sealed block #{} ({})", number, h);
    			self.state_db.lock().sync_cache(&route.enacted, &route.retracted, false);
    			route
    		};
    		let (enacted, retracted) = self.calculate_enacted_retracted(&[route]);
    		self.miner.chain_new_blocks(self, &[h.clone()], &[], &enacted, &retracted);
    		self.notify(|notify| {
    			notify.new_blocks(
    				vec![h.clone()],
    				vec![],
    				enacted.clone(),
    				retracted.clone(),
    				vec![h.clone()],
    				vec![],
    				precise_time_ns() - start,
    			);
    		});
    		self.db.read().flush().expect("DB flush failed.");
    		Ok(h)
    	}
    }

    impl EngineClient for Client {
    	fn update_sealing(&self) {
    		self.miner.update_sealing(self)
    	}

    	fn submit_seal(&self, block_hash: H256, seal: Vec<Bytes>) {
    		if self.miner.submit_seal(self, block_hash, seal).is_err() {
    			warn!(target: "poa", "Wrong internal seal submission!")
    		}
    	}

    	fn broadcast_consensus_message(&self, message: Bytes) {
    		self.notify(|notify| notify.broadcast(message.clone()));
    	}
    }

    impl MayPanic for Client {
    	fn on_panic<F>(&self, closure: F) where F: OnPanicListener {
    		self.panic_handler.on_panic(closure);
    	}
    }

    impl ::client::ProvingBlockChainClient for Client {
    	fn prove_storage(&self, key1: H256, key2: H256, from_level: u32, id: BlockId) -> Vec<Bytes> {
    		self.state_at(id)
    			.and_then(move |state| state.prove_storage(key1, key2, from_level).ok())
    			.unwrap_or_else(Vec::new)
    	}

    	fn prove_account(&self, key1: H256, from_level: u32, id: BlockId) -> Vec<Bytes> {
    		self.state_at(id)
    			.and_then(move |state| state.prove_account(key1, from_level).ok())
    			.unwrap_or_else(Vec::new)
    	}

    	fn code_by_hash(&self, account_key: H256, id: BlockId) -> Bytes {
    		self.state_at(id)
    			.and_then(move |state| state.code_by_address_hash(account_key).ok())
    			.and_then(|x| x)
    			.unwrap_or_else(Vec::new)
    	}
    }

    impl Drop for Client {
    	fn drop(&mut self) {
    		self.engine.stop();
    	}
    }

    /// Returns `LocalizedReceipt` given `LocalizedTransaction`
    /// and a vector of receipts from given block up to transaction index.
    fn transaction_receipt(mut tx: LocalizedTransaction, mut receipts: Vec<Receipt>) -> LocalizedReceipt {
    	assert_eq!(receipts.len(), tx.transaction_index + 1, "All previous receipts are provided.");

    	let sender = tx.sender();
    	let receipt = receipts.pop().expect("Current receipt is provided; qed");
    	let prior_gas_used = match tx.transaction_index {
    		0 => 0.into(),
    		i => receipts.get(i - 1).expect("All previous receipts are provided; qed").gas_used,
    	};
    	let no_of_logs = receipts.into_iter().map(|receipt| receipt.logs.len()).sum::<usize>();
    	let transaction_hash = tx.hash();
    	let block_hash = tx.block_hash;
    	let block_number = tx.block_number;
    	let transaction_index = tx.transaction_index;

    	LocalizedReceipt {
    		transaction_hash: transaction_hash,
    		transaction_index: transaction_index,
    		block_hash: block_hash,
    		block_number:block_number,
    		cumulative_gas_used: receipt.gas_used,
    		gas_used: receipt.gas_used - prior_gas_used,
    		contract_address: match tx.action {
    			Action::Call(_) => None,
    			Action::Create => Some(contract_address(&sender, &tx.nonce))
    		},
    		logs: receipt.logs.into_iter().enumerate().map(|(i, log)| LocalizedLogEntry {
    			entry: log,
    			block_hash: block_hash,
    			block_number: block_number,
    			transaction_hash: transaction_hash,
    			transaction_index: transaction_index,
    			transaction_log_index: i,
    			log_index: no_of_logs + i,
    		}).collect(),
    		log_bloom: receipt.log_bloom,
    		state_root: receipt.state_root,
    	}
    }

    #[cfg(test)]
    mod tests {

    	#[test]
    	fn should_not_cache_details_before_commit() {
    		use client::BlockChainClient;
    		use tests::helpers::*;

    		use std::thread;
    		use std::time::Duration;
    		use std::sync::Arc;
    		use std::sync::atomic::{AtomicBool, Ordering};
    		use util::kvdb::DBTransaction;

    		let client = generate_dummy_client(0);
    		let genesis = client.chain_info().best_block_hash;
    		let (new_hash, new_block) = get_good_dummy_block_hash();

    		let go = {
    			// Separate thread uncommited transaction
    			let go = Arc::new(AtomicBool::new(false));
    			let go_thread = go.clone();
    			let another_client = client.reference().clone();
    			thread::spawn(move || {
    				let mut batch = DBTransaction::new(&*another_client.chain.read().db().clone());
    				another_client.chain.read().insert_block(&mut batch, &new_block, Vec::new());
    				go_thread.store(true, Ordering::SeqCst);
    			});
    			go
    		};

    		while !go.load(Ordering::SeqCst) { thread::park_timeout(Duration::from_millis(5)); }

    		assert!(client.tree_route(&genesis, &new_hash).is_none());
    	}

    	#[test]
    	fn should_return_correct_log_index() {
    		use super::transaction_receipt;
    		use ethkey::KeyPair;
    		use log_entry::{LogEntry, LocalizedLogEntry};
    		use receipt::{Receipt, LocalizedReceipt};
    		use transaction::{Transaction, LocalizedTransaction, Action};
    		use util::Hashable;

    		// given
    		let key = KeyPair::from_secret_slice(&"test".sha3()).unwrap();
    		let secret = key.secret();

    		let block_number = 1;
    		let block_hash = 5.into();
    		let state_root = Some(99.into());
    		let gas_used = 10.into();
    		let raw_tx = Transaction {
    			nonce: 0.into(),
    			gas_price: 0.into(),
    			gas: 21000.into(),
    			action: Action::Call(10.into()),
    			value: 0.into(),
    			data: vec![],
    		};
    		let tx1 = raw_tx.clone().sign(secret, None);
    		let transaction = LocalizedTransaction {
    			signed: tx1.clone().into(),
    			block_number: block_number,
    			block_hash: block_hash,
    			transaction_index: 1,
    			cached_sender: Some(tx1.sender()),
    		};
    		let logs = vec![LogEntry {
    			address: 5.into(),
    			topics: vec![],
    			data: vec![],
    		}, LogEntry {
    			address: 15.into(),
    			topics: vec![],
    			data: vec![],
    		}];
    		let receipts = vec![Receipt {
    			state_root: state_root,
    			gas_used: 5.into(),
    			log_bloom: Default::default(),
    			logs: vec![logs[0].clone()],
    		}, Receipt {
    			state_root: state_root,
    			gas_used: gas_used,
    			log_bloom: Default::default(),
    			logs: logs.clone(),
    		}];

    		// when
    		let receipt = transaction_receipt(transaction, receipts);

    		// then
    		assert_eq!(receipt, LocalizedReceipt {
    			transaction_hash: tx1.hash(),
    			transaction_index: 1,
    			block_hash: block_hash,
    			block_number: block_number,
    			cumulative_gas_used: gas_used,
    			gas_used: gas_used - 5.into(),
    			contract_address: None,
    			logs: vec![LocalizedLogEntry {
    				entry: logs[0].clone(),
    				block_hash: block_hash,
    				block_number: block_number,
    				transaction_hash: tx1.hash(),
    				transaction_index: 1,
    				transaction_log_index: 0,
    				log_index: 1,
    			}, LocalizedLogEntry {
    				entry: logs[1].clone(),
    				block_hash: block_hash,
    				block_number: block_number,
    				transaction_hash: tx1.hash(),
    				transaction_index: 1,
    				transaction_log_index: 1,
    				log_index: 2,
    			}],
    			log_bloom: Default::default(),
    			state_root: state_root,
    		});
    	}
    }

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