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    //! Transactions memory pool
    //!
    //! `MemoryPool` keeps track of all transactions seen by the node (received from other peers) and own transactions
    //! and orders them by given strategies. It works like multi-indexed priority queue, giving option to pop 'top'
    //! transactions.
    //! It also guarantees that ancestor-descendant relation won't break during ordered removal (ancestors always removed
    //! before descendants). Removal using `remove_by_hash` can break this rule.
    use storage::{TransactionProvider, TransactionOutputProvider};
    use primitives::bytes::Bytes;
    use primitives::hash::H256;
    use chain::{IndexedTransaction, Transaction, OutPoint, TransactionOutput};
    use std::cmp::Ordering;
    use std::collections::HashMap;
    use std::collections::HashSet;
    use std::collections::BTreeSet;
    use std::collections::VecDeque;
    use std::hash::{Hash, Hasher};
    use ser::{Serializable, serialize};
    use heapsize::HeapSizeOf;

    /// Transactions ordering strategy
    #[cfg_attr(feature="cargo-clippy", allow(enum_variant_names))]
    #[derive(Debug, Clone, Copy)]
    pub enum OrderingStrategy {
    	/// Order transactions by the time they have entered the memory pool
    	ByTimestamp,
    	/// Order transactions by their individual mining score
    	ByTransactionScore,
    	/// Order transactions by their in-pool package mining score (score for mining this transaction + all descendants transactions)
    	ByPackageScore,
    }

    /// Information on current `MemoryPool` state
    #[derive(Debug)]
    pub struct Information {
    	/// Number of transactions currently in the `MemoryPool`
    	pub transactions_count: usize,
    	/// Total number of bytes occupied by transactions from the `MemoryPool`
    	pub transactions_size_in_bytes: usize,
    }

    /// Transactions memory pool
    #[derive(Debug)]
    pub struct MemoryPool {
    	/// Transactions storage
    	storage: Storage,
    }

    /// Single entry
    #[derive(Debug)]
    pub struct Entry {
    	/// Transaction
    	pub transaction: Transaction,
    	/// In-pool ancestors hashes for this transaction
    	pub ancestors: HashSet<H256>,
    	/// Transaction hash (stored for effeciency)
    	pub hash: H256,
    	/// Transaction size (stored for effeciency)
    	pub size: usize,
    	/// Throughout index of this transaction in memory pool (non persistent)
    	pub storage_index: u64,
    	/// Transaction fee (stored for efficiency)
    	pub miner_fee: i64,
    	/// Virtual transaction fee (a way to prioritize/penalize transaction)
    	pub miner_virtual_fee: i64,
    	/// size + Sum(size) for all in-pool descendants
    	pub package_size: usize,
    	/// miner_fee + Sum(miner_fee) for all in-pool descendants
    	pub package_miner_fee: i64,
    	/// miner_virtual_fee + Sum(miner_virtual_fee) for all in-pool descendants
    	pub package_miner_virtual_fee: i64,
    }

    /// Multi-index transactions storage
    #[derive(Debug)]
    struct Storage {
    	/// Throughout transactions counter
    	counter: u64,
    	/// Total transactions size (when serialized) in bytes
    	transactions_size_in_bytes: usize,
    	/// By-hash storage
    	by_hash: HashMap<H256, Entry>,
    	/// Transactions by previous output
    	by_previous_output: HashMap<HashedOutPoint, H256>,
    	/// References storage
    	references: ReferenceStorage,
    }

    /// Multi-index storage which holds references to entries from `Storage::by_hash`
    #[derive(Debug, Clone)]
    struct ReferenceStorage {
    	/// By-input storage
    	by_input: HashMap<H256, HashSet<H256>>,
    	/// Pending entries
    	pending: HashSet<H256>,
    	/// Ordered storage
    	ordered: OrderedReferenceStorage,
    }

    /// Multi-index orderings storage which holds ordered references to entries from `Storage::by_hash`
    #[derive(Debug, Clone)]
    struct OrderedReferenceStorage {
    	/// By-entry-time storage
    	by_storage_index: BTreeSet<ByTimestampOrderedEntry>,
    	/// By-score storage
    	by_transaction_score: BTreeSet<ByTransactionScoreOrderedEntry>,
    	/// By-package-score strategy
    	by_package_score: BTreeSet<ByPackageScoreOrderedEntry>,
    }

    #[derive(Debug, Clone, PartialEq, Eq)]
    struct ByTimestampOrderedEntry {
    	/// Transaction hash
    	hash: H256,
    	/// Throughout index of this transaction in memory pool (non persistent)
    	storage_index: u64,
    }

    #[derive(Debug, Eq, PartialEq, Clone)]
    struct ByTransactionScoreOrderedEntry {
    	/// Transaction hash
    	hash: H256,
    	/// Transaction size
    	size: usize,
    	/// Transaction fee
    	miner_fee: i64,
    	/// Virtual transaction fee
    	miner_virtual_fee: i64,
    }

    #[derive(Debug, Eq, PartialEq, Clone)]
    struct ByPackageScoreOrderedEntry {
    	/// Transaction hash
    	hash: H256,
    	/// size + Sum(size) for all in-pool descendants
    	package_size: usize,
    	/// miner_fee + Sum(miner_fee) for all in-pool descendants
    	package_miner_fee: i64,
    	/// miner_virtual_fee + Sum(miner_virtual_fee) for all in-pool descendants
    	package_miner_virtual_fee: i64,
    }

    #[derive(Debug, PartialEq, Eq, Clone)]
    pub struct HashedOutPoint {
    	/// Transaction output point
    	out_point: OutPoint,
    }

    /// Result of checking double spend with
    #[derive(Debug, PartialEq)]
    pub enum DoubleSpendCheckResult {
    	/// No double spend
    	NoDoubleSpend,
    	/// Input {self.1, self.2} of new transaction is already spent in previous final memory-pool transaction {self.0}
    	DoubleSpend(H256, H256, u32),
    	/// Some inputs of new transaction are already spent by non-final memory-pool transactions
    	NonFinalDoubleSpend(NonFinalDoubleSpendSet),
    }

    /// Set of transaction outputs, which can be replaced if newer transaction
    /// replaces non-final transaction in memory pool
    #[derive(Debug, PartialEq)]
    pub struct NonFinalDoubleSpendSet {
    	/// Double-spend outputs (outputs of newer transaction, which are also spent by nonfinal transactions of mempool)
    	pub double_spends: HashSet<HashedOutPoint>,
    	/// Outputs which also will be removed from memory pool in case of newer transaction insertion
    	/// (i.e. outputs of nonfinal transactions && their descendants)
    	pub dependent_spends: HashSet<HashedOutPoint>,
    }

    impl From<OutPoint> for HashedOutPoint {
    	fn from(out_point: OutPoint) -> Self {
    		HashedOutPoint {
    			out_point: out_point,
    		}
    	}
    }

    impl Hash for HashedOutPoint {
    	fn hash<H>(&self, state: &mut H) where H: Hasher {
    		state.write(&serialize(&self.out_point));
    		state.finish();
    	}
    }

    impl<'a> From<&'a Entry> for ByTimestampOrderedEntry {
    	fn from(entry: &'a Entry) -> Self {
    		ByTimestampOrderedEntry {
    			hash: entry.hash.clone(),
    			storage_index: entry.storage_index,
    		}
    	}
    }

    impl<'a> From<&'a Entry> for ByTransactionScoreOrderedEntry {
    	fn from(entry: &'a Entry) -> Self {
    		ByTransactionScoreOrderedEntry {
    			hash: entry.hash.clone(),
    			size: entry.size,
    			miner_fee: entry.miner_fee,
    			miner_virtual_fee: entry.miner_virtual_fee,
    		}
    	}
    }

    impl<'a> From<&'a Entry> for ByPackageScoreOrderedEntry {
    	fn from(entry: &'a Entry) -> Self {
    		ByPackageScoreOrderedEntry {
    			hash: entry.hash.clone(),
    			package_size: entry.package_size,
    			package_miner_fee: entry.package_miner_fee,
    			package_miner_virtual_fee: entry.package_miner_virtual_fee,
    		}
    	}
    }

    impl PartialOrd for ByTimestampOrderedEntry {
    	fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
    		Some(self.cmp(other))
    	}
    }

    impl Ord for ByTimestampOrderedEntry {
    	fn cmp(&self, other: &Self) -> Ordering {
    		let order = self.storage_index.cmp(&other.storage_index);
    		if order != Ordering::Equal {
    			return order
    		}

    		self.hash.cmp(&other.hash)
    	}
    }

    impl PartialOrd for ByTransactionScoreOrderedEntry {
    	fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
    		Some(self.cmp(other))
    	}
    }

    impl Ord for ByTransactionScoreOrderedEntry {
    	fn cmp(&self, other: &Self) -> Ordering {
    		// lesser miner score means later removal
    		let left = (self.miner_fee + self.miner_virtual_fee) * (other.size as i64);
    		let right = (other.miner_fee + other.miner_virtual_fee) * (self.size as i64);
    		let order = right.cmp(&left);
    		if order != Ordering::Equal {
    			return order
    		}

    		self.hash.cmp(&other.hash)
    	}
    }

    impl PartialOrd for ByPackageScoreOrderedEntry {
    	fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
    		Some(self.cmp(other))
    	}
    }

    impl Ord for ByPackageScoreOrderedEntry {
    	fn cmp(&self, other: &Self) -> Ordering {
    		// lesser miner score means later removal
    		let left = (self.package_miner_fee + self.package_miner_virtual_fee) * (other.package_size as i64);
    		let right = (other.package_miner_fee + other.package_miner_virtual_fee) * (self.package_size as i64);
    		let order = right.cmp(&left);
    		if order != Ordering::Equal {
    			return order
    		}

    		self.hash.cmp(&other.hash)
    	}
    }

    impl HeapSizeOf for Entry {
    	fn heap_size_of_children(&self) -> usize {
    		self.transaction.heap_size_of_children() + self.ancestors.heap_size_of_children()
    	}
    }

    impl Storage {
    	pub fn new() -> Self {
    		Storage {
    			counter: 0,
    			transactions_size_in_bytes: 0,
    			by_hash: HashMap::new(),
    			by_previous_output: HashMap::new(),
    			references: ReferenceStorage {
    				by_input: HashMap::new(),
    				pending: HashSet::new(),
    				ordered: OrderedReferenceStorage {
    					by_storage_index: BTreeSet::new(),
    					by_transaction_score: BTreeSet::new(),
    					by_package_score: BTreeSet::new(),
    				},
    			},
    		}
    	}

    	pub fn insert(&mut self, entry: Entry) {
    		// update pool information
    		self.transactions_size_in_bytes += entry.size;

    		// remember that this transactions depends on its inputs
    		for input_hash in entry.transaction.inputs.iter().map(|input| &input.previous_output.hash) {
    			self.references.by_input.entry(input_hash.clone()).or_insert_with(HashSet::new).insert(entry.hash.clone());
    		}

    		// update score of all packages this transaction is in
    		for ancestor_hash in &entry.ancestors {
    			if let Some(ancestor_entry) = self.by_hash.get_mut(ancestor_hash) {
    				let removed = self.references.ordered.by_package_score.remove(&(ancestor_entry as &Entry).into());

    				ancestor_entry.package_size += entry.size;
    				ancestor_entry.package_miner_fee += entry.package_miner_fee;
    				ancestor_entry.package_miner_virtual_fee += entry.package_miner_virtual_fee;

    				if removed {
    					self.references.ordered.by_package_score.insert((ancestor_entry as &Entry).into());
    				}
    			}
    		}

    		// insert either to pending queue or to orderings
    		if self.references.has_in_pool_ancestors(None, &self.by_hash, &entry.transaction) {
    			self.references.pending.insert(entry.hash.clone());
    		}
    		else {
    			self.references.ordered.insert_to_orderings(&entry);
    		}

    		// remember that all inputs of this transaction are spent
    		for input in &entry.transaction.inputs {
    			let previous_tx = self.by_previous_output.insert(input.previous_output.clone().into(), entry.hash.clone());
    			assert_eq!(previous_tx, None); // transaction must be verified before => no double spend
    		}

    		// add to by_hash storage
    		self.by_hash.insert(entry.hash.clone(), entry);
    	}

    	pub fn get_by_hash(&self, h: &H256) -> Option<&Entry> {
    		self.by_hash.get(h)
    	}

    	pub fn contains(&self, hash: &H256) -> bool {
    		self.by_hash.contains_key(hash)
    	}

    	pub fn is_output_spent(&self, prevout: &OutPoint) -> bool {
    		self.by_previous_output.contains_key(&prevout.clone().into())
    	}

    	pub fn set_virtual_fee(&mut self, h: &H256, virtual_fee: i64) {
    		// for updating ancestors
    		let mut miner_virtual_fee_change = 0i64;
    		let mut ancestors: Option<Vec<H256>> = None;

    		// modify the entry itself
    		if let Some(entry) = self.by_hash.get_mut(h) {
    			let insert_to_package_score = self.references.ordered.by_package_score.remove(&(entry as &Entry).into());
    			let insert_to_transaction_score = self.references.ordered.by_transaction_score.remove(&(entry as &Entry).into());

    			miner_virtual_fee_change = virtual_fee - entry.miner_virtual_fee;
    			if !entry.ancestors.is_empty() {
    				ancestors = Some(entry.ancestors.iter().cloned().collect());
    			}

    			entry.miner_virtual_fee = virtual_fee;

    			if insert_to_transaction_score {
    				self.references.ordered.by_transaction_score.insert((entry as &Entry).into());
    			}
    			if insert_to_package_score {
    				self.references.ordered.by_package_score.insert((entry as &Entry).into());
    			}
    		}

    		// now modify all ancestor entries
    		if miner_virtual_fee_change != 0 {
    			ancestors.map(|ancestors| {
    				for ancestor_hash in ancestors {
    					if let Some(ancestor_entry) = self.by_hash.get_mut(&ancestor_hash) {
    						let insert_to_package_score = self.references.ordered.by_package_score.remove(&(ancestor_entry as &Entry).into());
    						ancestor_entry.package_miner_virtual_fee += miner_virtual_fee_change;
    						if insert_to_package_score {
    							self.references.ordered.by_package_score.insert((ancestor_entry as &Entry).into());
    						}
    					}
    				}
    			});
    		}
    	}

    	pub fn read_by_hash(&self, h: &H256) -> Option<&Transaction> {
    		self.by_hash.get(h).map(|e| &e.transaction)
    	}

    	pub fn read_with_strategy(&self, strategy: OrderingStrategy) -> Option<H256> {
    		match strategy {
    			OrderingStrategy::ByTimestamp => self.references.ordered.by_storage_index.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByTransactionScore => self.references.ordered.by_transaction_score.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByPackageScore => self.references.ordered.by_package_score.iter().map(|entry| entry.hash.clone()).nth(0),
    		}
    	}

    	pub fn remove_by_hash(&mut self, h: &H256) -> Option<Entry> {
    		self.by_hash.remove(h)
    			.map(|entry| {
    				// update pool information
    				self.transactions_size_in_bytes -= entry.size;

    				// forget that all inputs of this transaction are spent
    				for input in &entry.transaction.inputs {
    					let spent_in_tx = self.by_previous_output.remove(&input.previous_output.clone().into())
    						.expect("by_spent_output is filled for each incoming transaction inputs; so the drained value should exist; qed");
    					assert_eq!(&spent_in_tx, h);
    				}

    				// remove from storage
    				self.references.remove(None, &self.by_hash, &entry);

    				entry
    			})
    	}

    	pub fn check_double_spend(&self, transaction: &Transaction) -> DoubleSpendCheckResult {
    		let mut double_spends: HashSet<HashedOutPoint> = HashSet::new();
    		let mut dependent_spends: HashSet<HashedOutPoint> = HashSet::new();

    		for input in &transaction.inputs {
    			// find transaction that spends the same output
    			let prevout: HashedOutPoint = input.previous_output.clone().into();
    			if let Some(entry_hash) = self.by_previous_output.get(&prevout).cloned() {
    				// check if this is final transaction. If so, that's a potential double-spend error
    				let entry = self.by_hash.get(&entry_hash).expect("checked that it exists line above; qed");
    				if entry.transaction.is_final() {
    					return DoubleSpendCheckResult::DoubleSpend(entry_hash,	 prevout.out_point.hash, prevout.out_point.index);
    				}
    				// else remember this double spend
    				double_spends.insert(prevout.clone());
    				// and 'virtually' remove entry && all descendants from mempool
    				let mut queue: VecDeque<HashedOutPoint> = VecDeque::new();
    				queue.push_back(prevout);
    				while let Some(dependent_prevout) = queue.pop_front() {
    					// if the same output is already spent with another in-pool transaction
    					if let Some(dependent_entry_hash) = self.by_previous_output.get(&dependent_prevout).cloned() {
    						let dependent_entry = self.by_hash.get(&dependent_entry_hash).expect("checked that it exists line above; qed");
    						let dependent_outputs: Vec<_> = dependent_entry.transaction.outputs.iter().enumerate().map(|(idx, _)| OutPoint {
    							hash: dependent_entry_hash.clone(),
    							index: idx as u32,
    						}.into()).collect();
    						dependent_spends.extend(dependent_outputs.clone());
    						queue.extend(dependent_outputs);
    					}
    				}
    			}
    		}

    		if double_spends.is_empty() {
    			DoubleSpendCheckResult::NoDoubleSpend
    		} else {
    			DoubleSpendCheckResult::NonFinalDoubleSpend(NonFinalDoubleSpendSet {
    				double_spends: double_spends,
    				dependent_spends: dependent_spends,
    			})
    		}
    	}

    	pub fn remove_by_prevout(&mut self, prevout: &OutPoint) -> Option<Vec<IndexedTransaction>> {
    		let mut queue: VecDeque<OutPoint> = VecDeque::new();
    		let mut removed: Vec<IndexedTransaction> = Vec::new();
    		queue.push_back(prevout.clone());

    		while let Some(prevout) = queue.pop_front() {
    			if let Some(entry_hash) = self.by_previous_output.get(&prevout.clone().into()).cloned() {
    				let entry = self.remove_by_hash(&entry_hash).expect("checked that it exists line above; qed");
    				queue.extend(entry.transaction.outputs.iter().enumerate().map(|(idx, _)| OutPoint {
    					hash: entry_hash.clone(),
    					index: idx as u32,
    				}));
    				removed.push(IndexedTransaction::new(entry.hash, entry.transaction));
    			}
    		}

    		Some(removed)
    	}

    	pub fn remove_by_parent_hash(&mut self, h: &H256) -> Option<Vec<IndexedTransaction>> {
    		// this code will run only when ancestor transaction is inserted
    		// in memory pool after its descendants
    		if let Some(mut descendants) = self.references.by_input.get(h).map(|d| d.iter().cloned().collect::<Vec<H256>>()) {
    			// prepare Vec of all descendants hashes
    			let mut all_descendants: HashSet<H256> = HashSet::new();
    			while let Some(descendant) = descendants.pop() {
    				if all_descendants.contains(&descendant) {
    					continue
    				}
    				all_descendants.insert(descendant.clone());

    				if let Some(grand_descendants) = self.references.by_input.get(&descendant) {
    					descendants.extend(grand_descendants.iter().cloned());
    				}
    			}

    			// topologically sort descendants
    			let mut all_descendants: Vec<_> = all_descendants.iter().collect();
    			all_descendants.sort_by(|left, right| {
    				let left = self.by_hash.get(left)
    					.expect("`left` is read from `by_input`; all entries from `by_input` have corresponding entries in `by_hash`; qed");
    				let right = self.by_hash.get(right)
    					.expect("`right` is read from `by_input`; all entries from `by_input` have corresponding entries in `by_hash`; qed");
    				if left.ancestors.contains(&right.hash) {
    					return Ordering::Greater;
    				}
    				if right.ancestors.contains(&left.hash) {
    					return Ordering::Less;
    				}
    				Ordering::Equal
    			});

    			// move all descendants out of storage for later insertion
    			Some(all_descendants.into_iter()
    					.filter_map(|hash| self.remove_by_hash(hash).map(|entry| IndexedTransaction::new(entry.hash, entry.transaction)))
    					.collect())
    		}
    		else {
    			None
    		}
    	}

    	pub fn remove_with_strategy(&mut self, strategy: OrderingStrategy) -> Option<IndexedTransaction> {
    		let top_hash = match strategy {
    			OrderingStrategy::ByTimestamp => self.references.ordered.by_storage_index.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByTransactionScore => self.references.ordered.by_transaction_score.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByPackageScore => self.references.ordered.by_package_score.iter().map(|entry| entry.hash.clone()).nth(0),
    		};
    		top_hash.map(|hash| {
    			let entry = self.remove_by_hash(&hash)
    				.expect("`hash` is read from `references`; entries in `references` have corresponging entries in `by_hash`; `remove_by_hash` removes entry from `by_hash`; qed");
    			IndexedTransaction::new(entry.hash, entry.transaction)
    		})
    	}

    	pub fn remove_n_with_strategy(&mut self, mut n: usize, strategy: OrderingStrategy) -> Vec<IndexedTransaction> {
    		let mut result: Vec<IndexedTransaction> = Vec::new();
    		loop {
    			if n == 0 {
    				break;
    			}
    			n -= 1;

    			result.push(match self.remove_with_strategy(strategy) {
    				Some(transaction) => transaction,
    				None => break,
    			})
    		}
    		result
    	}

    	pub fn get_transactions_ids(&self) -> Vec<H256> {
    		self.by_hash.keys().cloned().collect()
    	}
    }

    impl ReferenceStorage {
    	pub fn has_in_pool_ancestors(&self, removed: Option<&HashSet<H256>>, by_hash: &HashMap<H256, Entry>, transaction: &Transaction) -> bool {
    		transaction.inputs.iter()
    			.any(|input| by_hash.contains_key(&input.previous_output.hash)
    				&& !removed.map_or(false, |r| r.contains(&input.previous_output.hash)))
    	}

    	pub fn remove(&mut self, removed: Option<&HashSet<H256>>, by_hash: &HashMap<H256, Entry>, entry: &Entry) {
    		// for each pending descendant transaction
    		if let Some(descendants) = self.by_input.get(&entry.hash) {
    			let descendants = descendants.iter().filter_map(|hash| by_hash.get(hash));
    			for descendant in descendants {
    				// if there are no more ancestors of this transaction in the pool
    				// => can move from pending to orderings
    				if !self.has_in_pool_ancestors(removed, by_hash, &descendant.transaction) {
    					self.pending.remove(&descendant.hash);

    					if let Some(descendant_entry) = by_hash.get(&descendant.hash) {
    						self.ordered.insert_to_orderings(descendant_entry);
    					}
    				}
    			}
    		}
    		self.by_input.remove(&entry.hash);

    		// remove from pending
    		self.pending.remove(&entry.hash);

    		// remove from orderings
    		self.ordered.remove_from_orderings(entry);
    	}
    }

    impl OrderedReferenceStorage {
    	pub fn insert_to_orderings(&mut self, entry: &Entry) {
    		self.by_storage_index.insert(entry.into());
    		self.by_transaction_score.insert(entry.into());
    		self.by_package_score.insert(entry.into());
    	}

    	pub fn remove_from_orderings(&mut self, entry: &Entry) {
    		self.by_storage_index.remove(&entry.into());
    		self.by_transaction_score.remove(&entry.into());
    		self.by_package_score.remove(&entry.into());
    	}
    }

    impl HeapSizeOf for Storage {
    	fn heap_size_of_children(&self) -> usize {
    		self.by_hash.heap_size_of_children() + self.references.heap_size_of_children()
    	}
    }

    impl HeapSizeOf for ReferenceStorage {
    	fn heap_size_of_children(&self) -> usize {
    		self.by_input.heap_size_of_children()
    			+ self.pending.heap_size_of_children()
    			+ self.ordered.heap_size_of_children()
    	}
    }

    impl HeapSizeOf for OrderedReferenceStorage {
    	fn heap_size_of_children(&self) -> usize {
    		// HeapSizeOf is not implemented for BTreeSet => rough estimation here
    		use std::mem::size_of;
    		let len = self.by_storage_index.len();
    		len * (size_of::<ByTimestampOrderedEntry>()
    			+ size_of::<ByTransactionScoreOrderedEntry>()
    			+ size_of::<ByPackageScoreOrderedEntry>())
    	}
    }

    impl Default for MemoryPool {
    	fn default() -> Self {
    		MemoryPool {
    			storage: Storage::new(),
    		}
    	}
    }

    impl MemoryPool {
    	/// Creates new memory pool
    	pub fn new() -> Self {
    		MemoryPool::default()
    	}

    	/// Insert verified transaction to the `MemoryPool`
    	pub fn insert_verified(&mut self, t: IndexedTransaction) {
    		let entry = self.make_entry(t);
    		let descendants = self.storage.remove_by_parent_hash(&entry.hash);
    		self.storage.insert(entry);
    		if let Some(descendants_iter) = descendants.map(|d| d.into_iter()) {
    			for descendant in descendants_iter {
    				let descendant_entry = self.make_entry(descendant);
    				self.storage.insert(descendant_entry);
    			}
    		}
    	}

    	/// Iterator over memory pool transactions according to specified strategy
    	pub fn iter(&self, strategy: OrderingStrategy) -> MemoryPoolIterator {
    		MemoryPoolIterator::new(self, strategy)
    	}

    	/// Removes single transaction by its hash.
    	/// All descedants remain in the pool.
    	pub fn remove_by_hash(&mut self, h: &H256) -> Option<Transaction> {
    		self.storage.remove_by_hash(h).map(|entry| entry.transaction)
    	}

    	/// Checks if `transaction` spends some outputs, already spent by inpool transactions.
    	pub fn check_double_spend(&self, transaction: &Transaction) -> DoubleSpendCheckResult {
    		self.storage.check_double_spend(transaction)
    	}

    	/// Removes transaction (and all its descendants) which has spent given output
    	pub fn remove_by_prevout(&mut self, prevout: &OutPoint) -> Option<Vec<IndexedTransaction>> {
    		self.storage.remove_by_prevout(prevout)
    	}

    	/// Reads single transaction by its hash.
    	pub fn read_by_hash(&self, h: &H256) -> Option<&Transaction> {
    		self.storage.read_by_hash(h)
    	}

    	/// Reads hash of the 'top' transaction from the `MemoryPool` using selected strategy.
    	/// Ancestors are always returned before descendant transactions.
    	pub fn read_with_strategy(&mut self, strategy: OrderingStrategy) -> Option<H256> {
    		self.storage.read_with_strategy(strategy)
    	}

    	/// Reads hashes of up to n transactions from the `MemoryPool`, using selected strategy.
    	/// Ancestors are always returned before descendant transactions.
    	/// Use this function with care, only if really needed (heavy memory usage)
    	pub fn read_n_with_strategy(&mut self, n: usize, strategy: OrderingStrategy) -> Vec<H256> {
    		self.iter(strategy).map(|entry| entry.hash.clone()).take(n).collect()
    	}

    	/// Removes the 'top' transaction from the `MemoryPool` using selected strategy.
    	/// Ancestors are always removed before descendant transactions.
    	pub fn remove_with_strategy(&mut self, strategy: OrderingStrategy) -> Option<IndexedTransaction> {
    		self.storage.remove_with_strategy(strategy)
    	}

    	/// Removes up to n transactions from the `MemoryPool`, using selected strategy.
    	/// Ancestors are always removed before descendant transactions.
    	pub fn remove_n_with_strategy(&mut self, n: usize, strategy: OrderingStrategy) -> Vec<IndexedTransaction> {
    		self.storage.remove_n_with_strategy(n, strategy)
    	}

    	/// Set miner virtual fee for transaction
    	pub fn set_virtual_fee(&mut self, h: &H256, virtual_fee: i64) {
    		self.storage.set_virtual_fee(h, virtual_fee)
    	}

    	/// Get transaction by hash
    	pub fn get(&self, hash: &H256) -> Option<&Transaction> {
    		self.storage.get_by_hash(hash).map(|entry| &entry.transaction)
    	}

    	/// Checks if transaction is in the mempool
    	pub fn contains(&self, hash: &H256) -> bool {
    		self.storage.contains(hash)
    	}

    	/// Returns information on `MemoryPool` (as in GetMemPoolInfo RPC)
    	/// https://bitcoin.org/en/developer-reference#getmempoolinfo
    	pub fn information(&self) -> Information {
    		Information {
    			transactions_count: self.storage.by_hash.len(),
    			transactions_size_in_bytes: self.storage.transactions_size_in_bytes,
    		}
    	}

    	/// Returns TXIDs of all transactions in `MemoryPool` (as in GetRawMemPool RPC)
    	/// https://bitcoin.org/en/developer-reference#getrawmempool
    	pub fn get_transactions_ids(&self) -> Vec<H256> {
    		self.storage.get_transactions_ids()
    	}

    	/// Returns true if output was spent
    	pub fn is_spent(&self, prevout: &OutPoint) -> bool {
    		self.storage.is_output_spent(prevout)
    	}

    	fn make_entry(&mut self, t: IndexedTransaction) -> Entry {
    		let ancestors = self.get_ancestors(&t.raw);
    		let size = self.get_transaction_size(&t.raw);
    		let storage_index = self.get_storage_index();
    		let miner_fee = self.get_transaction_miner_fee(&t.raw);
    		Entry {
    			transaction: t.raw,
    			hash: t.hash,
    			ancestors: ancestors,
    			storage_index: storage_index,
    			size: size,
    			miner_fee: miner_fee,
    			miner_virtual_fee: 0,
    			// following fields are also updated when inserted to storage
    			package_size: size,
    			package_miner_fee: miner_fee,
    			package_miner_virtual_fee: 0,
    		}
    	}

    	fn get_ancestors(&self, t: &Transaction) -> HashSet<H256> {
    		let mut ancestors: HashSet<H256> = HashSet::new();
    		let ancestors_entries = t.inputs.iter()
    			.filter_map(|input| self.storage.get_by_hash(&input.previous_output.hash));
    		for ancestor_entry in ancestors_entries {
    			ancestors.insert(ancestor_entry.hash.clone());
    			for grand_ancestor in &ancestor_entry.ancestors {
    				ancestors.insert(grand_ancestor.clone());
    			}
    		}
    		ancestors
    	}

    	fn get_transaction_size(&self, t: &Transaction) -> usize {
    		t.serialized_size()
    	}

    	fn get_transaction_miner_fee(&self, t: &Transaction) -> i64 {
    		let input_value = 0; // TODO: sum all inputs of transaction
    		let output_value = t.outputs.iter().fold(0, |acc, output| acc + output.value);
    		(output_value - input_value) as i64
    	}

    	#[cfg(not(test))]
    	fn get_storage_index(&mut self) -> u64 {
    		self.storage.counter += 1;
    		self.storage.counter
    	}

    	#[cfg(test)]
    	fn get_storage_index(&self) -> u64 {
    		(self.storage.by_hash.len() % 3usize) as u64
    	}
    }

    impl TransactionProvider for MemoryPool {
    	fn transaction_bytes(&self, hash: &H256) -> Option<Bytes> {
    		self.get(hash).map(|t| serialize(t))
    	}

    	fn transaction(&self, hash: &H256) -> Option<Transaction> {
    		self.get(hash).cloned()
    	}
    }

    impl TransactionOutputProvider for MemoryPool {
    	fn transaction_output(&self, prevout: &OutPoint, _transaction_index: usize) -> Option<TransactionOutput> {
    		self.get(&prevout.hash)
    			.and_then(|tx| tx.outputs.get(prevout.index as usize))
    			.cloned()
    	}

    	fn is_spent(&self, outpoint: &OutPoint) -> bool {
    		self.is_spent(outpoint)
    	}
    }

    impl HeapSizeOf for MemoryPool {
    	fn heap_size_of_children(&self) -> usize {
    		self.storage.heap_size_of_children()
    	}
    }

    pub struct MemoryPoolIterator<'a> {
    	memory_pool: &'a MemoryPool,
    	references: ReferenceStorage,
    	removed: HashSet<H256>,
    	strategy: OrderingStrategy,
    }

    impl<'a> MemoryPoolIterator<'a> {
    	fn new(memory_pool: &'a MemoryPool, strategy: OrderingStrategy) -> Self {
    		MemoryPoolIterator {
    			memory_pool: memory_pool,
    			references: memory_pool.storage.references.clone(),
    			removed: HashSet::new(),
    			strategy: strategy,
    		}
    	}
    }

    impl<'a> Iterator for MemoryPoolIterator<'a> {
    	type Item = &'a Entry;

    	fn next(&mut self) -> Option<Self::Item> {
    		let top_hash = match self.strategy {
    			OrderingStrategy::ByTimestamp => self.references.ordered.by_storage_index.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByTransactionScore => self.references.ordered.by_transaction_score.iter().map(|entry| entry.hash.clone()).nth(0),
    			OrderingStrategy::ByPackageScore => self.references.ordered.by_package_score.iter().map(|entry| entry.hash.clone()).nth(0),
    		};

    		top_hash.map(|top_hash| {
    			let entry = self.memory_pool.storage.by_hash.get(&top_hash).expect("missing hash is a sign of MemoryPool internal inconsistancy");
    			self.removed.insert(top_hash.clone());
    			self.references.remove(Some(&self.removed), &self.memory_pool.storage.by_hash, entry);
    			entry
    		})
    	}
    }

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

    	use chain::{Transaction, OutPoint};
    	use heapsize::HeapSizeOf;
    	use super::{MemoryPool, OrderingStrategy, DoubleSpendCheckResult};
    	use self::test_data::{ChainBuilder, TransactionBuilder};

    	fn to_memory_pool(chain: &mut ChainBuilder) -> MemoryPool {
    		let mut pool = MemoryPool::new();
    		for transaction in chain.transactions.iter().cloned() {
    			pool.insert_verified(transaction.into());
    		}
    		pool
    	}

    	#[test]
    	fn test_memory_pool_heap_size() {
    		let mut pool = MemoryPool::new();

    		let size1 = pool.heap_size_of_children();

    		pool.insert_verified(Transaction::default().into());
    		let size2 = pool.heap_size_of_children();
    		assert!(size2 > size1);

    		pool.insert_verified(Transaction::default().into());
    		let size3 = pool.heap_size_of_children();
    		assert!(size3 > size2);
    	}

    	#[test]
    	fn test_memory_pool_insert_same_transaction() {
    		let mut pool = MemoryPool::new();
    		pool.insert_verified(Transaction::default().into());
    		assert_eq!(pool.get_transactions_ids().len(), 1);

    		// insert the same transaction again
    		pool.insert_verified(Transaction::default().into());
    		assert_eq!(pool.get_transactions_ids().len(), 1);
    	}

    	#[test]
    	fn test_memory_pool_read_with_strategy() {
    		let mut pool = MemoryPool::new();
    		assert_eq!(pool.read_with_strategy(OrderingStrategy::ByTimestamp), None);
    		assert_eq!(pool.read_n_with_strategy(100, OrderingStrategy::ByTimestamp), vec![]);

    		pool.insert_verified(Transaction::default().into());
    		assert_eq!(pool.read_with_strategy(OrderingStrategy::ByTimestamp), Some(Transaction::default().hash()));
    		assert_eq!(pool.read_n_with_strategy(100, OrderingStrategy::ByTimestamp), vec![Transaction::default().hash()]);
    		assert_eq!(pool.read_with_strategy(OrderingStrategy::ByTimestamp), Some(Transaction::default().hash()));
    		assert_eq!(pool.read_n_with_strategy(100, OrderingStrategy::ByTimestamp), vec![Transaction::default().hash()]);
    	}

    	#[test]
    	fn test_memory_pool_remove_with_strategy() {
    		let mut pool = MemoryPool::new();
    		assert_eq!(pool.remove_with_strategy(OrderingStrategy::ByTimestamp), None);
    		assert_eq!(pool.remove_n_with_strategy(100, OrderingStrategy::ByTimestamp), vec![]);

    		pool.insert_verified(Transaction::default().into());
    		let removed = pool.remove_with_strategy(OrderingStrategy::ByTimestamp);
    		assert!(removed.is_some());
    		assert_eq!(removed.unwrap(), Transaction::default().into());

    		pool.insert_verified(Transaction::default().into());
    		let removed = pool.remove_n_with_strategy(100, OrderingStrategy::ByTimestamp);
    		assert_eq!(removed.len(), 1);
    		assert_eq!(removed[0], Transaction::default().into());

    		assert_eq!(pool.remove_with_strategy(OrderingStrategy::ByTimestamp), None);
    		assert_eq!(pool.remove_n_with_strategy(100, OrderingStrategy::ByTimestamp), vec![]);
    	}

    	#[test]
    	fn test_memory_pool_remove_by_hash() {
    		let mut pool = MemoryPool::new();

    		pool.insert_verified(Transaction::default().into());
    		assert_eq!(pool.get_transactions_ids().len(), 1);

    		// remove and check remaining transactions
    		let removed = pool.remove_by_hash(&Transaction::default().hash());
    		assert!(removed.is_some());
    		assert_eq!(removed.unwrap(), Transaction::default());
    		assert_eq!(pool.get_transactions_ids().len(), 0);

    		// remove non-existant transaction
    		assert_eq!(pool.remove_by_hash(&TransactionBuilder::with_version(1).hash()), None);
    		assert_eq!(pool.get_transactions_ids().len(), 0);
    	}

    	#[test]
    	fn test_memory_pool_insert_parent_after_child() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain);

    		// insert child, then parent
    		let mut pool = MemoryPool::new();
    		pool.insert_verified(chain.at(2).into()); // timestamp 0
    		pool.insert_verified(chain.at(1).into()); // timestamp 1
    		pool.insert_verified(chain.at(0).into()); // timestamp 2

    		// check that parent transaction was removed before child trnasaction
    		let transactions = pool.remove_n_with_strategy(3, OrderingStrategy::ByTimestamp);
    		assert_eq!(transactions.len(), 3);
    		assert_eq!(transactions[0], chain.at(0).into());
    		assert_eq!(transactions[1], chain.at(1).into());
    		assert_eq!(transactions[2], chain.at(2).into());
    	}

    	#[test]
    	fn test_memory_pool_insert_parent_before_child() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain);

    		// insert parent, then child
    		let mut pool = to_memory_pool(chain);

    		// check that parent transaction was removed before child trnasaction
    		let transactions = pool.remove_n_with_strategy(3, OrderingStrategy::ByTimestamp);
    		assert_eq!(transactions.len(), 3);
    		assert_eq!(transactions[0], chain.at(0).into());
    		assert_eq!(transactions[1], chain.at(1).into());
    		assert_eq!(transactions[2], chain.at(2).into());
    	}

    	#[test]
    	fn test_memory_pool_insert_child_after_remove_by_hash() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain)
    			.into_input(0).add_output(100).store(chain);

    		// insert parent, then child
    		let mut pool = to_memory_pool(chain);

    		// remove child transaction & make sure that other transactions are still there
    		pool.remove_by_hash(&chain.hash(1));
    		assert_eq!(pool.get_transactions_ids().len(), 2);

    		// insert child transaction back to the pool & assert transactions are removed in correct order
    		pool.insert_verified(chain.at(1).into());
    		let transactions = pool.remove_n_with_strategy(3, OrderingStrategy::ByTransactionScore);
    		assert_eq!(transactions.len(), 3);
    		assert_eq!(transactions[0], chain.at(0).into());
    		assert_eq!(transactions[1], chain.at(1).into());
    		assert_eq!(transactions[2], chain.at(2).into());
    	}

    	#[test]
    	fn test_memory_pool_get_information() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(10).store(chain)
    			.into_input(0).add_output(20).store(chain)
    			.into_input(0).add_output(30).store(chain)
    			.into_input(0).add_output(40).store(chain);
    		let mut pool = MemoryPool::new();

    		let mut transactions_size = 0;
    		for transaction_index in 0..4 {
    			pool.insert_verified(chain.at(transaction_index).into());
    			transactions_size += chain.size(transaction_index);

    			let info = pool.information();
    			assert_eq!(info.transactions_count, transaction_index + 1);
    			assert_eq!(info.transactions_size_in_bytes, transactions_size);
    		}
    	}

    	#[test]
    	fn test_memory_pool_timestamp_ordering_strategy() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(10).store(chain)
    			.set_output(20).store(chain)
    			.set_output(30).store(chain)
    			.set_output(40).store(chain);
    		let mut pool = to_memory_pool(chain);

    		// remove transactions [0, 3, 1] (timestamps: [0, 0, 1]) {conflict resolved by hash}
    		let transactions = pool.remove_n_with_strategy(3, OrderingStrategy::ByTimestamp);
    		assert_eq!(transactions.len(), 3);
    		assert_eq!(transactions[0], chain.at(0).into());
    		assert_eq!(transactions[1], chain.at(3).into());
    		assert_eq!(transactions[2], chain.at(1).into());
    		assert_eq!(pool.get_transactions_ids().len(), 1);

    		// remove transactions [2] (timestamps: [2])
    		let transactions = pool.remove_n_with_strategy(3, OrderingStrategy::ByTimestamp);
    		assert_eq!(transactions.len(), 1);
    		assert_eq!(transactions[0], chain.at(2).into());
    	}

    	#[test]
    	fn test_memory_pool_transaction_score_ordering_strategy() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(10).store(chain)
    			.set_output(40).store(chain)
    			.set_output(30).store(chain)
    			.set_output(20).store(chain);
    		let mut pool = to_memory_pool(chain);

    		let transactions = pool.remove_n_with_strategy(4, OrderingStrategy::ByTransactionScore);
    		assert_eq!(transactions.len(), 4);
    		assert_eq!(transactions[0], chain.at(1).into());
    		assert_eq!(transactions[1], chain.at(2).into());
    		assert_eq!(transactions[2], chain.at(3).into());
    		assert_eq!(transactions[3], chain.at(0).into());
    	}

    	#[test]
    	fn test_memory_pool_transaction_score_ordering_strategy_with_virtual_fee() {
    		let chain = &mut ChainBuilder::new();
    		TransactionBuilder::with_output(10).store(chain)
    			.set_output(40).store(chain)
    			.set_output(30).store(chain)
    			.set_output(20).store(chain);
    		let mut pool = to_memory_pool(chain);

    		// increase miner score of transaction 3 to move it to position #1
    		pool.set_virtual_fee(&chain.hash(3), 100);
    		// decrease miner score of transaction 1 to move it to position #4
    		pool.set_virtual_fee(&chain.hash(1), -30);

    		let transactions = pool.remove_n_with_strategy(4, OrderingStrategy::ByTransactionScore);
    		assert_eq!(transactions.len(), 4);
    		assert_eq!(transactions[0], chain.at(3).into());
    		assert_eq!(transactions[1], chain.at(2).into());
    		assert_eq!(transactions[2], chain.at(0).into());
    		assert_eq!(transactions[3], chain.at(1).into());
    	}

    	#[test]
    	fn test_memory_pool_package_score_ordering_strategy() {
    		let chain = &mut ChainBuilder::new();
    		// all transactions of same size
    		TransactionBuilder::with_default_input(0).set_output(30).store(chain)	// transaction0
    			.into_input(0).set_output(50).store(chain)							// transaction0 -> transaction1
    			.set_default_input(1).set_output(35).store(chain)					// transaction2
    			.into_input(0).set_output(10).store(chain)							// transaction2 -> transaction3
    			.into_input(0).set_output(100).store(chain);							// transaction2 -> transaction3 -> transaction4

    		let mut pool = MemoryPool::new();

    		// compared by simple transaction score:
    		// score({ transaction0 }) = 30/60
    		// <
    		// score({ transaction2 }) = 35/60
    		let expected = vec![chain.hash(2), chain.hash(0)];
    		pool.insert_verified(chain.at(0).into());
    		pool.insert_verified(chain.at(2).into());
    		assert_eq!(pool.read_n_with_strategy(2, OrderingStrategy::ByPackageScore), expected);

    		// { transaction0, transaction1 } now have bigger score than { transaction2 }:
    		// score({ transaction0, transaction1 }) = (30 + 50) / 120 ~ 0.667
    		// >
    		// score({ transaction2 }) = 35/60 ~ 0.583
    		// => chain1 is boosted
    		// => so transaction with lesser individual score (but with bigger package score) is mined first
    		pool.insert_verified(chain.at(1).into());
    		let expected = vec![chain.hash(0), chain.hash(1), chain.hash(2)];
    		assert_eq!(pool.read_n_with_strategy(3, OrderingStrategy::ByPackageScore), expected);

    		// { transaction0, transaction1 } still have bigger score than { transaction2, transaction3 }
    		// score({ transaction0, transaction1 }) = (30 + 35) / 120 ~ 0.625
    		// >
    		// score({ transaction2, transaction3 }) = (35 + 10) / 120 ~ 0.375
    		// => chain2 is not boosted
    		pool.insert_verified(chain.at(3).into());
    		let expected = vec![chain.hash(0), chain.hash(1), chain.hash(2), chain.hash(3)];
    		assert_eq!(pool.read_n_with_strategy(4, OrderingStrategy::ByPackageScore), expected);

    		// { transaction0, transaction1 } now have lesser score than { transaction2, transaction3, transaction4 }
    		// score({ transaction0, transaction1 }) = (30 + 35) / 120 ~ 0.625
    		// <
    		// score({ transaction2, transaction3, transaction4 }) = (35 + 10 + 100) / 180 ~ 0.806
    		// => chain2 is boosted
    		pool.insert_verified(chain.at(4).into());
    		let expected = vec![chain.hash(2), chain.hash(3), chain.hash(4), chain.hash(0), chain.hash(1)];
    		assert_eq!(pool.read_n_with_strategy(5, OrderingStrategy::ByPackageScore), expected);

    		// add virtual fee to the transaction1 so that chain1 is back to the position #1
    		pool.set_virtual_fee(&chain.hash(1), 500i64);
    		let expected = vec![chain.hash(0), chain.hash(1), chain.hash(2), chain.hash(3), chain.hash(4)];
    		assert_eq!(pool.read_n_with_strategy(5, OrderingStrategy::ByPackageScore), expected);
    	}

    	#[test]
    	fn test_memory_pool_package_score_ordering_strategy_opposite_insert_order() {
    		let chain = &mut ChainBuilder::new();
    		// all transactions of same size
    		TransactionBuilder::with_default_input(0).set_output(17).store(chain)	// transaction0
    			.into_input(0).set_output(50).store(chain)							// transaction0 -> transaction1
    			.into_input(0).set_output(7).store(chain)							// transaction0 -> transaction1 -> transaction2
    			.set_default_input(1).set_output(20).store(chain);					// transaction3

    		let mut pool = MemoryPool::new();

    		// chain1_parent is not linked to the chain1_grandchild
    		// => they are in separate chains now
    		// => chain2 has greater score than both of these chains
    		pool.insert_verified(chain.at(3).into());
    		pool.insert_verified(chain.at(0).into());
    		pool.insert_verified(chain.at(2).into());
    		let expected = vec![chain.hash(3), chain.hash(0), chain.hash(2)];
    		assert_eq!(pool.read_n_with_strategy(3, OrderingStrategy::ByPackageScore), expected);

    		// insert the missing transaction to link together chain1
    		// => it now will have better score than chain2
    		pool.insert_verified(chain.at(1).into());
    		let expected = vec![chain.hash(0), chain.hash(1), chain.hash(3), chain.hash(2)];
    		assert_eq!(pool.read_n_with_strategy(4, OrderingStrategy::ByPackageScore), expected);
    	}

    	#[test]
    	fn test_memory_pool_complex_transactions_tree_opposite_insert_order() {
    		let chain = &mut ChainBuilder::new();
    		// all transactions of same size (=> 3 inputs)
    		// construct level0
    		TransactionBuilder::with_default_input(0).add_default_input(1).add_default_input(2).set_output(10).add_output(10).store(chain)		// transaction0
    			.set_default_input(3).add_default_input(4).add_default_input(5).set_output(20).add_output(20).store(chain)						// transaction1
    			.set_default_input(6).add_default_input(7).add_default_input(8).set_output(30).add_output(30).store(chain)						// transaction2
    			// construct level1
    			.set_default_input(9).add_default_input(10).add_input(&chain.at(0), 0).set_output(40).add_output(40).store(chain)				// transaction0 -> transaction3
    			.set_default_input(11).add_input(&chain.at(0), 1).add_input(&chain.at(1), 0).set_output(50).add_output(50).store(chain)			// transaction0 + transaction1 -> transaction4
    			// construct level3
    			.set_input(&chain.at(2), 0).add_input(&chain.at(3), 0).add_input(&chain.at(4), 0).set_output(60).add_output(60).store(chain);	// transaction2 + transaction3 + transaction4 -> transaction5

    		let mut pool = MemoryPool::new();

    		// insert level1 + level2. There are two chains:
    		// score({ transaction3, transaction5 }) = 40 + 60
    		// score({ transaction4, transaction5 }) = 50 + 60
    		pool.insert_verified(chain.at(5).into());
    		pool.insert_verified(chain.at(3).into());
    		pool.insert_verified(chain.at(4).into());
    		let expected = vec![chain.hash(4), chain.hash(3), chain.hash(5)];
    		assert_eq!(pool.read_n_with_strategy(3, OrderingStrategy::ByTransactionScore), expected);
    		assert_eq!(pool.read_n_with_strategy(3, OrderingStrategy::ByPackageScore), expected);

    		// insert another one transaction from the chain. Three chains:
    		// score({ transaction3, transaction5 }) = 40 + 60
    		// score({ transaction4, transaction5 }) = 50 + 60
    		// score({ transaction2, transaction5 }) = 30 + 60
    		pool.insert_verified(chain.at(2).into());
    		let expected = vec![chain.hash(4), chain.hash(3), chain.hash(2), chain.hash(5)];
    		assert_eq!(pool.read_n_with_strategy(4, OrderingStrategy::ByTransactionScore), expected);
    		assert_eq!(pool.read_n_with_strategy(4, OrderingStrategy::ByPackageScore), expected);

    		// insert another one transaction from the chain. Three chains:
    		// score({ transaction3, transaction5 }) = 40 + 60 / 2 = 0.5
    		// score({ transaction1, transaction4, transaction5 }) = 20 + 50 + 60 / 3 ~ 0.333
    		// score({ transaction2, transaction5 }) = 30 + 60 / 2 = 0.45
    		// but second chain will be removed first anyway because previous #1 ({ transaction4, transaction5}) now depends on level 01
    		pool.insert_verified(chain.at(1).into());
    		let expected = vec![chain.hash(3), chain.hash(2), chain.hash(1), chain.hash(4), chain.hash(5)];
    		assert_eq!(pool.read_n_with_strategy(5, OrderingStrategy::ByTransactionScore), expected);
    		assert_eq!(pool.read_n_with_strategy(5, OrderingStrategy::ByPackageScore), expected);

    		// insert another one transaction from the chain. Four chains:
    		// score({ transaction0, transaction3, transaction5 }) = (10 + 40 + 60) / (60 + 60 + 142) ~ 0.420
    		// score({ transaction0, transaction4, transaction5 }) = (10 + 50 + 60) / (60 + 60 + 142) ~ 0.458
    		// score({ transaction1, transaction3, transaction5 }) = (20 + 50 + 60) / (60 + 60 + 142) ~ 0.496
    		// score({ transaction2, transaction5 }) = (30 + 60) / (60 + 142) ~ 0.445
    		pool.insert_verified(chain.at(0).into());
    		let expected = vec![chain.hash(2), chain.hash(1), chain.hash(0), chain.hash(4), chain.hash(3), chain.hash(5)];
    		assert_eq!(pool.read_n_with_strategy(6, OrderingStrategy::ByTransactionScore), expected);
    		assert_eq!(pool.read_n_with_strategy(6, OrderingStrategy::ByPackageScore), expected);
    	}

    	#[test]
    	fn test_memory_pool_spent_transaction_output() {
    		let chain = &mut ChainBuilder::new();

    		// all transactions of same size (=> 3 inputs)
    		// construct level0
    		TransactionBuilder::with_output(10).store(chain)				// transaction0
    			.set_output(20).store(chain)								// transaction1
    			.set_input(&chain.at(0), 0).add_output(30).store(chain);	// transaction0 -> transaction2

    		let mut pool = MemoryPool::new();
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(0), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(1), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(2), index: 0, }));

    		pool.insert_verified(chain.at(0).into());
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(0), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(1), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(2), index: 0, }));

    		pool.insert_verified(chain.at(1).into());
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(0), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(1), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(2), index: 0, }));

    		pool.insert_verified(chain.at(2).into());
    		assert!(pool.is_spent(&OutPoint { hash: chain.hash(0), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(1), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(2), index: 0, }));

    		pool.remove_by_hash(&chain.at(2).hash());
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(0), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(1), index: 0, }));
    		assert!(!pool.is_spent(&OutPoint { hash: chain.hash(2), index: 0, }));
    	}

    	#[test]
    	fn test_memory_pool_remove_by_prevout() {
    		let chain = &mut ChainBuilder::new();

    		// all transactions of same size (=> 3 inputs)
    		// construct level0
    		TransactionBuilder::with_output(10).store(chain)	// transaction0
    			.into_input(0).add_output(20).store(chain)		// transaction0 -> transaction1
    			.into_input(0).add_output(30).store(chain)		// transaction0 -> transaction1 -> transaction2
    			.reset().add_output(40).store(chain);			// transaction3
    		let mut pool = MemoryPool::new();

    		pool.insert_verified(chain.at(0).into());
    		pool.insert_verified(chain.at(1).into());
    		pool.insert_verified(chain.at(2).into());
    		pool.insert_verified(chain.at(3).into());
    		assert_eq!(pool.information().transactions_count, 4);

    		assert_eq!(pool.remove_by_prevout(&OutPoint { hash: chain.hash(0), index: 0 }), Some(vec![chain.at(1).into(), chain.at(2).into()]));
    		assert_eq!(pool.information().transactions_count, 2);
    	}

    	#[test]
    	fn test_memory_pool_check_double_spend() {
    		let chain = &mut ChainBuilder::new();

    		TransactionBuilder::with_output(10).add_output(10).add_output(10).store(chain)	// t0
    			.reset().set_input(&chain.at(0), 0).add_output(20).lock().store(chain)		// nonfinal: t0[0] -> t1
    			.reset().set_input(&chain.at(1), 0).add_output(30).store(chain)				// dependent: t0[0] -> t1[0] -> t2
    			.reset().set_input(&chain.at(0), 0).add_output(40).store(chain)				// good replacement: t0[0] -> t3
    			.reset().set_input(&chain.at(0), 1).add_output(50).store(chain)				// final: t0[1] -> t4
    			.reset().set_input(&chain.at(0), 1).add_output(60).store(chain)				// bad replacement: t0[1] -> t5
    			.reset().set_input(&chain.at(0), 2).add_output(70).store(chain);			// no double spend: t0[2] -> t6

    		let mut pool = MemoryPool::new();
    		pool.insert_verified(chain.at(1).into());
    		pool.insert_verified(chain.at(2).into());
    		pool.insert_verified(chain.at(4).into());
    		// when output is spent by nonfinal transaction
    		match pool.check_double_spend(&chain.at(3)) {
    			DoubleSpendCheckResult::NonFinalDoubleSpend(set) => {
    				assert_eq!(set.double_spends.len(), 1);
    				assert!(set.double_spends.contains(&chain.at(1).inputs[0].previous_output.clone().into()));
    				assert_eq!(set.dependent_spends.len(), 2);
    				assert!(set.dependent_spends.contains(&OutPoint {
    					hash: chain.at(1).hash(),
    					index: 0,
    				}.into()));
    				assert!(set.dependent_spends.contains(&OutPoint {
    					hash: chain.at(2).hash(),
    					index: 0,
    				}.into()));
    			},
    			_ => panic!("unexpected"),
    		}
    		// when output is spent by final transaction
    		match pool.check_double_spend(&chain.at(5)) {
    			DoubleSpendCheckResult::DoubleSpend(inpool_hash, prev_hash, prev_index) => {
    				assert_eq!(inpool_hash, chain.at(4).hash());
    				assert_eq!(prev_hash, chain.at(0).hash());
    				assert_eq!(prev_index, 1);
    			},
    			_ => panic!("unexpected"),
    		}
    		// when output is not spent at all
    		match pool.check_double_spend(&chain.at(6)) {
    			DoubleSpendCheckResult::NoDoubleSpend => (),
    			_ => panic!("unexpected"),
    		}
    	}

    	#[test]
    	fn test_memory_pool_check_double_spend_multiple_dependent_outputs() {
    		let chain = &mut ChainBuilder::new();

    		TransactionBuilder::with_output(100).store(chain)															// t0
    			.reset().set_input(&chain.at(0), 0).add_output(20).add_output(30).add_output(50).lock().store(chain)	// nonfinal: t0[0] -> t1
    			.reset().set_input(&chain.at(0), 0).add_output(40).store(chain);										// good replacement: t0[0] -> t2

    		let mut pool = MemoryPool::new();
    		pool.insert_verified(chain.at(1).into());

    		// when output is spent by nonfinal transaction
    		match pool.check_double_spend(&chain.at(2)) {
    			DoubleSpendCheckResult::NonFinalDoubleSpend(set) => {
    				assert_eq!(set.double_spends.len(), 1);
    				assert!(set.double_spends.contains(&chain.at(1).inputs[0].previous_output.clone().into()));
    				assert_eq!(set.dependent_spends.len(), 3);
    				assert!(set.dependent_spends.contains(&OutPoint {
    					hash: chain.at(1).hash(),
    					index: 0,
    				}.into()));
    				assert!(set.dependent_spends.contains(&OutPoint {
    					hash: chain.at(1).hash(),
    					index: 1,
    				}.into()));
    				assert!(set.dependent_spends.contains(&OutPoint {
    					hash: chain.at(1).hash(),
    					index: 2,
    				}.into()));
    			},
    			_ => panic!("unexpected"),
    		}

    	}

    	#[test]
    	fn test_memory_poolis_spent() {
    		let tx1: Transaction = TransactionBuilder::with_default_input(0).into();
    		let tx2: Transaction = TransactionBuilder::with_default_input(1).into();
    		let out1 = tx1.inputs[0].previous_output.clone();
    		let out2 = tx2.inputs[0].previous_output.clone();
    		let mut memory_pool = MemoryPool::new();
    		memory_pool.insert_verified(tx1.into());
    		assert!(memory_pool.is_spent(&out1));
    		assert!(!memory_pool.is_spent(&out2));
    	}
    }

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