sc_statement_store/

lib.rs

// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program 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.

// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.

//! Disk-backed statement store.
//!
//! This module contains an implementation of `sp_statement_store::StatementStore` which is backed
//! by a database.
//!
//! Constraint management.
//!
//! The statement store validates statements using node-side signature verification and
//! static runtime allowance limits.
//! The following constraints are then checked:
//! * For a given account id, there may be at most `max_count` statements with `max_size` total data
//!   size. To satisfy this, statements for this account ID are removed from the store starting with
//!   the lowest priority until a constraint is satisfied.
//! * There may not be more than `MAX_TOTAL_STATEMENTS` total statements with `MAX_TOTAL_SIZE` size.
//!   To satisfy this, statements are removed from the store starting with the lowest
//!   `global_priority` until a constraint is satisfied.
//!
//! When a new statement is inserted that would not satisfy constraints in the first place, no
//! statements are deleted and `Ignored` result is returned.
//! The order in which statements with the same priority are deleted is unspecified.
//!
//! Statement expiration.
//!
//! Each time a statement is removed from the store (Either evicted by higher priority statement or
//! explicitly with the `remove` function) the statement is marked as expired. Expired statements
//! can't be added to the store for `Options::purge_after_sec` seconds. This is to prevent old
//! statements from being propagated on the network.

#![warn(missing_docs)]
#![warn(unused_extern_crates)]

mod metrics;
mod subscription;

use crate::subscription::{SubscriptionStatementsStream, SubscriptionsHandle};
use futures::FutureExt;
use metrics::MetricsLink as PrometheusMetrics;
use parking_lot::{lock_api::RwLockUpgradableReadGuard, RwLock};
use prometheus_endpoint::Registry as PrometheusRegistry;
use sc_client_api::{backend::StorageProvider, Backend, StorageKey};
use sc_keystore::LocalKeystore;
use sp_blockchain::HeaderBackend;
use sp_core::{crypto::UncheckedFrom, hexdisplay::HexDisplay, traits::SpawnNamed, Decode, Encode};
use sp_runtime::traits::Block as BlockT;
use sp_statement_store::{
	runtime_api::{StatementSource, StatementStoreExt},
	AccountId, BlockHash, Channel, DecryptionKey, FilterDecision, Hash, InvalidReason,
	OptimizedTopicFilter, Proof, RejectionReason, Result, SignatureVerificationResult, Statement,
	StatementAllowance, StatementEvent, SubmitResult, Topic,
};
pub use sp_statement_store::{Error, StatementStore, MAX_TOPICS};
use std::{
	collections::{BTreeMap, HashMap, HashSet},
	sync::Arc,
	time::{Duration, Instant},
};
pub use subscription::StatementStoreSubscriptionApi;

const KEY_VERSION: &[u8] = b"version".as_slice();
const CURRENT_VERSION: u32 = 1;

const LOG_TARGET: &str = "statement-store";

/// The amount of time an expired statement is kept before it is removed from the store entirely.
pub const DEFAULT_PURGE_AFTER_SEC: u64 = 2 * 24 * 60 * 60; // 48h
/// The maximum number of statements the statement store can hold.
pub const DEFAULT_MAX_TOTAL_STATEMENTS: usize = 4 * 1024 * 1024; // ~4 million
/// The maximum amount of data the statement store can hold, regardless of the number of
/// statements from which the data originates.
pub const DEFAULT_MAX_TOTAL_SIZE: usize = 2 * 1024 * 1024 * 1024; // 2GiB
/// The maximum size of a single statement in bytes.
/// Accounts for the 1-byte vector length prefix when statements are gossiped as `Vec<Statement>`.
pub const MAX_STATEMENT_SIZE: usize =
	sc_network_statement::config::MAX_STATEMENT_NOTIFICATION_SIZE as usize - 1;

/// Maximum number of statements to expire in a single iteration.
const MAX_EXPIRY_STATEMENTS_PER_ITERATION: usize = 10_000;
/// Maximum number of accounts to check for expiry in a single iteration.
const MAX_EXPIRY_ACCOUNTS_PER_ITERATION: usize = 10_000;
/// Maximum time in milliseconds to spend checking for expiry in a single iteration.
const MAX_EXPIRY_TIME_PER_ITERATION: Duration = Duration::from_millis(100);

/// Number of subscription filter worker tasks.
const NUM_FILTER_WORKERS: usize = 1;

const MAINTENANCE_PERIOD: std::time::Duration = std::time::Duration::from_secs(29);

/// Specifies which block hash to use when reading statement allowances.
enum AllowanceBlock {
	/// Use a specific block hash.
	Block(BlockHash),
	/// Use the best (latest) block hash.
	Best,
	/// Use the finalized block hash.
	Finalized,
}

// Period between enforcing limits (checking for expired statements and making sure statements stay
// within allowances). Different from maintenance period to avoid keeping the lock for too long for
// maintenance tasks.
const ENFORCE_LIMITS_PERIOD: std::time::Duration = std::time::Duration::from_secs(31);

mod col {
	pub const META: u8 = 0;
	pub const STATEMENTS: u8 = 1;
	pub const EXPIRED: u8 = 2;

	pub const COUNT: u8 = 3;
}

#[derive(Eq, PartialEq, Debug, Ord, PartialOrd, Clone, Copy)]
struct Expiry(u64);

#[derive(PartialEq, Eq)]
struct PriorityKey {
	hash: Hash,
	expiry: Expiry,
}

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

impl Ord for PriorityKey {
	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
		self.expiry.cmp(&other.expiry).then_with(|| self.hash.cmp(&other.hash))
	}
}

#[derive(PartialEq, Eq)]
struct ChannelEntry {
	hash: Hash,
	expiry: Expiry,
}

#[derive(Default)]
struct StatementsForAccount {
	// Statements ordered by priority.
	by_priority: BTreeMap<PriorityKey, (Option<Channel>, usize)>,
	// Channel to statement map. Only one statement per channel is allowed.
	channels: HashMap<Channel, ChannelEntry>,
	// Sum of all `Data` field sizes.
	data_size: usize,
}

impl StatementsForAccount {
	/// Returns an iterator over statements that have expired by `current_time`.
	fn expired_by_iter(
		&self,
		current_time: u64,
	) -> impl Iterator<Item = (&PriorityKey, &(Option<Channel>, usize))> {
		let range = PriorityKey { hash: Hash::default(), expiry: Expiry(0) }..PriorityKey {
			hash: Hash::default(),
			expiry: Expiry(current_time << 32),
		};
		self.by_priority.range(range)
	}
}

/// Default number of concurrent workers for statement validation.
pub const DEFAULT_NETWORK_WORKERS: usize = 1;

/// Default maximum statements per second per peer before rate limiting kicks in.
pub use sc_network_statement::config::DEFAULT_STATEMENTS_PER_SECOND as DEFAULT_RATE_LIMIT;

/// Statement store and network handler configuration.
#[derive(Debug, Clone, Copy)]
pub struct Config {
	/// Maximum statements allowed in the store. Once this limit is reached lower-priority
	/// statements may be evicted.
	pub max_total_statements: usize,
	/// Maximum total data size allowed in the store. Once this limit is reached lower-priority
	/// statements may be evicted.
	pub max_total_size: usize,
	/// Number of seconds for which removed statements won't be allowed to be added back in.
	pub purge_after_sec: u64,
	/// Number of concurrent workers for statement validation from the network.
	pub network_workers: usize,
	/// Maximum statements per second per peer before rate limiting kicks in.
	pub rate_limit: u32,
}

impl Config {
	/// Validate the configuration, returning an error if any values are invalid.
	pub fn validate(&self) -> Result<()> {
		if self.max_total_statements == 0 {
			return Err(Error::InvalidConfig(
				"max_total_statements must be greater than zero".into(),
			));
		}
		if self.max_total_size == 0 {
			return Err(Error::InvalidConfig("max_total_size must be greater than zero".into()));
		}
		if self.network_workers == 0 {
			return Err(Error::InvalidConfig("network_workers must be greater than zero".into()));
		}
		Ok(())
	}
}

impl Default for Config {
	fn default() -> Self {
		Config {
			max_total_statements: DEFAULT_MAX_TOTAL_STATEMENTS,
			max_total_size: DEFAULT_MAX_TOTAL_SIZE,
			purge_after_sec: DEFAULT_PURGE_AFTER_SEC,
			network_workers: DEFAULT_NETWORK_WORKERS,
			rate_limit: DEFAULT_RATE_LIMIT,
		}
	}
}

#[derive(Default)]
struct Index {
	recent: HashSet<Hash>,
	by_topic: HashMap<Topic, HashSet<Hash>>,
	by_dec_key: HashMap<Option<DecryptionKey>, HashSet<Hash>>,
	topics_and_keys: HashMap<Hash, ([Option<Topic>; MAX_TOPICS], Option<DecryptionKey>)>,
	entries: HashMap<Hash, (AccountId, Expiry, usize)>,
	expired: HashMap<Hash, u64>, // Value is expiration timestamp.
	accounts: HashMap<AccountId, StatementsForAccount>,
	accounts_to_check_for_expiry_stmts: Vec<AccountId>,
	config: Config,
	total_size: usize,
}

struct ClientWrapper<Block, Client, BE> {
	client: Arc<Client>,
	_block: std::marker::PhantomData<Block>,
	_backend: std::marker::PhantomData<BE>,
}

impl<Block, Client, BE> ClientWrapper<Block, Client, BE>
where
	Block: BlockT,
	Block::Hash: From<BlockHash>,
	BE: Backend<Block> + 'static,
	Client: HeaderBackend<Block> + StorageProvider<Block, BE> + Send + Sync + 'static,
{
	fn read_allowance(
		&self,
		account_id: &AccountId,
		allowance_block: AllowanceBlock,
	) -> Result<Option<StatementAllowance>> {
		use sp_statement_store::{statement_allowance_key, StatementAllowance};

		let block_hash = match allowance_block {
			AllowanceBlock::Block(hash) => hash.into(),
			AllowanceBlock::Best => self.client.info().best_hash,
			AllowanceBlock::Finalized => self.client.info().finalized_hash,
		};
		let key = statement_allowance_key(account_id);
		let storage_key = StorageKey(key);
		self.client
			.storage(block_hash, &storage_key)
			.map_err(|e| Error::Storage(format!("Failed to read allowance: {:?}", e)))?
			.map(|value| {
				StatementAllowance::decode(&mut &value.0[..])
					.map_err(|e| Error::Decode(format!("Failed to decode allowance: {:?}", e)))
			})
			.transpose()
	}
}

/// Statement store.
pub struct Store {
	db: parity_db::Db,
	index: RwLock<Index>,
	read_allowance_fn:
		Box<dyn Fn(&AccountId, AllowanceBlock) -> Result<Option<StatementAllowance>> + Send + Sync>,
	subscription_manager: SubscriptionsHandle,
	keystore: Arc<LocalKeystore>,
	// Used for testing
	time_override: Option<u64>,
	metrics: PrometheusMetrics,
}

enum IndexQuery {
	Unknown,
	Exists,
	Expired,
}

impl Index {
	fn new(config: Config) -> Index {
		Index { config, ..Default::default() }
	}

	fn insert_new(
		&mut self,
		hash: Hash,
		account: AccountId,
		statement: &Statement,
		is_recent: bool,
	) {
		let mut all_topics = [None; MAX_TOPICS];
		let mut nt = 0;
		while let Some(t) = statement.topic(nt) {
			self.by_topic.entry(t).or_default().insert(hash);
			all_topics[nt] = Some(t);
			nt += 1;
		}
		let key = statement.decryption_key();
		self.by_dec_key.entry(key).or_default().insert(hash);
		if nt > 0 || key.is_some() {
			self.topics_and_keys.insert(hash, (all_topics, key));
		}
		let expiry = Expiry(statement.expiry());
		self.entries.insert(hash, (account, expiry, statement.data_len()));
		if is_recent {
			self.recent.insert(hash);
		}
		self.total_size += statement.data_len();
		let account_info = self.accounts.entry(account).or_default();
		account_info.data_size += statement.data_len();
		if let Some(channel) = statement.channel() {
			account_info.channels.insert(channel, ChannelEntry { hash, expiry });
		}
		account_info
			.by_priority
			.insert(PriorityKey { hash, expiry }, (statement.channel(), statement.data_len()));
	}

	fn query(&self, hash: &Hash) -> IndexQuery {
		if self.entries.contains_key(hash) {
			return IndexQuery::Exists;
		}
		if self.expired.contains_key(hash) {
			return IndexQuery::Expired;
		}
		IndexQuery::Unknown
	}

	fn insert_expired(&mut self, hash: Hash, timestamp: u64) {
		self.expired.insert(hash, timestamp);
	}

	fn iterate_with(
		&self,
		key: Option<DecryptionKey>,
		topic: &OptimizedTopicFilter,
		f: impl FnMut(&Hash) -> Result<()>,
	) -> Result<()> {
		match topic {
			OptimizedTopicFilter::Any => self.iterate_with_any(key, f),
			OptimizedTopicFilter::MatchAll(topics) => {
				self.iterate_with_match_all(key, topics.iter(), f)
			},
			OptimizedTopicFilter::MatchAny(topics) => {
				self.iterate_with_match_any(key, topics.iter(), f)
			},
		}
	}

	fn iterate_with_match_any<'a>(
		&self,
		key: Option<DecryptionKey>,
		match_any_topics: impl ExactSizeIterator<Item = &'a Topic>,
		mut f: impl FnMut(&Hash) -> Result<()>,
	) -> Result<()> {
		let Some(key_set) = self.by_dec_key.get(&key).filter(|k| !k.is_empty()) else {
			return Ok(());
		};

		for t in match_any_topics {
			let set = self.by_topic.get(t);

			for item in set.iter().flat_map(|set| set.iter()) {
				if key_set.contains(item) {
					log::trace!(
						target: LOG_TARGET,
						"Iterating by topic/key: statement {:?}",
						HexDisplay::from(item)
					);
					f(item)?
				}
			}
		}
		Ok(())
	}

	fn iterate_with_any(
		&self,
		key: Option<DecryptionKey>,
		mut f: impl FnMut(&Hash) -> Result<()>,
	) -> Result<()> {
		let key_set = self.by_dec_key.get(&key);
		if key_set.map_or(true, |s| s.is_empty()) {
			// Key does not exist in the index.
			return Ok(());
		}

		for item in key_set.map(|hashes| hashes.iter()).into_iter().flatten() {
			f(item)?
		}
		Ok(())
	}

	fn iterate_with_match_all<'a>(
		&self,
		key: Option<DecryptionKey>,
		match_all_topics: impl ExactSizeIterator<Item = &'a Topic>,
		mut f: impl FnMut(&Hash) -> Result<()>,
	) -> Result<()> {
		let empty = HashSet::new();
		let mut sets: [&HashSet<Hash>; MAX_TOPICS + 1] = [&empty; MAX_TOPICS + 1];
		let num_topics = match_all_topics.len();
		if num_topics > MAX_TOPICS {
			return Ok(());
		}
		let key_set = self.by_dec_key.get(&key);
		if key_set.map_or(true, |s| s.is_empty()) {
			// Key does not exist in the index.
			return Ok(());
		}
		sets[0] = key_set.expect("Function returns if key_set is None");
		for (i, t) in match_all_topics.enumerate() {
			let set = self.by_topic.get(t);
			if set.map_or(0, |s| s.len()) == 0 {
				// At least one of the match_all_topics does not exist in the index.
				return Ok(());
			}
			sets[i + 1] = set.expect("Function returns if set is None");
		}
		let sets = &mut sets[0..num_topics + 1];
		// Start with the smallest topic set or the key set.
		sets.sort_by_key(|s| s.len());
		for item in sets[0] {
			if sets[1..].iter().all(|set| set.contains(item)) {
				log::trace!(
					target: LOG_TARGET,
					"Iterating by topic/key: statement {:?}",
					HexDisplay::from(item)
				);
				f(item)?
			}
		}
		Ok(())
	}

	fn maintain(&mut self, current_time: u64) -> Vec<Hash> {
		// Purge previously expired messages.
		let mut purged = Vec::new();
		self.expired.retain(|hash, timestamp| {
			if *timestamp + self.config.purge_after_sec <= current_time {
				purged.push(*hash);
				log::trace!(target: LOG_TARGET, "Purged statement {:?}", HexDisplay::from(hash));
				false
			} else {
				true
			}
		});
		purged
	}

	fn take_recent(&mut self) -> HashSet<Hash> {
		std::mem::take(&mut self.recent)
	}

	fn make_expired(&mut self, hash: &Hash, current_time: u64) -> bool {
		if let Some((account, expiry, len)) = self.entries.remove(hash) {
			self.total_size -= len;
			if let Some((topics, key)) = self.topics_and_keys.remove(hash) {
				for t in topics.into_iter().flatten() {
					if let std::collections::hash_map::Entry::Occupied(mut set) =
						self.by_topic.entry(t)
					{
						set.get_mut().remove(hash);
						if set.get().is_empty() {
							set.remove_entry();
						}
					}
				}
				if let std::collections::hash_map::Entry::Occupied(mut set) =
					self.by_dec_key.entry(key)
				{
					set.get_mut().remove(hash);
					if set.get().is_empty() {
						set.remove_entry();
					}
				}
			}
			let _ = self.recent.remove(hash);
			self.expired.insert(*hash, current_time);
			if let std::collections::hash_map::Entry::Occupied(mut account_rec) =
				self.accounts.entry(account)
			{
				let key = PriorityKey { hash: *hash, expiry };
				if let Some((channel, len)) = account_rec.get_mut().by_priority.remove(&key) {
					account_rec.get_mut().data_size -= len;
					if let Some(channel) = channel {
						account_rec.get_mut().channels.remove(&channel);
					}
				}
				if account_rec.get().by_priority.is_empty() {
					account_rec.remove_entry();
				}
			}
			log::trace!(target: LOG_TARGET, "Expired statement {:?}", HexDisplay::from(hash));
			true
		} else {
			false
		}
	}

	fn insert(
		&mut self,
		hash: Hash,
		statement: &Statement,
		account: &AccountId,
		validation: &StatementAllowance,
		current_time: u64,
	) -> std::result::Result<HashSet<Hash>, RejectionReason> {
		let statement_len = statement.data_len();
		if statement_len > validation.max_size as usize {
			log::debug!(
				target: LOG_TARGET,
				"Ignored oversize message: {:?} ({} bytes)",
				HexDisplay::from(&hash),
				statement_len,
			);
			return Err(RejectionReason::DataTooLarge {
				submitted_size: statement_len,
				available_size: validation.max_size as usize,
			});
		}

		let mut evicted = HashSet::new();
		let mut would_free_size = 0;
		let expiry = Expiry(statement.expiry());
		let (max_size, max_count) = (validation.max_size as usize, validation.max_count as usize);
		// It may happen that we can't delete enough lower priority messages
		// to satisfy size constraints. We check for that before deleting anything,
		// taking into account channel message replacement.
		if let Some(account_rec) = self.accounts.get(account) {
			if let Some(channel) = statement.channel() {
				if let Some(channel_record) = account_rec.channels.get(&channel) {
					if expiry <= channel_record.expiry {
						// Trying to replace channel message with lower expiry.
						log::debug!(
							target: LOG_TARGET,
							"Ignored lower priority channel message: {:?} {:?} <= {:?}",
							HexDisplay::from(&hash),
							expiry,
							channel_record.expiry,
						);
						return Err(RejectionReason::ChannelPriorityTooLow {
							submitted_expiry: expiry.0,
							min_expiry: channel_record.expiry.0,
						});
					} else {
						// Would replace channel message. Still need to check for size constraints
						// below.
						log::debug!(
							target: LOG_TARGET,
							"Replacing higher priority channel message: {:?} ({:?}) > {:?} ({:?})",
							HexDisplay::from(&hash),
							expiry,
							HexDisplay::from(&channel_record.hash),
							channel_record.expiry,
						);
						let key = PriorityKey {
							hash: channel_record.hash,
							expiry: channel_record.expiry,
						};
						if let Some((_channel, len)) = account_rec.by_priority.get(&key) {
							would_free_size += *len;
							evicted.insert(channel_record.hash);
						}
					}
				}
			}
			// Check if we can evict enough lower priority statements to satisfy constraints
			for (entry, (_, len)) in account_rec.by_priority.iter() {
				if (account_rec.data_size - would_free_size + statement_len <= max_size) &&
					account_rec.by_priority.len() + 1 - evicted.len() <= max_count
				{
					// Satisfied
					break;
				}
				if evicted.contains(&entry.hash) {
					// Already accounted for above
					continue;
				}
				if entry.expiry >= expiry {
					log::debug!(
						target: LOG_TARGET,
						"Ignored message due to constraints {:?} {:?} < {:?}",
						HexDisplay::from(&hash),
						expiry,
						entry.expiry,
					);
					return Err(RejectionReason::AccountFull {
						submitted_expiry: expiry.0,
						min_expiry: entry.expiry.0,
					});
				}
				evicted.insert(entry.hash);
				would_free_size += len;
			}
		}
		// Now check global constraints as well.
		if !((self.total_size - would_free_size + statement_len <= self.config.max_total_size) &&
			self.entries.len() + 1 - evicted.len() <= self.config.max_total_statements)
		{
			log::debug!(
				target: LOG_TARGET,
				"Ignored statement {} because the store is full (size={}, count={})",
				HexDisplay::from(&hash),
				self.total_size,
				self.entries.len(),
			);
			return Err(RejectionReason::StoreFull);
		}

		for h in &evicted {
			self.make_expired(h, current_time);
		}
		self.insert_new(hash, *account, statement, true);
		Ok(evicted)
	}
}

impl Store {
	/// Create a new shared store instance. There should only be one per process.
	/// `path` will be used to open a statement database or create a new one if it does not exist.
	pub fn new_shared<Block, Client, BE>(
		path: &std::path::Path,
		config: Config,
		client: Arc<Client>,
		keystore: Arc<LocalKeystore>,
		prometheus: Option<&PrometheusRegistry>,
		task_spawner: Box<dyn SpawnNamed>,
	) -> Result<Arc<Store>>
	where
		Block: BlockT,
		Block::Hash: From<BlockHash>,
		BE: Backend<Block> + 'static,
		Client: HeaderBackend<Block> + StorageProvider<Block, BE> + Send + Sync + 'static,
	{
		let store =
			Arc::new(Self::new(path, config, client, keystore, prometheus, task_spawner.clone())?);

		// Perform periodic statement store maintenance
		let worker_store = store.clone();
		task_spawner.spawn(
			"statement-store-maintenance",
			Some("statement-store"),
			Box::pin(async move {
				let mut maintenance_interval = tokio::time::interval(MAINTENANCE_PERIOD);
				let mut enforce_limits_interval = tokio::time::interval(ENFORCE_LIMITS_PERIOD);
				loop {
					futures::select! {
						_ = maintenance_interval.tick().fuse() => {worker_store.maintain();}
						_ = enforce_limits_interval.tick().fuse() => {worker_store.enforce_limits();}
					}
				}
			}),
		);

		Ok(store)
	}

	/// Create a new instance.
	/// `path` will be used to open a statement database or create a new one if it does not exist.
	#[doc(hidden)]
	pub fn new<Block, Client, BE>(
		path: &std::path::Path,
		config: Config,
		client: Arc<Client>,
		keystore: Arc<LocalKeystore>,
		prometheus: Option<&PrometheusRegistry>,
		task_spawner: Box<dyn SpawnNamed>,
	) -> Result<Store>
	where
		Block: BlockT,
		Block::Hash: From<BlockHash>,
		BE: Backend<Block> + 'static,
		Client: HeaderBackend<Block> + StorageProvider<Block, BE> + Send + Sync + 'static,
	{
		config.validate()?;

		let mut path: std::path::PathBuf = path.into();
		path.push("statements");

		let mut db_config = parity_db::Options::with_columns(&path, col::COUNT);

		let statement_col = &mut db_config.columns[col::STATEMENTS as usize];
		statement_col.ref_counted = false;
		statement_col.preimage = true;
		statement_col.uniform = true;
		let db = parity_db::Db::open_or_create(&db_config).map_err(|e| Error::Db(e.to_string()))?;
		match db.get(col::META, &KEY_VERSION).map_err(|e| Error::Db(e.to_string()))? {
			Some(version) => {
				let version = u32::from_le_bytes(
					version
						.try_into()
						.map_err(|_| Error::Db("Error reading database version".into()))?,
				);
				if version != CURRENT_VERSION {
					return Err(Error::Db(format!("Unsupported database version: {version}")));
				}
			},
			None => {
				db.commit([(
					col::META,
					KEY_VERSION.to_vec(),
					Some(CURRENT_VERSION.to_le_bytes().to_vec()),
				)])
				.map_err(|e| Error::Db(e.to_string()))?;
			},
		}

		let storage_reader =
			ClientWrapper { client, _block: Default::default(), _backend: Default::default() };
		let read_allowance_fn =
			Box::new(move |account_id: &AccountId, allowance_block: AllowanceBlock| {
				storage_reader.read_allowance(account_id, allowance_block)
			});

		let store = Store {
			db,
			index: RwLock::new(Index::new(config)),
			read_allowance_fn,
			keystore,
			time_override: None,
			metrics: PrometheusMetrics::new(prometheus),
			subscription_manager: SubscriptionsHandle::new(
				task_spawner.clone(),
				NUM_FILTER_WORKERS,
			),
		};
		store.populate()?;
		Ok(store)
	}

	/// Create memory index from the data.
	// This may be moved to a background thread if it slows startup too much.
	// This function should only be used on startup. There should be no other DB operations when
	// iterating the index.
	fn populate(&self) -> Result<()> {
		{
			let mut index = self.index.write();
			self.db
				.iter_column_while(col::STATEMENTS, |item| {
					let statement = item.value;
					if let Ok(statement) = Statement::decode(&mut statement.as_slice()) {
						let hash = statement.hash();
						log::trace!(
							target: LOG_TARGET,
							"Statement loaded {:?}",
							HexDisplay::from(&hash)
						);
						if let Some(account_id) = statement.account_id() {
							index.insert_new(hash, account_id, &statement, false);
						} else {
							log::debug!(
								target: LOG_TARGET,
								"Error decoding statement loaded from the DB: {:?}",
								HexDisplay::from(&hash)
							);
						}
					}
					true
				})
				.map_err(|e| Error::Db(e.to_string()))?;
			self.db
				.iter_column_while(col::EXPIRED, |item| {
					let expired_info = item.value;
					if let Ok((hash, timestamp)) =
						<(Hash, u64)>::decode(&mut expired_info.as_slice())
					{
						log::trace!(
							target: LOG_TARGET,
							"Statement loaded (expired): {:?}",
							HexDisplay::from(&hash)
						);
						index.insert_expired(hash, timestamp);
					}
					true
				})
				.map_err(|e| Error::Db(e.to_string()))?;
		}

		self.maintain();
		Ok(())
	}

	fn collect_statements_locked<R>(
		&self,
		key: Option<DecryptionKey>,
		topic_filter: &OptimizedTopicFilter,
		index: &Index,
		result: &mut Vec<R>,
		mut f: impl FnMut(Statement) -> Option<R>,
	) -> Result<()> {
		index.iterate_with(key, topic_filter, |hash| {
			match self.db.get(col::STATEMENTS, hash).map_err(|e| Error::Db(e.to_string()))? {
				Some(entry) => {
					if let Ok(statement) = Statement::decode(&mut entry.as_slice()) {
						if let Some(data) = f(statement) {
							result.push(data);
						}
					} else {
						// DB inconsistency
						log::warn!(
							target: LOG_TARGET,
							"Corrupt statement {:?}",
							HexDisplay::from(hash)
						);
					}
				},
				None => {
					// DB inconsistency
					log::warn!(
						target: LOG_TARGET,
						"Missing statement {:?}",
						HexDisplay::from(hash)
					);
				},
			}
			Ok(())
		})?;
		Ok(())
	}

	fn collect_statements<R>(
		&self,
		key: Option<DecryptionKey>,
		topic_filter: &OptimizedTopicFilter,
		f: impl FnMut(Statement) -> Option<R>,
	) -> Result<Vec<R>> {
		let mut result = Vec::new();
		let index = self.index.read();
		self.collect_statements_locked(key, topic_filter, &index, &mut result, f)?;
		Ok(result)
	}

	// Collects expired and over-allowance statement hashes for a single account.
	fn collect_evictions(
		&self,
		account: &AccountId,
		account_rec: &StatementsForAccount,
		current_time: u64,
	) -> Vec<Hash> {
		let mut to_evict = Vec::new();
		let mut expired_count = 0usize;
		let mut expired_size = 0usize;
		for (key, (_, len)) in account_rec.expired_by_iter(current_time) {
			to_evict.push(key.hash);
			expired_count += 1;
			expired_size += len;
		}

		// Enforce allowances for remaining (non-expired) statements, we use the finalized block to
		// make sure we enforce allowances based on the correct chain state.
		let allowance = match (self.read_allowance_fn)(account, AllowanceBlock::Finalized) {
			Ok(Some(allowance)) => allowance,
			Ok(None) => {
				log::debug!(
					target: LOG_TARGET,
					"No allowance found for account {:?}, treating as zero allowance",
					HexDisplay::from(account)
				);
				StatementAllowance { max_count: 0, max_size: 0 }
			},
			Err(e) => {
				log::error!(target: LOG_TARGET, "Error reading allowance: {:?}", e);
				// Skip allowance enforcement for this account on error
				return to_evict;
			},
		};

		// Calculate remaining count and size after expiring statements
		let mut remaining_count = account_rec.by_priority.len() - expired_count;
		let mut remaining_size = account_rec.data_size - expired_size;

		// Evict lowest priority statements that exceed allowance
		if remaining_count > allowance.max_count as usize ||
			remaining_size > allowance.max_size as usize
		{
			log::debug!(
				target: LOG_TARGET,
				"Account {:?} exceeds allowance: count={}/{}, size={}/{}",
				HexDisplay::from(account),
				remaining_count,
				allowance.max_count,
				remaining_size,
				allowance.max_size
			);

			// Skip expired statements (they're at the beginning due to BTreeMap ordering)
			for (key, (_, len)) in account_rec.by_priority.iter().skip(expired_count) {
				if remaining_count <= allowance.max_count as usize &&
					remaining_size <= allowance.max_size as usize
				{
					break;
				}
				to_evict.push(key.hash);
				remaining_count -= 1;
				remaining_size -= len;
				log::debug!(
					target: LOG_TARGET,
					"Evicting statement {:?} due to allowance enforcement",
					HexDisplay::from(&key.hash)
				);
			}
		}

		to_evict
	}

	// Checks for expired statements and enforces allowances, marking violating statements
	// as expired in the index.
	//
	// This function performs incremental checking to avoid blocking the store for too long.
	// It processes accounts in batches and stops when any of these limits are reached:
	// - `MAX_EXPIRY_STATEMENTS_PER_ITERATION` statements found to expire/evict
	// - `MAX_EXPIRY_ACCOUNTS_PER_ITERATION` accounts checked
	// - `MAX_EXPIRY_TIME_MS_PER_ITERATION` milliseconds elapsed
	//
	// The function maintains a list of accounts to check (`accounts_to_check_for_expiry_stmts`).
	// When this list is empty, it repopulates it with all current accounts and returns early,
	// deferring the actual check to the next call. This ensures the process eventually covers
	// all accounts across multiple invocations.
	//
	// Statements are considered expired when their priority (which encodes the expiration
	// timestamp in the upper 32 bits) is less than the current timestamp.
	fn enforce_limits(&self) {
		let _start_check_expiration_timer = self.metrics.start_check_expiration_timer();
		let current_time = self.timestamp();

		let (to_evict, num_accounts_checked) = {
			let index = self.index.upgradable_read();
			if index.accounts_to_check_for_expiry_stmts.is_empty() {
				let existing_accounts = index.accounts.keys().cloned().collect::<Vec<_>>();
				let mut index = RwLockUpgradableReadGuard::upgrade(index);
				index.accounts_to_check_for_expiry_stmts = existing_accounts;
				return;
			}

			let mut to_evict = Vec::new();
			let mut num_accounts_checked = 0;
			let start = Instant::now();

			for account in index.accounts_to_check_for_expiry_stmts.iter().rev() {
				num_accounts_checked += 1;
				if let Some(account_rec) = index.accounts.get(account) {
					to_evict.extend(self.collect_evictions(account, account_rec, current_time));
				}

				if to_evict.len() >= MAX_EXPIRY_STATEMENTS_PER_ITERATION ||
					num_accounts_checked >= MAX_EXPIRY_ACCOUNTS_PER_ITERATION ||
					start.elapsed() >= MAX_EXPIRY_TIME_PER_ITERATION
				{
					break;
				}
			}

			(to_evict, num_accounts_checked)
		};

		let mut expired = 0;

		for hash in to_evict {
			if let Err(e) = self.remove(&hash) {
				log::debug!(
					target: LOG_TARGET,
					"Error marking statement {:?} as expired: {:?}",
					HexDisplay::from(&hash),
					e
				);
			} else {
				expired += 1;
				log::trace!(
					target: LOG_TARGET,
					"Marked statement {:?} as expired",
					HexDisplay::from(&hash)
				);
			}
		}

		let mut index = self.index.write();
		let new_len = index
			.accounts_to_check_for_expiry_stmts
			.len()
			.saturating_sub(num_accounts_checked);
		index.accounts_to_check_for_expiry_stmts.truncate(new_len);

		drop(_start_check_expiration_timer);

		self.metrics.report(|metrics| {
			metrics.statements_expired_total.inc_by(expired);
		});
	}

	/// Perform periodic store maintenance
	pub fn maintain(&self) {
		log::trace!(target: LOG_TARGET, "Started store maintenance");
		let (
			deleted,
			active_count,
			expired_count,
			total_size,
			accounts_count,
			capacity_statements,
			capacity_bytes,
		): (Vec<_>, usize, usize, usize, usize, usize, usize) = {
			let mut index = self.index.write();
			let deleted = index.maintain(self.timestamp());
			(
				deleted,
				index.entries.len(),
				index.expired.len(),
				index.total_size,
				index.accounts.len(),
				index.config.max_total_statements,
				index.config.max_total_size,
			)
		};
		let deleted: Vec<_> =
			deleted.into_iter().map(|hash| (col::EXPIRED, hash.to_vec(), None)).collect();
		let deleted_count = deleted.len() as u64;
		if let Err(e) = self.db.commit(deleted) {
			log::warn!(target: LOG_TARGET, "Error writing to the statement database: {:?}", e);
		} else {
			self.metrics.report(|metrics| metrics.statements_pruned.inc_by(deleted_count));
		}

		self.metrics.report(|metrics| {
			metrics.statements_total.set(active_count as u64);
			metrics.bytes_total.set(total_size as u64);
			metrics.accounts_total.set(accounts_count as u64);
			metrics.expired_total.set(expired_count as u64);
			metrics.capacity_statements.set(capacity_statements as u64);
			metrics.capacity_bytes.set(capacity_bytes as u64);
		});

		log::trace!(
			target: LOG_TARGET,
			"Completed store maintenance. Purged: {}, Active: {}, Expired: {}",
			deleted_count,
			active_count,
			expired_count
		);
	}

	fn timestamp(&self) -> u64 {
		self.time_override.unwrap_or_else(|| {
			std::time::SystemTime::now()
				.duration_since(std::time::UNIX_EPOCH)
				.unwrap_or_default()
				.as_secs()
		})
	}

	#[cfg(test)]
	fn set_time(&mut self, time: u64) {
		self.time_override = Some(time);
	}

	/// Returns `self` as [`StatementStoreExt`].
	pub fn as_statement_store_ext(self: Arc<Self>) -> StatementStoreExt {
		StatementStoreExt::new(self)
	}

	/// Return information of all known statements whose decryption key is identified as
	/// `dest`. The key must be available to the client.
	fn posted_clear_inner<R>(
		&self,
		match_all_topics: &[Topic],
		dest: [u8; 32],
		// Map the statement and the decrypted data to the desired result.
		mut map_f: impl FnMut(Statement, Vec<u8>) -> R,
	) -> Result<Vec<R>> {
		self.collect_statements(
			Some(dest),
			&OptimizedTopicFilter::MatchAll(match_all_topics.iter().cloned().collect()),
			|statement| {
				if let (Some(key), Some(_)) = (statement.decryption_key(), statement.data()) {
					let public: sp_core::ed25519::Public = UncheckedFrom::unchecked_from(key);
					let public: sp_statement_store::ed25519::Public = public.into();
					match self.keystore.key_pair::<sp_statement_store::ed25519::Pair>(&public) {
						Err(e) => {
							log::debug!(
								target: LOG_TARGET,
								"Keystore error: {:?}, for statement {:?}",
								e,
								HexDisplay::from(&statement.hash())
							);
							None
						},
						Ok(None) => {
							log::debug!(
								target: LOG_TARGET,
								"Keystore is missing key for statement {:?}",
								HexDisplay::from(&statement.hash())
							);
							None
						},
						Ok(Some(pair)) => match statement.decrypt_private(&pair.into_inner()) {
							Ok(r) => r.map(|data| map_f(statement, data)),
							Err(e) => {
								log::debug!(
									target: LOG_TARGET,
									"Decryption error: {:?}, for statement {:?}",
									e,
									HexDisplay::from(&statement.hash())
								);
								None
							},
						},
					}
				} else {
					None
				}
			},
		)
	}
}

impl StatementStore for Store {
	/// Return all statements.
	fn statements(&self) -> Result<Vec<(Hash, Statement)>> {
		let index = self.index.read();
		let mut result = Vec::with_capacity(index.entries.len());
		for hash in index.entries.keys().cloned() {
			let Some(encoded) =
				self.db.get(col::STATEMENTS, &hash).map_err(|e| Error::Db(e.to_string()))?
			else {
				continue;
			};
			if let Ok(statement) = Statement::decode(&mut encoded.as_slice()) {
				result.push((hash, statement));
			}
		}
		Ok(result)
	}

	fn take_recent_statements(&self) -> Result<Vec<(Hash, Statement)>> {
		let mut index = self.index.write();
		let recent = index.take_recent();
		let mut result = Vec::with_capacity(recent.len());
		for hash in recent {
			let Some(encoded) =
				self.db.get(col::STATEMENTS, &hash).map_err(|e| Error::Db(e.to_string()))?
			else {
				continue;
			};
			if let Ok(statement) = Statement::decode(&mut encoded.as_slice()) {
				result.push((hash, statement));
			}
		}
		Ok(result)
	}

	/// Returns a statement by hash.
	fn statement(&self, hash: &Hash) -> Result<Option<Statement>> {
		Ok(
			match self
				.db
				.get(col::STATEMENTS, hash.as_slice())
				.map_err(|e| Error::Db(e.to_string()))?
			{
				Some(entry) => {
					log::trace!(
						target: LOG_TARGET,
						"Queried statement {:?}",
						HexDisplay::from(hash)
					);
					Some(
						Statement::decode(&mut entry.as_slice())
							.map_err(|e| Error::Decode(e.to_string()))?,
					)
				},
				None => {
					log::trace!(
						target: LOG_TARGET,
						"Queried missing statement {:?}",
						HexDisplay::from(hash)
					);
					None
				},
			},
		)
	}

	fn has_statement(&self, hash: &Hash) -> bool {
		self.index.read().entries.contains_key(hash)
	}

	fn statement_hashes(&self) -> Vec<Hash> {
		self.index.read().entries.keys().cloned().collect()
	}

	fn statements_by_hashes(
		&self,
		hashes: &[Hash],
		filter: &mut dyn FnMut(&Hash, &[u8], &Statement) -> FilterDecision,
	) -> Result<(Vec<(Hash, Statement)>, usize)> {
		let mut result = Vec::new();
		let mut processed = 0;
		for hash in hashes {
			processed += 1;
			let Some(encoded) =
				self.db.get(col::STATEMENTS, hash).map_err(|e| Error::Db(e.to_string()))?
			else {
				continue;
			};
			let Ok(statement) = Statement::decode(&mut encoded.as_slice()) else { continue };
			match filter(hash, &encoded, &statement) {
				FilterDecision::Skip => {},
				FilterDecision::Take => {
					result.push((*hash, statement));
				},
				FilterDecision::Abort => {
					// We did not process it :)
					processed -= 1;
					break;
				},
			}
		}

		Ok((result, processed))
	}

	/// Return the data of all known statements which include all topics and have no `DecryptionKey`
	/// field.
	fn broadcasts(&self, match_all_topics: &[Topic]) -> Result<Vec<Vec<u8>>> {
		self.collect_statements(
			None,
			&OptimizedTopicFilter::MatchAll(match_all_topics.iter().cloned().collect()),
			|statement| statement.into_data(),
		)
	}

	/// Return the data of all known statements whose decryption key is identified as `dest` (this
	/// will generally be the public key or a hash thereof for symmetric ciphers, or a hash of the
	/// private key for symmetric ciphers).
	fn posted(&self, match_all_topics: &[Topic], dest: [u8; 32]) -> Result<Vec<Vec<u8>>> {
		self.collect_statements(
			Some(dest),
			&OptimizedTopicFilter::MatchAll(match_all_topics.iter().cloned().collect()),
			|statement| statement.into_data(),
		)
	}

	/// Return the decrypted data of all known statements whose decryption key is identified as
	/// `dest`. The key must be available to the client.
	fn posted_clear(&self, match_all_topics: &[Topic], dest: [u8; 32]) -> Result<Vec<Vec<u8>>> {
		self.posted_clear_inner(match_all_topics, dest, |_statement, data| data)
	}

	/// Return all known statements which include all topics and have no `DecryptionKey`
	/// field.
	fn broadcasts_stmt(&self, match_all_topics: &[Topic]) -> Result<Vec<Vec<u8>>> {
		self.collect_statements(
			None,
			&OptimizedTopicFilter::MatchAll(match_all_topics.iter().cloned().collect()),
			|statement| Some(statement.encode()),
		)
	}

	/// Return all known statements whose decryption key is identified as `dest` (this
	/// will generally be the public key or a hash thereof for symmetric ciphers, or a hash of the
	/// private key for symmetric ciphers).
	fn posted_stmt(&self, match_all_topics: &[Topic], dest: [u8; 32]) -> Result<Vec<Vec<u8>>> {
		self.collect_statements(
			Some(dest),
			&OptimizedTopicFilter::MatchAll(match_all_topics.iter().cloned().collect()),
			|statement| Some(statement.encode()),
		)
	}

	/// Return the statement and the decrypted data of all known statements whose decryption key is
	/// identified as `dest`. The key must be available to the client.
	fn posted_clear_stmt(
		&self,
		match_all_topics: &[Topic],
		dest: [u8; 32],
	) -> Result<Vec<Vec<u8>>> {
		self.posted_clear_inner(match_all_topics, dest, |statement, data| {
			let mut res = Vec::with_capacity(statement.size_hint() + data.len());
			statement.encode_to(&mut res);
			res.extend_from_slice(&data);
			res
		})
	}

	/// Submit a statement to the store. Validates the statement and returns validation result.
	fn submit(&self, statement: Statement, source: StatementSource) -> SubmitResult {
		let _histogram_submit_start_timer = self.metrics.start_submit_timer();
		let hash = statement.hash();
		// Get unix timestamp
		if self.timestamp() >= statement.get_expiration_timestamp_secs().into() {
			log::debug!(
				target: LOG_TARGET,
				"Statement is already expired: {:?}",
				HexDisplay::from(&hash),
			);
			self.metrics.report(|metrics| metrics.validations_invalid.inc());
			return SubmitResult::Invalid(InvalidReason::AlreadyExpired);
		}
		let encoded_size = statement.encoded_size();
		if encoded_size > MAX_STATEMENT_SIZE {
			log::debug!(
				target: LOG_TARGET,
				"Statement is too big for propogation: {:?} ({}/{} bytes)",
				HexDisplay::from(&hash),
				statement.encoded_size(),
				MAX_STATEMENT_SIZE
			);
			self.metrics.report(|metrics| metrics.validations_invalid.inc());
			return SubmitResult::Invalid(InvalidReason::EncodingTooLarge {
				submitted_size: encoded_size,
				max_size: MAX_STATEMENT_SIZE,
			});
		}

		match self.index.read().query(&hash) {
			IndexQuery::Expired => {
				if !source.can_be_resubmitted() {
					return SubmitResult::KnownExpired;
				}
			},
			IndexQuery::Exists => {
				if !source.can_be_resubmitted() {
					return SubmitResult::Known;
				}
			},
			IndexQuery::Unknown => {},
		}

		let Some(account_id) = statement.account_id() else {
			log::debug!(
				target: LOG_TARGET,
				"Statement validation failed: Missing proof ({:?})",
				HexDisplay::from(&hash),
			);
			self.metrics.report(|metrics| metrics.validations_invalid.inc());
			return SubmitResult::Invalid(InvalidReason::NoProof);
		};

		match statement.verify_signature() {
			SignatureVerificationResult::Valid(_) => {},
			SignatureVerificationResult::Invalid => {
				log::debug!(
					target: LOG_TARGET,
					"Statement validation failed: BadProof, {:?}",
					HexDisplay::from(&hash),
				);
				self.metrics.report(|metrics| metrics.validations_invalid.inc());
				return SubmitResult::Invalid(InvalidReason::BadProof);
			},
			SignatureVerificationResult::NoSignature => {
				if let Some(Proof::OnChain { .. }) = statement.proof() {
					log::debug!(
						target: LOG_TARGET,
						"Statement with OnChain proof accepted: {:?}",
						HexDisplay::from(&hash),
					);
				} else {
					log::debug!(
						target: LOG_TARGET,
						"Statement validation failed: NoProof, {:?}",
						HexDisplay::from(&hash),
					);
					self.metrics.report(|metrics| metrics.validations_invalid.inc());
					return SubmitResult::Invalid(InvalidReason::NoProof);
				}
			},
		};

		// Check statement allowance for the account and evict statements if necessary to make room
		// for the new statement. We use the best block for allowance checks to allow for more
		// up-to-date allowances. This means that in some cases, a statement may be accepted but
		// then later evicted when we enforce limits based on the finalized block, if the best_hash
		// does not make it into the finalized chain, but this is an acceptable tradeoff for
		// better responsiveness to allowance changes.
		let validation = match (self.read_allowance_fn)(
			&account_id,
			match statement.proof() {
				Some(Proof::OnChain { block_hash, .. }) => AllowanceBlock::Block(*block_hash),
				_ => AllowanceBlock::Best,
			},
		) {
			Ok(Some(allowance)) => allowance,
			Ok(None) => {
				log::debug!(
					target: LOG_TARGET,
					"Account {} has no statement allowance set",
					HexDisplay::from(&account_id),
				);
				return SubmitResult::Rejected(RejectionReason::NoAllowance);
			},
			Err(e) => {
				log::debug!(
					target: LOG_TARGET,
					"Reading statement allowance for account {} failed",
					HexDisplay::from(&account_id),
				);
				return SubmitResult::InternalError(e);
			},
		};

		let current_time = self.timestamp();
		let mut commit = Vec::new();
		{
			let mut index = self.index.write();

			let evicted =
				match index.insert(hash, &statement, &account_id, &validation, current_time) {
					Ok(evicted) => evicted,
					Err(reason) => {
						self.metrics.report(|metrics| {
							metrics.rejections.with_label_values(&[reason.label()]).inc();
						});
						return SubmitResult::Rejected(reason);
					},
				};

			commit.push((col::STATEMENTS, hash.to_vec(), Some(statement.encode())));
			for hash in evicted {
				commit.push((col::STATEMENTS, hash.to_vec(), None));
				commit.push((col::EXPIRED, hash.to_vec(), Some((hash, current_time).encode())));
			}
			if let Err(e) = self.db.commit(commit) {
				log::debug!(
					target: LOG_TARGET,
					"Statement validation failed: database error {}, {:?}",
					e,
					statement
				);
				return SubmitResult::InternalError(Error::Db(e.to_string()));
			}
			self.subscription_manager.notify(statement);
		} // Release index lock
		self.metrics.report(|metrics| metrics.submitted_statements.inc());
		log::trace!(target: LOG_TARGET, "Statement submitted: {:?}", HexDisplay::from(&hash));
		SubmitResult::New
	}

	/// Remove a statement by hash.
	fn remove(&self, hash: &Hash) -> Result<()> {
		let current_time = self.timestamp();
		{
			let mut index = self.index.write();
			if index.make_expired(hash, current_time) {
				let commit = [
					(col::STATEMENTS, hash.to_vec(), None),
					(col::EXPIRED, hash.to_vec(), Some((hash, current_time).encode())),
				];
				if let Err(e) = self.db.commit(commit) {
					log::debug!(
						target: LOG_TARGET,
						"Error removing statement: database error {}, {:?}",
						e,
						HexDisplay::from(hash),
					);
					return Err(Error::Db(e.to_string()));
				}
			}
		}
		Ok(())
	}

	/// Remove all statements by an account.
	fn remove_by(&self, who: [u8; 32]) -> Result<()> {
		let mut index = self.index.write();
		let mut evicted = Vec::new();
		if let Some(account_rec) = index.accounts.get(&who) {
			evicted.extend(account_rec.by_priority.keys().map(|k| k.hash));
		}

		let current_time = self.timestamp();
		let mut commit = Vec::new();
		for hash in evicted {
			index.make_expired(&hash, current_time);
			commit.push((col::STATEMENTS, hash.to_vec(), None));
			commit.push((col::EXPIRED, hash.to_vec(), Some((hash, current_time).encode())));
		}
		self.db.commit(commit).map_err(|e| {
			log::debug!(
				target: LOG_TARGET,
				"Error removing statement: database error {}, remove by {:?}",
				e,
				HexDisplay::from(&who),
			);

			Error::Db(e.to_string())
		})
	}
}

impl StatementStoreSubscriptionApi for Store {
	fn subscribe_statement(
		&self,
		topic_filter: OptimizedTopicFilter,
	) -> Result<(Vec<Vec<u8>>, async_channel::Sender<StatementEvent>, SubscriptionStatementsStream)>
	{
		// Keep the index read lock until after we have subscribed to avoid missing statements.
		let mut existing_statements = Vec::new();
		let index = self.index.read();
		self.collect_statements_locked(
			None,
			&topic_filter,
			&index,
			&mut existing_statements,
			|statement| Some(statement.encode()),
		)?;
		let (subscription_sender, subscription_stream) =
			self.subscription_manager.subscribe(topic_filter);
		if existing_statements.is_empty() {
			subscription_sender
				.send_blocking(StatementEvent::NewStatements {
					statements: vec![],
					remaining: Some(0),
				})
				.ok();
		}
		Ok((existing_statements, subscription_sender, subscription_stream))
	}
}

#[cfg(test)]
mod tests {

	use crate::{col, Store};
	use sc_keystore::Keystore;
	use sp_core::{Decode, Encode, Pair};
	use sp_statement_store::{
		AccountId, Channel, DecryptionKey, InvalidReason, Proof, Statement, StatementSource,
		StatementStore, SubmitResult, Topic,
	};

	type Extrinsic = sp_runtime::OpaqueExtrinsic;
	type Hash = sp_core::H256;
	type Hashing = sp_runtime::traits::BlakeTwo256;
	type BlockNumber = u64;
	type Header = sp_runtime::generic::Header<BlockNumber, Hashing>;
	type Block = sp_runtime::generic::Block<Header, Extrinsic>;

	const CORRECT_BLOCK_HASH: [u8; 32] = [1u8; 32];

	#[derive(Clone)]
	pub(crate) struct TestClient;

	pub(crate) type TestBackend = sc_client_api::in_mem::Backend<Block>;

	impl sc_client_api::StorageProvider<Block, TestBackend> for TestClient {
		fn storage(
			&self,
			_hash: Hash,
			key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<sc_client_api::StorageData>> {
			use sp_statement_store::StatementAllowance;

			assert_eq!(&key.0[0..21], b":statement_allowance:" as &[u8],);

			// Extract account ID (32 bytes) from the storage key
			let account_bytes = &key.0[21..53];
			let account_id: u64 = u64::from_le_bytes(account_bytes[0..8].try_into().unwrap());
			let allowance = match account_id {
				// Account 0 has no allowance (used to test eviction of all statements)
				0 => return Ok(None),
				1 => StatementAllowance::new(1, 1000),
				2 => StatementAllowance::new(2, 1000),
				3 => StatementAllowance::new(3, 1000),
				4 => StatementAllowance::new(4, 1000),
				42 => StatementAllowance::new(42, (42 * crate::MAX_STATEMENT_SIZE) as u32),
				_ => StatementAllowance::new(100, 1000),
			};
			Ok(Some(sc_client_api::StorageData(allowance.encode())))
		}

		fn storage_hash(
			&self,
			_hash: Hash,
			_key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<Hash>> {
			unimplemented!()
		}

		fn storage_keys(
			&self,
			_hash: Hash,
			_prefix: Option<&sc_client_api::StorageKey>,
			_start_key: Option<&sc_client_api::StorageKey>,
		) -> sp_blockchain::Result<
			sc_client_api::backend::KeysIter<
				<TestBackend as sc_client_api::Backend<Block>>::State,
				Block,
			>,
		> {
			unimplemented!()
		}

		fn storage_pairs(
			&self,
			_hash: Hash,
			_prefix: Option<&sc_client_api::StorageKey>,
			_start_key: Option<&sc_client_api::StorageKey>,
		) -> sp_blockchain::Result<
			sc_client_api::backend::PairsIter<
				<TestBackend as sc_client_api::Backend<Block>>::State,
				Block,
			>,
		> {
			unimplemented!()
		}

		fn child_storage(
			&self,
			_hash: Hash,
			_child_info: &sc_client_api::ChildInfo,
			_key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<sc_client_api::StorageData>> {
			unimplemented!()
		}

		fn child_storage_keys(
			&self,
			_hash: Hash,
			_child_info: sc_client_api::ChildInfo,
			_prefix: Option<&sc_client_api::StorageKey>,
			_start_key: Option<&sc_client_api::StorageKey>,
		) -> sp_blockchain::Result<
			sc_client_api::backend::KeysIter<
				<TestBackend as sc_client_api::Backend<Block>>::State,
				Block,
			>,
		> {
			unimplemented!()
		}

		fn child_storage_hash(
			&self,
			_hash: Hash,
			_child_info: &sc_client_api::ChildInfo,
			_key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<Hash>> {
			unimplemented!()
		}

		fn closest_merkle_value(
			&self,
			_hash: Hash,
			_key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<sc_client_api::MerkleValue<Hash>>> {
			unimplemented!()
		}

		fn child_closest_merkle_value(
			&self,
			_hash: Hash,
			_child_info: &sc_client_api::ChildInfo,
			_key: &sc_client_api::StorageKey,
		) -> sp_blockchain::Result<Option<sc_client_api::MerkleValue<Hash>>> {
			unimplemented!()
		}
	}

	impl sp_blockchain::HeaderBackend<Block> for TestClient {
		fn header(&self, _hash: Hash) -> sp_blockchain::Result<Option<Header>> {
			unimplemented!()
		}
		fn info(&self) -> sp_blockchain::Info<Block> {
			sp_blockchain::Info {
				best_hash: CORRECT_BLOCK_HASH.into(),
				best_number: 0,
				genesis_hash: Default::default(),
				finalized_hash: CORRECT_BLOCK_HASH.into(),
				finalized_number: 1,
				finalized_state: None,
				number_leaves: 0,
				block_gap: None,
			}
		}
		fn status(&self, _hash: Hash) -> sp_blockchain::Result<sp_blockchain::BlockStatus> {
			unimplemented!()
		}
		fn number(&self, _hash: Hash) -> sp_blockchain::Result<Option<BlockNumber>> {
			unimplemented!()
		}
		fn hash(&self, _number: BlockNumber) -> sp_blockchain::Result<Option<Hash>> {
			unimplemented!()
		}
	}

	fn test_store() -> (Store, tempfile::TempDir) {
		sp_tracing::init_for_tests();
		let temp_dir = tempfile::Builder::new().tempdir().expect("Error creating test dir");

		let client = std::sync::Arc::new(TestClient);
		let mut path: std::path::PathBuf = temp_dir.path().into();
		path.push("db");
		let keystore = std::sync::Arc::new(sc_keystore::LocalKeystore::in_memory());
		let store = Store::new::<Block, TestClient, TestBackend>(
			&path,
			Default::default(),
			client,
			keystore,
			None,
			Box::new(sp_core::testing::TaskExecutor::new()),
		)
		.unwrap();
		(store, temp_dir) // return order is important. Store must be dropped before TempDir
	}

	pub fn signed_statement(data: u8) -> Statement {
		signed_statement_with_topics(data, &[], None)
	}

	fn signed_statement_with_topics(
		data: u8,
		topics: &[Topic],
		dec_key: Option<DecryptionKey>,
	) -> Statement {
		let mut statement = Statement::new();
		statement.set_plain_data(vec![data]);
		statement.set_expiry(u64::MAX);

		for i in 0..topics.len() {
			statement.set_topic(i, topics[i]);
		}
		if let Some(key) = dec_key {
			statement.set_decryption_key(key);
		}
		let kp = sp_core::ed25519::Pair::from_string("//Alice", None).unwrap();
		statement.sign_ed25519_private(&kp);
		statement
	}

	fn topic(data: u64) -> Topic {
		let mut bytes = [0u8; 32];
		bytes[0..8].copy_from_slice(&data.to_le_bytes());
		Topic::from(bytes)
	}

	fn dec_key(data: u64) -> DecryptionKey {
		let mut dec_key: DecryptionKey = Default::default();
		dec_key[0..8].copy_from_slice(&data.to_le_bytes());
		dec_key
	}

	fn account(id: u64) -> AccountId {
		let mut account: AccountId = Default::default();
		account[0..8].copy_from_slice(&id.to_le_bytes());
		account
	}

	fn channel(id: u64) -> Channel {
		let mut channel: Channel = Default::default();
		channel[0..8].copy_from_slice(&id.to_le_bytes());
		channel
	}

	fn statement(account_id: u64, priority: u32, c: Option<u64>, data_len: usize) -> Statement {
		let mut statement = Statement::new();
		let mut data = Vec::new();
		data.resize(data_len, 0);
		statement.set_plain_data(data);
		statement.set_expiry_from_parts(u32::MAX, priority);
		if let Some(c) = c {
			statement.set_channel(channel(c));
		}
		statement.set_proof(Proof::OnChain {
			block_hash: CORRECT_BLOCK_HASH,
			who: account(account_id),
			event_index: 0,
		});
		statement
	}

	#[test]
	fn submit_one() {
		let (store, _temp) = test_store();
		let statement0 = signed_statement(0);
		assert_eq!(store.submit(statement0, StatementSource::Network), SubmitResult::New);
		let unsigned = statement(1, 1, None, 0);
		assert_eq!(store.submit(unsigned, StatementSource::Network), SubmitResult::New);
	}

	#[test]
	fn save_and_load_statements() {
		let (store, temp) = test_store();
		let statement0 = signed_statement(0);
		let statement1 = signed_statement(1);
		let statement2 = signed_statement(2);
		assert_eq!(store.submit(statement0.clone(), StatementSource::Network), SubmitResult::New);
		assert_eq!(store.submit(statement1.clone(), StatementSource::Network), SubmitResult::New);
		assert_eq!(store.submit(statement2.clone(), StatementSource::Network), SubmitResult::New);
		assert_eq!(store.statements().unwrap().len(), 3);
		assert_eq!(store.broadcasts(&[]).unwrap().len(), 3);
		assert_eq!(store.statement(&statement1.hash()).unwrap(), Some(statement1.clone()));
		let keystore = store.keystore.clone();
		drop(store);

		let client = std::sync::Arc::new(TestClient);
		let mut path: std::path::PathBuf = temp.path().into();
		path.push("db");
		let store = Store::new::<Block, TestClient, TestBackend>(
			&path,
			Default::default(),
			client,
			keystore,
			None,
			Box::new(sp_core::testing::TaskExecutor::new()),
		)
		.unwrap();
		assert_eq!(store.statements().unwrap().len(), 3);
		assert_eq!(store.broadcasts(&[]).unwrap().len(), 3);
		assert_eq!(store.statement(&statement1.hash()).unwrap(), Some(statement1));
	}

	#[test]
	fn take_recent_statements_clears_index() {
		let (store, _temp) = test_store();
		let statement0 = signed_statement(0);
		let statement1 = signed_statement(1);
		let statement2 = signed_statement(2);
		let statement3 = signed_statement(3);

		let _ = store.submit(statement0.clone(), StatementSource::Local);
		let _ = store.submit(statement1.clone(), StatementSource::Local);
		let _ = store.submit(statement2.clone(), StatementSource::Local);

		let recent1 = store.take_recent_statements().unwrap();
		let (recent1_hashes, recent1_statements): (Vec<_>, Vec<_>) = recent1.into_iter().unzip();
		let expected1 = vec![statement0, statement1, statement2];
		assert!(expected1.iter().all(|s| recent1_hashes.contains(&s.hash())));
		assert!(expected1.iter().all(|s| recent1_statements.contains(s)));

		// Recent statements are cleared.
		let recent2 = store.take_recent_statements().unwrap();
		assert_eq!(recent2.len(), 0);

		store.submit(statement3.clone(), StatementSource::Network);

		let recent3 = store.take_recent_statements().unwrap();
		let (recent3_hashes, recent3_statements): (Vec<_>, Vec<_>) = recent3.into_iter().unzip();
		let expected3 = vec![statement3];
		assert!(expected3.iter().all(|s| recent3_hashes.contains(&s.hash())));
		assert!(expected3.iter().all(|s| recent3_statements.contains(s)));

		// Recent statements are cleared, but statements remain in the store.
		assert_eq!(store.statements().unwrap().len(), 4);
	}

	#[test]
	fn search_by_topic_and_key() {
		let (store, _temp) = test_store();
		let statement0 = signed_statement(0);
		let statement1 = signed_statement_with_topics(1, &[topic(0)], None);
		let statement2 = signed_statement_with_topics(2, &[topic(0), topic(1)], Some(dec_key(2)));
		let statement3 = signed_statement_with_topics(3, &[topic(0), topic(1), topic(2)], None);
		let statement4 =
			signed_statement_with_topics(4, &[topic(0), topic(42), topic(2), topic(3)], None);
		let statements = vec![statement0, statement1, statement2, statement3, statement4];
		for s in &statements {
			store.submit(s.clone(), StatementSource::Network);
		}

		let assert_topics = |topics: &[u64], key: Option<u64>, expected: &[u8]| {
			let key = key.map(dec_key);
			let topics: Vec<_> = topics.iter().map(|t| topic(*t)).collect();
			let mut got_vals: Vec<_> = if let Some(key) = key {
				store.posted(&topics, key).unwrap().into_iter().map(|d| d[0]).collect()
			} else {
				store.broadcasts(&topics).unwrap().into_iter().map(|d| d[0]).collect()
			};
			got_vals.sort();
			assert_eq!(expected.to_vec(), got_vals);
		};

		assert_topics(&[], None, &[0, 1, 3, 4]);
		assert_topics(&[], Some(2), &[2]);
		assert_topics(&[0], None, &[1, 3, 4]);
		assert_topics(&[1], None, &[3]);
		assert_topics(&[2], None, &[3, 4]);
		assert_topics(&[3], None, &[4]);
		assert_topics(&[42], None, &[4]);

		assert_topics(&[0, 1], None, &[3]);
		assert_topics(&[0, 1], Some(2), &[2]);
		assert_topics(&[0, 1, 99], Some(2), &[]);
		assert_topics(&[1, 2], None, &[3]);
		assert_topics(&[99], None, &[]);
		assert_topics(&[0, 99], None, &[]);
		assert_topics(&[0, 1, 2, 3, 42], None, &[]);
	}

	#[test]
	fn constraints() {
		let (store, _temp) = test_store();

		store.index.write().config.max_total_size = 3000;
		let source = StatementSource::Network;
		let ok = SubmitResult::New;

		// Account 1 (limit = 1 msg, 1000 bytes)

		// Oversized statement is not allowed. Limit for account 1 is 1 msg, 1000 bytes
		assert!(matches!(
			store.submit(statement(1, 1, Some(1), 2000), source),
			SubmitResult::Rejected(_)
		));
		assert_eq!(store.submit(statement(1, 1, Some(1), 500), source), ok);
		// Would not replace channel message with same priority
		assert!(matches!(
			store.submit(statement(1, 1, Some(1), 200), source),
			SubmitResult::Rejected(_)
		));
		assert_eq!(store.submit(statement(1, 2, Some(1), 600), source), ok);
		// Submit another message to another channel with lower priority. Should not be allowed
		// because msg count limit is 1
		assert!(matches!(
			store.submit(statement(1, 1, Some(2), 100), source),
			SubmitResult::Rejected(_)
		));
		assert_eq!(store.index.read().expired.len(), 1);

		// Account 2 (limit = 2 msg, 1000 bytes)

		assert_eq!(store.submit(statement(2, 1, None, 500), source), ok);
		assert_eq!(store.submit(statement(2, 2, None, 100), source), ok);
		// Should evict priority 1
		assert_eq!(store.submit(statement(2, 3, None, 500), source), ok);
		assert_eq!(store.index.read().expired.len(), 2);
		// Should evict all
		assert_eq!(store.submit(statement(2, 4, None, 1000), source), ok);
		assert_eq!(store.index.read().expired.len(), 4);

		// Account 3 (limit = 3 msg, 1000 bytes)

		assert_eq!(store.submit(statement(3, 2, Some(1), 300), source), ok);
		assert_eq!(store.submit(statement(3, 3, Some(2), 300), source), ok);
		assert_eq!(store.submit(statement(3, 4, Some(3), 300), source), ok);
		// Should evict 2 and 3
		assert_eq!(store.submit(statement(3, 5, None, 500), source), ok);
		assert_eq!(store.index.read().expired.len(), 6);

		assert_eq!(store.index.read().total_size, 2400);
		assert_eq!(store.index.read().entries.len(), 4);

		// Should be over the global size limit
		assert!(matches!(
			store.submit(statement(1, 1, None, 700), source),
			SubmitResult::Rejected(_)
		));
		// Should be over the global count limit
		store.index.write().config.max_total_statements = 4;
		assert!(matches!(
			store.submit(statement(1, 1, None, 100), source),
			SubmitResult::Rejected(_)
		));

		let mut expected_statements = vec![
			statement(1, 2, Some(1), 600).hash(),
			statement(2, 4, None, 1000).hash(),
			statement(3, 4, Some(3), 300).hash(),
			statement(3, 5, None, 500).hash(),
		];
		expected_statements.sort();
		let mut statements: Vec<_> =
			store.statements().unwrap().into_iter().map(|(hash, _)| hash).collect();
		statements.sort();
		assert_eq!(expected_statements, statements);
	}

	#[test]
	fn max_statement_size_for_gossiping() {
		let (store, _temp) = test_store();
		store.index.write().config.max_total_size = 42 * crate::MAX_STATEMENT_SIZE;

		assert_eq!(
			store.submit(
				statement(42, 1, Some(1), crate::MAX_STATEMENT_SIZE - 500),
				StatementSource::Local
			),
			SubmitResult::New
		);

		assert!(matches!(
			store.submit(
				statement(42, 2, Some(1), 2 * crate::MAX_STATEMENT_SIZE),
				StatementSource::Local
			),
			SubmitResult::Invalid(_)
		));
	}

	#[test]
	fn expired_statements_are_purged() {
		use super::DEFAULT_PURGE_AFTER_SEC;
		let (mut store, temp) = test_store();
		let mut statement = statement(1, 1, Some(3), 100);
		store.set_time(0);
		statement.set_topic(0, topic(4));
		store.submit(statement.clone(), StatementSource::Network);
		assert_eq!(store.index.read().entries.len(), 1);
		store.remove(&statement.hash()).unwrap();
		assert_eq!(store.index.read().entries.len(), 0);
		assert_eq!(store.index.read().accounts.len(), 0);
		store.set_time(DEFAULT_PURGE_AFTER_SEC + 1);
		store.maintain();
		assert_eq!(store.index.read().expired.len(), 0);
		let keystore = store.keystore.clone();
		drop(store);

		let client = std::sync::Arc::new(TestClient);
		let mut path: std::path::PathBuf = temp.path().into();
		path.push("db");
		let store = Store::new::<Block, TestClient, TestBackend>(
			&path,
			Default::default(),
			client,
			keystore,
			None,
			Box::new(sp_core::testing::TaskExecutor::new()),
		)
		.unwrap();
		assert_eq!(store.statements().unwrap().len(), 0);
		assert_eq!(store.index.read().expired.len(), 0);
	}

	#[test]
	fn posted_clear_decrypts() {
		let (store, _temp) = test_store();
		let public = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();
		let statement1 = statement(1, 1, None, 100);
		let mut statement2 = statement(1, 2, None, 0);
		let plain = b"The most valuable secret".to_vec();
		statement2.encrypt(&plain, &public).unwrap();
		store.submit(statement1, StatementSource::Network);
		store.submit(statement2, StatementSource::Network);
		let posted_clear = store.posted_clear(&[], public.into()).unwrap();
		assert_eq!(posted_clear, vec![plain]);
	}

	#[test]
	fn broadcasts_stmt_returns_encoded_statements() {
		let (store, _tmp) = test_store();

		// no key, no topic
		let s0 = signed_statement_with_topics(0, &[], None);
		// same, but with a topic = 42
		let s1 = signed_statement_with_topics(1, &[topic(42)], None);
		// has a decryption key -> must NOT be returned by broadcasts_stmt
		let s2 = signed_statement_with_topics(2, &[topic(42)], Some(dec_key(99)));

		for s in [&s0, &s1, &s2] {
			store.submit(s.clone(), StatementSource::Network);
		}

		// no topic filter
		let mut hashes: Vec<_> = store
			.broadcasts_stmt(&[])
			.unwrap()
			.into_iter()
			.map(|bytes| Statement::decode(&mut &bytes[..]).unwrap().hash())
			.collect();
		hashes.sort();
		let expected_hashes = {
			let mut e = vec![s0.hash(), s1.hash()];
			e.sort();
			e
		};
		assert_eq!(hashes, expected_hashes);

		// filter on topic 42
		let got = store.broadcasts_stmt(&[topic(42)]).unwrap();
		assert_eq!(got.len(), 1);
		let st = Statement::decode(&mut &got[0][..]).unwrap();
		assert_eq!(st.hash(), s1.hash());
	}

	#[test]
	fn posted_stmt_returns_encoded_statements_for_dest() {
		let (store, _tmp) = test_store();

		let public1 = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();
		let dest: [u8; 32] = public1.into();

		let public2 = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();

		// A statement that does have dec_key = dest
		let mut s_with_key = statement(1, 1, None, 0);
		let plain1 = b"The most valuable secret".to_vec();
		s_with_key.encrypt(&plain1, &public1).unwrap();

		// A statement with a different dec_key
		let mut s_other_key = statement(2, 2, None, 0);
		let plain2 = b"The second most valuable secret".to_vec();
		s_other_key.encrypt(&plain2, &public2).unwrap();

		// Submit them all
		for s in [&s_with_key, &s_other_key] {
			store.submit(s.clone(), StatementSource::Network);
		}

		// posted_stmt should only return the one with dec_key = dest
		let retrieved = store.posted_stmt(&[], dest).unwrap();
		assert_eq!(retrieved.len(), 1, "Only one statement has dec_key=dest");

		// Re-decode that returned statement to confirm it is correct
		let returned_stmt = Statement::decode(&mut &retrieved[0][..]).unwrap();
		assert_eq!(
			returned_stmt.hash(),
			s_with_key.hash(),
			"Returned statement must match s_with_key"
		);
	}

	#[test]
	fn posted_clear_stmt_returns_statement_followed_by_plain_data() {
		let (store, _tmp) = test_store();

		let public1 = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();
		let dest: [u8; 32] = public1.into();

		let public2 = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();

		// A statement that does have dec_key = dest
		let mut s_with_key = statement(1, 1, None, 0);
		let plain1 = b"The most valuable secret".to_vec();
		s_with_key.encrypt(&plain1, &public1).unwrap();

		// A statement with a different dec_key
		let mut s_other_key = statement(2, 2, None, 0);
		let plain2 = b"The second most valuable secret".to_vec();
		s_other_key.encrypt(&plain2, &public2).unwrap();

		// Submit them all
		for s in [&s_with_key, &s_other_key] {
			store.submit(s.clone(), StatementSource::Network);
		}

		// posted_stmt should only return the one with dec_key = dest
		let retrieved = store.posted_clear_stmt(&[], dest).unwrap();
		assert_eq!(retrieved.len(), 1, "Only one statement has dec_key=dest");

		// We expect: [ encoded Statement ] + [ the decrypted bytes ]
		let encoded_stmt = s_with_key.encode();
		let stmt_len = encoded_stmt.len();

		// 1) statement is first
		assert_eq!(&retrieved[0][..stmt_len], &encoded_stmt[..]);

		// 2) followed by the decrypted payload
		let trailing = &retrieved[0][stmt_len..];
		assert_eq!(trailing, &plain1[..]);
	}

	#[test]
	fn posted_clear_returns_plain_data_for_dest_and_topics() {
		let (store, _tmp) = test_store();

		// prepare two key-pairs
		let public_dest = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();
		let dest: [u8; 32] = public_dest.into();

		let public_other = store
			.keystore
			.ed25519_generate_new(sp_core::crypto::key_types::STATEMENT, None)
			.unwrap();

		// statement that SHOULD be returned (matches dest & topic 42)
		let mut s_good = statement(1, 1, None, 0);
		let plaintext_good = b"The most valuable secret".to_vec();
		s_good.encrypt(&plaintext_good, &public_dest).unwrap();
		s_good.set_topic(0, topic(42));

		// statement that should NOT be returned (same dest but different topic)
		let mut s_wrong_topic = statement(2, 2, None, 0);
		s_wrong_topic.encrypt(b"Wrong topic", &public_dest).unwrap();
		s_wrong_topic.set_topic(0, topic(99));

		// statement that should NOT be returned (different dest)
		let mut s_other_dest = statement(3, 3, None, 0);
		s_other_dest.encrypt(b"Other dest", &public_other).unwrap();
		s_other_dest.set_topic(0, topic(42));

		// submit all
		for s in [&s_good, &s_wrong_topic, &s_other_dest] {
			store.submit(s.clone(), StatementSource::Network);
		}

		// call posted_clear with the topic filter and dest
		let retrieved = store.posted_clear(&[topic(42)], dest).unwrap();

		// exactly one element, equal to the expected plaintext
		assert_eq!(retrieved, vec![plaintext_good]);
	}

	#[test]
	fn already_expired_statement_is_rejected() {
		let (mut store, _temp) = test_store();

		// Set current time to 1000 seconds
		store.set_time(1000);

		// Create a statement that has already expired (expiration at 500 seconds, before current
		// time)
		let mut expired_statement = statement(1, 1, None, 100);
		// set_expiry_from_parts: first arg is expiration timestamp in seconds, second is priority
		expired_statement.set_expiry_from_parts(500, 1);

		// Submit should fail with AlreadyExpired
		assert_eq!(
			store.submit(expired_statement, StatementSource::Network),
			SubmitResult::Invalid(InvalidReason::AlreadyExpired)
		);

		// Verify the statement was not added
		assert_eq!(store.statements().unwrap().len(), 0);

		// Now create a statement that is not expired (expiration at 2000 seconds, after current
		// time)
		let mut valid_statement = statement(1, 1, None, 100);
		valid_statement.set_expiry_from_parts(2000, 1);

		// Submit should succeed
		assert_eq!(store.submit(valid_statement, StatementSource::Network), SubmitResult::New);
		assert_eq!(store.statements().unwrap().len(), 1);
	}

	#[test]
	fn remove_by_covers_various_situations() {
		use sp_statement_store::{StatementSource, StatementStore, SubmitResult};

		// Use a fresh store and fixed time so we can control purging.
		let (mut store, _temp) = test_store();
		store.set_time(0);

		// Reuse helpers from this module.
		let t42 = topic(42);
		let k7 = dec_key(7);

		// Account A = 4 (has per-account limits (4, 1000) in the mock runtime)
		// - Mix of topic, decryption-key and channel to exercise every index.
		let mut s_a1 = statement(4, 10, Some(100), 100);
		s_a1.set_topic(0, t42);
		let h_a1 = s_a1.hash();

		let mut s_a2 = statement(4, 20, Some(200), 150);
		s_a2.set_decryption_key(k7);
		let h_a2 = s_a2.hash();

		let s_a3 = statement(4, 30, None, 50);
		let h_a3 = s_a3.hash();

		// Account B = 3 (control group that must remain untouched).
		let s_b1 = statement(3, 10, None, 100);
		let h_b1 = s_b1.hash();

		let mut s_b2 = statement(3, 15, Some(300), 100);
		s_b2.set_topic(0, t42);
		s_b2.set_decryption_key(k7);
		let h_b2 = s_b2.hash();

		// Submit all statements.
		for s in [&s_a1, &s_a2, &s_a3, &s_b1, &s_b2] {
			assert_eq!(store.submit(s.clone(), StatementSource::Network), SubmitResult::New);
		}

		// --- Pre-conditions: everything is indexed as expected.
		{
			let idx = store.index.read();
			assert_eq!(idx.entries.len(), 5, "all 5 should be present");
			assert!(idx.accounts.contains_key(&account(4)));
			assert!(idx.accounts.contains_key(&account(3)));
			assert_eq!(idx.total_size, 100 + 150 + 50 + 100 + 100);

			// Topic and key sets contain both A & B entries.
			let set_t = idx.by_topic.get(&t42).expect("topic set exists");
			assert!(set_t.contains(&h_a1) && set_t.contains(&h_b2));

			let set_k = idx.by_dec_key.get(&Some(k7)).expect("key set exists");
			assert!(set_k.contains(&h_a2) && set_k.contains(&h_b2));
		}

		// --- Action: remove all statements by Account A.
		store.remove_by(account(4)).expect("remove_by should succeed");

		// --- Post-conditions: A's statements are gone and marked expired; B's remain.
		{
			// A's statements removed from DB view.
			for h in [h_a1, h_a2, h_a3] {
				assert!(store.statement(&h).unwrap().is_none(), "A's statement should be removed");
			}

			// B's statements still present.
			for h in [h_b1, h_b2] {
				assert!(store.statement(&h).unwrap().is_some(), "B's statement should remain");
			}

			let idx = store.index.read();

			// Account map updated.
			assert!(!idx.accounts.contains_key(&account(4)), "Account A must be gone");
			assert!(idx.accounts.contains_key(&account(3)), "Account B must remain");

			// Removed statements are marked expired.
			assert!(idx.expired.contains_key(&h_a1));
			assert!(idx.expired.contains_key(&h_a2));
			assert!(idx.expired.contains_key(&h_a3));
			assert_eq!(idx.expired.len(), 3);

			// Entry count & total_size reflect only B's data.
			assert_eq!(idx.entries.len(), 2);
			assert_eq!(idx.total_size, 100 + 100);

			// Topic index: only B2 remains for topic 42.
			let set_t = idx.by_topic.get(&t42).expect("topic set exists");
			assert!(set_t.contains(&h_b2));
			assert!(!set_t.contains(&h_a1));

			// Decryption-key index: only B2 remains for key 7.
			let set_k = idx.by_dec_key.get(&Some(k7)).expect("key set exists");
			assert!(set_k.contains(&h_b2));
			assert!(!set_k.contains(&h_a2));
		}

		// --- Idempotency: removing again is a no-op and should not error.
		store.remove_by(account(4)).expect("second remove_by should be a no-op");

		// --- Purge: advance time beyond TTL and run maintenance; expired entries disappear.
		let purge_after = store.index.read().config.purge_after_sec;
		store.set_time(purge_after + 1);
		store.maintain();
		assert_eq!(store.index.read().expired.len(), 0, "expired entries should be purged");

		// --- Reuse: Account A can submit again after purge.
		let s_new = statement(4, 40, None, 10);
		assert_eq!(store.submit(s_new, StatementSource::Network), SubmitResult::New);
	}

	#[test]
	fn check_expiration_repopulates_account_list_when_empty() {
		let (mut store, _temp) = test_store();
		store.set_time(1000);

		// Create statements for multiple accounts
		// Note: The statement() helper uses set_expiry_from_parts(u32::MAX, priority)
		// which creates a very large expiry value that won't trigger expiration
		let s1 = statement(1, 1, None, 100);
		let s2 = statement(2, 1, None, 100);
		let s3 = statement(3, 1, None, 100);

		for s in [&s1, &s2, &s3] {
			store.submit(s.clone(), StatementSource::Network);
		}

		// Initially, accounts_to_check_for_expiry_stmts is empty
		assert!(store.index.read().accounts_to_check_for_expiry_stmts.is_empty());

		// First call to check_expiration should populate the list
		store.enforce_limits();

		// Now accounts_to_check_for_expiry_stmts should contain all 3 accounts
		let accounts = store.index.read().accounts_to_check_for_expiry_stmts.clone();
		assert_eq!(accounts.len(), 3, "Should have 3 accounts to check");
		assert!(accounts.contains(&account(1)));
		assert!(accounts.contains(&account(2)));
		assert!(accounts.contains(&account(3)));

		// No statements should have been expired since they're all valid
		assert_eq!(store.index.read().expired.len(), 0);
		assert_eq!(store.index.read().entries.len(), 3);
	}

	#[test]
	fn check_expiration_expires_statements_past_current_time() {
		let (mut store, _temp) = test_store();

		// The check_expiration function compares Expiry(current_time << 32) against
		// Expiry(expiry) where expiry is the full 64-bit value with timestamp in high 32 bits.
		// Statements with expiration timestamp < current_time will be expired.

		store.set_time(100);

		// Create a statement that will expire at timestamp 500
		let mut expired_stmt = statement(1, 1, None, 100);
		expired_stmt.set_expiry_from_parts(500, 1);
		let expired_hash = expired_stmt.hash();
		store.submit(expired_stmt, StatementSource::Network);

		// Create a statement that won't expire (far future expiry)
		let valid_stmt = statement(2, 1, None, 100); // Uses u32::MAX as timestamp
		let valid_hash = valid_stmt.hash();
		store.submit(valid_stmt, StatementSource::Network);

		// Verify both statements are in the store
		assert_eq!(store.index.read().entries.len(), 2);

		// First check_expiration populates the account list
		store.enforce_limits();
		assert!(!store.index.read().accounts_to_check_for_expiry_stmts.is_empty());

		// Advance time past the expiry of the first statement
		store.set_time(1000);

		// Second check_expiration should find and expire the statement
		store.enforce_limits();

		// Check the expired statement is now in the expired list
		let index = store.index.read();
		assert!(index.expired.contains_key(&expired_hash), "Expired statement should be marked");
		assert!(
			!index.entries.contains_key(&expired_hash),
			"Expired statement should be removed from entries"
		);

		// The valid statement should still be in entries
		assert!(
			index.entries.contains_key(&valid_hash),
			"Valid statement should still be in entries"
		);
		assert!(!index.expired.contains_key(&valid_hash), "Valid statement should not be expired");
	}

	#[test]
	fn check_expiration_removes_checked_accounts_from_list_when_expiring() {
		let (mut store, _temp) = test_store();
		store.set_time(100);

		// Create statements with expiry at timestamp 200
		let mut stmt1 = statement(1, 1, None, 100);
		stmt1.set_expiry_from_parts(200, 1);
		store.submit(stmt1, StatementSource::Network);

		let mut stmt2 = statement(2, 1, None, 100);
		stmt2.set_expiry_from_parts(200, 1);
		store.submit(stmt2, StatementSource::Network);

		let mut stmt3 = statement(3, 1, None, 100);
		stmt3.set_expiry_from_parts(200, 1);
		store.submit(stmt3, StatementSource::Network);

		// First call populates the list
		store.enforce_limits();
		assert_eq!(
			store.index.read().accounts_to_check_for_expiry_stmts.len(),
			3,
			"Should have 3 accounts to check"
		);

		// Advance time past expiry
		store.set_time(300);

		// Second call should check accounts, expire statements, and remove checked accounts
		store.enforce_limits();

		// The list should now be empty (all accounts checked and removed)
		assert!(
			store.index.read().accounts_to_check_for_expiry_stmts.is_empty(),
			"All accounts should have been checked and removed after expiration"
		);

		// All statements should have been expired
		assert_eq!(store.index.read().expired.len(), 3);
		assert_eq!(store.index.read().entries.len(), 0);
	}

	#[test]
	fn check_expiration_truncates_list_even_when_nothing_expires() {
		let (mut store, _temp) = test_store();
		store.set_time(1000);

		// Create statements for multiple accounts with far future expiry (using statement helper)
		// The statement() helper uses set_expiry_from_parts(u32::MAX, priority) which creates
		// a very large expiry value that won't trigger expiration
		for acc_id in 1..=5u64 {
			let stmt = statement(acc_id, 1, None, 100);
			store.submit(stmt, StatementSource::Network);
		}

		// First call populates the list
		store.enforce_limits();
		assert_eq!(store.index.read().accounts_to_check_for_expiry_stmts.len(), 5);

		// Second call checks accounts and truncates the list (even though nothing expires)
		store.enforce_limits();

		// The list should now be empty - accounts are removed after being checked
		assert!(
			store.index.read().accounts_to_check_for_expiry_stmts.is_empty(),
			"List should be empty after all accounts have been checked"
		);

		// No statements should have been expired
		assert_eq!(store.index.read().expired.len(), 0);
		assert_eq!(store.index.read().entries.len(), 5);
	}

	#[test]
	fn check_expiration_handles_multiple_statements_per_account() {
		let (mut store, _temp) = test_store();
		store.set_time(100);

		// Create multiple statements for the same account with different expiry timestamps
		// Account 42 has limit of 42 statements
		let mut stmt1 = statement(42, 1, Some(1), 100);
		stmt1.set_expiry_from_parts(200, 1); // Expires at timestamp 200
		let hash1 = stmt1.hash();
		store.submit(stmt1, StatementSource::Network);

		let mut stmt2 = statement(42, 2, Some(2), 100);
		stmt2.set_expiry_from_parts(300, 2); // Expires at timestamp 300
		let hash2 = stmt2.hash();
		store.submit(stmt2, StatementSource::Network);

		let mut stmt3 = statement(42, 3, Some(3), 100);
		stmt3.set_expiry_from_parts(500, 3); // Expires at timestamp 500
		let hash3 = stmt3.hash();
		store.submit(stmt3, StatementSource::Network);

		// Verify all statements are in the store
		assert_eq!(store.index.read().entries.len(), 3);

		// First check_expiration populates the account list
		store.enforce_limits();

		// Advance time to 250 (stmt1 should expire since 250 > 200)
		store.set_time(250);
		store.enforce_limits();

		{
			let index = store.index.read();
			assert!(index.expired.contains_key(&hash1), "stmt1 should be expired");
			assert!(!index.expired.contains_key(&hash2), "stmt2 should not be expired yet");
			assert!(!index.expired.contains_key(&hash3), "stmt3 should not be expired yet");
			assert_eq!(index.entries.len(), 2);
		}

		// Repopulate the account list for next check
		store.enforce_limits();

		// Advance time to 400 (stmt2 should also expire since 400 > 300)
		store.set_time(400);
		store.enforce_limits();

		{
			let index = store.index.read();
			assert!(index.expired.contains_key(&hash1));
			assert!(index.expired.contains_key(&hash2), "stmt2 should be expired");
			assert!(!index.expired.contains_key(&hash3), "stmt3 should not be expired yet");
			assert_eq!(index.entries.len(), 1);
		}

		// Repopulate and check again at time 600 (stmt3 should expire since 600 > 500)
		store.enforce_limits();
		store.set_time(600);
		store.enforce_limits();

		{
			let index = store.index.read();
			assert!(index.expired.contains_key(&hash1));
			assert!(index.expired.contains_key(&hash2));
			assert!(index.expired.contains_key(&hash3), "stmt3 should be expired");
			assert_eq!(index.entries.len(), 0);
		}
	}

	#[test]
	fn check_expiration_does_nothing_when_no_expired_statements() {
		let (mut store, _temp) = test_store();
		store.set_time(1000);

		// Create statement with expiry far in the future
		// The statement() helper uses set_expiry_from_parts(u32::MAX, priority)
		let stmt = statement(1, 1, None, 100);
		let hash = stmt.hash();
		store.submit(stmt, StatementSource::Network);

		// Populate the account list
		store.enforce_limits();

		// Check expiration - nothing should happen
		store.enforce_limits();

		// Statement should still be there
		let index = store.index.read();
		assert!(index.entries.contains_key(&hash));
		assert!(!index.expired.contains_key(&hash));
		assert_eq!(index.entries.len(), 1);
		assert_eq!(index.expired.len(), 0);
	}

	#[test]
	fn check_expiration_correctly_updates_account_data() {
		let (mut store, _temp) = test_store();
		store.set_time(100);

		// Create a statement with expiry at timestamp 200
		let mut stmt = statement(1, 1, Some(1), 100);
		stmt.set_expiry_from_parts(200, 1);
		let hash = stmt.hash();
		store.submit(stmt, StatementSource::Network);

		// Verify account exists before expiration
		{
			let index = store.index.read();
			assert!(index.accounts.contains_key(&account(1)));
			assert_eq!(index.total_size, 100);
		}

		// Populate and then expire
		store.enforce_limits();
		store.set_time(300);
		store.enforce_limits();

		// Verify account is removed after its only statement expires
		{
			let index = store.index.read();
			assert!(
				!index.accounts.contains_key(&account(1)),
				"Account should be removed when all its statements expire"
			);
			assert_eq!(index.total_size, 0, "Total size should be zero");
			assert!(index.expired.contains_key(&hash));
		}
	}

	#[test]
	fn check_expiration_clears_topic_and_key_indexes() {
		let (mut store, _temp) = test_store();
		store.set_time(100);

		// Create a statement with topic and decryption key
		let mut stmt = statement(1, 1, Some(1), 100);
		stmt.set_expiry_from_parts(200, 1);
		stmt.set_topic(0, topic(42));
		stmt.set_decryption_key(dec_key(7));
		let hash = stmt.hash();
		store.submit(stmt, StatementSource::Network);

		// Verify indexes are populated
		{
			let index = store.index.read();
			assert!(index.by_topic.get(&topic(42)).map_or(false, |s| s.contains(&hash)));
			assert!(index.by_dec_key.get(&Some(dec_key(7))).map_or(false, |s| s.contains(&hash)));
		}

		// Populate and then expire
		store.enforce_limits();
		store.set_time(300);
		store.enforce_limits();

		// Verify indexes are cleared
		{
			let index = store.index.read();
			// Topic set should be empty or removed
			assert!(
				index.by_topic.get(&topic(42)).map_or(true, |s| s.is_empty()),
				"Topic index should be cleared"
			);
			// Key set should be empty or removed
			assert!(
				index.by_dec_key.get(&Some(dec_key(7))).map_or(true, |s| s.is_empty()),
				"Decryption key index should be cleared"
			);
			assert!(index.expired.contains_key(&hash));
		}
	}

	#[test]
	fn check_expiration_handles_empty_store() {
		let (mut store, _temp) = test_store();
		store.set_time(1000);

		// With no statements, check_expiration should not panic
		store.enforce_limits();

		// Second call should also work (empty repopulation)
		store.enforce_limits();

		assert!(store.index.read().accounts_to_check_for_expiry_stmts.is_empty());
		assert_eq!(store.index.read().entries.len(), 0);
		assert_eq!(store.index.read().expired.len(), 0);
	}

	#[test]
	fn check_expiration_expires_properly_formatted_statements() {
		// With the fix (Expiry(current_time << 32)), check_expiration properly
		// compares timestamps and can expire statements submitted through normal flow.

		let (mut store, _temp) = test_store();
		store.set_time(1000);

		// Create a statement with expiration timestamp just 1 second in the future
		let mut stmt = statement(1, 1, None, 100);
		stmt.set_expiry_from_parts(1001, 1); // Expires at timestamp 1001
		let hash = stmt.hash();
		store.submit(stmt, StatementSource::Network);

		assert_eq!(store.index.read().entries.len(), 1);

		// Populate the accounts list
		store.enforce_limits();

		// Advance time past the expiration timestamp
		store.set_time(2000);
		store.enforce_limits();

		// Statement SHOULD be expired because check_expiration now compares
		// Expiry(2000 << 32) against Expiry(1001 << 32 | 1), and
		// (2000 << 32) > (1001 << 32 | 1)
		let index = store.index.read();
		assert!(
			!index.entries.contains_key(&hash),
			"Statement should be removed from entries after expiration"
		);
		assert!(index.expired.contains_key(&hash), "Statement should be in expired list");
	}

	#[test]
	fn check_expiration_updates_database_columns() {
		// This test verifies that check_expiration properly updates the database.
		let (mut store, _temp) = test_store();
		store.set_time(100);

		// Create a statement with expiry at timestamp 200
		let mut stmt = statement(1, 1, None, 100);
		stmt.set_expiry_from_parts(200, 1);
		let hash = stmt.hash();
		store.submit(stmt.clone(), StatementSource::Network);

		// Verify statement is in the database
		let db_entry = store.db.get(col::STATEMENTS, &hash).unwrap();
		assert!(db_entry.is_some(), "Statement should be in col::STATEMENTS after submit");

		// Populate the accounts list
		store.enforce_limits();

		// Advance time past expiry and run check_expiration
		store.set_time(300);
		store.enforce_limits();

		// Verify in-memory state is updated correctly
		{
			let index = store.index.read();
			assert!(
				!index.entries.contains_key(&hash),
				"Statement should be removed from in-memory entries"
			);
			assert!(
				index.expired.contains_key(&hash),
				"Statement should be in in-memory expired map"
			);
		}

		let db_entry = store.db.get(col::STATEMENTS, &hash).unwrap();
		assert!(
			db_entry.is_none(),
			"Statement should be removed from col::STATEMENTS after expiration"
		);

		let expired_entry = store.db.get(col::EXPIRED, &hash).unwrap();
		assert!(expired_entry.is_some(), "Expiration info should be written to col::EXPIRED");
	}

	#[test]
	fn enforce_allowances_evicts_excess_statements() {
		// This test verifies that check_expiration correctly evicts statements
		// when statements exceed the current allowance. We directly insert into
		// the index (bypassing submit's validation) to simulate statements that
		// existed before allowances were reduced.
		let (mut store, _temp) = test_store();
		store.set_time(0);

		// Account 4 has allowance (4 statements, 1000 bytes) from TestClient
		let s1 = statement(4, 10, None, 100); // lowest priority - will be evicted
		let s2 = statement(4, 20, None, 100);
		let s3 = statement(4, 30, None, 100);
		let s4 = statement(4, 40, None, 100);
		let s5 = statement(4, 50, None, 100); // highest priority

		let h1 = s1.hash();
		let h5 = s5.hash();

		// Directly insert into index, bypassing `submit`'s allowance check
		{
			let mut index = store.index.write();
			for s in [&s1, &s2, &s3, &s4, &s5] {
				index.insert_new(s.hash(), account(4), s, false);
			}
		}

		// Verify initial state - all 5 should be present
		assert_eq!(store.index.read().entries.len(), 5);
		assert_eq!(store.index.read().total_size, 500);

		// Run check_expiration which handles both expiration and allowance enforcement
		// First call populates the accounts list, second call processes them
		// Since account 4 has max_count=4, one statement should be evicted
		store.enforce_limits();
		store.enforce_limits();

		// Should evict the lowest priority statement (s1)
		let index = store.index.read();
		assert_eq!(index.entries.len(), 4, "Should have 4 statements after eviction");
		assert!(!index.entries.contains_key(&h1), "Lowest priority should be evicted");
		assert!(index.entries.contains_key(&h5), "Highest priority should remain");
		assert_eq!(index.total_size, 400);

		// Evicted statement should be marked as expired
		assert!(index.expired.contains_key(&h1));
	}

	#[test]
	fn enforce_allowances_evicts_all_when_no_allowance_found() {
		let (mut store, _temp) = test_store();
		store.set_time(0);

		// Account 0 has NO allowance in TestClient
		let s1 = statement(0, 10, None, 100);
		let s2 = statement(0, 20, None, 150);

		let h1 = s1.hash();
		let h2 = s2.hash();

		// Directly insert statements for account with no allowance
		{
			let mut index = store.index.write();
			index.insert_new(h1, account(0), &s1, false);
			index.insert_new(h2, account(0), &s2, false);
		}

		assert_eq!(store.index.read().entries.len(), 2);

		// Run check_expiration - should evict ALL statements since no allowance exists
		// First call populates the accounts list, second call processes them
		store.enforce_limits();
		store.enforce_limits();

		let index = store.index.read();
		assert_eq!(index.entries.len(), 0, "All statements should be evicted");
		assert!(!index.accounts.contains_key(&account(0)), "Account should be removed");
		assert!(index.expired.contains_key(&h1));
		assert!(index.expired.contains_key(&h2));
	}

	#[test]
	fn enforce_allowances_based_on_size() {
		// This test verifies that check_expiration evicts based on size limits.
		let (mut store, _temp) = test_store();
		store.set_time(0);

		// Account 2 has allowance (2, 1000) from TestClient
		// Insert 2 statements that together exceed 1000 bytes
		let s1 = statement(2, 10, None, 600); // lowest priority
		let s2 = statement(2, 20, None, 600); // higher priority

		let h1 = s1.hash();
		let h2 = s2.hash();

		// Directly insert both statements (total 1200 bytes > 1000 limit)
		{
			let mut index = store.index.write();
			index.insert_new(h1, account(2), &s1, false);
			index.insert_new(h2, account(2), &s2, false);
		}

		assert_eq!(store.index.read().total_size, 1200);

		// Run check_expiration - should evict s1 to get under 1000 bytes
		// First call populates the accounts list, second call processes them
		store.enforce_limits();
		store.enforce_limits();

		let index = store.index.read();
		assert_eq!(index.entries.len(), 1);
		assert!(index.entries.contains_key(&h2), "Higher priority should remain");
		assert!(!index.entries.contains_key(&h1), "Lower priority should be evicted");
		assert_eq!(index.total_size, 600);
	}
}