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// Copyright 2015-2018 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

//! Disk-backed `HashDB` implementation.

use std::io;
use std::sync::Arc;

use bytes::Bytes;
use ethereum_types::H256;
use hashdb::*;
use keccak_hasher::KeccakHasher;
use kvdb::{self, DBTransaction};

/// A `HashDB` which can manage a short-term journal potentially containing many forks of mutually
/// exclusive actions.
pub trait JournalDB: HashDB<KeccakHasher> {
	/// Return a copy of ourself, in a box.
	fn boxed_clone(&self) -> Box<JournalDB>;

	/// Returns heap memory size used
	fn mem_used(&self) -> usize;

	/// Returns the size of journalled state in memory.
	/// This function has a considerable speed requirement --
	/// it must be fast enough to call several times per block imported.
	fn journal_size(&self) -> usize { 0 }

	/// Check if this database has any commits
	fn is_empty(&self) -> bool;

	/// Get the earliest era in the DB. None if there isn't yet any data in there.
	fn earliest_era(&self) -> Option<u64> { None }

	/// Get the latest era in the DB. None if there isn't yet any data in there.
	fn latest_era(&self) -> Option<u64>;

	/// Journal recent database operations as being associated with a given era and id.
	// TODO: give the overlay to this function so journaldbs don't manage the overlays themeselves.
	fn journal_under(&mut self, batch: &mut DBTransaction, now: u64, id: &H256) -> io::Result<u32>;

	/// Mark a given block as canonical, indicating that competing blocks' states may be pruned out.
	fn mark_canonical(&mut self, batch: &mut DBTransaction, era: u64, id: &H256) -> io::Result<u32>;

	/// Commit all queued insert and delete operations without affecting any journalling -- this requires that all insertions
	/// and deletions are indeed canonical and will likely lead to an invalid database if that assumption is violated.
	///
	/// Any keys or values inserted or deleted must be completely independent of those affected
	/// by any previous `commit` operations. Essentially, this means that `inject` can be used
	/// either to restore a state to a fresh database, or to insert data which may only be journalled
	/// from this point onwards.
	fn inject(&mut self, batch: &mut DBTransaction) -> io::Result<u32>;

	/// State data query
	fn state(&self, _id: &H256) -> Option<Bytes>;

	/// Whether this database is pruned.
	fn is_pruned(&self) -> bool { true }

	/// Get backing database.
	fn backing(&self) -> &Arc<kvdb::KeyValueDB>;

	/// Clear internal strucutres. This should called after changes have been written
	/// to the backing strage
	fn flush(&self) {}

	/// Consolidate all the insertions and deletions in the given memory overlay.
	fn consolidate(&mut self, overlay: ::memorydb::MemoryDB<KeccakHasher>);

	/// Commit all changes in a single batch
	#[cfg(test)]
	fn commit_batch(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> io::Result<u32> {
		let mut batch = self.backing().transaction();
		let mut ops = self.journal_under(&mut batch, now, id)?;

		if let Some((end_era, canon_id)) = end {
			ops += self.mark_canonical(&mut batch, end_era, &canon_id)?;
		}

		let result = self.backing().write(batch).map(|_| ops).map_err(Into::into);
		self.flush();
		result
	}

	/// Inject all changes in a single batch.
	#[cfg(test)]
	fn inject_batch(&mut self) -> io::Result<u32> {
		let mut batch = self.backing().transaction();
		let res = self.inject(&mut batch)?;
		self.backing().write(batch).map(|_| res).map_err(Into::into)
	}
}