// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

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

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

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

use bigint::hash::H256;
use keccak::keccak;
use hashdb::{HashDB, DBValue};
use super::{TrieDBMut, TrieMut};

/// A mutable `Trie` implementation which hashes keys and uses a generic `HashDB` backing database.
/// Additionaly it stores inserted hash-key mappings for later retrieval.
///
/// Use it as a `Trie` or `TrieMut` trait object.
pub struct FatDBMut<'db> {
	raw: TrieDBMut<'db>,
}

impl<'db> FatDBMut<'db> {
	/// Create a new trie with the backing database `db` and empty `root`
	/// Initialise to the state entailed by the genesis block.
	/// This guarantees the trie is built correctly.
	pub fn new(db: &'db mut HashDB, root: &'db mut H256) -> Self {
		FatDBMut { raw: TrieDBMut::new(db, root) }
	}

	/// Create a new trie with the backing database `db` and `root`.
	///
	/// Returns an error if root does not exist.
	pub fn from_existing(db: &'db mut HashDB, root: &'db mut H256) -> super::Result<Self> {
		Ok(FatDBMut { raw: TrieDBMut::from_existing(db, root)? })
	}

	/// Get the backing database.
	pub fn db(&self) -> &HashDB {
		self.raw.db()
	}

	/// Get the backing database.
	pub fn db_mut(&mut self) -> &mut HashDB {
		self.raw.db_mut()
	}

	fn to_aux_key(key: &[u8]) -> H256 {
		keccak(key)
	}
}

impl<'db> TrieMut for FatDBMut<'db> {
	fn root(&mut self) -> &H256 {
		self.raw.root()
	}

	fn is_empty(&self) -> bool {
		self.raw.is_empty()
	}

	fn contains(&self, key: &[u8]) -> super::Result<bool> {
		self.raw.contains(&keccak(key))
	}

	fn get<'a, 'key>(&'a self, key: &'key [u8]) -> super::Result<Option<DBValue>>
		where 'a: 'key
	{
		self.raw.get(&keccak(key))
	}

	fn insert(&mut self, key: &[u8], value: &[u8]) -> super::Result<Option<DBValue>> {
		let hash = keccak(key);
		let out = self.raw.insert(&hash, value)?;
		let db = self.raw.db_mut();

		// don't insert if it doesn't exist.
		if out.is_none() {
			db.emplace(Self::to_aux_key(&hash), DBValue::from_slice(key));
		}
		Ok(out)
	}

	fn remove(&mut self, key: &[u8]) -> super::Result<Option<DBValue>> {
		let hash = keccak(key);
		let out = self.raw.remove(&hash)?;

		// don't remove if it already exists.
		if out.is_some() {
			self.raw.db_mut().remove(&Self::to_aux_key(&hash));
		}

		Ok(out)
	}
}

#[test]
fn fatdb_to_trie() {
	use memorydb::MemoryDB;
	use super::TrieDB;
	use super::Trie;

	let mut memdb = MemoryDB::new();
	let mut root = H256::default();
	{
		let mut t = FatDBMut::new(&mut memdb, &mut root);
		t.insert(&[0x01u8, 0x23], &[0x01u8, 0x23]).unwrap();
	}
	let t = TrieDB::new(&memdb, &root).unwrap();
	assert_eq!(t.get(&keccak(&[0x01u8, 0x23])).unwrap().unwrap(), DBValue::from_slice(&[0x01u8, 0x23]));
}