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

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

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

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

    use hash::H256;
    use sha3::Hashable;
    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 {
    		key.sha3()
    	}
    }

    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(&key.sha3())
    	}

    	fn get<'a, 'key>(&'a self, key: &'key [u8]) -> super::Result<Option<DBValue>>
    		where 'a: 'key
    	{
    		self.raw.get(&key.sha3())
    	}

    	fn insert(&mut self, key: &[u8], value: &[u8]) -> super::Result<Option<DBValue>> {
    		let hash = key.sha3();
    		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 = key.sha3();
    		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(&(&[0x01u8, 0x23]).sha3()).unwrap().unwrap(), DBValue::from_slice(&[0x01u8, 0x23]));
    }

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