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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/>.

    //! Account state encoding and decoding

    use account_db::{AccountDB, AccountDBMut};
    use basic_account::BasicAccount;
    use snapshot::Error;

    use util::{U256, FixedHash, H256, Bytes, HashDB, SHA3_EMPTY, SHA3_NULL_RLP};
    use util::trie::{TrieDB, Trie};
    use rlp::{RlpStream, Stream, UntrustedRlp, View};

    use std::collections::HashSet;

    // An empty account -- these are replaced with RLP null data for a space optimization.
    const ACC_EMPTY: BasicAccount = BasicAccount {
    	nonce: U256([0, 0, 0, 0]),
    	balance: U256([0, 0, 0, 0]),
    	storage_root: SHA3_NULL_RLP,
    	code_hash: SHA3_EMPTY,
    };

    // whether an encoded account has code and how it is referred to.
    #[repr(u8)]
    enum CodeState {
    	// the account has no code.
    	Empty = 0,
    	// raw code is encoded.
    	Inline = 1,
    	// the code is referred to by hash.
    	Hash = 2,
    }

    impl CodeState {
    	fn from(x: u8) -> Result<Self, Error> {
    		match x {
    			0 => Ok(CodeState::Empty),
    			1 => Ok(CodeState::Inline),
    			2 => Ok(CodeState::Hash),
    			_ => Err(Error::UnrecognizedCodeState(x))
    		}
    	}

    	fn raw(self) -> u8 {
    		self as u8
    	}
    }

    // walk the account's storage trie, returning an RLP item containing the
    // account properties and the storage.
    pub fn to_fat_rlp(acc: &BasicAccount, acct_db: &AccountDB, used_code: &mut HashSet<H256>) -> Result<Bytes, Error> {
    	if acc == &ACC_EMPTY {
    		return Ok(::rlp::NULL_RLP.to_vec());
    	}

    	let db = TrieDB::new(acct_db, &acc.storage_root)?;

    	let mut pairs = Vec::new();

    	for item in db.iter()? {
    		let (k, v) = item?;
    		pairs.push((k, v));
    	}

    	let mut stream = RlpStream::new_list(pairs.len());

    	for (k, v) in pairs {
    		stream.begin_list(2).append(&k).append(&&*v);
    	}

    	let pairs_rlp = stream.out();

    	let mut account_stream = RlpStream::new_list(5);
    	account_stream.append(&acc.nonce)
    				  .append(&acc.balance);

    	// [has_code, code_hash].
    	if acc.code_hash == SHA3_EMPTY {
    		account_stream.append(&CodeState::Empty.raw()).append_empty_data();
    	} else if used_code.contains(&acc.code_hash) {
    		account_stream.append(&CodeState::Hash.raw()).append(&acc.code_hash);
    	} else {
    		match acct_db.get(&acc.code_hash) {
    			Some(c) => {
    				used_code.insert(acc.code_hash.clone());
    				account_stream.append(&CodeState::Inline.raw()).append(&&*c);
    			}
    			None => {
    				warn!("code lookup failed during snapshot");
    				account_stream.append(&false).append_empty_data();
    			}
    		}
    	}

    	account_stream.append_raw(&pairs_rlp, 1);

    	Ok(account_stream.out())
    }

    // decode a fat rlp, and rebuild the storage trie as we go.
    // returns the account structure along with its newly recovered code,
    // if it exists.
    pub fn from_fat_rlp(
    	acct_db: &mut AccountDBMut,
    	rlp: UntrustedRlp,
    ) -> Result<(BasicAccount, Option<Bytes>), Error> {
    	use util::{TrieDBMut, TrieMut};

    	// check for special case of empty account.
    	if rlp.is_empty() {
    		return Ok((ACC_EMPTY, None));
    	}

    	let nonce = rlp.val_at(0)?;
    	let balance = rlp.val_at(1)?;
    	let code_state: CodeState = {
    		let raw: u8 = rlp.val_at(2)?;
    		CodeState::from(raw)?
    	};

    	// load the code if it exists.
    	let (code_hash, new_code) = match code_state {
    		CodeState::Empty => (SHA3_EMPTY, None),
    		CodeState::Inline => {
    			let code: Bytes = rlp.val_at(3)?;
    			let code_hash = acct_db.insert(&code);

    			(code_hash, Some(code))
    		}
    		CodeState::Hash => {
    			let code_hash = rlp.val_at(3)?;

    			(code_hash, None)
    		}
    	};

    	let mut storage_root = H256::zero();

    	{
    		let mut storage_trie = TrieDBMut::new(acct_db, &mut storage_root);
    		let pairs = rlp.at(4)?;
    		for pair_rlp in pairs.iter() {
    			let k: Bytes  = pair_rlp.val_at(0)?;
    			let v: Bytes = pair_rlp.val_at(1)?;

    			storage_trie.insert(&k, &v)?;
    		}
    	}

    	let acc = BasicAccount {
    		nonce: nonce,
    		balance: balance,
    		storage_root: storage_root,
    		code_hash: code_hash,
    	};

    	Ok((acc, new_code))
    }

    #[cfg(test)]
    mod tests {
    	use account_db::{AccountDB, AccountDBMut};
    	use basic_account::BasicAccount;
    	use tests::helpers::get_temp_state_db;
    	use snapshot::tests::helpers::fill_storage;

    	use util::sha3::{SHA3_EMPTY, SHA3_NULL_RLP};
    	use util::{Address, FixedHash, H256, HashDB, DBValue};
    	use rlp::{UntrustedRlp, View};

    	use std::collections::HashSet;

    	use super::{ACC_EMPTY, to_fat_rlp, from_fat_rlp};

    	#[test]
    	fn encoding_basic() {
    		let mut db = get_temp_state_db();
    		let addr = Address::random();

    		let account = BasicAccount {
    			nonce: 50.into(),
    			balance: 123456789.into(),
    			storage_root: SHA3_NULL_RLP,
    			code_hash: SHA3_EMPTY,
    		};

    		let thin_rlp = ::rlp::encode(&account);
    		assert_eq!(::rlp::decode::<BasicAccount>(&thin_rlp), account);

    		let fat_rlp = to_fat_rlp(&account, &AccountDB::new(db.as_hashdb(), &addr), &mut Default::default()).unwrap();
    		let fat_rlp = UntrustedRlp::new(&fat_rlp);
    		assert_eq!(from_fat_rlp(&mut AccountDBMut::new(db.as_hashdb_mut(), &addr), fat_rlp).unwrap().0, account);
    	}

    	#[test]
    	fn encoding_storage() {
    		let mut db = get_temp_state_db();
    		let addr = Address::random();

    		let account = {
    			let acct_db = AccountDBMut::new(db.as_hashdb_mut(), &addr);
    			let mut root = SHA3_NULL_RLP;
    			fill_storage(acct_db, &mut root, &mut H256::zero());
    			BasicAccount {
    				nonce: 25.into(),
    				balance: 987654321.into(),
    				storage_root: root,
    				code_hash: SHA3_EMPTY,
    			}
    		};

    		let thin_rlp = ::rlp::encode(&account);
    		assert_eq!(::rlp::decode::<BasicAccount>(&thin_rlp), account);

    		let fat_rlp = to_fat_rlp(&account, &AccountDB::new(db.as_hashdb(), &addr), &mut Default::default()).unwrap();
    		let fat_rlp = UntrustedRlp::new(&fat_rlp);
    		assert_eq!(from_fat_rlp(&mut AccountDBMut::new(db.as_hashdb_mut(), &addr), fat_rlp).unwrap().0, account);
    	}

    	#[test]
    	fn encoding_code() {
    		let mut db = get_temp_state_db();

    		let addr1 = Address::random();
    		let addr2 = Address::random();

    		let code_hash = {
    			let mut acct_db = AccountDBMut::new(db.as_hashdb_mut(), &addr1);
    			acct_db.insert(b"this is definitely code")
    		};

    		{
    			let mut acct_db = AccountDBMut::new(db.as_hashdb_mut(), &addr2);
    			acct_db.emplace(code_hash.clone(), DBValue::from_slice(b"this is definitely code"));
    		}

    		let account1 = BasicAccount {
    			nonce: 50.into(),
    			balance: 123456789.into(),
    			storage_root: SHA3_NULL_RLP,
    			code_hash: code_hash,
    		};

    		let account2 = BasicAccount {
    			nonce: 400.into(),
    			balance: 98765432123456789usize.into(),
    			storage_root: SHA3_NULL_RLP,
    			code_hash: code_hash,
    		};

    		let mut used_code = HashSet::new();

    		let fat_rlp1 = to_fat_rlp(&account1, &AccountDB::new(db.as_hashdb(), &addr1), &mut used_code).unwrap();
    		let fat_rlp2 = to_fat_rlp(&account2, &AccountDB::new(db.as_hashdb(), &addr2), &mut used_code).unwrap();
    		assert_eq!(used_code.len(), 1);

    		let fat_rlp1 = UntrustedRlp::new(&fat_rlp1);
    		let fat_rlp2 = UntrustedRlp::new(&fat_rlp2);

    		let (acc, maybe_code) = from_fat_rlp(&mut AccountDBMut::new(db.as_hashdb_mut(), &addr2), fat_rlp2).unwrap();
    		assert!(maybe_code.is_none());
    		assert_eq!(acc, account2);

    		let (acc, maybe_code) = from_fat_rlp(&mut AccountDBMut::new(db.as_hashdb_mut(), &addr1), fat_rlp1).unwrap();
    		assert_eq!(maybe_code, Some(b"this is definitely code".to_vec()));
    		assert_eq!(acc, account1);
    	}

    	#[test]
    	fn encoding_empty_acc() {
    		let mut db = get_temp_state_db();
    		let mut used_code = HashSet::new();

    		assert_eq!(to_fat_rlp(&ACC_EMPTY, &AccountDB::new(db.as_hashdb(), &Address::default()), &mut used_code).unwrap(), ::rlp::NULL_RLP.to_vec());
    		assert_eq!(from_fat_rlp(&mut AccountDBMut::new(db.as_hashdb_mut(), &Address::default()), UntrustedRlp::new(&::rlp::NULL_RLP)).unwrap(), (ACC_EMPTY, None));
    	}
    }

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