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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/>.

    //! A blockchain engine that supports a basic, non-BFT proof-of-authority.

    use std::sync::Weak;
    use util::*;
    use ethkey::{recover, public_to_address, Signature};
    use account_provider::AccountProvider;
    use block::*;
    use builtin::Builtin;
    use spec::CommonParams;
    use engines::{Engine, Seal};
    use env_info::EnvInfo;
    use error::{BlockError, Error};
    use evm::Schedule;
    use ethjson;
    use header::Header;
    use client::Client;
    use super::signer::EngineSigner;
    use super::validator_set::{ValidatorSet, new_validator_set};

    /// `BasicAuthority` params.
    #[derive(Debug, PartialEq)]
    pub struct BasicAuthorityParams {
    	/// Gas limit divisor.
    	pub gas_limit_bound_divisor: U256,
    	/// Valid signatories.
    	pub validators: ethjson::spec::ValidatorSet,
    }

    impl From<ethjson::spec::BasicAuthorityParams> for BasicAuthorityParams {
    	fn from(p: ethjson::spec::BasicAuthorityParams) -> Self {
    		BasicAuthorityParams {
    			gas_limit_bound_divisor: p.gas_limit_bound_divisor.into(),
    			validators: p.validators,
    		}
    	}
    }

    /// Engine using `BasicAuthority` proof-of-work consensus algorithm, suitable for Ethereum
    /// mainnet chains in the Olympic, Frontier and Homestead eras.
    pub struct BasicAuthority {
    	params: CommonParams,
    	gas_limit_bound_divisor: U256,
    	builtins: BTreeMap<Address, Builtin>,
    	signer: EngineSigner,
    	validators: Box<ValidatorSet + Send + Sync>,
    }

    impl BasicAuthority {
    	/// Create a new instance of BasicAuthority engine
    	pub fn new(params: CommonParams, our_params: BasicAuthorityParams, builtins: BTreeMap<Address, Builtin>) -> Self {
    		BasicAuthority {
    			params: params,
    			gas_limit_bound_divisor: our_params.gas_limit_bound_divisor,
    			builtins: builtins,
    			validators: new_validator_set(our_params.validators),
    			signer: Default::default(),
    		}
    	}
    }

    impl Engine for BasicAuthority {
    	fn name(&self) -> &str { "BasicAuthority" }
    	fn version(&self) -> SemanticVersion { SemanticVersion::new(1, 0, 0) }
    	// One field - the signature
    	fn seal_fields(&self) -> usize { 1 }

    	fn params(&self) -> &CommonParams { &self.params }
    	fn builtins(&self) -> &BTreeMap<Address, Builtin> { &self.builtins }

    	/// Additional engine-specific information for the user/developer concerning `header`.
    	fn extra_info(&self, _header: &Header) -> BTreeMap<String, String> { map!["signature".to_owned() => "TODO".to_owned()] }

    	fn schedule(&self, _env_info: &EnvInfo) -> Schedule {
    		Schedule::new_homestead()
    	}

    	fn populate_from_parent(&self, header: &mut Header, parent: &Header, gas_floor_target: U256, _gas_ceil_target: U256) {
    		header.set_difficulty(parent.difficulty().clone());
    		header.set_gas_limit({
    			let gas_limit = parent.gas_limit().clone();
    			let bound_divisor = self.gas_limit_bound_divisor;
    			if gas_limit < gas_floor_target {
    				min(gas_floor_target, gas_limit + gas_limit / bound_divisor - 1.into())
    			} else {
    				max(gas_floor_target, gas_limit - gas_limit / bound_divisor + 1.into())
    			}
    		});
    	}

    	fn is_sealer(&self, author: &Address) -> Option<bool> {
    		Some(self.validators.contains(author))
    	}

    	/// Attempt to seal the block internally.
    	fn generate_seal(&self, block: &ExecutedBlock) -> Seal {
    		let header = block.header();
    		let author = header.author();
    		if self.validators.contains(author) {
    			// account should be pernamently unlocked, otherwise sealing will fail
    			if let Ok(signature) = self.signer.sign(header.bare_hash()) {
    				return Seal::Regular(vec![::rlp::encode(&(&H520::from(signature) as &[u8])).to_vec()]);
    			} else {
    				trace!(target: "basicauthority", "generate_seal: FAIL: accounts secret key unavailable");
    			}
    		}
    		Seal::None
    	}

    	fn verify_block_basic(&self, header: &Header, _block: Option<&[u8]>) -> result::Result<(), Error> {
    		// check the seal fields.
    		// TODO: pull this out into common code.
    		if header.seal().len() != self.seal_fields() {
    			return Err(From::from(BlockError::InvalidSealArity(
    				Mismatch { expected: self.seal_fields(), found: header.seal().len() }
    			)));
    		}
    		Ok(())
    	}

    	fn verify_block_unordered(&self, header: &Header, _block: Option<&[u8]>) -> result::Result<(), Error> {
    		use rlp::{UntrustedRlp, View};

    		// check the signature is legit.
    		let sig = UntrustedRlp::new(&header.seal()[0]).as_val::<H520>()?;
    		let signer = public_to_address(&recover(&sig.into(), &header.bare_hash())?);
    		if !self.validators.contains(&signer) {
    			return Err(BlockError::InvalidSeal)?;
    		}
    		Ok(())
    	}

    	fn verify_block_family(&self, header: &Header, parent: &Header, _block: Option<&[u8]>) -> result::Result<(), Error> {
    		// we should not calculate difficulty for genesis blocks
    		if header.number() == 0 {
    			return Err(From::from(BlockError::RidiculousNumber(OutOfBounds { min: Some(1), max: None, found: header.number() })));
    		}

    		// Check difficulty is correct given the two timestamps.
    		if header.difficulty() != parent.difficulty() {
    			return Err(From::from(BlockError::InvalidDifficulty(Mismatch { expected: *parent.difficulty(), found: *header.difficulty() })))
    		}
    		let gas_limit_divisor = self.gas_limit_bound_divisor;
    		let min_gas = parent.gas_limit().clone() - parent.gas_limit().clone() / gas_limit_divisor;
    		let max_gas = parent.gas_limit().clone() + parent.gas_limit().clone() / gas_limit_divisor;
    		if header.gas_limit() <= &min_gas || header.gas_limit() >= &max_gas {
    			return Err(From::from(BlockError::InvalidGasLimit(OutOfBounds { min: Some(min_gas), max: Some(max_gas), found: header.gas_limit().clone() })));
    		}
    		Ok(())
    	}

    	fn register_client(&self, client: Weak<Client>) {
    		self.validators.register_contract(client);
    	}

    	fn set_signer(&self, ap: Arc<AccountProvider>, address: Address, password: String) {
    		self.signer.set(ap, address, password);
    	}

    	fn sign(&self, hash: H256) -> Result<Signature, Error> {
    		self.signer.sign(hash).map_err(Into::into)
    	}
    }

    #[cfg(test)]
    mod tests {
    	use util::*;
    	use block::*;
    	use env_info::EnvInfo;
    	use error::{BlockError, Error};
    	use tests::helpers::*;
    	use account_provider::AccountProvider;
    	use ethkey::Secret;
    	use header::Header;
    	use spec::Spec;
    	use engines::Seal;

    	/// Create a new test chain spec with `BasicAuthority` consensus engine.
    	fn new_test_authority() -> Spec {
    		let bytes: &[u8] = include_bytes!("../../res/basic_authority.json");
    		Spec::load(bytes).expect("invalid chain spec")
    	}

    	#[test]
    	fn has_valid_metadata() {
    		let engine = new_test_authority().engine;
    		assert!(!engine.name().is_empty());
    		assert!(engine.version().major >= 1);
    	}

    	#[test]
    	fn can_return_schedule() {
    		let engine = new_test_authority().engine;
    		let schedule = engine.schedule(&EnvInfo {
    			number: 10000000,
    			author: 0.into(),
    			timestamp: 0,
    			difficulty: 0.into(),
    			last_hashes: Arc::new(vec![]),
    			gas_used: 0.into(),
    			gas_limit: 0.into(),
    		});

    		assert!(schedule.stack_limit > 0);
    	}

    	#[test]
    	fn can_do_seal_verification_fail() {
    		let engine = new_test_authority().engine;
    		let header: Header = Header::default();

    		let verify_result = engine.verify_block_basic(&header, None);

    		match verify_result {
    			Err(Error::Block(BlockError::InvalidSealArity(_))) => {},
    			Err(_) => { panic!("should be block seal-arity mismatch error (got {:?})", verify_result); },
    			_ => { panic!("Should be error, got Ok"); },
    		}
    	}

    	#[test]
    	fn can_do_signature_verification_fail() {
    		let engine = new_test_authority().engine;
    		let mut header: Header = Header::default();
    		header.set_seal(vec![::rlp::encode(&H520::default()).to_vec()]);

    		let verify_result = engine.verify_block_unordered(&header, None);
    		assert!(verify_result.is_err());
    	}

    	#[test]
    	fn can_generate_seal() {
    		let tap = AccountProvider::transient_provider();
    		let addr = tap.insert_account(Secret::from_slice(&"".sha3()).unwrap(), "").unwrap();

    		let spec = new_test_authority();
    		let engine = &*spec.engine;
    		engine.set_signer(Arc::new(tap), addr, "".into());
    		let genesis_header = spec.genesis_header();
    		let mut db_result = get_temp_state_db();
    		let db = spec.ensure_db_good(db_result.take(), &Default::default()).unwrap();
    		let last_hashes = Arc::new(vec![genesis_header.hash()]);
    		let b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, addr, (3141562.into(), 31415620.into()), vec![]).unwrap();
    		let b = b.close_and_lock();
    		if let Seal::Regular(seal) = engine.generate_seal(b.block()) {
    			assert!(b.try_seal(engine, seal).is_ok());
    		}
    	}

    	#[test]
    	fn seals_internally() {
    		let tap = AccountProvider::transient_provider();
    		let authority = tap.insert_account(Secret::from_slice(&"".sha3()).unwrap(), "").unwrap();

    		let engine = new_test_authority().engine;
    		assert!(!engine.is_sealer(&Address::default()).unwrap());
    		assert!(engine.is_sealer(&authority).unwrap());
    	}
    }

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