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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/>.

    /// Validator set maintained in a contract, updated using `getValidators` method.

    use std::sync::Weak;
    use util::*;
    use client::{Client, BlockChainClient};
    use client::chain_notify::ChainNotify;
    use super::ValidatorSet;
    use super::simple_list::SimpleList;

    /// The validator contract should have the following interface:
    /// [{"constant":true,"inputs":[],"name":"getValidators","outputs":[{"name":"","type":"address[]"}],"payable":false,"type":"function"}]
    pub struct ValidatorSafeContract {
    	pub address: Address,
    	validators: RwLock<SimpleList>,
    	provider: RwLock<Option<provider::Contract>>,
    }

    impl ValidatorSafeContract {
    	pub fn new(contract_address: Address) -> Self {
    		ValidatorSafeContract {
    			address: contract_address,
    			validators: Default::default(),
    			provider: RwLock::new(None),
    		}
    	}

    	/// Queries the state and updates the set of validators.
    	pub fn update(&self) {
    		if let Some(ref provider) = *self.provider.read() {
    			match provider.get_validators() {
    				Ok(new) => {
    					debug!(target: "engine", "Set of validators obtained: {:?}", new);
    					*self.validators.write() = SimpleList::new(new);
    				},
    				Err(s) => warn!(target: "engine", "Set of validators could not be updated: {}", s),
    			}
    		} else {
    			warn!(target: "engine", "Set of validators could not be updated: no provider contract.")
    		}
    	}
    }

    /// Checks validators on every block.
    impl ChainNotify for ValidatorSafeContract {
    	fn new_blocks(
    		&self,
    		_: Vec<H256>,
    		_: Vec<H256>,
    		enacted: Vec<H256>,
    		_: Vec<H256>,
    		_: Vec<H256>,
    		_: Vec<Bytes>,
    		_duration: u64) {
    		if !enacted.is_empty() {
    			self.update();
    		}
    	}
    }

    impl ValidatorSet for Arc<ValidatorSafeContract> {
    	fn contains(&self, address: &Address) -> bool {
    		self.validators.read().contains(address)
    	}

    	fn get(&self, nonce: usize) -> Address {
    		self.validators.read().get(nonce)
    	}

    	fn count(&self) -> usize {
    		self.validators.read().count()
    	}

    	fn register_contract(&self, client: Weak<Client>) {
    		if let Some(c) = client.upgrade() {
    			c.add_notify(self.clone());
    		}
    		{
    			*self.provider.write() = Some(provider::Contract::new(self.address, move |a, d| client.upgrade().ok_or("No client!".into()).and_then(|c| c.call_contract(a, d))));
    		}
    		self.update();
    	}
    }

    mod provider {
    	// Autogenerated from JSON contract definition using Rust contract convertor.
    	#![allow(unused_imports)]
    	use std::string::String;
    	use std::result::Result;
    	use std::fmt;
    	use {util, ethabi};
    	use util::{FixedHash, Uint};

    	pub struct Contract {
    		contract: ethabi::Contract,
    		address: util::Address,
    		do_call: Box<Fn(util::Address, Vec<u8>) -> Result<Vec<u8>, String> + Send + Sync + 'static>,
    	}
    	impl Contract {
    		pub fn new<F>(address: util::Address, do_call: F) -> Self where F: Fn(util::Address, Vec<u8>) -> Result<Vec<u8>, String> + Send + Sync + 'static {
    			Contract {
    				contract: ethabi::Contract::new(ethabi::Interface::load(b"[{\"constant\":true,\"inputs\":[],\"name\":\"getValidators\",\"outputs\":[{\"name\":\"\",\"type\":\"address[]\"}],\"payable\":false,\"type\":\"function\"}]").expect("JSON is autogenerated; qed")),
    				address: address,
    				do_call: Box::new(do_call),
    			}
    		}
    		fn as_string<T: fmt::Debug>(e: T) -> String { format!("{:?}", e) }

    		/// Auto-generated from: `{"constant":true,"inputs":[],"name":"getValidators","outputs":[{"name":"","type":"address[]"}],"payable":false,"type":"function"}`
    		#[allow(dead_code)]
    		pub fn get_validators(&self) -> Result<Vec<util::Address>, String> {
    			let call = self.contract.function("getValidators".into()).map_err(Self::as_string)?;
    			let data = call.encode_call(
    				vec![]
    			).map_err(Self::as_string)?;
    			let output = call.decode_output((self.do_call)(self.address.clone(), data)?).map_err(Self::as_string)?;
    			let mut result = output.into_iter().rev().collect::<Vec<_>>();
    			Ok(({ let r = result.pop().ok_or("Invalid return arity")?; let r = r.to_array().and_then(|v| v.into_iter().map(|a| a.to_address()).collect::<Option<Vec<[u8; 20]>>>()).ok_or("Invalid type returned")?; r.into_iter().map(|a| util::Address::from(a)).collect::<Vec<_>>() }))
    		}
    	}
    }

    #[cfg(test)]
    mod tests {
    	use util::*;
    	use spec::Spec;
    	use account_provider::AccountProvider;
    	use transaction::{Transaction, Action};
    	use client::{BlockChainClient, EngineClient};
    	use ethkey::Secret;
    	use miner::MinerService;
    	use tests::helpers::generate_dummy_client_with_spec_and_accounts;
    	use super::super::ValidatorSet;
    	use super::ValidatorSafeContract;

    	#[test]
    	fn fetches_validators() {
    		let client = generate_dummy_client_with_spec_and_accounts(Spec::new_validator_safe_contract, None);
    		let vc = Arc::new(ValidatorSafeContract::new(Address::from_str("0000000000000000000000000000000000000005").unwrap()));
    		vc.register_contract(Arc::downgrade(&client));
    		assert!(vc.contains(&Address::from_str("7d577a597b2742b498cb5cf0c26cdcd726d39e6e").unwrap()));
    		assert!(vc.contains(&Address::from_str("82a978b3f5962a5b0957d9ee9eef472ee55b42f1").unwrap()));
    	}

    	#[test]
    	fn updates_validators() {
    		let tap = Arc::new(AccountProvider::transient_provider());
    		let s0 = Secret::from_slice(&"1".sha3()).unwrap();
    		let v0 = tap.insert_account(s0.clone(), "").unwrap();
    		let v1 = tap.insert_account(Secret::from_slice(&"0".sha3()).unwrap(), "").unwrap();
    		let client = generate_dummy_client_with_spec_and_accounts(Spec::new_validator_safe_contract, Some(tap));
    		client.engine().register_client(Arc::downgrade(&client));
    		let validator_contract = Address::from_str("0000000000000000000000000000000000000005").unwrap();

    		client.miner().set_engine_signer(v1, "".into()).unwrap();
    		// Remove "1" validator.
    		let tx = Transaction {
    			nonce: 0.into(),
    			gas_price: 0.into(),
    			gas: 500_000.into(),
    			action: Action::Call(validator_contract),
    			value: 0.into(),
    			data: "bfc708a000000000000000000000000082a978b3f5962a5b0957d9ee9eef472ee55b42f1".from_hex().unwrap(),
    		}.sign(&s0, None);
    		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
    		client.update_sealing();
    		assert_eq!(client.chain_info().best_block_number, 1);
    		// Add "1" validator back in.
    		let tx = Transaction {
    			nonce: 1.into(),
    			gas_price: 0.into(),
    			gas: 500_000.into(),
    			action: Action::Call(validator_contract),
    			value: 0.into(),
    			data: "4d238c8e00000000000000000000000082a978b3f5962a5b0957d9ee9eef472ee55b42f1".from_hex().unwrap(),
    		}.sign(&s0, None);
    		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
    		client.update_sealing();
    		// The transaction is not yet included so still unable to seal.
    		assert_eq!(client.chain_info().best_block_number, 1);

    		// Switch to the validator that is still there.
    		client.miner().set_engine_signer(v0, "".into()).unwrap();
    		client.update_sealing();
    		assert_eq!(client.chain_info().best_block_number, 2);
    		// Switch back to the added validator, since the state is updated.
    		client.miner().set_engine_signer(v1, "".into()).unwrap();
    		let tx = Transaction {
    			nonce: 2.into(),
    			gas_price: 0.into(),
    			gas: 21000.into(),
    			action: Action::Call(Address::default()),
    			value: 0.into(),
    			data: Vec::new(),
    		}.sign(&s0, None);
    		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
    		client.update_sealing();
    		// Able to seal again.
    		assert_eq!(client.chain_info().best_block_number, 3);
    	}
    }

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