// Copyright 2015-2018 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/>.

//! Consensus engine specification and basic implementations.

mod authority_round;
mod basic_authority;
mod instant_seal;
mod null_engine;
mod signer;
mod tendermint;
mod transition;
mod validator_set;
mod vote_collector;

pub mod block_reward;
pub mod epoch;

pub use self::authority_round::AuthorityRound;
pub use self::basic_authority::BasicAuthority;
pub use self::epoch::{EpochVerifier, Transition as EpochTransition};
pub use self::instant_seal::InstantSeal;
pub use self::null_engine::NullEngine;
pub use self::tendermint::Tendermint;

use std::sync::{Weak, Arc};
use std::collections::{BTreeMap, HashMap};
use std::{fmt, error};

use self::epoch::PendingTransition;

use account_provider::AccountProvider;
use builtin::Builtin;
use vm::{EnvInfo, Schedule, CreateContractAddress};
use error::Error;
use header::{Header, BlockNumber};
use snapshot::SnapshotComponents;
use spec::CommonParams;
use transaction::{self, UnverifiedTransaction, SignedTransaction};

use ethkey::Signature;
use parity_machine::{Machine, LocalizedMachine as Localized, TotalScoredHeader};
use ethereum_types::{H256, U256, Address};
use unexpected::{Mismatch, OutOfBounds};
use bytes::Bytes;
use types::ancestry_action::AncestryAction;

/// Default EIP-210 contract code.
/// As defined in https://github.com/ethereum/EIPs/pull/210
pub const DEFAULT_BLOCKHASH_CONTRACT: &'static str = "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";

/// Fork choice.
#[derive(Debug, PartialEq, Eq)]
pub enum ForkChoice {
	/// Choose the new block.
	New,
	/// Choose the current best block.
	Old,
}

/// Voting errors.
#[derive(Debug)]
pub enum EngineError {
	/// Signature or author field does not belong to an authority.
	NotAuthorized(Address),
	/// The same author issued different votes at the same step.
	DoubleVote(Address),
	/// The received block is from an incorrect proposer.
	NotProposer(Mismatch<Address>),
	/// Message was not expected.
	UnexpectedMessage,
	/// Seal field has an unexpected size.
	BadSealFieldSize(OutOfBounds<usize>),
	/// Validation proof insufficient.
	InsufficientProof(String),
	/// Failed system call.
	FailedSystemCall(String),
	/// Malformed consensus message.
	MalformedMessage(String),
	/// Requires client ref, but none registered.
	RequiresClient,
}

impl fmt::Display for EngineError {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		use self::EngineError::*;
		let msg = match *self {
			DoubleVote(ref address) => format!("Author {} issued too many blocks.", address),
			NotProposer(ref mis) => format!("Author is not a current proposer: {}", mis),
			NotAuthorized(ref address) => format!("Signer {} is not authorized.", address),
			UnexpectedMessage => "This Engine should not be fed messages.".into(),
			BadSealFieldSize(ref oob) => format!("Seal field has an unexpected length: {}", oob),
			InsufficientProof(ref msg) => format!("Insufficient validation proof: {}", msg),
			FailedSystemCall(ref msg) => format!("Failed to make system call: {}", msg),
			MalformedMessage(ref msg) => format!("Received malformed consensus message: {}", msg),
			RequiresClient => format!("Call requires client but none registered"),
		};

		f.write_fmt(format_args!("Engine error ({})", msg))
	}
}

impl error::Error for EngineError {
	fn description(&self) -> &str {
		"Engine error"
	}
}

/// Seal type.
#[derive(Debug, PartialEq, Eq)]
pub enum Seal {
	/// Proposal seal; should be broadcasted, but not inserted into blockchain.
	Proposal(Vec<Bytes>),
	/// Regular block seal; should be part of the blockchain.
	Regular(Vec<Bytes>),
	/// Engine does generate seal for this block right now.
	None,
}

/// A system-calling closure. Enacts calls on a block's state from the system address.
pub type SystemCall<'a> = FnMut(Address, Vec<u8>) -> Result<Vec<u8>, String> + 'a;

/// Type alias for a function we can get headers by hash through.
pub type Headers<'a, H> = Fn(H256) -> Option<H> + 'a;

/// Type alias for a function we can query pending transitions by block hash through.
pub type PendingTransitionStore<'a> = Fn(H256) -> Option<PendingTransition> + 'a;

/// Proof dependent on state.
pub trait StateDependentProof<M: Machine>: Send + Sync {
	/// Generate a proof, given the state.
	// TODO: make this into an &M::StateContext
	fn generate_proof<'a>(&self, state: &<M as Localized<'a>>::StateContext) -> Result<Vec<u8>, String>;
	/// Check a proof generated elsewhere (potentially by a peer).
	// `engine` needed to check state proofs, while really this should
	// just be state machine params.
	fn check_proof(&self, machine: &M, proof: &[u8]) -> Result<(), String>;
}

/// Proof generated on epoch change.
pub enum Proof<M: Machine> {
	/// Known proof (extracted from signal)
	Known(Vec<u8>),
	/// State dependent proof.
	WithState(Arc<StateDependentProof<M>>),
}

/// Generated epoch verifier.
pub enum ConstructedVerifier<'a, M: Machine> {
	/// Fully trusted verifier.
	Trusted(Box<EpochVerifier<M>>),
	/// Verifier unconfirmed. Check whether given finality proof finalizes given hash
	/// under previous epoch.
	Unconfirmed(Box<EpochVerifier<M>>, &'a [u8], H256),
	/// Error constructing verifier.
	Err(Error),
}

impl<'a, M: Machine> ConstructedVerifier<'a, M> {
	/// Convert to a result, indicating that any necessary confirmation has been done
	/// already.
	pub fn known_confirmed(self) -> Result<Box<EpochVerifier<M>>, Error> {
		match self {
			ConstructedVerifier::Trusted(v) | ConstructedVerifier::Unconfirmed(v, _, _) => Ok(v),
			ConstructedVerifier::Err(e) => Err(e),
		}
	}
}

/// Results of a query of whether an epoch change occurred at the given block.
pub enum EpochChange<M: Machine> {
	/// Cannot determine until more data is passed.
	Unsure(M::AuxiliaryRequest),
	/// No epoch change.
	No,
	/// The epoch will change, with proof.
	Yes(Proof<M>),
}

/// A consensus mechanism for the chain. Generally either proof-of-work or proof-of-stake-based.
/// Provides hooks into each of the major parts of block import.
pub trait Engine<M: Machine>: Sync + Send {
	/// The name of this engine.
	fn name(&self) -> &str;

	/// Get access to the underlying state machine.
	// TODO: decouple.
	fn machine(&self) -> &M;

	/// The number of additional header fields required for this engine.
	fn seal_fields(&self, _header: &M::Header) -> usize { 0 }

	/// Additional engine-specific information for the user/developer concerning `header`.
	fn extra_info(&self, _header: &M::Header) -> BTreeMap<String, String> { BTreeMap::new() }

	/// Maximum number of uncles a block is allowed to declare.
	fn maximum_uncle_count(&self, _block: BlockNumber) -> usize { 0 }

	/// The number of generations back that uncles can be.
	fn maximum_uncle_age(&self) -> usize { 6 }

	/// Block transformation functions, before the transactions.
	/// `epoch_begin` set to true if this block kicks off an epoch.
	fn on_new_block(
		&self,
		_block: &mut M::LiveBlock,
		_epoch_begin: bool,
		_ancestry: &mut Iterator<Item=M::ExtendedHeader>,
	) -> Result<(), M::Error> {
		Ok(())
	}

	/// Block transformation functions, after the transactions.
	fn on_close_block(&self, _block: &mut M::LiveBlock) -> Result<(), M::Error> {
		Ok(())
	}

	/// None means that it requires external input (e.g. PoW) to seal a block.
	/// Some(true) means the engine is currently prime for seal generation (i.e. node is the current validator).
	/// Some(false) means that the node might seal internally but is not qualified now.
	fn seals_internally(&self) -> Option<bool> { None }

	/// Attempt to seal the block internally.
	///
	/// If `Some` is returned, then you get a valid seal.
	///
	/// This operation is synchronous and may (quite reasonably) not be available, in which None will
	/// be returned.
	///
	/// It is fine to require access to state or a full client for this function, since
	/// light clients do not generate seals.
	fn generate_seal(&self, _block: &M::LiveBlock, _parent: &M::Header) -> Seal { Seal::None }

	/// Verify a locally-generated seal of a header.
	///
	/// If this engine seals internally,
	/// no checks have to be done here, since all internally generated seals
	/// should be valid.
	///
	/// Externally-generated seals (e.g. PoW) will need to be checked for validity.
	///
	/// It is fine to require access to state or a full client for this function, since
	/// light clients do not generate seals.
	fn verify_local_seal(&self, header: &M::Header) -> Result<(), M::Error>;

	/// Phase 1 quick block verification. Only does checks that are cheap. Returns either a null `Ok` or a general error detailing the problem with import.
	fn verify_block_basic(&self, _header: &M::Header) -> Result<(), M::Error> { Ok(()) }

	/// Phase 2 verification. Perform costly checks such as transaction signatures. Returns either a null `Ok` or a general error detailing the problem with import.
	fn verify_block_unordered(&self, _header: &M::Header) -> Result<(), M::Error> { Ok(()) }

	/// Phase 3 verification. Check block information against parent. Returns either a null `Ok` or a general error detailing the problem with import.
	fn verify_block_family(&self, _header: &M::Header, _parent: &M::Header) -> Result<(), M::Error> { Ok(()) }

	/// Phase 4 verification. Verify block header against potentially external data.
	/// Should only be called when `register_client` has been called previously.
	fn verify_block_external(&self, _header: &M::Header) -> Result<(), M::Error> { Ok(()) }

	/// Genesis epoch data.
	fn genesis_epoch_data<'a>(&self, _header: &M::Header, _state: &<M as Localized<'a>>::StateContext) -> Result<Vec<u8>, String> { Ok(Vec::new()) }

	/// Whether an epoch change is signalled at the given header but will require finality.
	/// If a change can be enacted immediately then return `No` from this function but
	/// `Yes` from `is_epoch_end`.
	///
	/// If auxiliary data of the block is required, return an auxiliary request and the function will be
	/// called again with them.
	/// Return `Yes` or `No` when the answer is definitively known.
	///
	/// Should not interact with state.
	fn signals_epoch_end<'a>(&self, _header: &M::Header, _aux: <M as Localized<'a>>::AuxiliaryData)
		-> EpochChange<M>
	{
		EpochChange::No
	}

	/// Whether a block is the end of an epoch.
	///
	/// This either means that an immediate transition occurs or a block signalling transition
	/// has reached finality. The `Headers` given are not guaranteed to return any blocks
	/// from any epoch other than the current.
	///
	/// Return optional transition proof.
	fn is_epoch_end(
		&self,
		_chain_head: &M::Header,
		_chain: &Headers<M::Header>,
		_transition_store: &PendingTransitionStore,
	) -> Option<Vec<u8>> {
		None
	}

	/// Create an epoch verifier from validation proof and a flag indicating
	/// whether finality is required.
	fn epoch_verifier<'a>(&self, _header: &M::Header, _proof: &'a [u8]) -> ConstructedVerifier<'a, M> {
		ConstructedVerifier::Trusted(Box::new(self::epoch::NoOp))
	}

	/// Populate a header's fields based on its parent's header.
	/// Usually implements the chain scoring rule based on weight.
	fn populate_from_parent(&self, _header: &mut M::Header, _parent: &M::Header) { }

	/// Handle any potential consensus messages;
	/// updating consensus state and potentially issuing a new one.
	fn handle_message(&self, _message: &[u8]) -> Result<(), EngineError> { Err(EngineError::UnexpectedMessage) }

	/// Find out if the block is a proposal block and should not be inserted into the DB.
	/// Takes a header of a fully verified block.
	fn is_proposal(&self, _verified_header: &M::Header) -> bool { false }

	/// Register an account which signs consensus messages.
	fn set_signer(&self, _account_provider: Arc<AccountProvider>, _address: Address, _password: String) {}

	/// Sign using the EngineSigner, to be used for consensus tx signing.
	fn sign(&self, _hash: H256) -> Result<Signature, M::Error> { unimplemented!() }

	/// Add Client which can be used for sealing, potentially querying the state and sending messages.
	fn register_client(&self, _client: Weak<M::EngineClient>) {}

	/// Trigger next step of the consensus engine.
	fn step(&self) {}

	/// Stops any services that the may hold the Engine and makes it safe to drop.
	fn stop(&self) {}

	/// Create a factory for building snapshot chunks and restoring from them.
	/// Returning `None` indicates that this engine doesn't support snapshot creation.
	fn snapshot_components(&self) -> Option<Box<SnapshotComponents>> {
		None
	}

	/// Whether this engine supports warp sync.
	fn supports_warp(&self) -> bool {
		self.snapshot_components().is_some()
	}

	/// Return a new open block header timestamp based on the parent timestamp.
	fn open_block_header_timestamp(&self, parent_timestamp: u64) -> u64 {
		use std::{time, cmp};

		let now = time::SystemTime::now().duration_since(time::UNIX_EPOCH).unwrap_or_default();
		cmp::max(now.as_secs() as u64, parent_timestamp + 1)
	}

	/// Check whether the parent timestamp is valid.
	fn is_timestamp_valid(&self, header_timestamp: u64, parent_timestamp: u64) -> bool {
		header_timestamp > parent_timestamp
	}

	/// Gather all ancestry actions. Called at the last stage when a block is committed. The Engine must guarantee that
	/// the ancestry exists.
	fn ancestry_actions(&self, _block: &M::LiveBlock, _ancestry: &mut Iterator<Item=M::ExtendedHeader>) -> Vec<AncestryAction> {
		Vec::new()
	}

	/// Check whether the given new block is the best block, after finalization check.
	fn fork_choice(&self, new: &M::ExtendedHeader, best: &M::ExtendedHeader) -> ForkChoice;
}

/// Check whether a given block is the best block based on the default total difficulty rule.
pub fn total_difficulty_fork_choice<T: TotalScoredHeader>(new: &T, best: &T) -> ForkChoice where <T as TotalScoredHeader>::Value: Ord {
	if new.total_score() > best.total_score() {
		ForkChoice::New
	} else {
		ForkChoice::Old
	}
}

/// Common type alias for an engine coupled with an Ethereum-like state machine.
// TODO: make this a _trait_ alias when those exist.
// fortunately the effect is largely the same since engines are mostly used
// via trait objects.
pub trait EthEngine: Engine<::machine::EthereumMachine> {
	/// Get the general parameters of the chain.
	fn params(&self) -> &CommonParams {
		self.machine().params()
	}

	/// Get the EVM schedule for the given block number.
	fn schedule(&self, block_number: BlockNumber) -> Schedule {
		self.machine().schedule(block_number)
	}

	/// Builtin-contracts for the chain..
	fn builtins(&self) -> &BTreeMap<Address, Builtin> {
		self.machine().builtins()
	}

	/// Attempt to get a handle to a built-in contract.
	/// Only returns references to activated built-ins.
	fn builtin(&self, a: &Address, block_number: BlockNumber) -> Option<&Builtin> {
		self.machine().builtin(a, block_number)
	}

	/// Some intrinsic operation parameters; by default they take their value from the `spec()`'s `engine_params`.
	fn maximum_extra_data_size(&self) -> usize {
		self.machine().maximum_extra_data_size()
	}

	/// The nonce with which accounts begin at given block.
	fn account_start_nonce(&self, block: BlockNumber) -> U256 {
		self.machine().account_start_nonce(block)
	}

	/// The network ID that transactions should be signed with.
	fn signing_chain_id(&self, env_info: &EnvInfo) -> Option<u64> {
		self.machine().signing_chain_id(env_info)
	}

	/// Returns new contract address generation scheme at given block number.
	fn create_address_scheme(&self, number: BlockNumber) -> CreateContractAddress {
		self.machine().create_address_scheme(number)
	}

	/// Verify a particular transaction is valid.
	///
	/// Unordered verification doesn't rely on the transaction execution order,
	/// i.e. it should only verify stuff that doesn't assume any previous transactions
	/// has already been verified and executed.
	///
	/// NOTE This function consumes an `UnverifiedTransaction` and produces `SignedTransaction`
	/// which implies that a heavy check of the signature is performed here.
	fn verify_transaction_unordered(&self, t: UnverifiedTransaction, header: &Header) -> Result<SignedTransaction, transaction::Error> {
		self.machine().verify_transaction_unordered(t, header)
	}

	/// Perform basic/cheap transaction verification.
	///
	/// This should include all cheap checks that can be done before
	/// actually checking the signature, like chain-replay protection.
	///
	/// NOTE This is done before the signature is recovered so avoid
	/// doing any state-touching checks that might be expensive.
	///
	/// TODO: Add flags for which bits of the transaction to check.
	/// TODO: consider including State in the params.
	fn verify_transaction_basic(&self, t: &UnverifiedTransaction, header: &Header) -> Result<(), transaction::Error> {
		self.machine().verify_transaction_basic(t, header)
	}

	/// Additional information.
	fn additional_params(&self) -> HashMap<String, String> {
		self.machine().additional_params()
	}

	/// Performs pre-validation of RLP decoded transaction before other processing
	fn decode_transaction(&self, transaction: &[u8]) -> Result<UnverifiedTransaction, transaction::Error> {
		self.machine().decode_transaction(transaction)
	}
}

// convenience wrappers for existing functions.
impl<T> EthEngine for T where T: Engine<::machine::EthereumMachine> { }