// This file is part of Substrate.

// Copyright (C) 2017-2020 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! GRANDPA Consensus module for runtime.
//!
//! This manages the GRANDPA authority set ready for the native code.
//! These authorities are only for GRANDPA finality, not for consensus overall.
//!
//! In the future, it will also handle misbehavior reports, and on-chain
//! finality notifications.
//!
//! For full integration with GRANDPA, the `GrandpaApi` should be implemented.
//! The necessary items are re-exported via the `fg_primitives` crate.

#![cfg_attr(not(feature = "std"), no_std)]

// re-export since this is necessary for `impl_apis` in runtime.
pub use sp_finality_grandpa as fg_primitives;

use sp_std::prelude::*;

use codec::{self as codec, Decode, Encode};
pub use fg_primitives::{AuthorityId, AuthorityList, AuthorityWeight, VersionedAuthorityList};
use fg_primitives::{
	ConsensusLog, EquivocationProof, ScheduledChange, SetId, GRANDPA_AUTHORITIES_KEY,
	GRANDPA_ENGINE_ID,
};
use frame_support::{
	decl_error, decl_event, decl_module, decl_storage, storage, traits::KeyOwnerProofSystem,
	Parameter,
};
use frame_system::{ensure_none, ensure_root, ensure_signed};
use pallet_finality_tracker::OnFinalizationStalled;
use sp_runtime::{
	generic::DigestItem,
	traits::Zero,
	DispatchResult, KeyTypeId,
};
use sp_session::{GetSessionNumber, GetValidatorCount};
use sp_staking::SessionIndex;

mod equivocation;

#[cfg(any(feature = "runtime-benchmarks", test))]
mod benchmarking;
#[cfg(all(feature = "std", test))]
mod mock;
#[cfg(all(feature = "std", test))]
mod tests;

pub use equivocation::{
	EquivocationHandler, GrandpaEquivocationOffence, GrandpaOffence, GrandpaTimeSlot,
	HandleEquivocation,
};

pub trait Trait: frame_system::Trait {
	/// The event type of this module.
	type Event: From<Event> + Into<<Self as frame_system::Trait>::Event>;

	/// The function call.
	type Call: From<Call<Self>>;

	/// The proof of key ownership, used for validating equivocation reports.
	/// The proof must include the session index and validator count of the
	/// session at which the equivocation occurred.
	type KeyOwnerProof: Parameter + GetSessionNumber + GetValidatorCount;

	/// The identification of a key owner, used when reporting equivocations.
	type KeyOwnerIdentification: Parameter;

	/// A system for proving ownership of keys, i.e. that a given key was part
	/// of a validator set, needed for validating equivocation reports.
	type KeyOwnerProofSystem: KeyOwnerProofSystem<
		(KeyTypeId, AuthorityId),
		Proof = Self::KeyOwnerProof,
		IdentificationTuple = Self::KeyOwnerIdentification,
	>;

	/// The equivocation handling subsystem, defines methods to report an
	/// offence (after the equivocation has been validated) and for submitting a
	/// transaction to report an equivocation (from an offchain context).
	/// NOTE: when enabling equivocation handling (i.e. this type isn't set to
	/// `()`) you must use this pallet's `ValidateUnsigned` in the runtime
	/// definition.
	type HandleEquivocation: HandleEquivocation<Self>;
}

/// A stored pending change, old format.
// TODO: remove shim
// https://github.com/paritytech/substrate/issues/1614
#[derive(Encode, Decode)]
pub struct OldStoredPendingChange<N> {
	/// The block number this was scheduled at.
	pub scheduled_at: N,
	/// The delay in blocks until it will be applied.
	pub delay: N,
	/// The next authority set.
	pub next_authorities: AuthorityList,
}

/// A stored pending change.
#[derive(Encode)]
pub struct StoredPendingChange<N> {
	/// The block number this was scheduled at.
	pub scheduled_at: N,
	/// The delay in blocks until it will be applied.
	pub delay: N,
	/// The next authority set.
	pub next_authorities: AuthorityList,
	/// If defined it means the change was forced and the given block number
	/// indicates the median last finalized block when the change was signaled.
	pub forced: Option<N>,
}

impl<N: Decode> Decode for StoredPendingChange<N> {
	fn decode<I: codec::Input>(value: &mut I) -> core::result::Result<Self, codec::Error> {
		let old = OldStoredPendingChange::decode(value)?;
		let forced = <Option<N>>::decode(value).unwrap_or(None);

		Ok(StoredPendingChange {
			scheduled_at: old.scheduled_at,
			delay: old.delay,
			next_authorities: old.next_authorities,
			forced,
		})
	}
}

/// Current state of the GRANDPA authority set. State transitions must happen in
/// the same order of states defined below, e.g. `Paused` implies a prior
/// `PendingPause`.
#[derive(Decode, Encode)]
#[cfg_attr(test, derive(Debug, PartialEq))]
pub enum StoredState<N> {
	/// The current authority set is live, and GRANDPA is enabled.
	Live,
	/// There is a pending pause event which will be enacted at the given block
	/// height.
	PendingPause {
		/// Block at which the intention to pause was scheduled.
		scheduled_at: N,
		/// Number of blocks after which the change will be enacted.
		delay: N
	},
	/// The current GRANDPA authority set is paused.
	Paused,
	/// There is a pending resume event which will be enacted at the given block
	/// height.
	PendingResume {
		/// Block at which the intention to resume was scheduled.
		scheduled_at: N,
		/// Number of blocks after which the change will be enacted.
		delay: N,
	},
}

decl_event! {
	pub enum Event {
		/// New authority set has been applied. [authority_set]
		NewAuthorities(AuthorityList),
		/// Current authority set has been paused.
		Paused,
		/// Current authority set has been resumed.
		Resumed,
	}
}

decl_error! {
	pub enum Error for Module<T: Trait> {
		/// Attempt to signal GRANDPA pause when the authority set isn't live
		/// (either paused or already pending pause).
		PauseFailed,
		/// Attempt to signal GRANDPA resume when the authority set isn't paused
		/// (either live or already pending resume).
		ResumeFailed,
		/// Attempt to signal GRANDPA change with one already pending.
		ChangePending,
		/// Cannot signal forced change so soon after last.
		TooSoon,
		/// A key ownership proof provided as part of an equivocation report is invalid.
		InvalidKeyOwnershipProof,
		/// An equivocation proof provided as part of an equivocation report is invalid.
		InvalidEquivocationProof,
		/// A given equivocation report is valid but already previously reported.
		DuplicateOffenceReport,
	}
}

decl_storage! {
	trait Store for Module<T: Trait> as GrandpaFinality {
		/// State of the current authority set.
		State get(fn state): StoredState<T::BlockNumber> = StoredState::Live;

		/// Pending change: (signaled at, scheduled change).
		PendingChange get(fn pending_change): Option<StoredPendingChange<T::BlockNumber>>;

		/// next block number where we can force a change.
		NextForced get(fn next_forced): Option<T::BlockNumber>;

		/// `true` if we are currently stalled.
		Stalled get(fn stalled): Option<(T::BlockNumber, T::BlockNumber)>;

		/// The number of changes (both in terms of keys and underlying economic responsibilities)
		/// in the "set" of Grandpa validators from genesis.
		CurrentSetId get(fn current_set_id) build(|_| fg_primitives::SetId::default()): SetId;

		/// A mapping from grandpa set ID to the index of the *most recent* session for which its
		/// members were responsible.
		///
		/// TWOX-NOTE: `SetId` is not under user control.
		SetIdSession get(fn session_for_set): map hasher(twox_64_concat) SetId => Option<SessionIndex>;
	}
	add_extra_genesis {
		config(authorities): AuthorityList;
		build(|config| {
			Module::<T>::initialize(&config.authorities)
		})
	}
}

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		type Error = Error<T>;

		fn deposit_event() = default;

		/// Report voter equivocation/misbehavior. This method will verify the
		/// equivocation proof and validate the given key ownership proof
		/// against the extracted offender. If both are valid, the offence
		/// will be reported.
		#[weight = weight_for::report_equivocation::<T>(key_owner_proof.validator_count())]
		fn report_equivocation(
			origin,
			equivocation_proof: EquivocationProof<T::Hash, T::BlockNumber>,
			key_owner_proof: T::KeyOwnerProof,
		) {
			let reporter = ensure_signed(origin)?;

			Self::do_report_equivocation(
				Some(reporter),
				equivocation_proof,
				key_owner_proof,
			)?;
		}

		/// Report voter equivocation/misbehavior. This method will verify the
		/// equivocation proof and validate the given key ownership proof
		/// against the extracted offender. If both are valid, the offence
		/// will be reported.
		///
		/// This extrinsic must be called unsigned and it is expected that only
		/// block authors will call it (validated in `ValidateUnsigned`), as such
		/// if the block author is defined it will be defined as the equivocation
		/// reporter.
		#[weight = weight_for::report_equivocation::<T>(key_owner_proof.validator_count())]
		fn report_equivocation_unsigned(
			origin,
			equivocation_proof: EquivocationProof<T::Hash, T::BlockNumber>,
			key_owner_proof: T::KeyOwnerProof,
		) {
			ensure_none(origin)?;

			Self::do_report_equivocation(
				T::HandleEquivocation::block_author(),
				equivocation_proof,
				key_owner_proof,
			)?;
		}

		/// Note that the current authority set of the GRANDPA finality gadget has
		/// stalled. This will trigger a forced authority set change at the beginning
		/// of the next session, to be enacted `delay` blocks after that. The delay
		/// should be high enough to safely assume that the block signalling the
		/// forced change will not be re-orged (e.g. 1000 blocks). The GRANDPA voters
		/// will start the new authority set using the given finalized block as base.
		/// Only callable by root.
		#[weight = weight_for::note_stalled::<T>()]
		fn note_stalled(
			origin,
			delay: T::BlockNumber,
			best_finalized_block_number: T::BlockNumber,
		) {
			ensure_root(origin)?;

			Self::on_stalled(delay, best_finalized_block_number)
		}

		fn on_finalize(block_number: T::BlockNumber) {
			// check for scheduled pending authority set changes
			if let Some(pending_change) = <PendingChange<T>>::get() {
				// emit signal if we're at the block that scheduled the change
				if block_number == pending_change.scheduled_at {
					if let Some(median) = pending_change.forced {
						Self::deposit_log(ConsensusLog::ForcedChange(
							median,
							ScheduledChange {
								delay: pending_change.delay,
								next_authorities: pending_change.next_authorities.clone(),
							}
						))
					} else {
						Self::deposit_log(ConsensusLog::ScheduledChange(
							ScheduledChange {
								delay: pending_change.delay,
								next_authorities: pending_change.next_authorities.clone(),
							}
						));
					}
				}

				// enact the change if we've reached the enacting block
				if block_number == pending_change.scheduled_at + pending_change.delay {
					Self::set_grandpa_authorities(&pending_change.next_authorities);
					Self::deposit_event(
						Event::NewAuthorities(pending_change.next_authorities)
					);
					<PendingChange<T>>::kill();
				}
			}

			// check for scheduled pending state changes
			match <State<T>>::get() {
				StoredState::PendingPause { scheduled_at, delay } => {
					// signal change to pause
					if block_number == scheduled_at {
						Self::deposit_log(ConsensusLog::Pause(delay));
					}

					// enact change to paused state
					if block_number == scheduled_at + delay {
						<State<T>>::put(StoredState::Paused);
						Self::deposit_event(Event::Paused);
					}
				},
				StoredState::PendingResume { scheduled_at, delay } => {
					// signal change to resume
					if block_number == scheduled_at {
						Self::deposit_log(ConsensusLog::Resume(delay));
					}

					// enact change to live state
					if block_number == scheduled_at + delay {
						<State<T>>::put(StoredState::Live);
						Self::deposit_event(Event::Resumed);
					}
				},
				_ => {},
			}
		}
	}
}

mod weight_for {
	use frame_support::{
		traits::Get,
		weights::{
			constants::{WEIGHT_PER_MICROS, WEIGHT_PER_NANOS},
			Weight,
		},
	};

	pub fn report_equivocation<T: super::Trait>(validator_count: u32) -> Weight {
		// we take the validator set count from the membership proof to
		// calculate the weight but we set a floor of 100 validators.
		let validator_count = validator_count.max(100) as u64;

		// worst case we are considering is that the given offender
		// is backed by 200 nominators
		const MAX_NOMINATORS: u64 = 200;

		// checking membership proof
		(35 * WEIGHT_PER_MICROS)
			.saturating_add((175 * WEIGHT_PER_NANOS).saturating_mul(validator_count))
			.saturating_add(T::DbWeight::get().reads(5))
			// check equivocation proof
			.saturating_add(95 * WEIGHT_PER_MICROS)
			// report offence
			.saturating_add(110 * WEIGHT_PER_MICROS)
			.saturating_add(25 * WEIGHT_PER_MICROS * MAX_NOMINATORS)
			.saturating_add(T::DbWeight::get().reads(14 + 3 * MAX_NOMINATORS))
			.saturating_add(T::DbWeight::get().writes(10 + 3 * MAX_NOMINATORS))
			// fetching set id -> session index mappings
			.saturating_add(T::DbWeight::get().reads(2))
	}

	pub fn note_stalled<T: super::Trait>() -> Weight {
		(3 * WEIGHT_PER_MICROS)
			.saturating_add(T::DbWeight::get().writes(1))
	}
}

impl<T: Trait> Module<T> {
	/// Get the current set of authorities, along with their respective weights.
	pub fn grandpa_authorities() -> AuthorityList {
		storage::unhashed::get_or_default::<VersionedAuthorityList>(GRANDPA_AUTHORITIES_KEY).into()
	}

	/// Set the current set of authorities, along with their respective weights.
	fn set_grandpa_authorities(authorities: &AuthorityList) {
		storage::unhashed::put(
			GRANDPA_AUTHORITIES_KEY,
			&VersionedAuthorityList::from(authorities),
		);
	}

	/// Schedule GRANDPA to pause starting in the given number of blocks.
	/// Cannot be done when already paused.
	pub fn schedule_pause(in_blocks: T::BlockNumber) -> DispatchResult {
		if let StoredState::Live = <State<T>>::get() {
			let scheduled_at = <frame_system::Module<T>>::block_number();
			<State<T>>::put(StoredState::PendingPause {
				delay: in_blocks,
				scheduled_at,
			});

			Ok(())
		} else {
			Err(Error::<T>::PauseFailed)?
		}
	}

	/// Schedule a resume of GRANDPA after pausing.
	pub fn schedule_resume(in_blocks: T::BlockNumber) -> DispatchResult {
		if let StoredState::Paused = <State<T>>::get() {
			let scheduled_at = <frame_system::Module<T>>::block_number();
			<State<T>>::put(StoredState::PendingResume {
				delay: in_blocks,
				scheduled_at,
			});

			Ok(())
		} else {
			Err(Error::<T>::ResumeFailed)?
		}
	}

	/// Schedule a change in the authorities.
	///
	/// The change will be applied at the end of execution of the block
	/// `in_blocks` after the current block. This value may be 0, in which
	/// case the change is applied at the end of the current block.
	///
	/// If the `forced` parameter is defined, this indicates that the current
	/// set has been synchronously determined to be offline and that after
	/// `in_blocks` the given change should be applied. The given block number
	/// indicates the median last finalized block number and it should be used
	/// as the canon block when starting the new grandpa voter.
	///
	/// No change should be signaled while any change is pending. Returns
	/// an error if a change is already pending.
	pub fn schedule_change(
		next_authorities: AuthorityList,
		in_blocks: T::BlockNumber,
		forced: Option<T::BlockNumber>,
	) -> DispatchResult {
		if !<PendingChange<T>>::exists() {
			let scheduled_at = <frame_system::Module<T>>::block_number();

			if let Some(_) = forced {
				if Self::next_forced().map_or(false, |next| next > scheduled_at) {
					Err(Error::<T>::TooSoon)?
				}

				// only allow the next forced change when twice the window has passed since
				// this one.
				<NextForced<T>>::put(scheduled_at + in_blocks * 2.into());
			}

			<PendingChange<T>>::put(StoredPendingChange {
				delay: in_blocks,
				scheduled_at,
				next_authorities,
				forced,
			});

			Ok(())
		} else {
			Err(Error::<T>::ChangePending)?
		}
	}

	/// Deposit one of this module's logs.
	fn deposit_log(log: ConsensusLog<T::BlockNumber>) {
		let log: DigestItem<T::Hash> = DigestItem::Consensus(GRANDPA_ENGINE_ID, log.encode());
		<frame_system::Module<T>>::deposit_log(log.into());
	}

	// Perform module initialization, abstracted so that it can be called either through genesis
	// config builder or through `on_genesis_session`.
	fn initialize(authorities: &AuthorityList) {
		if !authorities.is_empty() {
			assert!(
				Self::grandpa_authorities().is_empty(),
				"Authorities are already initialized!"
			);
			Self::set_grandpa_authorities(authorities);
		}

		// NOTE: initialize first session of first set. this is necessary for
		// the genesis set and session since we only update the set -> session
		// mapping whenever a new session starts, i.e. through `on_new_session`.
		SetIdSession::insert(0, 0);
	}

	fn do_report_equivocation(
		reporter: Option<T::AccountId>,
		equivocation_proof: EquivocationProof<T::Hash, T::BlockNumber>,
		key_owner_proof: T::KeyOwnerProof,
	) -> Result<(), Error<T>> {
		// we check the equivocation within the context of its set id (and
		// associated session) and round. we also need to know the validator
		// set count when the offence since it is required to calculate the
		// slash amount.
		let set_id = equivocation_proof.set_id();
		let round = equivocation_proof.round();
		let session_index = key_owner_proof.session();
		let validator_count = key_owner_proof.validator_count();

		// validate the key ownership proof extracting the id of the offender.
		let offender =
			T::KeyOwnerProofSystem::check_proof(
				(fg_primitives::KEY_TYPE, equivocation_proof.offender().clone()),
				key_owner_proof,
			).ok_or(Error::<T>::InvalidKeyOwnershipProof)?;

		// validate equivocation proof (check votes are different and
		// signatures are valid).
		if !sp_finality_grandpa::check_equivocation_proof(equivocation_proof) {
			return Err(Error::<T>::InvalidEquivocationProof.into());
		}

		// fetch the current and previous sets last session index. on the
		// genesis set there's no previous set.
		let previous_set_id_session_index = if set_id == 0 {
			None
		} else {
			let session_index =
				if let Some(session_id) = Self::session_for_set(set_id - 1) {
					session_id
				} else {
					return Err(Error::<T>::InvalidEquivocationProof.into());
				};

			Some(session_index)
		};

		let set_id_session_index =
			if let Some(session_id) = Self::session_for_set(set_id) {
				session_id
			} else {
				return Err(Error::<T>::InvalidEquivocationProof.into());
			};

		// check that the session id for the membership proof is within the
		// bounds of the set id reported in the equivocation.
		if session_index > set_id_session_index ||
			previous_set_id_session_index
			.map(|previous_index| session_index <= previous_index)
			.unwrap_or(false)
		{
			return Err(Error::<T>::InvalidEquivocationProof.into());
		}

		// report to the offences module rewarding the sender.
		T::HandleEquivocation::report_offence(
			reporter.into_iter().collect(),
			<T::HandleEquivocation as HandleEquivocation<T>>::Offence::new(
				session_index,
				validator_count,
				offender,
				set_id,
				round,
			),
		).map_err(|_| Error::<T>::DuplicateOffenceReport)
	}

	/// Submits an extrinsic to report an equivocation. This method will create
	/// an unsigned extrinsic with a call to `report_equivocation_unsigned` and
	/// will push the transaction to the pool. Only useful in an offchain
	/// context.
	pub fn submit_unsigned_equivocation_report(
		equivocation_proof: EquivocationProof<T::Hash, T::BlockNumber>,
		key_owner_proof: T::KeyOwnerProof,
	) -> Option<()> {
		T::HandleEquivocation::submit_unsigned_equivocation_report(
			equivocation_proof,
			key_owner_proof,
		)
		.ok()
	}
}

impl<T: Trait> sp_runtime::BoundToRuntimeAppPublic for Module<T> {
	type Public = AuthorityId;
}

impl<T: Trait> pallet_session::OneSessionHandler<T::AccountId> for Module<T>
	where T: pallet_session::Trait
{
	type Key = AuthorityId;

	fn on_genesis_session<'a, I: 'a>(validators: I)
		where I: Iterator<Item=(&'a T::AccountId, AuthorityId)>
	{
		let authorities = validators.map(|(_, k)| (k, 1)).collect::<Vec<_>>();
		Self::initialize(&authorities);
	}

	fn on_new_session<'a, I: 'a>(changed: bool, validators: I, _queued_validators: I)
		where I: Iterator<Item=(&'a T::AccountId, AuthorityId)>
	{
		// Always issue a change if `session` says that the validators have changed.
		// Even if their session keys are the same as before, the underlying economic
		// identities have changed.
		let current_set_id = if changed || <Stalled<T>>::exists() {
			let next_authorities = validators.map(|(_, k)| (k, 1)).collect::<Vec<_>>();

			let res = if let Some((further_wait, median)) = <Stalled<T>>::take() {
				Self::schedule_change(next_authorities, further_wait, Some(median))
			} else {
				Self::schedule_change(next_authorities, Zero::zero(), None)
			};

			if res.is_ok() {
				CurrentSetId::mutate(|s| {
					*s += 1;
					*s
				})
			} else {
				// either the session module signalled that the validators have changed
				// or the set was stalled. but since we didn't successfully schedule
				// an authority set change we do not increment the set id.
				Self::current_set_id()
			}
		} else {
			// nothing's changed, neither economic conditions nor session keys. update the pointer
			// of the current set.
			Self::current_set_id()
		};

		// if we didn't issue a change, we update the mapping to note that the current
		// set corresponds to the latest equivalent session (i.e. now).
		let session_index = <pallet_session::Module<T>>::current_index();
		SetIdSession::insert(current_set_id, &session_index);
	}

	fn on_disabled(i: usize) {
		Self::deposit_log(ConsensusLog::OnDisabled(i as u64))
	}
}

impl<T: Trait> OnFinalizationStalled<T::BlockNumber> for Module<T> {
	fn on_stalled(further_wait: T::BlockNumber, median: T::BlockNumber) {
		// when we record old authority sets, we can use `pallet_finality_tracker::median`
		// to figure out _who_ failed. until then, we can't meaningfully guard
		// against `next == last` the way that normal session changes do.
		<Stalled<T>>::put((further_wait, median));
	}
}