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// Copyright 2017-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! # Aura Module
//!
//! - [`aura::Trait`](./trait.Trait.html)
//! - [`Module`](./struct.Module.html)
//!
//! ## Overview
//!
//! The Aura module extends Aura consensus by managing offline reporting.
//!
//! ## Interface
//!
//! ### Public Functions
//!
//! - `slot_duration` - Determine the Aura slot-duration based on the Timestamp module configuration.
//!
//! ## Related Modules
//!
//! - [Timestamp](../srml_timestamp/index.html): The Timestamp module is used in Aura to track
//! consensus rounds (via `slots`).
//! - [Consensus](../srml_consensus/index.html): The Consensus module does not relate directly to Aura,
//!  but serves to manage offline reporting by implementing `ProvideInherent` in a similar way.
//!
//! ## References
//!
//! If you're interested in hacking on this module, it is useful to understand the interaction with
//! `substrate/core/inherents/src/lib.rs` and, specifically, the required implementation of
//! [`ProvideInherent`](../substrate_inherents/trait.ProvideInherent.html) and
//! [`ProvideInherentData`](../substrate_inherents/trait.ProvideInherentData.html) to create and check inherents.

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

pub use timestamp;

use rstd::{result, prelude::*};
use codec::{Encode, Decode};
use srml_support::{
	decl_storage, decl_module, Parameter, storage::StorageValue, traits::{Get, FindAuthor},
	ConsensusEngineId,
};
use app_crypto::AppPublic;
use sr_primitives::{
	traits::{SaturatedConversion, Saturating, Zero, Member, IsMember}, generic::DigestItem,
};
use timestamp::OnTimestampSet;
#[cfg(feature = "std")]
use timestamp::TimestampInherentData;
use inherents::{RuntimeString, InherentIdentifier, InherentData, ProvideInherent, MakeFatalError};
#[cfg(feature = "std")]
use inherents::{InherentDataProviders, ProvideInherentData};
use substrate_consensus_aura_primitives::{AURA_ENGINE_ID, ConsensusLog, AuthorityIndex};

mod mock;
mod tests;

/// The Aura inherent identifier.
pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"auraslot";

/// The type of the Aura inherent.
pub type InherentType = u64;

/// Auxiliary trait to extract Aura inherent data.
pub trait AuraInherentData {
	/// Get aura inherent data.
	fn aura_inherent_data(&self) -> result::Result<InherentType, RuntimeString>;
	/// Replace aura inherent data.
	fn aura_replace_inherent_data(&mut self, new: InherentType);
}

impl AuraInherentData for InherentData {
	fn aura_inherent_data(&self) -> result::Result<InherentType, RuntimeString> {
		self.get_data(&INHERENT_IDENTIFIER)
			.and_then(|r| r.ok_or_else(|| "Aura inherent data not found".into()))
	}

	fn aura_replace_inherent_data(&mut self, new: InherentType) {
		self.replace_data(INHERENT_IDENTIFIER, &new);
	}
}

/// Provides the slot duration inherent data for `Aura`.
#[cfg(feature = "std")]
pub struct InherentDataProvider {
	slot_duration: u64,
}

#[cfg(feature = "std")]
impl InherentDataProvider {
	pub fn new(slot_duration: u64) -> Self {
		Self {
			slot_duration
		}
	}
}

#[cfg(feature = "std")]
impl ProvideInherentData for InherentDataProvider {
	fn on_register(
		&self,
		providers: &InherentDataProviders,
	) -> result::Result<(), RuntimeString> {
		if !providers.has_provider(&timestamp::INHERENT_IDENTIFIER) {
			// Add the timestamp inherent data provider, as we require it.
			providers.register_provider(timestamp::InherentDataProvider)
		} else {
			Ok(())
		}
	}

	fn inherent_identifier(&self) -> &'static inherents::InherentIdentifier {
		&INHERENT_IDENTIFIER
	}

	fn provide_inherent_data(
		&self,
		inherent_data: &mut InherentData,
	) -> result::Result<(), RuntimeString> {
		let timestamp = inherent_data.timestamp_inherent_data()?;
		let slot_num = timestamp / self.slot_duration;
		inherent_data.put_data(INHERENT_IDENTIFIER, &slot_num)
	}

	fn error_to_string(&self, error: &[u8]) -> Option<String> {
		RuntimeString::decode(&mut &error[..]).map(Into::into).ok()
	}
}

pub trait Trait: timestamp::Trait {
	/// The identifier type for an authority.
	type AuthorityId: Member + Parameter + AppPublic + Default;
}

decl_storage! {
	trait Store for Module<T: Trait> as Aura {
		/// The last timestamp.
		LastTimestamp get(last) build(|_| 0.into()): T::Moment;

		/// The current authorities
		pub Authorities get(authorities): Vec<T::AuthorityId>;
	}
	add_extra_genesis {
		config(authorities): Vec<T::AuthorityId>;
		build(|
			storage: &mut (sr_primitives::StorageOverlay, sr_primitives::ChildrenStorageOverlay),
			config: &GenesisConfig<T>
		| {
			runtime_io::with_storage(
				storage,
				|| Module::<T>::initialize_authorities(&config.authorities),
			);
		})
	}
}

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin { }
}

impl<T: Trait> Module<T> {
	fn change_authorities(new: Vec<T::AuthorityId>) {
		<Authorities<T>>::put(&new);

		let log: DigestItem<T::Hash> = DigestItem::Consensus(
			AURA_ENGINE_ID,
			ConsensusLog::AuthoritiesChange(new).encode()
		);
		<system::Module<T>>::deposit_log(log.into());
	}

	fn initialize_authorities(authorities: &[T::AuthorityId]) {
		if !authorities.is_empty() {
			assert!(<Authorities<T>>::get().is_empty(), "Authorities are already initialized!");
			<Authorities<T>>::put_ref(authorities);
		}
	}
}

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

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

	fn on_new_session<'a, I: 'a>(changed: bool, validators: I, _queued_validators: I)
		where I: Iterator<Item=(&'a T::AccountId, T::AuthorityId)>
	{
		// instant changes
		if changed {
			let next_authorities = validators.map(|(_, k)| k).collect::<Vec<_>>();
			let last_authorities = <Module<T>>::authorities();
			if next_authorities != last_authorities {
				Self::change_authorities(next_authorities);
			}
		}
	}

	fn on_disabled(i: usize) {
		let log: DigestItem<T::Hash> = DigestItem::Consensus(
			AURA_ENGINE_ID,
			ConsensusLog::<T::AuthorityId>::OnDisabled(i as AuthorityIndex).encode(),
		);

		<system::Module<T>>::deposit_log(log.into());
	}
}

impl<T: Trait> FindAuthor<u32> for Module<T> {
	fn find_author<'a, I>(digests: I) -> Option<u32> where
		I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>
	{
		for (id, mut data) in digests.into_iter() {
			if id == AURA_ENGINE_ID {
				if let Ok(slot_num) = u64::decode(&mut data) {
					let author_index = slot_num % Self::authorities().len() as u64;
					return Some(author_index as u32)
				}
			}
		}

		None
	}
}

impl<T: Trait> IsMember<T::AuthorityId> for Module<T> {
	fn is_member(authority_id: &T::AuthorityId) -> bool {
		Self::authorities()
			.iter()
			.any(|id| id == authority_id)
	}
}

impl<T: Trait> Module<T> {
	/// Determine the Aura slot-duration based on the Timestamp module configuration.
	pub fn slot_duration() -> T::Moment {
		// we double the minimum block-period so each author can always propose within
		// the majority of its slot.
		<T as timestamp::Trait>::MinimumPeriod::get().saturating_mul(2.into())
	}

	fn on_timestamp_set(now: T::Moment, slot_duration: T::Moment) {
		let last = Self::last();
		<Self as Store>::LastTimestamp::put(now.clone());

		if last.is_zero() {
			return;
		}

		assert!(!slot_duration.is_zero(), "Aura slot duration cannot be zero.");

		let last_slot = last / slot_duration.clone();
		let cur_slot = now / slot_duration;

		assert!(last_slot < cur_slot, "Only one block may be authored per slot.");

		// TODO [#3398] Generate offence report for all authorities that skipped their slots.
	}
}

impl<T: Trait> OnTimestampSet<T::Moment> for Module<T> {
	fn on_timestamp_set(moment: T::Moment) {
		Self::on_timestamp_set(moment, Self::slot_duration())
	}
}

impl<T: Trait> ProvideInherent for Module<T> {
	type Call = timestamp::Call<T>;
	type Error = MakeFatalError<RuntimeString>;
	const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;

	fn create_inherent(_: &InherentData) -> Option<Self::Call> {
		None
	}

	/// Verify the validity of the inherent using the timestamp.
	fn check_inherent(call: &Self::Call, data: &InherentData) -> result::Result<(), Self::Error> {
		let timestamp = match call {
			timestamp::Call::set(ref timestamp) => timestamp.clone(),
			_ => return Ok(()),
		};

		let timestamp_based_slot = timestamp / Self::slot_duration();

		let seal_slot = data.aura_inherent_data()?.saturated_into();

		if timestamp_based_slot == seal_slot {
			Ok(())
		} else {
			Err(RuntimeString::from("timestamp set in block doesn't match slot in seal").into())
		}
	}
}