mod.rs

		cycle_once -
			(cycle_once.saturating_sub(self.session_start_block) % self.group_rotation_frequency)
	}

	/// Returns the block number of the last rotation before or including the current block. If the
	/// current block is 10 and the rotation frequency is 5, this should return 10.
	pub fn last_rotation_at(&self) -> N {
		self.now -
			(self.now.saturating_sub(self.session_start_block) % self.group_rotation_frequency)
	}
}

/// Information about a core which is currently occupied.
#[derive(Clone, Encode, Decode, TypeInfo, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct OccupiedCore<H = Hash, N = BlockNumber> {
	// NOTE: this has no ParaId as it can be deduced from the candidate descriptor.
	/// If this core is freed by availability, this is the assignment that is next up on this
	/// core, if any. None if there is nothing queued for this core.
	pub next_up_on_available: Option<ScheduledCore>,
	/// The relay-chain block number this began occupying the core at.
	pub occupied_since: N,
	/// The relay-chain block this will time-out at, if any.
	pub time_out_at: N,
	/// If this core is freed by being timed-out, this is the assignment that is next up on this
	/// core. None if there is nothing queued for this core or there is no possibility of timing
	/// out.
	pub next_up_on_time_out: Option<ScheduledCore>,
	/// A bitfield with 1 bit for each validator in the set. `1` bits mean that the corresponding
	/// validators has attested to availability on-chain. A 2/3+ majority of `1` bits means that
	/// this will be available.
	pub availability: BitVec<u8, bitvec::order::Lsb0>,
	/// The group assigned to distribute availability pieces of this candidate.
	pub group_responsible: GroupIndex,
	/// The hash of the candidate occupying the core.
	pub candidate_hash: CandidateHash,
	/// The descriptor of the candidate occupying the core.
	pub candidate_descriptor: CandidateDescriptor<H>,
}

impl<H, N> OccupiedCore<H, N> {
	/// Get the Para currently occupying this core.
	pub fn para_id(&self) -> Id {
		self.candidate_descriptor.para_id
	}
}

/// Information about a core which is currently occupied.
#[derive(Clone, Encode, Decode, TypeInfo, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct ScheduledCore {
	/// The ID of a para scheduled.
	pub para_id: Id,
	/// DEPRECATED: see: <https://github.com/paritytech/polkadot/issues/7575>
	///
	/// Will be removed in a future version.
	pub collator: Option<CollatorId>,
}

/// The state of a particular availability core.
#[derive(Clone, Encode, Decode, TypeInfo, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub enum CoreState<H = Hash, N = BlockNumber> {
	/// The core is currently occupied.
	#[codec(index = 0)]
	Occupied(OccupiedCore<H, N>),
	/// The core is currently free, with a para scheduled and given the opportunity
	/// to occupy.
	///
	/// If a particular Collator is required to author this block, that is also present in this
	/// variant.
	#[codec(index = 1)]
	Scheduled(ScheduledCore),
	/// The core is currently free and there is nothing scheduled. This can be the case for
	/// parathread cores when there are no parathread blocks queued. Parachain cores will never be
	/// left idle.
	#[codec(index = 2)]
	Free,
}

impl<N> CoreState<N> {
	/// If this core state has a `para_id`, return it.
	pub fn para_id(&self) -> Option<Id> {
		match self {
			Self::Occupied(ref core) => Some(core.para_id()),
			Self::Scheduled(core) => Some(core.para_id),
			Self::Free => None,
		}
	}

	/// Is this core state `Self::Occupied`?
	pub fn is_occupied(&self) -> bool {
		matches!(self, Self::Occupied(_))
	}
}

/// An assumption being made about the state of an occupied core.
#[derive(Clone, Copy, Encode, Decode, TypeInfo, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(PartialEq, Eq, Hash))]
pub enum OccupiedCoreAssumption {
	/// The candidate occupying the core was made available and included to free the core.
	#[codec(index = 0)]
	Included,
	/// The candidate occupying the core timed out and freed the core without advancing the para.
	#[codec(index = 1)]
	TimedOut,
	/// The core was not occupied to begin with.
	#[codec(index = 2)]
	Free,
}

/// An even concerning a candidate.
#[derive(Clone, Encode, Decode, TypeInfo, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub enum CandidateEvent<H = Hash> {
	/// This candidate receipt was backed in the most recent block.
	/// This includes the core index the candidate is now occupying.
	#[codec(index = 0)]
	CandidateBacked(CandidateReceipt<H>, HeadData, CoreIndex, GroupIndex),
	/// This candidate receipt was included and became a parablock at the most recent block.
	/// This includes the core index the candidate was occupying as well as the group responsible
	/// for backing the candidate.
	#[codec(index = 1)]
	CandidateIncluded(CandidateReceipt<H>, HeadData, CoreIndex, GroupIndex),
	/// This candidate receipt was not made available in time and timed out.
	/// This includes the core index the candidate was occupying.
	#[codec(index = 2)]
	CandidateTimedOut(CandidateReceipt<H>, HeadData, CoreIndex),
}

/// Scraped runtime backing votes and resolved disputes.
#[derive(Clone, Encode, Decode, RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct ScrapedOnChainVotes<H: Encode + Decode = Hash> {
	/// The session in which the block was included.
	pub session: SessionIndex,
	/// Set of backing validators for each candidate, represented by its candidate
	/// receipt.
	pub backing_validators_per_candidate:
		Vec<(CandidateReceipt<H>, Vec<(ValidatorIndex, ValidityAttestation)>)>,
	/// On-chain-recorded set of disputes.
	/// Note that the above `backing_validators` are
	/// unrelated to the backers of the disputes candidates.
	pub disputes: MultiDisputeStatementSet,
}

/// A vote of approval on a candidate.
#[derive(Clone, RuntimeDebug)]
pub struct ApprovalVote(pub CandidateHash);

impl ApprovalVote {
	/// Yields the signing payload for this approval vote.
	pub fn signing_payload(&self, session_index: SessionIndex) -> Vec<u8> {
		const MAGIC: [u8; 4] = *b"APPR";

		(MAGIC, &self.0, session_index).encode()
	}
}

/// A vote of approval for multiple candidates.
#[derive(Clone, RuntimeDebug)]
pub struct ApprovalVoteMultipleCandidates<'a>(pub &'a [CandidateHash]);

impl<'a> ApprovalVoteMultipleCandidates<'a> {
	/// Yields the signing payload for this approval vote.
	pub fn signing_payload(&self, session_index: SessionIndex) -> Vec<u8> {
		const MAGIC: [u8; 4] = *b"APPR";
		// Make this backwards compatible with `ApprovalVote` so if we have just on candidate the
		// signature will look the same.
		// This gives us the nice benefit that old nodes can still check signatures when len is 1
		// and the new node can check the signature coming from old nodes.
		if self.0.len() == 1 {
			(MAGIC, self.0.first().expect("QED: we just checked"), session_index).encode()
		} else {
			(MAGIC, &self.0, session_index).encode()
		}
	}
}

/// Custom validity errors used in Polkadot while validating transactions.
#[repr(u8)]
pub enum ValidityError {
	/// The Ethereum signature is invalid.
	InvalidEthereumSignature = 0,
	/// The signer has no claim.
	SignerHasNoClaim = 1,
	/// No permission to execute the call.
	NoPermission = 2,
	/// An invalid statement was made for a claim.
	InvalidStatement = 3,
}

impl From<ValidityError> for u8 {
	fn from(err: ValidityError) -> Self {
		err as u8
	}
}

/// Abridged version of `HostConfiguration` (from the `Configuration` parachains host runtime
/// module) meant to be used by a parachain or PDK such as cumulus.
#[derive(Clone, Encode, Decode, RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct AbridgedHostConfiguration {
	/// The maximum validation code size, in bytes.
	pub max_code_size: u32,
	/// The maximum head-data size, in bytes.
	pub max_head_data_size: u32,
	/// Total number of individual messages allowed in the parachain -> relay-chain message queue.
	pub max_upward_queue_count: u32,
	/// Total size of messages allowed in the parachain -> relay-chain message queue before which
	/// no further messages may be added to it. If it exceeds this then the queue may contain only
	/// a single message.
	pub max_upward_queue_size: u32,
	/// The maximum size of an upward message that can be sent by a candidate.
	///
	/// This parameter affects the size upper bound of the `CandidateCommitments`.
	pub max_upward_message_size: u32,
	/// The maximum number of messages that a candidate can contain.
	///
	/// This parameter affects the size upper bound of the `CandidateCommitments`.
	pub max_upward_message_num_per_candidate: u32,
	/// The maximum number of outbound HRMP messages can be sent by a candidate.
	///
	/// This parameter affects the upper bound of size of `CandidateCommitments`.
	pub hrmp_max_message_num_per_candidate: u32,
	/// The minimum period, in blocks, between which parachains can update their validation code.
	pub validation_upgrade_cooldown: BlockNumber,
	/// The delay, in blocks, before a validation upgrade is applied.
	pub validation_upgrade_delay: BlockNumber,
	/// Asynchronous backing parameters.
	pub async_backing_params: AsyncBackingParams,
}

/// Abridged version of `HrmpChannel` (from the `Hrmp` parachains host runtime module) meant to be
/// used by a parachain or PDK such as cumulus.
#[derive(Clone, Encode, Decode, RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct AbridgedHrmpChannel {
	/// The maximum number of messages that can be pending in the channel at once.
	pub max_capacity: u32,
	/// The maximum total size of the messages that can be pending in the channel at once.
	pub max_total_size: u32,
	/// The maximum message size that could be put into the channel.
	pub max_message_size: u32,
	/// The current number of messages pending in the channel.
	/// Invariant: should be less or equal to `max_capacity`.s`.
	pub msg_count: u32,
	/// The total size in bytes of all message payloads in the channel.
	/// Invariant: should be less or equal to `max_total_size`.
	pub total_size: u32,
	/// A head of the Message Queue Chain for this channel. Each link in this chain has a form:
	/// `(prev_head, B, H(M))`, where
	/// - `prev_head`: is the previous value of `mqc_head` or zero if none.
	/// - `B`: is the [relay-chain] block number in which a message was appended
	/// - `H(M)`: is the hash of the message being appended.
	/// This value is initialized to a special value that consists of all zeroes which indicates
	/// that no messages were previously added.
	pub mqc_head: Option<Hash>,
}

/// A possible upgrade restriction that prevents a parachain from performing an upgrade.
#[derive(Copy, Clone, Encode, Decode, PartialEq, RuntimeDebug, TypeInfo)]
pub enum UpgradeRestriction {
	/// There is an upgrade restriction and there are no details about its specifics nor how long
	/// it could last.
	#[codec(index = 0)]
	Present,
}

/// A struct that the relay-chain communicates to a parachain indicating what course of action the
/// parachain should take in the coordinated parachain validation code upgrade process.
///
/// This data type appears in the last step of the upgrade process. After the parachain observes it
/// and reacts to it the upgrade process concludes.
#[derive(Copy, Clone, Encode, Decode, PartialEq, RuntimeDebug, TypeInfo)]
pub enum UpgradeGoAhead {
	/// Abort the upgrade process. There is something wrong with the validation code previously
	/// submitted by the parachain. This variant can also be used to prevent upgrades by the
	/// governance should an emergency emerge.
	///
	/// The expected reaction on this variant is that the parachain will admit this message and
	/// remove all the data about the pending upgrade. Depending on the nature of the problem (to
	/// be examined offchain for now), it can try to send another validation code or just retry
	/// later.
	#[codec(index = 0)]
	Abort,
	/// Apply the pending code change. The parablock that is built on a relay-parent that is
	/// descendant of the relay-parent where the parachain observed this signal must use the
	/// upgraded validation code.
	#[codec(index = 1)]
	GoAhead,
}

/// Consensus engine id for polkadot v1 consensus engine.
pub const POLKADOT_ENGINE_ID: runtime_primitives::ConsensusEngineId = *b"POL1";

/// A consensus log item for polkadot validation. To be used with [`POLKADOT_ENGINE_ID`].
#[derive(Decode, Encode, Clone, PartialEq, Eq)]
pub enum ConsensusLog {
	/// A parachain upgraded its code.
	#[codec(index = 1)]
	ParaUpgradeCode(Id, ValidationCodeHash),
	/// A parachain scheduled a code upgrade.
	#[codec(index = 2)]
	ParaScheduleUpgradeCode(Id, ValidationCodeHash, BlockNumber),
	/// Governance requests to auto-approve every candidate included up to the given block
	/// number in the current chain, inclusive.
	#[codec(index = 3)]
	ForceApprove(BlockNumber),
	/// A signal to revert the block number in the same chain as the
	/// header this digest is part of and all of its descendants.
	///
	/// It is a no-op for a block to contain a revert digest targeting
	/// its own number or a higher number.
	///
	/// In practice, these are issued when on-chain logic has detected an
	/// invalid parachain block within its own chain, due to a dispute.
	#[codec(index = 4)]
	Revert(BlockNumber),
}

impl ConsensusLog {
	/// Attempt to convert a reference to a generic digest item into a consensus log.
	pub fn from_digest_item(
		digest_item: &runtime_primitives::DigestItem,
	) -> Result<Option<Self>, parity_scale_codec::Error> {
		match digest_item {
			runtime_primitives::DigestItem::Consensus(id, encoded) if id == &POLKADOT_ENGINE_ID =>
				Ok(Some(Self::decode(&mut &encoded[..])?)),
			_ => Ok(None),
		}
	}
}

impl From<ConsensusLog> for runtime_primitives::DigestItem {
	fn from(c: ConsensusLog) -> runtime_primitives::DigestItem {
		Self::Consensus(POLKADOT_ENGINE_ID, c.encode())
	}
}

/// A statement about a candidate, to be used within the dispute resolution process.
///
/// Statements are either in favor of the candidate's validity or against it.
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub enum DisputeStatement {
	/// A valid statement, of the given kind.
	#[codec(index = 0)]
	Valid(ValidDisputeStatementKind),
	/// An invalid statement, of the given kind.
	#[codec(index = 1)]
	Invalid(InvalidDisputeStatementKind),
}

impl DisputeStatement {
	/// Get the payload data for this type of dispute statement.
	///
	/// Returns Error if the candidate_hash is not included in the list of signed
	/// candidate from ApprovalCheckingMultipleCandidate.
	pub fn payload_data(
		&self,
		candidate_hash: CandidateHash,
		session: SessionIndex,
	) -> Result<Vec<u8>, ()> {
		match self {
			DisputeStatement::Valid(ValidDisputeStatementKind::Explicit) =>
				Ok(ExplicitDisputeStatement { valid: true, candidate_hash, session }
					.signing_payload()),
			DisputeStatement::Valid(ValidDisputeStatementKind::BackingSeconded(
				inclusion_parent,
			)) => Ok(CompactStatement::Seconded(candidate_hash).signing_payload(&SigningContext {
				session_index: session,
				parent_hash: *inclusion_parent,
			})),
			DisputeStatement::Valid(ValidDisputeStatementKind::BackingValid(inclusion_parent)) =>
				Ok(CompactStatement::Valid(candidate_hash).signing_payload(&SigningContext {
					session_index: session,
					parent_hash: *inclusion_parent,
				})),
			DisputeStatement::Valid(ValidDisputeStatementKind::ApprovalChecking) =>
				Ok(ApprovalVote(candidate_hash).signing_payload(session)),
			DisputeStatement::Valid(
				ValidDisputeStatementKind::ApprovalCheckingMultipleCandidates(candidate_hashes),
			) =>
				if candidate_hashes.contains(&candidate_hash) {
					Ok(ApprovalVoteMultipleCandidates(candidate_hashes).signing_payload(session))
				} else {
					Err(())
				},
			DisputeStatement::Invalid(InvalidDisputeStatementKind::Explicit) =>
				Ok(ExplicitDisputeStatement { valid: false, candidate_hash, session }
					.signing_payload()),
		}
	}

	/// Check the signature on a dispute statement.
	pub fn check_signature(
		&self,
		validator_public: &ValidatorId,
		candidate_hash: CandidateHash,
		session: SessionIndex,
		validator_signature: &ValidatorSignature,
	) -> Result<(), ()> {
		let payload = self.payload_data(candidate_hash, session)?;

		if validator_signature.verify(&payload[..], &validator_public) {
			Ok(())
		} else {
			Err(())
		}
	}

	/// Whether the statement indicates validity.
	pub fn indicates_validity(&self) -> bool {
		match *self {
			DisputeStatement::Valid(_) => true,
			DisputeStatement::Invalid(_) => false,
		}
	}

	/// Whether the statement indicates invalidity.
	pub fn indicates_invalidity(&self) -> bool {
		match *self {
			DisputeStatement::Valid(_) => false,
			DisputeStatement::Invalid(_) => true,
		}
	}

	/// Statement is backing statement.
	pub fn is_backing(&self) -> bool {
		match self {
			Self::Valid(s) => s.is_backing(),
			Self::Invalid(_) => false,
		}
	}
}

/// Different kinds of statements of validity on  a candidate.
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub enum ValidDisputeStatementKind {
	/// An explicit statement issued as part of a dispute.
	#[codec(index = 0)]
	Explicit,
	/// A seconded statement on a candidate from the backing phase.
	#[codec(index = 1)]
	BackingSeconded(Hash),
	/// A valid statement on a candidate from the backing phase.
	#[codec(index = 2)]
	BackingValid(Hash),
	/// An approval vote from the approval checking phase.
	#[codec(index = 3)]
	ApprovalChecking,
	/// An approval vote from the new version.
	/// We can't create this version untill all nodes
	/// have been updated to support it and max_approval_coalesce_count
	/// is set to more than 1.
	#[codec(index = 4)]
	ApprovalCheckingMultipleCandidates(Vec<CandidateHash>),
}

impl ValidDisputeStatementKind {
	/// Whether the statement is from the backing phase.
	pub fn is_backing(&self) -> bool {
		match self {
			ValidDisputeStatementKind::BackingSeconded(_) |
			ValidDisputeStatementKind::BackingValid(_) => true,
			ValidDisputeStatementKind::Explicit |
			ValidDisputeStatementKind::ApprovalChecking |
			ValidDisputeStatementKind::ApprovalCheckingMultipleCandidates(_) => false,
		}
	}
}

/// Different kinds of statements of invalidity on a candidate.
#[derive(Encode, Decode, Copy, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub enum InvalidDisputeStatementKind {
	/// An explicit statement issued as part of a dispute.
	#[codec(index = 0)]
	Explicit,
}

/// An explicit statement on a candidate issued as part of a dispute.
#[derive(Clone, PartialEq, RuntimeDebug)]
pub struct ExplicitDisputeStatement {
	/// Whether the candidate is valid
	pub valid: bool,
	/// The candidate hash.
	pub candidate_hash: CandidateHash,
	/// The session index of the candidate.
	pub session: SessionIndex,
}

impl ExplicitDisputeStatement {
	/// Produce the payload used for signing this type of statement.
	pub fn signing_payload(&self) -> Vec<u8> {
		const MAGIC: [u8; 4] = *b"DISP";

		(MAGIC, self.valid, self.candidate_hash, self.session).encode()
	}
}

/// A set of statements about a specific candidate.
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub struct DisputeStatementSet {
	/// The candidate referenced by this set.
	pub candidate_hash: CandidateHash,
	/// The session index of the candidate.
	pub session: SessionIndex,
	/// Statements about the candidate.
	pub statements: Vec<(DisputeStatement, ValidatorIndex, ValidatorSignature)>,
}

impl From<CheckedDisputeStatementSet> for DisputeStatementSet {
	fn from(other: CheckedDisputeStatementSet) -> Self {
		other.0
	}
}

impl AsRef<DisputeStatementSet> for DisputeStatementSet {
	fn as_ref(&self) -> &DisputeStatementSet {
		&self
	}
}

/// A set of dispute statements.
pub type MultiDisputeStatementSet = Vec<DisputeStatementSet>;

/// A _checked_ set of dispute statements.
#[derive(Clone, PartialEq, RuntimeDebug, Encode)]
pub struct CheckedDisputeStatementSet(DisputeStatementSet);

impl AsRef<DisputeStatementSet> for CheckedDisputeStatementSet {
	fn as_ref(&self) -> &DisputeStatementSet {
		&self.0
	}
}

impl core::cmp::PartialEq<DisputeStatementSet> for CheckedDisputeStatementSet {
	fn eq(&self, other: &DisputeStatementSet) -> bool {
		self.0.eq(other)
	}
}

impl CheckedDisputeStatementSet {
	/// Convert from an unchecked, the verification of correctness of the `unchecked` statement set
	/// _must_ be done before calling this function!
	pub fn unchecked_from_unchecked(unchecked: DisputeStatementSet) -> Self {
		Self(unchecked)
	}
}

/// A set of _checked_ dispute statements.
pub type CheckedMultiDisputeStatementSet = Vec<CheckedDisputeStatementSet>;

/// The entire state of a dispute.
#[derive(Encode, Decode, Clone, RuntimeDebug, PartialEq, TypeInfo)]
pub struct DisputeState<N = BlockNumber> {
	/// A bitfield indicating all validators for the candidate.
	pub validators_for: BitVec<u8, bitvec::order::Lsb0>, // one bit per validator.
	/// A bitfield indicating all validators against the candidate.
	pub validators_against: BitVec<u8, bitvec::order::Lsb0>, // one bit per validator.
	/// The block number at which the dispute started on-chain.
	pub start: N,
	/// The block number at which the dispute concluded on-chain.
	pub concluded_at: Option<N>,
}

/// Parachains inherent-data passed into the runtime by a block author
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub struct InherentData<HDR: HeaderT = Header> {
	/// Signed bitfields by validators about availability.
	pub bitfields: UncheckedSignedAvailabilityBitfields,
	/// Backed candidates for inclusion in the block.
	pub backed_candidates: Vec<BackedCandidate<HDR::Hash>>,
	/// Sets of dispute votes for inclusion,
	pub disputes: MultiDisputeStatementSet,
	/// The parent block header. Used for checking state proofs.
	pub parent_header: HDR,
}

/// An either implicit or explicit attestation to the validity of a parachain
/// candidate.
#[derive(Clone, Eq, PartialEq, Decode, Encode, RuntimeDebug, TypeInfo)]
pub enum ValidityAttestation {
	/// Implicit validity attestation by issuing.
	/// This corresponds to issuance of a `Candidate` statement.
	#[codec(index = 1)]
	Implicit(ValidatorSignature),
	/// An explicit attestation. This corresponds to issuance of a
	/// `Valid` statement.
	#[codec(index = 2)]
	Explicit(ValidatorSignature),
}

impl ValidityAttestation {
	/// Produce the underlying signed payload of the attestation, given the hash of the candidate,
	/// which should be known in context.
	pub fn to_compact_statement(&self, candidate_hash: CandidateHash) -> CompactStatement {
		// Explicit and implicit map directly from
		// `ValidityVote::Valid` and `ValidityVote::Issued`, and hence there is a
		// `1:1` relationshow which enables the conversion.
		match *self {
			ValidityAttestation::Implicit(_) => CompactStatement::Seconded(candidate_hash),
			ValidityAttestation::Explicit(_) => CompactStatement::Valid(candidate_hash),
		}
	}

	/// Get a reference to the signature.
	pub fn signature(&self) -> &ValidatorSignature {
		match *self {
			ValidityAttestation::Implicit(ref sig) => sig,
			ValidityAttestation::Explicit(ref sig) => sig,
		}
	}

	/// Produce the underlying signed payload of the attestation, given the hash of the candidate,
	/// which should be known in context.
	pub fn signed_payload<H: Encode>(
		&self,
		candidate_hash: CandidateHash,
		signing_context: &SigningContext<H>,
	) -> Vec<u8> {
		match *self {
			ValidityAttestation::Implicit(_) =>
				(CompactStatement::Seconded(candidate_hash), signing_context).encode(),
			ValidityAttestation::Explicit(_) =>
				(CompactStatement::Valid(candidate_hash), signing_context).encode(),
		}
	}
}

/// A type returned by runtime with current session index and a parent hash.
#[derive(Clone, Eq, PartialEq, Default, Decode, Encode, RuntimeDebug)]
pub struct SigningContext<H = Hash> {
	/// Current session index.
	pub session_index: sp_staking::SessionIndex,
	/// Hash of the parent.
	pub parent_hash: H,
}

const BACKING_STATEMENT_MAGIC: [u8; 4] = *b"BKNG";

/// Statements that can be made about parachain candidates. These are the
/// actual values that are signed.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, RuntimeDebug)]
#[cfg_attr(feature = "std", derive(Hash))]
pub enum CompactStatement {
	/// Proposal of a parachain candidate.
	Seconded(CandidateHash),
	/// State that a parachain candidate is valid.
	Valid(CandidateHash),
}

impl CompactStatement {
	/// Yields the payload used for validator signatures on this kind
	/// of statement.
	pub fn signing_payload(&self, context: &SigningContext) -> Vec<u8> {
		(self, context).encode()
	}

	/// Get the underlying candidate hash this references.
	pub fn candidate_hash(&self) -> &CandidateHash {
		match *self {
			CompactStatement::Seconded(ref h) | CompactStatement::Valid(ref h) => h,
		}
	}
}

// Inner helper for codec on `CompactStatement`.
#[derive(Encode, Decode, TypeInfo)]
enum CompactStatementInner {
	#[codec(index = 1)]
	Seconded(CandidateHash),
	#[codec(index = 2)]
	Valid(CandidateHash),
}

impl From<CompactStatement> for CompactStatementInner {
	fn from(s: CompactStatement) -> Self {
		match s {
			CompactStatement::Seconded(h) => CompactStatementInner::Seconded(h),
			CompactStatement::Valid(h) => CompactStatementInner::Valid(h),
		}
	}
}

impl parity_scale_codec::Encode for CompactStatement {
	fn size_hint(&self) -> usize {
		// magic + discriminant + payload
		4 + 1 + 32
	}

	fn encode_to<T: parity_scale_codec::Output + ?Sized>(&self, dest: &mut T) {
		dest.write(&BACKING_STATEMENT_MAGIC);
		CompactStatementInner::from(self.clone()).encode_to(dest)
	}
}

impl parity_scale_codec::Decode for CompactStatement {
	fn decode<I: parity_scale_codec::Input>(
		input: &mut I,
	) -> Result<Self, parity_scale_codec::Error> {
		let maybe_magic = <[u8; 4]>::decode(input)?;
		if maybe_magic != BACKING_STATEMENT_MAGIC {
			return Err(parity_scale_codec::Error::from("invalid magic string"))
		}

		Ok(match CompactStatementInner::decode(input)? {
			CompactStatementInner::Seconded(h) => CompactStatement::Seconded(h),
			CompactStatementInner::Valid(h) => CompactStatement::Valid(h),
		})
	}
}

/// `IndexedVec` struct indexed by type specific indices.
#[derive(Clone, Encode, Decode, RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct IndexedVec<K, V>(Vec<V>, PhantomData<fn(K) -> K>);

impl<K, V> Default for IndexedVec<K, V> {
	fn default() -> Self {
		Self(vec![], PhantomData)
	}
}

impl<K, V> From<Vec<V>> for IndexedVec<K, V> {
	fn from(validators: Vec<V>) -> Self {
		Self(validators, PhantomData)
	}
}

impl<K, V> FromIterator<V> for IndexedVec<K, V> {
	fn from_iter<T: IntoIterator<Item = V>>(iter: T) -> Self {
		Self(Vec::from_iter(iter), PhantomData)
	}
}

impl<K, V> IndexedVec<K, V>
where
	V: Clone,
{
	/// Returns a reference to an element indexed using `K`.
	pub fn get(&self, index: K) -> Option<&V>
	where
		K: TypeIndex,
	{
		self.0.get(index.type_index())
	}

	/// Returns number of elements in vector.
	pub fn len(&self) -> usize {
		self.0.len()
	}

	/// Returns contained vector.
	pub fn to_vec(&self) -> Vec<V> {
		self.0.clone()
	}

	/// Returns an iterator over the underlying vector.
	pub fn iter(&self) -> Iter<'_, V> {
		self.0.iter()
	}

	/// Returns a mutable iterator over the underlying vector.
	pub fn iter_mut(&mut self) -> IterMut<'_, V> {
		self.0.iter_mut()
	}

	/// Creates a consuming iterator.
	pub fn into_iter(self) -> IntoIter<V> {
		self.0.into_iter()
	}

	/// Returns true if the underlying container is empty.
	pub fn is_empty(&self) -> bool {
		self.0.is_empty()
	}
}

/// The maximum number of validators `f` which may safely be faulty.
///
/// The total number of validators is `n = 3f + e` where `e in { 1, 2, 3 }`.
pub const fn byzantine_threshold(n: usize) -> usize {
	n.saturating_sub(1) / 3
}

/// The supermajority threshold of validators which represents a subset
/// guaranteed to have at least f+1 honest validators.
pub const fn supermajority_threshold(n: usize) -> usize {
	n - byzantine_threshold(n)
}

/// Adjust the configured needed backing votes with the size of the backing group.
pub fn effective_minimum_backing_votes(
	group_len: usize,
	configured_minimum_backing_votes: u32,
) -> usize {
	sp_std::cmp::min(group_len, configured_minimum_backing_votes as usize)
}

/// Information about validator sets of a session.
///
/// NOTE: `SessionInfo` is frozen. Do not include new fields, consider creating a separate runtime
/// API. Reasoning and further outlook [here](https://github.com/paritytech/polkadot/issues/6586).
#[derive(Clone, Encode, Decode, RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(PartialEq))]
pub struct SessionInfo {
	/****** New in v2 ****** */
	/// All the validators actively participating in parachain consensus.
	/// Indices are into the broader validator set.
	pub active_validator_indices: Vec<ValidatorIndex>,
	/// A secure random seed for the session, gathered from BABE.
	pub random_seed: [u8; 32],
	/// The amount of sessions to keep for disputes.
	pub dispute_period: SessionIndex,

	/****** Old fields ***** */
	/// Validators in canonical ordering.
	///
	/// NOTE: There might be more authorities in the current session, than `validators`
	/// participating in parachain consensus. See
	/// [`max_validators`](https://github.com/paritytech/polkadot/blob/a52dca2be7840b23c19c153cf7e110b1e3e475f8/runtime/parachains/src/configuration.rs#L148).
	///
	/// `SessionInfo::validators` will be limited to to `max_validators` when set.
	pub validators: IndexedVec<ValidatorIndex, ValidatorId>,
	/// Validators' authority discovery keys for the session in canonical ordering.
	///
	/// NOTE: The first `validators.len()` entries will match the corresponding validators in
	/// `validators`, afterwards any remaining authorities can be found. This is any authorities
	/// not participating in parachain consensus - see
	/// [`max_validators`](https://github.com/paritytech/polkadot/blob/a52dca2be7840b23c19c153cf7e110b1e3e475f8/runtime/parachains/src/configuration.rs#L148)
	pub discovery_keys: Vec<AuthorityDiscoveryId>,
	/// The assignment keys for validators.
	///
	/// NOTE: There might be more authorities in the current session, than validators participating
	/// in parachain consensus. See
	/// [`max_validators`](https://github.com/paritytech/polkadot/blob/a52dca2be7840b23c19c153cf7e110b1e3e475f8/runtime/parachains/src/configuration.rs#L148).
	///
	/// Therefore:
	/// ```ignore
	/// 	assignment_keys.len() == validators.len() && validators.len() <= discovery_keys.len()
	/// ```
	pub assignment_keys: Vec<AssignmentId>,
	/// Validators in shuffled ordering - these are the validator groups as produced
	/// by the `Scheduler` module for the session and are typically referred to by
	/// `GroupIndex`.
	pub validator_groups: IndexedVec<GroupIndex, Vec<ValidatorIndex>>,
	/// The number of availability cores used by the protocol during this session.
	pub n_cores: u32,
	/// The zeroth delay tranche width.
	pub zeroth_delay_tranche_width: u32,
	/// The number of samples we do of `relay_vrf_modulo`.
	pub relay_vrf_modulo_samples: u32,
	/// The number of delay tranches in total.
	pub n_delay_tranches: u32,
	/// How many slots (BABE / SASSAFRAS) must pass before an assignment is considered a
	/// no-show.
	pub no_show_slots: u32,
	/// The number of validators needed to approve a block.
	pub needed_approvals: u32,
}

/// A statement from the specified validator whether the given validation code passes PVF
/// pre-checking or not anchored to the given session index.
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub struct PvfCheckStatement {
	/// `true` if the subject passed pre-checking and `false` otherwise.
	pub accept: bool,
	/// The validation code hash that was checked.
	pub subject: ValidationCodeHash,
	/// The index of a session during which this statement is considered valid.
	pub session_index: SessionIndex,
	/// The index of the validator from which this statement originates.
	pub validator_index: ValidatorIndex,
}

impl PvfCheckStatement {
	/// Produce the payload used for signing this type of statement.
	///
	/// It is expected that it will be signed by the validator at `validator_index` in the
	/// `session_index`.
	pub fn signing_payload(&self) -> Vec<u8> {
		const MAGIC: [u8; 4] = *b"VCPC"; // for "validation code pre-checking"
		(MAGIC, self.accept, self.subject, self.session_index, self.validator_index).encode()
	}
}

/// A well-known and typed storage key.
///
/// Allows for type-safe access to raw well-known storage keys.
pub struct WellKnownKey<T> {
	/// The raw storage key.
	pub key: Vec<u8>,
	_p: sp_std::marker::PhantomData<T>,
}

impl<T> From<Vec<u8>> for WellKnownKey<T> {
	fn from(key: Vec<u8>) -> Self {
		Self { key, _p: Default::default() }
	}
}

impl<T> AsRef<[u8]> for WellKnownKey<T> {
	fn as_ref(&self) -> &[u8] {
		self.key.as_ref()
	}
}

impl<T: Decode> WellKnownKey<T> {
	/// Gets the value or `None` if it does not exist or decoding failed.
	pub fn get(&self) -> Option<T> {
		sp_io::storage::get(&self.key)
			.and_then(|raw| parity_scale_codec::DecodeAll::decode_all(&mut raw.as_ref()).ok())
	}
}

impl<T: Encode> WellKnownKey<T> {
	/// Sets the value.
	pub fn set(&self, value: T) {
		sp_io::storage::set(&self.key, &value.encode());
	}
}

/// Type discriminator for PVF preparation.
#[derive(Encode, Decode, TypeInfo, Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub enum PvfPrepKind {
	/// For prechecking requests.
	Precheck,

	/// For execution and heads-up requests.
	Prepare,
}

/// Type discriminator for PVF execution.
#[derive(Encode, Decode, TypeInfo, Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub enum PvfExecKind {
	/// For backing requests.
	Backing,
	/// For approval and dispute request.
	Approval,
}

#[cfg(test)]
mod tests {
	use super::*;
	use bitvec::bitvec;
	use primitives::sr25519;

	pub fn dummy_committed_candidate_receipt() -> CommittedCandidateReceipt {
		let zeros = Hash::zero();

		CommittedCandidateReceipt {
			descriptor: CandidateDescriptor {
				para_id: 0.into(),
				relay_parent: zeros,
				collator: CollatorId::from(sr25519::Public::default()),
				persisted_validation_data_hash: zeros,
				pov_hash: zeros,
				erasure_root: zeros,
				signature: CollatorSignature::from(sr25519::Signature::default()),
				para_head: zeros,
				validation_code_hash: ValidationCode(vec![1, 2, 3, 4, 5, 6, 7, 8, 9]).hash(),
			},
			commitments: CandidateCommitments {
				head_data: HeadData(vec![]),
				upward_messages: vec![].try_into().expect("empty vec fits within bounds"),
				new_validation_code: None,
				horizontal_messages: vec![].try_into().expect("empty vec fits within bounds"),
				processed_downward_messages: 0,
				hrmp_watermark: 0_u32,
			},
		}
	}

	#[test]
	fn group_rotation_info_calculations() {
		let info =
			GroupRotationInfo { session_start_block: 10u32, now: 15, group_rotation_frequency: 5 };

		assert_eq!(info.next_rotation_at(), 20);
		assert_eq!(info.last_rotation_at(), 15);
	}

	#[test]
	fn group_for_core_is_core_for_group() {
		for cores in 1..=256 {
			for rotations in 0..(cores * 2) {
				let info = GroupRotationInfo {
					session_start_block: 0u32,
					now: rotations,
					group_rotation_frequency: 1,
				};

				for core in 0..cores {
					let group = info.group_for_core(CoreIndex(core), cores as usize);
					assert_eq!(info.core_for_group(group, cores as usize).0, core);
				}
			}
		}
	}