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// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot 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.

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

//! Common traits and types used by the scheduler and assignment providers.

use frame_support::pallet_prelude::*;
use primitives::{
	v5::{Assignment, ParasEntry},
	CoreIndex, Id as ParaId,
};
use scale_info::TypeInfo;
use sp_std::prelude::*;

// Only used to link to configuration documentation.
#[allow(unused)]
use crate::configuration::HostConfiguration;

/// Reasons a core might be freed
#[derive(Clone, Copy)]
pub enum FreedReason {
	/// The core's work concluded and the parablock assigned to it is considered available.
	Concluded,
	/// The core's work timed out.
	TimedOut,
}

/// A set of variables required by the scheduler in order to operate.
pub struct AssignmentProviderConfig<BlockNumber> {
	/// The availability period specified by the implementation.
	/// See [`HostConfiguration::paras_availability_period`] for more information.
	pub availability_period: BlockNumber,

	/// How many times a collation can time out on availability.
	/// Zero timeouts still means that a collation can be provided as per the slot auction
	/// assignment provider.
	pub max_availability_timeouts: u32,

	/// How long the collator has to provide a collation to the backing group before being dropped.
	pub ttl: BlockNumber,
}

pub trait AssignmentProvider<BlockNumber> {
	/// How many cores are allocated to this provider.
	fn session_core_count() -> u32;

	/// Pops an [`Assignment`] from the provider for a specified [`CoreIndex`].
	/// The `concluded_para` field makes the caller report back to the provider
	/// which [`ParaId`] it processed last on the supplied [`CoreIndex`].
	fn pop_assignment_for_core(
		core_idx: CoreIndex,
		concluded_para: Option<ParaId>,
	) -> Option<Assignment>;

	/// Push back an already popped assignment. Intended for provider implementations
	/// that need to be able to keep track of assignments over session boundaries,
	/// such as the on demand assignment provider.
	fn push_assignment_for_core(core_idx: CoreIndex, assignment: Assignment);

	/// Returns a set of variables needed by the scheduler
	fn get_provider_config(core_idx: CoreIndex) -> AssignmentProviderConfig<BlockNumber>;
}

/// How a core is mapped to a backing group and a `ParaId`
#[derive(Clone, Encode, Decode, PartialEq, TypeInfo)]
#[cfg_attr(feature = "std", derive(Debug))]
pub struct CoreAssignment<BlockNumber> {
	/// The core that is assigned.
	pub core: CoreIndex,
	/// The para id and accompanying information needed to collate and back a parablock.
	pub paras_entry: ParasEntry<BlockNumber>,
}

impl<BlockNumber> CoreAssignment<BlockNumber> {
	/// Returns the [`ParaId`] of the assignment.
	pub fn para_id(&self) -> ParaId {
		self.paras_entry.para_id()
	}

	/// Returns the inner [`ParasEntry`] of the assignment.
	pub fn to_paras_entry(self) -> ParasEntry<BlockNumber> {
		self.paras_entry
	}
}