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// Copyright 2022 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/>.

use codec::{Decode, Encode};
pub use sp_finality_grandpa::{AuthorityList, SetId};
use sp_runtime::traits::{Block as BlockT, NumberFor};
use std::fmt;

/// Scale-encoded warp sync proof response.
pub struct EncodedProof(pub Vec<u8>);

/// Warp sync request
#[derive(Encode, Decode, Debug)]
pub struct WarpProofRequest<B: BlockT> {
	/// Start collecting proofs from this block.
	pub begin: B::Hash,
}

/// Proof verification result.
pub enum VerificationResult<Block: BlockT> {
	/// Proof is valid, but the target was not reached.
	Partial(SetId, AuthorityList, Block::Hash),
	/// Target finality is proved.
	Complete(SetId, AuthorityList, Block::Header),
}

/// Warp sync backend. Handles retrieveing and verifying warp sync proofs.
pub trait WarpSyncProvider<Block: BlockT>: Send + Sync {
	/// Generate proof starting at given block hash. The proof is accumulated until maximum proof
	/// size is reached.
	fn generate(
		&self,
		start: Block::Hash,
	) -> Result<EncodedProof, Box<dyn std::error::Error + Send + Sync>>;
	/// Verify warp proof against current set of authorities.
	fn verify(
		&self,
		proof: &EncodedProof,
		set_id: SetId,
		authorities: AuthorityList,
	) -> Result<VerificationResult<Block>, Box<dyn std::error::Error + Send + Sync>>;
	/// Get current list of authorities. This is supposed to be genesis authorities when starting
	/// sync.
	fn current_authorities(&self) -> AuthorityList;
}

/// Reported warp sync phase.
#[derive(Clone, Eq, PartialEq, Debug)]
pub enum WarpSyncPhase<Block: BlockT> {
	/// Waiting for peers to connect.
	AwaitingPeers,
	/// Downloading and verifying grandpa warp proofs.
	DownloadingWarpProofs,
	/// Downloading target block.
	DownloadingTargetBlock,
	/// Downloading state data.
	DownloadingState,
	/// Importing state.
	ImportingState,
	/// Downloading block history.
	DownloadingBlocks(NumberFor<Block>),
}

impl<Block: BlockT> fmt::Display for WarpSyncPhase<Block> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			Self::AwaitingPeers => write!(f, "Waiting for peers"),
			Self::DownloadingWarpProofs => write!(f, "Downloading finality proofs"),
			Self::DownloadingTargetBlock => write!(f, "Downloading target block"),
			Self::DownloadingState => write!(f, "Downloading state"),
			Self::ImportingState => write!(f, "Importing state"),
			Self::DownloadingBlocks(n) => write!(f, "Downloading block history (#{})", n),
		}
	}
}

/// Reported warp sync progress.
#[derive(Clone, Eq, PartialEq, Debug)]
pub struct WarpSyncProgress<Block: BlockT> {
	/// Estimated download percentage.
	pub phase: WarpSyncPhase<Block>,
	/// Total bytes downloaded so far.
	pub total_bytes: u64,
}