// 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/>.

//! Primitives for Substrate Proof-of-Work (PoW) consensus.

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

use rstd::vec::Vec;
use sr_primitives::ConsensusEngineId;
use codec::Decode;

/// The `ConsensusEngineId` of PoW.
pub const POW_ENGINE_ID: ConsensusEngineId = [b'p', b'o', b'w', b'_'];

/// Type of seal.
pub type Seal = Vec<u8>;

/// Define methods that total difficulty should implement.
pub trait TotalDifficulty {
	fn increment(&mut self, other: Self);
}

impl TotalDifficulty for primitives::U256 {
	fn increment(&mut self, other: Self) {
		let ret = self.saturating_add(other);
		*self = ret;
	}
}

impl TotalDifficulty for u128 {
	fn increment(&mut self, other: Self) {
		let ret = self.saturating_add(other);
		*self = ret;
	}
}

sr_api::decl_runtime_apis! {
	/// API necessary for timestamp-based difficulty adjustment algorithms.
	pub trait TimestampApi<Moment: Decode> {
		/// Return the timestamp in the current block.
		fn timestamp() -> Moment;
	}

	/// API for those chains that put their difficulty adjustment algorithm directly
	/// onto runtime. Note that while putting difficulty adjustment algorithm to
	/// runtime is safe, putting the PoW algorithm on runtime is not.
	pub trait DifficultyApi<Difficulty: Decode> {
		/// Return the target difficulty of the next block.
		fn difficulty() -> Difficulty;
	}
}