// Copyright 2016 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! The proof of work needs to strike a balance between fast header
//! verification to avoid DoS attacks and difficulty for block verifiers to
//! build new blocks. In addition, mining new blocks should also be as
//! difficult on high end custom-made hardware (ASICs) as on commodity hardware
//! or smartphones. For this reason we use Cuckoo Cycle (see the cuckoo
//! module for more information).
//!
//! Note that this miner implementation is here mostly for tests and
//! reference. It's not optimized for speed.

mod siphash;
pub mod cuckoo;

use time;

use consensus::EASINESS;
use core::BlockHeader;
use core::hash::Hashed;
use core::Proof;
use core::target::Difficulty;
use pow::cuckoo::{Cuckoo, Error};


/// Should be implemented by anything providing mining services
///

pub trait MiningWorker {
	
	/// This only sets parameters and does initialisation work now
	fn new(ease: u32, sizeshift: u32) -> Self;
	
	/// Actually perform a mining attempt on the given input and
	/// return a proof if found
	fn mine(&mut self, header: &[u8]) -> Result<Proof, Error>;

}

/// Validates the proof of work of a given header, and that the proof of work
/// satisfies the requirements of the header.
pub fn verify_size(bh: &BlockHeader, cuckoo_sz: u32) -> bool {
	// make sure the pow hash shows a difficulty at least as large as the target
	// difficulty
	if bh.difficulty > bh.pow.to_difficulty() {
		return false;
	}
	Cuckoo::new(&bh.hash()[..], cuckoo_sz).verify(bh.pow, EASINESS as u64)
}

/// Uses the much easier Cuckoo20 (mostly for
/// tests).
pub fn pow20<T: MiningWorker>(miner:&mut T, bh: &mut BlockHeader, diff: Difficulty) -> Result<(), Error> {
	pow_size(miner, bh, diff, 20)
}

/// Runs a proof of work computation over the provided block using the provided Mining Worker,
/// until the required difficulty target is reached. May take a while for a low target...
pub fn pow_size<T: MiningWorker>(miner:&mut T, bh: &mut BlockHeader, 
								 diff: Difficulty, sizeshift: u32) -> Result<(), Error> {
	let start_nonce = bh.nonce;

	// try to find a cuckoo cycle on that header hash
	loop {
		// can be trivially optimized by avoiding re-serialization every time but this
		// is not meant as a fast miner implementation
		let pow_hash = bh.hash();

		// if we found a cycle (not guaranteed) and the proof hash is higher that the
		// diff, we're all good

		if let Ok(proof) = miner.mine(&pow_hash[..]) {
			if proof.to_difficulty() >= diff {
				bh.pow = proof;
				return Ok(());
			}
		}

		// otherwise increment the nonce
		bh.nonce += 1;

		// and if we're back where we started, update the time (changes the hash as
		// well)
		if bh.nonce == start_nonce {
			bh.timestamp = time::at_utc(time::Timespec { sec: 0, nsec: 0 });
		}
	}
}

#[cfg(test)]
mod test {
	use super::*;
	use core::target::Difficulty;
	use genesis;

	#[test]
	fn genesis_pow() {
		let mut b = genesis::genesis();
		b.header.nonce = 310;
		let mut internal_miner = cuckoo::Miner::new(EASINESS, 12);
		pow_size(&mut internal_miner, &mut b.header, Difficulty::from_num(MINIMUM_DIFFICULTY), 12).unwrap();
		assert!(b.header.nonce != 310);
		assert!(b.header.pow.to_difficulty() >= Difficulty::from_num(MINIMUM_DIFFICULTY));
		assert!(verify_size(&b.header, 12));
	}
}