// Copyright 2021 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.

//! Implementation of Cuckaroo Cycle, based on Cuckoo Cycle designed by
//! John Tromp. Ported to Rust from https://github.com/tromp/cuckoo.
//!
//! Cuckaroo is an ASIC-Resistant variation of Cuckoo (CuckARoo) that's
//! aimed at making the lean mining mode of Cuckoo extremely ineffective.
//! It is one of the 2 proof of works used in Grin (the other one being the
//! more ASIC friendly Cuckatoo).
//!
//! In Cuckaroo, edges are calculated by repeatedly hashing the seeds to
//! obtain blocks of values. Nodes are then extracted from those edges.

use crate::global;
use crate::pow::common::CuckooParams;
use crate::pow::error::{Error, ErrorKind};
use crate::pow::siphash::siphash_block;
use crate::pow::{PoWContext, Proof};

/// Instantiate a new CuckarooContext as a PowContext. Note that this can't
/// be moved in the PoWContext trait as this particular trait needs to be
/// convertible to an object trait.
pub fn new_cuckaroo_ctx(edge_bits: u8, proof_size: usize) -> Result<Box<dyn PoWContext>, Error> {
	let params = CuckooParams::new(edge_bits, edge_bits, proof_size)?;
	Ok(Box::new(CuckarooContext { params }))
}

/// Error returned for cuckaroo request beyond HardFork4
pub fn no_cuckaroo_ctx() -> Result<Box<dyn PoWContext>, Error> {
	Err(ErrorKind::Verification("no cuckaroo past HardFork4".to_owned()).into())
}

/// Cuckaroo cycle context. Only includes the verifier for now.
pub struct CuckarooContext {
	params: CuckooParams,
}

impl PoWContext for CuckarooContext {
	fn set_header_nonce(
		&mut self,
		header: Vec<u8>,
		nonce: Option<u32>,
		_solve: bool,
	) -> Result<(), Error> {
		self.params.reset_header_nonce(header, nonce)
	}

	fn find_cycles(&mut self) -> Result<Vec<Proof>, Error> {
		unimplemented!()
	}

	fn verify(&self, proof: &Proof) -> Result<(), Error> {
		let size = proof.proof_size();
		if size != global::proofsize() {
			return Err(ErrorKind::Verification("wrong cycle length".to_owned()).into());
		}
		let nonces = &proof.nonces;
		let mut uvs = vec![0u64; 2 * size];
		let mut xor0: u64 = 0;
		let mut xor1: u64 = 0;
		let mask = u64::MAX >> size.leading_zeros(); // round size up to 2-power - 1
											 // the next three arrays form a linked list of nodes with matching bits 6..1
		let mut headu = vec![2 * size; 1 + mask as usize];
		let mut headv = vec![2 * size; 1 + mask as usize];
		let mut prev = vec![0usize; 2 * size];

		for n in 0..size {
			if nonces[n] > self.params.edge_mask {
				return Err(ErrorKind::Verification("edge too big".to_owned()).into());
			}
			if n > 0 && nonces[n] <= nonces[n - 1] {
				return Err(ErrorKind::Verification("edges not ascending".to_owned()).into());
			}
			// 21 is standard siphash rotation constant
			let edge: u64 = siphash_block(&self.params.siphash_keys, nonces[n], 21, false);
			let u = edge & self.params.node_mask;
			let v = (edge >> 32) & self.params.node_mask;

			uvs[2 * n] = u;
			let ubits = (u & mask) as usize;
			prev[2 * n] = headu[ubits];
			headu[ubits] = 2 * n;

			uvs[2 * n + 1] = v;
			let vbits = (v & mask) as usize;
			prev[2 * n + 1] = headv[vbits];
			headv[vbits] = 2 * n + 1;

			xor0 ^= u;
			xor1 ^= v;
		}
		if xor0 | xor1 != 0 {
			return Err(ErrorKind::Verification("endpoints don't match up".to_owned()).into());
		}
		// make prev lists circular
		for n in 0..size {
			if prev[2 * n] == 2 * size {
				let ubits = (uvs[2 * n] & mask) as usize;
				prev[2 * n] = headu[ubits];
			}
			if prev[2 * n + 1] == 2 * size {
				let vbits = (uvs[2 * n + 1] & mask) as usize;
				prev[2 * n + 1] = headv[vbits];
			}
		}
		let mut n = 0;
		let mut i = 0;
		let mut j;
		loop {
			// follow cycle
			j = i;
			let mut k = j;
			loop {
				k = prev[k];
				if k == i {
					break;
				}
				if uvs[k] == uvs[i] {
					// find other edge endpoint matching one at i
					if j != i {
						return Err(ErrorKind::Verification("branch in cycle".to_owned()).into());
					}
					j = k;
				}
			}
			if j == i {
				return Err(ErrorKind::Verification("cycle dead ends".to_owned()).into());
			}
			i = j ^ 1;
			n += 1;
			if i == 0 {
				break;
			}
		}
		if n == size {
			Ok(())
		} else {
			Err(ErrorKind::Verification("cycle too short".to_owned()).into())
		}
	}
}

#[cfg(test)]
mod test {
	use super::*;

	// empty header, nonce 71
	static V1_19_HASH: [u64; 4] = [
		0x23796193872092ea,
		0xf1017d8a68c4b745,
		0xd312bd53d2cd307b,
		0x840acce5833ddc52,
	];
	static V1_19_SOL: [u64; 42] = [
		0x45e9, 0x6a59, 0xf1ad, 0x10ef7, 0x129e8, 0x13e58, 0x17936, 0x19f7f, 0x208df, 0x23704,
		0x24564, 0x27e64, 0x2b828, 0x2bb41, 0x2ffc0, 0x304c5, 0x31f2a, 0x347de, 0x39686, 0x3ab6c,
		0x429ad, 0x45254, 0x49200, 0x4f8f8, 0x5697f, 0x57ad1, 0x5dd47, 0x607f8, 0x66199, 0x686c7,
		0x6d5f3, 0x6da7a, 0x6dbdf, 0x6f6bf, 0x6ffbb, 0x7580e, 0x78594, 0x785ac, 0x78b1d, 0x7b80d,
		0x7c11c, 0x7da35,
	];

	// empty header, nonce 143
	static V2_19_HASH: [u64; 4] = [
		0x6a54f2a35ab7e976,
		0x68818717ff5cd30e,
		0x9c14260c1bdbaf7,
		0xea5b4cd5d0de3cf0,
	];
	static V2_19_SOL: [u64; 42] = [
		0x2b1e, 0x67d3, 0xb041, 0xb289, 0xc6c3, 0xd31e, 0xd75c, 0x111d7, 0x145aa, 0x1712e, 0x1a3af,
		0x1ecc5, 0x206b1, 0x2a55c, 0x2a9cd, 0x2b67e, 0x321d8, 0x35dde, 0x3721e, 0x37ac0, 0x39edb,
		0x3b80b, 0x3fc79, 0x4148b, 0x42a48, 0x44395, 0x4bbc9, 0x4f775, 0x515c5, 0x56f97, 0x5aa10,
		0x5bc1b, 0x5c56d, 0x5d552, 0x60a2e, 0x66646, 0x6c3aa, 0x70709, 0x71d13, 0x762a3, 0x79d88,
		0x7e3ae,
	];

	#[test]
	fn cuckaroo19_vectors() {
		global::set_local_chain_type(global::ChainTypes::Mainnet);
		let mut ctx = new_impl(19, 42);
		ctx.params.siphash_keys = V1_19_HASH;
		assert!(ctx.verify(&Proof::new(V1_19_SOL.to_vec())).is_ok());
		assert!(ctx.verify(&Proof::new(V2_19_SOL.to_vec())).is_err());
		ctx.params.siphash_keys = V2_19_HASH.clone();
		assert!(ctx.verify(&Proof::new(V1_19_SOL.to_vec())).is_err());
		assert!(ctx.verify(&Proof::new(V2_19_SOL.to_vec())).is_ok());
		assert!(ctx.verify(&Proof::zero(42)).is_err());
	}

	fn new_impl(edge_bits: u8, proof_size: usize) -> CuckarooContext {
		let params = CuckooParams::new(edge_bits, edge_bits, proof_size).unwrap();
		CuckarooContext { params }
	}
}