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//! Equihash Solution and related items.

use std::{fmt, io};

use serde_big_array::BigArray;

use crate::{
serialization::{
zcash_serialize_bytes, SerializationError, ZcashDeserialize, ZcashDeserializeInto,
ZcashSerialize,
},
};

/// The error type for Equihash
#[non_exhaustive]
#[derive(Debug, thiserror::Error)]
pub struct Error(#[from] equihash::Error);

/// The size of an Equihash solution in bytes (always 1344).
pub(crate) const SOLUTION_SIZE: usize = 1344;

/// Equihash Solution.
///
/// A wrapper around [u8; 1344] because Rust doesn't implement common
/// traits like Debug, Clone, etc for collections like array
/// beyond lengths 0 to 32.
///
/// The size of an Equihash solution in bytes is always 1344 so the
/// length of this type is fixed.
#[derive(Deserialize, Serialize)]
pub struct Solution(#[serde(with = "BigArray")] pub [u8; SOLUTION_SIZE]);

impl Solution {
/// The length of the portion of the header used as input when verifying
/// equihash solutions, in bytes.
///
/// Excludes the 32-byte nonce, which is passed as a separate argument
/// to the verification function.
pub const INPUT_LENGTH: usize = 4 + 32 * 3 + 4 * 2;

/// Returns Ok(()) if EquihashSolution is valid for header
#[allow(clippy::unwrap_in_result)]
let n = 200;
let k = 9;
let solution = &self.0;
let mut input = Vec::new();

.zcash_serialize(&mut input)
.expect("serialization into a vec can't fail");

let input = &input[0..Solution::INPUT_LENGTH];

equihash::is_valid_solution(n, k, input, nonce.as_ref(), solution)?;

Ok(())
}

#[cfg(feature = "getblocktemplate-rpcs")]
/// Returns a [Solution] of [0; SOLUTION_SIZE] to be used in block proposals.
pub fn for_proposal() -> Self {
Self([0; SOLUTION_SIZE])
}
}

impl PartialEq<Solution> for Solution {
fn eq(&self, other: &Solution) -> bool {
self.0.as_ref() == other.0.as_ref()
}
}

impl fmt::Debug for Solution {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_tuple("EquihashSolution")
.field(&hex::encode(&self.0[..]))
.finish()
}
}

// These impls all only exist because of array length restrictions.

impl Copy for Solution {}

impl Clone for Solution {
fn clone(&self) -> Self {
*self
}
}

impl Eq for Solution {}

impl ZcashSerialize for Solution {
fn zcash_serialize<W: io::Write>(&self, writer: W) -> Result<(), io::Error> {
zcash_serialize_bytes(&self.0.to_vec(), writer)
}
}

impl ZcashDeserialize for Solution {
let solution: Vec<u8> = (&mut reader).zcash_deserialize_into()?;

if solution.len() != SOLUTION_SIZE {
return Err(SerializationError::Parse(
"incorrect equihash solution size",
));
}

let mut bytes = [0; SOLUTION_SIZE];
// Won't panic, because we just checked the length.
bytes.copy_from_slice(&solution);

Ok(Self(bytes))
}
}