//! Equihash Solution and related items.

use std::{fmt, io};

#[cfg(test)]
use proptest::{arbitrary::Arbitrary, collection::vec, prelude::*};

use crate::{
    serde_helpers,
    serialization::{
        ReadZcashExt, SerializationError, WriteZcashExt, ZcashDeserialize, ZcashSerialize,
    },
};

/// The size of an Equihash solution in bytes (always 1344).
pub(crate) const EQUIHASH_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 EquihashSolution(
    #[serde(with = "serde_helpers::BigArray")] pub [u8; EQUIHASH_SOLUTION_SIZE],
);

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

impl fmt::Debug for EquihashSolution {
    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 EquihashSolution {}

impl Clone for EquihashSolution {
    fn clone(&self) -> Self {
        let mut bytes = [0; EQUIHASH_SOLUTION_SIZE];
        bytes[..].copy_from_slice(&self.0[..]);
        Self(bytes)
    }
}

impl Eq for EquihashSolution {}

impl ZcashSerialize for EquihashSolution {
    fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
        writer.write_compactsize(EQUIHASH_SOLUTION_SIZE as u64)?;
        writer.write_all(&self.0[..])?;
        Ok(())
    }
}

impl ZcashDeserialize for EquihashSolution {
    fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
        let solution_size = reader.read_compactsize()?;
        if solution_size != (EQUIHASH_SOLUTION_SIZE as u64) {
            return Err(SerializationError::Parse(
                "incorrect equihash solution size",
            ));
        }
        let mut bytes = [0; EQUIHASH_SOLUTION_SIZE];
        reader.read_exact(&mut bytes[..])?;
        Ok(Self(bytes))
    }
}

#[cfg(test)]
impl Arbitrary for EquihashSolution {
    type Parameters = ();

    fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
        (vec(any::<u8>(), EQUIHASH_SOLUTION_SIZE))
            .prop_map(|v| {
                let mut bytes = [0; EQUIHASH_SOLUTION_SIZE];
                bytes.copy_from_slice(v.as_slice());
                Self(bytes)
            })
            .boxed()
    }

    type Strategy = BoxedStrategy<Self>;
}

#[cfg(test)]
mod tests {

    use super::*;

    proptest! {

        #[test]
        fn equihash_solution_roundtrip(solution in any::<EquihashSolution>()) {

            let mut data = Vec::new();

            solution.zcash_serialize(&mut data).expect("randomized EquihashSolution should serialize");

            let solution2 = EquihashSolution::zcash_deserialize(&data[..])
                .expect("randomized EquihashSolution should deserialize");

            prop_assert_eq![solution, solution2];
        }

    }

    const EQUIHASH_SOLUTION_BLOCK_OFFSET: usize = 4 + 32 * 3 + 4 * 2 + 32;

    #[test]
    fn equihash_solution_test_vector() {
        let solution_bytes =
            &zebra_test_vectors::HEADER_MAINNET_415000_BYTES[EQUIHASH_SOLUTION_BLOCK_OFFSET..];
        let solution = EquihashSolution::zcash_deserialize(solution_bytes)
            .expect("Test vector EquihashSolution should deserialize");

        let mut data = Vec::new();
        solution
            .zcash_serialize(&mut data)
            .expect("Test vector EquihashSolution should serialize");

        assert_eq!(solution_bytes, data.as_slice());
    }

    static EQUIHASH_SIZE_TESTS: &[u64] = &[
        0,
        1,
        (EQUIHASH_SOLUTION_SIZE - 1) as u64,
        EQUIHASH_SOLUTION_SIZE as u64,
        (EQUIHASH_SOLUTION_SIZE + 1) as u64,
        u64::MAX - 1,
        u64::MAX,
    ];

    #[test]
    fn equihash_solution_size_field() {
        for size in EQUIHASH_SIZE_TESTS {
            let mut data = Vec::new();
            data.write_compactsize(*size as u64)
                .expect("Compact size should serialize");
            data.resize(data.len() + EQUIHASH_SOLUTION_SIZE, 0);
            let result = EquihashSolution::zcash_deserialize(data.as_slice());
            if *size == (EQUIHASH_SOLUTION_SIZE as u64) {
                result.expect("Correct size field in EquihashSolution should deserialize");
            } else {
                result
                    .expect_err("Wrong size field in EquihashSolution should fail on deserialize");
            }
        }
    }
}