//! Sprout key types
//!
//! "The receiving key sk_enc, the incoming viewing key ivk = (apk,
//! sk_enc), and the shielded payment address addr_pk = (a_pk, pk_enc) are
//! derived from a_sk, as described in [‘Sprout Key Components’][ps]
//!
//! [ps]: https://zips.z.cash/protocol/protocol.pdf#sproutkeycomponents

use std::{
    fmt,
    io::{self},
};

use byteorder::{ByteOrder, LittleEndian};

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

use sha2::sha256_utils::compress256;

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

/// Our root secret key of the Sprout key derivation tree.
///
/// All other Sprout key types derive from the SpendingKey value.
/// Actually 252 bits.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct SpendingKey(pub [u8; 32]);

/// Derived from a _SpendingKey_.
pub type ReceivingKey = x25519_dalek::StaticSecret;

impl From<SpendingKey> for ReceivingKey {
    fn from(spending_key: SpendingKey) -> ReceivingKey {
        let mut state = [0u32; 8];
        let mut block = [0u8; 64];

        block[0..32].copy_from_slice(&spending_key.0[..]);
        block[0] |= 0b11000000;

        compress256(&mut state, &block);

        let mut derived_bytes = [0u8; 32];
        LittleEndian::write_u32_into(&state, &mut derived_bytes);

        ReceivingKey::from(derived_bytes)
    }
}

/// Derived from a _SpendingKey_.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct PayingKey(pub [u8; 32]);

/// Derived from a _ReceivingKey_.
pub type TransmissionKey = x25519_dalek::PublicKey;

///
pub struct IncomingViewingKey {
    paying_key: PayingKey,
    receiving_key: ReceivingKey,
}

#[cfg(test)]
mod tests {

    use rand_core::{OsRng, RngCore};

    use super::*;

    #[test]
    fn derive_receiving_key() {
        let mut bytes = [0u8; 32];
        OsRng.fill_bytes(&mut bytes);

        let spending_key = SpendingKey(bytes);

        println!("{:?}", spending_key);

        let receiving_key = ReceivingKey::from(spending_key);

        // println!("{}", receiving_key);
    }
}

#[cfg(test)]
proptest! {

    // #[test]
    // fn test() {}
}