use std::{
  io,
  collections::{HashSet, HashMap},
};

use rand_core::{RngCore, OsRng};

use blake2::{Digest, Blake2s256};

use ciphersuite::{
  group::{ff::Field, Group},
  Ciphersuite, Ristretto,
};
use schnorr::SchnorrSignature;

use crate::{
  ReadWrite, TransactionError, Signed, TransactionKind, Transaction, ProvidedTransactions, Block,
};
// A transaction solely defined by its nonce and a distinguisher (to allow creating distinct TXs
// sharing a nonce).
#[derive(Clone, PartialEq, Eq, Debug)]
struct NonceTransaction(u32, u8);

impl ReadWrite for NonceTransaction {
  fn read<R: io::Read>(reader: &mut R) -> io::Result<Self> {
    let mut nonce = [0; 4];
    reader.read_exact(&mut nonce)?;
    let mut distinguisher = [0];
    reader.read_exact(&mut distinguisher)?;
    Ok(Self(u32::from_le_bytes(nonce), distinguisher[0]))
  }

  fn write<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
    writer.write_all(&self.0.to_le_bytes())?;
    writer.write_all(&[self.1])
  }
}

impl Transaction for NonceTransaction {
  fn kind(&self) -> TransactionKind {
    TransactionKind::Signed(Signed {
      signer: <Ristretto as Ciphersuite>::G::identity(),
      nonce: self.0,
      signature: SchnorrSignature::<Ristretto> {
        R: <Ristretto as Ciphersuite>::G::identity(),
        s: <Ristretto as Ciphersuite>::F::ZERO,
      },
    })
  }

  fn hash(&self) -> [u8; 32] {
    Blake2s256::digest([self.0.to_le_bytes().as_ref(), &[self.1]].concat()).into()
  }

  fn verify(&self) -> Result<(), TransactionError> {
    Ok(())
  }
}

#[test]
fn empty_block() {
  const GENESIS: [u8; 32] = [0xff; 32];
  const LAST: [u8; 32] = [0x01; 32];
  Block::new(LAST, &ProvidedTransactions::<NonceTransaction>::new(), HashMap::new())
    .verify(GENESIS, LAST, &mut HashSet::new(), &mut HashMap::new())
    .unwrap();
}

#[test]
fn duplicate_nonces() {
  const GENESIS: [u8; 32] = [0xff; 32];
  const LAST: [u8; 32] = [0x01; 32];

  // Run once without duplicating a nonce, and once with, so that's confirmed to be the faulty
  // component
  for i in [1, 0] {
    let mut mempool = HashMap::new();
    let mut insert = |tx: NonceTransaction| mempool.insert(tx.hash(), tx);
    insert(NonceTransaction(0, 0));
    insert(NonceTransaction(i, 1));

    let mut nonces = HashMap::new();
    let res = Block::new(LAST, &ProvidedTransactions::new(), mempool).verify(
      GENESIS,
      LAST,
      &mut HashSet::new(),
      &mut nonces,
    );
    if i == 1 {
      res.unwrap();
      assert_eq!(nonces[&<Ristretto as Ciphersuite>::G::identity()], 2);
    } else {
      assert!(res.is_err());
    }
  }
}

#[test]
fn unsorted_nonces() {
  let mut mempool = HashMap::new();
  // Create a large amount of nonces so the retrieval from the HashMapis effectively guaranteed to
  // be out of order
  let mut nonces = (0 .. 64).collect::<Vec<_>>();
  // Insert in a random order
  while !nonces.is_empty() {
    let nonce = nonces.swap_remove(
      usize::try_from(OsRng.next_u64() % u64::try_from(nonces.len()).unwrap()).unwrap(),
    );
    let tx = NonceTransaction(nonce, 0);
    mempool.insert(tx.hash(), tx);
  }

  // Create and verify the block
  const GENESIS: [u8; 32] = [0xff; 32];
  const LAST: [u8; 32] = [0x01; 32];
  let mut nonces = HashMap::new();
  Block::new(LAST, &ProvidedTransactions::new(), mempool)
    .verify(GENESIS, LAST, &mut HashSet::new(), &mut nonces)
    .unwrap();

  // Make sure the nonce was properly set
  assert_eq!(nonces[&<Ristretto as Ciphersuite>::G::identity()], 64);
}