//! Vote program
//! Receive and processes votes from validators

use bincode::{deserialize, serialize};
use byteorder::{ByteOrder, LittleEndian};
use solana_sdk::account::Account;
use solana_sdk::pubkey::Pubkey;
use std;
use std::collections::VecDeque;
use std::mem;
use transaction::Transaction;

// Maximum number of votes to keep around
const MAX_VOTE_HISTORY: usize = 32;

#[derive(Debug, PartialEq)]
pub enum Error {
    UserdataDeserializeFailure,
    InvalidArguments,
    InvalidUserdata,
    UserdataTooSmall,
}
impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "error")
    }
}
pub type Result<T> = std::result::Result<T, Error>;

#[derive(Serialize, Default, Deserialize, Debug, PartialEq, Eq, Clone)]
pub struct Vote {
    // TODO: add signature of the state here as well
    /// A vote for height tick_height
    pub tick_height: u64,
}

#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub enum VoteInstruction {
    /// Register a new "vote account" to represent a particular validator in the Vote Contract,
    /// and initialize the VoteState for this "vote account"
    /// * Transaction::keys[0] - the validator id
    /// * Transaction::keys[1] - the new "vote account" to be associated with the validator
    /// identified by keys[0] for voting
    RegisterAccount,
    NewVote(Vote),
}

#[derive(Debug, Default, Serialize, Deserialize, PartialEq, Eq)]
pub struct VoteProgram {
    pub votes: VecDeque<Vote>,
    pub node_id: Pubkey,
}

const VOTE_PROGRAM_ID: [u8; 32] = [
    132, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0,
];

impl VoteProgram {
    pub fn check_id(program_id: &Pubkey) -> bool {
        program_id.as_ref() == VOTE_PROGRAM_ID
    }

    pub fn id() -> Pubkey {
        Pubkey::new(&VOTE_PROGRAM_ID)
    }

    pub fn deserialize(input: &[u8]) -> Result<VoteProgram> {
        let len = LittleEndian::read_u16(&input[0..2]) as usize;

        if len == 0 || input.len() < len + 2 {
            Err(Error::InvalidUserdata)
        } else {
            deserialize(&input[2..=len + 1]).map_err(|err| {
                error!("Unable to deserialize vote state: {:?}", err);
                Error::InvalidUserdata
            })
        }
    }

    pub fn serialize(self: &VoteProgram, output: &mut [u8]) -> Result<()> {
        let self_serialized = serialize(self).unwrap();

        if output.len() + 2 < self_serialized.len() {
            warn!(
                "{} bytes required to serialize but only have {} bytes",
                self_serialized.len(),
                output.len() + 2,
            );
            return Err(Error::UserdataTooSmall);
        }

        let serialized_len = self_serialized.len() as u16;
        LittleEndian::write_u16(&mut output[0..2], serialized_len);
        output[2..=serialized_len as usize + 1].clone_from_slice(&self_serialized);
        Ok(())
    }

    pub fn process_transaction(
        tx: &Transaction,
        instruction_index: usize,
        accounts: &mut [&mut Account],
    ) -> Result<()> {
        match deserialize(tx.userdata(instruction_index)) {
            Ok(VoteInstruction::RegisterAccount) => {
                // TODO: a single validator could register multiple "vote accounts"
                // which would clutter the "accounts" structure.
                accounts[1].program_id = Self::id();

                let mut vote_state = VoteProgram {
                    votes: VecDeque::new(),
                    node_id: *tx.from(),
                };

                vote_state.serialize(&mut accounts[1].userdata)?;

                Ok(())
            }
            Ok(VoteInstruction::NewVote(vote)) => {
                if !Self::check_id(&accounts[0].program_id) {
                    error!("accounts[0] is not assigned to the VOTE_PROGRAM");
                    Err(Error::InvalidArguments)?;
                }

                let mut vote_state = Self::deserialize(&accounts[0].userdata)?;

                // TODO: Integrity checks
                // a) Verify the vote's bank hash matches what is expected
                // b) Verify vote is older than previous votes

                // Only keep around the most recent MAX_VOTE_HISTORY votes
                if vote_state.votes.len() == MAX_VOTE_HISTORY {
                    vote_state.votes.pop_front();
                }

                vote_state.votes.push_back(vote);
                vote_state.serialize(&mut accounts[0].userdata)?;

                Ok(())
            }
            Err(_) => {
                info!(
                    "Invalid vote transaction userdata: {:?}",
                    tx.userdata(instruction_index)
                );
                Err(Error::UserdataDeserializeFailure)
            }
        }
    }

    pub fn get_max_size() -> usize {
        // Upper limit on the size of the Vote State. Equal to
        // sizeof(VoteProgram) + MAX_VOTE_HISTORY * sizeof(Vote) +
        // 32 (the size of the Pubkey) + 2 (2 bytes for the size)
        mem::size_of::<VoteProgram>()
            + MAX_VOTE_HISTORY * mem::size_of::<Vote>()
            + mem::size_of::<Pubkey>()
            + mem::size_of::<u16>()
    }
}

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

    #[test]
    fn test_serde() -> Result<()> {
        let mut buffer: Vec<u8> = vec![0; VoteProgram::get_max_size()];
        let mut vote_program = VoteProgram::default();
        vote_program.votes = (0..MAX_VOTE_HISTORY).map(|_| Vote::default()).collect();
        vote_program.serialize(&mut buffer).unwrap();
        assert_eq!(VoteProgram::deserialize(&buffer).unwrap(), vote_program);
        Ok(())
    }
}