// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use block::ExecutedBlock;
use engines::{Engine, Seal};
use machine::Machine;
use std::sync::atomic::{AtomicU64, Ordering};
use types::header::{ExtendedHeader, Header};

/// `InstantSeal` params.
#[derive(Default, Debug, PartialEq)]
pub struct InstantSealParams {
    /// Whether to use millisecond timestamp
    pub millisecond_timestamp: bool,
}

impl From<::ethjson::spec::InstantSealParams> for InstantSealParams {
    fn from(p: ::ethjson::spec::InstantSealParams) -> Self {
        InstantSealParams {
            millisecond_timestamp: p.millisecond_timestamp,
        }
    }
}

/// An engine which does not provide any consensus mechanism, just seals blocks internally.
/// Only seals blocks which have transactions.
pub struct InstantSeal<M> {
    params: InstantSealParams,
    machine: M,
    last_sealed_block: AtomicU64,
}

impl<M> InstantSeal<M> {
    /// Returns new instance of InstantSeal over the given state machine.
    pub fn new(params: InstantSealParams, machine: M) -> Self {
        InstantSeal {
            params,
            machine,
            last_sealed_block: AtomicU64::new(0),
        }
    }
}

impl<M: Machine> Engine<M> for InstantSeal<M> {
    fn name(&self) -> &str {
        "InstantSeal"
    }

    fn machine(&self) -> &M {
        &self.machine
    }

    fn seals_internally(&self) -> Option<bool> {
        Some(true)
    }

    fn should_reseal_on_update(&self) -> bool {
        // We would like for the miner to `update_sealing` if there are local_pending_transactions
        // in the pool to prevent transactions sent in parallel from stalling in the transaction
        // pool. (see #9660)
        true
    }

    fn generate_seal(&self, block: &ExecutedBlock, _parent: &Header) -> Seal {
        if !block.transactions.is_empty() {
            let block_number = block.header.number();
            let last_sealed_block = self.last_sealed_block.load(Ordering::SeqCst);
            // Return a regular seal if the given block is _higher_ than
            // the last sealed one
            if block_number > last_sealed_block {
                let prev_last_sealed_block = self.last_sealed_block.compare_and_swap(
                    last_sealed_block,
                    block_number,
                    Ordering::SeqCst,
                );
                if prev_last_sealed_block == last_sealed_block {
                    return Seal::Regular(Vec::new());
                }
            }
        }
        Seal::None
    }

    fn verify_local_seal(&self, _header: &Header) -> Result<(), M::Error> {
        Ok(())
    }

    fn open_block_header_timestamp(&self, parent_timestamp: u64) -> u64 {
        use std::{cmp, time};

        let dur = time::SystemTime::now()
            .duration_since(time::UNIX_EPOCH)
            .unwrap_or_default();
        let mut now = dur.as_secs();
        if self.params.millisecond_timestamp {
            now = now * 1000 + dur.subsec_millis() as u64;
        }
        cmp::max(now, parent_timestamp)
    }

    fn is_timestamp_valid(&self, header_timestamp: u64, parent_timestamp: u64) -> bool {
        header_timestamp >= parent_timestamp
    }

    fn fork_choice(&self, new: &ExtendedHeader, current: &ExtendedHeader) -> super::ForkChoice {
        super::total_difficulty_fork_choice(new, current)
    }
}

#[cfg(test)]
mod tests {
    use block::*;
    use engines::Seal;
    use ethereum_types::{Address, H520};
    use spec::Spec;
    use std::sync::Arc;
    use test_helpers::get_temp_state_db;
    use types::header::Header;

    #[test]
    fn instant_can_seal() {
        let spec = Spec::new_instant();
        let engine = &*spec.engine;
        let db = spec
            .ensure_db_good(get_temp_state_db(), &Default::default())
            .unwrap();
        let genesis_header = spec.genesis_header();
        let last_hashes = Arc::new(vec![genesis_header.hash()]);
        let b = OpenBlock::new(
            engine,
            Default::default(),
            false,
            db,
            &genesis_header,
            last_hashes,
            Address::default(),
            (3141562.into(), 31415620.into()),
            vec![],
            false,
            None,
        )
        .unwrap();
        let b = b.close_and_lock().unwrap();
        if let Seal::Regular(seal) = engine.generate_seal(&b, &genesis_header) {
            assert!(b.try_seal(engine, seal).is_ok());
        }
    }

    #[test]
    fn instant_cant_verify() {
        let engine = Spec::new_instant().engine;
        let mut header: Header = Header::default();

        assert!(engine.verify_block_basic(&header).is_ok());

        header.set_seal(vec![::rlp::encode(&H520::default())]);

        assert!(engine.verify_block_unordered(&header).is_ok());
    }
}