//! Optimism Consensus implementation.

#![doc(
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#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]
// The `optimism` feature must be enabled to use this crate.
#![cfg(feature = "optimism")]

use reth_consensus::{Consensus, ConsensusError};
use reth_consensus_common::{validation, validation::validate_header_extradata};
use reth_primitives::{ChainSpec, Header, SealedBlock, SealedHeader, EMPTY_OMMER_ROOT_HASH, U256};
use std::{sync::Arc, time::SystemTime};

/// Optimism consensus implementation.
///
/// Provides basic checks as outlined in the execution specs.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OptimismBeaconConsensus {
    /// Configuration
    chain_spec: Arc<ChainSpec>,
}

impl OptimismBeaconConsensus {
    /// Create a new instance of [OptimismBeaconConsensus]
    ///
    /// # Panics
    ///
    /// If given chain spec is not optimism [ChainSpec::is_optimism]
    pub fn new(chain_spec: Arc<ChainSpec>) -> Self {
        assert!(chain_spec.is_optimism(), "optimism consensus only valid for optimism chains");
        Self { chain_spec }
    }
}

impl Consensus for OptimismBeaconConsensus {
    fn validate_header(&self, header: &SealedHeader) -> Result<(), ConsensusError> {
        validation::validate_header_standalone(header, &self.chain_spec)?;
        Ok(())
    }

    fn validate_header_against_parent(
        &self,
        header: &SealedHeader,
        parent: &SealedHeader,
    ) -> Result<(), ConsensusError> {
        header.validate_against_parent(parent, &self.chain_spec).map_err(ConsensusError::from)?;
        Ok(())
    }

    fn validate_header_with_total_difficulty(
        &self,
        header: &Header,
        _total_difficulty: U256,
    ) -> Result<(), ConsensusError> {
        // with OP-stack Bedrock activation number determines when TTD (eth Merge) has been reached.
        let is_post_merge = self.chain_spec.is_bedrock_active_at_block(header.number);

        if is_post_merge {
            if header.nonce != 0 {
                return Err(ConsensusError::TheMergeNonceIsNotZero)
            }

            if header.ommers_hash != EMPTY_OMMER_ROOT_HASH {
                return Err(ConsensusError::TheMergeOmmerRootIsNotEmpty)
            }

            // Post-merge, the consensus layer is expected to perform checks such that the block
            // timestamp is a function of the slot. This is different from pre-merge, where blocks
            // are only allowed to be in the future (compared to the system's clock) by a certain
            // threshold.
            //
            // Block validation with respect to the parent should ensure that the block timestamp
            // is greater than its parent timestamp.

            // validate header extradata for all networks post merge
            validate_header_extradata(header)?;

            // mixHash is used instead of difficulty inside EVM
            // https://eips.ethereum.org/EIPS/eip-4399#using-mixhash-field-instead-of-difficulty
        } else {
            // Check if timestamp is in the future. Clock can drift but this can be consensus issue.
            let present_timestamp =
                SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_secs();

            if header.exceeds_allowed_future_timestamp(present_timestamp) {
                return Err(ConsensusError::TimestampIsInFuture {
                    timestamp: header.timestamp,
                    present_timestamp,
                })
            }
        }

        Ok(())
    }

    fn validate_block(&self, block: &SealedBlock) -> Result<(), ConsensusError> {
        validation::validate_block_standalone(block, &self.chain_spec)
    }
}