//! Beacon consensus implementation.

#![doc(
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#![cfg_attr(not(test), warn(unused_crate_dependencies))]
#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]

use reth_chainspec::{ChainSpec, EthereumHardfork, EthereumHardforks};
use reth_consensus::{Consensus, ConsensusError, PostExecutionInput};
use reth_consensus_common::validation::{
    validate_4844_header_standalone, validate_against_parent_4844,
    validate_against_parent_eip1559_base_fee, validate_against_parent_hash_number,
    validate_against_parent_timestamp, validate_block_pre_execution, validate_header_base_fee,
    validate_header_extradata, validate_header_gas,
};
use reth_primitives::{
    constants::MINIMUM_GAS_LIMIT, BlockWithSenders, Header, SealedBlock, SealedHeader,
    EMPTY_OMMER_ROOT_HASH, U256,
};
use std::{sync::Arc, time::SystemTime};

/// The bound divisor of the gas limit, used in update calculations.
const GAS_LIMIT_BOUND_DIVISOR: u64 = 1024;

mod validation;
pub use validation::validate_block_post_execution;

/// Ethereum beacon consensus
///
/// This consensus engine does basic checks as outlined in the execution specs.
#[derive(Debug)]
pub struct EthBeaconConsensus {
    /// Configuration
    chain_spec: Arc<ChainSpec>,
}

impl EthBeaconConsensus {
    /// Create a new instance of [`EthBeaconConsensus`]
    pub const fn new(chain_spec: Arc<ChainSpec>) -> Self {
        Self { chain_spec }
    }

    /// Checks the gas limit for consistency between parent and self headers.
    ///
    /// The maximum allowable difference between self and parent gas limits is determined by the
    /// parent's gas limit divided by the [`GAS_LIMIT_BOUND_DIVISOR`].
    fn validate_against_parent_gas_limit(
        &self,
        header: &SealedHeader,
        parent: &SealedHeader,
    ) -> Result<(), ConsensusError> {
        // Determine the parent gas limit, considering elasticity multiplier on the London fork.
        let parent_gas_limit =
            if self.chain_spec.fork(EthereumHardfork::London).transitions_at_block(header.number) {
                parent.gas_limit *
                    self.chain_spec
                        .base_fee_params_at_timestamp(header.timestamp)
                        .elasticity_multiplier as u64
            } else {
                parent.gas_limit
            };

        // Check for an increase in gas limit beyond the allowed threshold.
        if header.gas_limit > parent_gas_limit {
            if header.gas_limit - parent_gas_limit >= parent_gas_limit / GAS_LIMIT_BOUND_DIVISOR {
                return Err(ConsensusError::GasLimitInvalidIncrease {
                    parent_gas_limit,
                    child_gas_limit: header.gas_limit,
                })
            }
        }
        // Check for a decrease in gas limit beyond the allowed threshold.
        else if parent_gas_limit - header.gas_limit >= parent_gas_limit / GAS_LIMIT_BOUND_DIVISOR
        {
            return Err(ConsensusError::GasLimitInvalidDecrease {
                parent_gas_limit,
                child_gas_limit: header.gas_limit,
            })
        }
        // Check if the self gas limit is below the minimum required limit.
        else if header.gas_limit < MINIMUM_GAS_LIMIT {
            return Err(ConsensusError::GasLimitInvalidMinimum { child_gas_limit: header.gas_limit })
        }

        Ok(())
    }
}

impl Consensus for EthBeaconConsensus {
    fn validate_header(&self, header: &SealedHeader) -> Result<(), ConsensusError> {
        validate_header_gas(header)?;
        validate_header_base_fee(header, &self.chain_spec)?;

        // EIP-4895: Beacon chain push withdrawals as operations
        if self.chain_spec.is_shanghai_active_at_timestamp(header.timestamp) &&
            header.withdrawals_root.is_none()
        {
            return Err(ConsensusError::WithdrawalsRootMissing)
        } else if !self.chain_spec.is_shanghai_active_at_timestamp(header.timestamp) &&
            header.withdrawals_root.is_some()
        {
            return Err(ConsensusError::WithdrawalsRootUnexpected)
        }

        // Ensures that EIP-4844 fields are valid once cancun is active.
        if self.chain_spec.is_cancun_active_at_timestamp(header.timestamp) {
            validate_4844_header_standalone(header)?;
        } else if header.blob_gas_used.is_some() {
            return Err(ConsensusError::BlobGasUsedUnexpected)
        } else if header.excess_blob_gas.is_some() {
            return Err(ConsensusError::ExcessBlobGasUnexpected)
        } else if header.parent_beacon_block_root.is_some() {
            return Err(ConsensusError::ParentBeaconBlockRootUnexpected)
        }

        if self.chain_spec.is_prague_active_at_timestamp(header.timestamp) {
            if header.requests_root.is_none() {
                return Err(ConsensusError::RequestsRootMissing)
            }
        } else if header.requests_root.is_some() {
            return Err(ConsensusError::RequestsRootUnexpected)
        }

        Ok(())
    }

    fn validate_header_against_parent(
        &self,
        header: &SealedHeader,
        parent: &SealedHeader,
    ) -> Result<(), ConsensusError> {
        validate_against_parent_hash_number(header, parent)?;

        validate_against_parent_timestamp(header, parent)?;

        // TODO Check difficulty increment between parent and self
        // Ace age did increment it by some formula that we need to follow.
        self.validate_against_parent_gas_limit(header, parent)?;

        validate_against_parent_eip1559_base_fee(header, parent, &self.chain_spec)?;

        // ensure that the blob gas fields for this block
        if self.chain_spec.is_cancun_active_at_timestamp(header.timestamp) {
            validate_against_parent_4844(header, parent)?;
        }

        Ok(())
    }

    fn validate_header_with_total_difficulty(
        &self,
        header: &Header,
        total_difficulty: U256,
    ) -> Result<(), ConsensusError> {
        let is_post_merge = self
            .chain_spec
            .fork(EthereumHardfork::Paris)
            .active_at_ttd(total_difficulty, header.difficulty);

        if is_post_merge {
            if !header.is_zero_difficulty() {
                return Err(ConsensusError::TheMergeDifficultyIsNotZero)
            }

            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 {
            // TODO Consensus checks for old blocks:
            //  * difficulty, mix_hash & nonce aka PoW stuff
            // low priority as syncing is done in reverse order

            // 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,
                })
            }

            validate_header_extradata(header)?;
        }

        Ok(())
    }

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

    fn validate_block_post_execution(
        &self,
        block: &BlockWithSenders,
        input: PostExecutionInput<'_>,
    ) -> Result<(), ConsensusError> {
        validate_block_post_execution(block, &self.chain_spec, input.receipts, input.requests)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use reth_chainspec::ChainSpecBuilder;
    use reth_primitives::{proofs, B256};

    fn header_with_gas_limit(gas_limit: u64) -> SealedHeader {
        let header = Header { gas_limit, ..Default::default() };
        header.seal(B256::ZERO)
    }

    #[test]
    fn test_valid_gas_limit_increase() {
        let parent = header_with_gas_limit(GAS_LIMIT_BOUND_DIVISOR * 10);
        let child = header_with_gas_limit(parent.gas_limit + 5);

        assert_eq!(
            EthBeaconConsensus::new(Arc::new(ChainSpec::default()))
                .validate_against_parent_gas_limit(&child, &parent),
            Ok(())
        );
    }

    #[test]
    fn test_gas_limit_below_minimum() {
        let parent = header_with_gas_limit(MINIMUM_GAS_LIMIT);
        let child = header_with_gas_limit(MINIMUM_GAS_LIMIT - 1);

        assert_eq!(
            EthBeaconConsensus::new(Arc::new(ChainSpec::default()))
                .validate_against_parent_gas_limit(&child, &parent),
            Err(ConsensusError::GasLimitInvalidMinimum { child_gas_limit: child.gas_limit })
        );
    }

    #[test]
    fn test_invalid_gas_limit_increase_exceeding_limit() {
        let parent = header_with_gas_limit(GAS_LIMIT_BOUND_DIVISOR * 10);
        let child = header_with_gas_limit(
            parent.gas_limit + parent.gas_limit / GAS_LIMIT_BOUND_DIVISOR + 1,
        );

        assert_eq!(
            EthBeaconConsensus::new(Arc::new(ChainSpec::default()))
                .validate_against_parent_gas_limit(&child, &parent),
            Err(ConsensusError::GasLimitInvalidIncrease {
                parent_gas_limit: parent.gas_limit,
                child_gas_limit: child.gas_limit,
            })
        );
    }

    #[test]
    fn test_valid_gas_limit_decrease_within_limit() {
        let parent = header_with_gas_limit(GAS_LIMIT_BOUND_DIVISOR * 10);
        let child = header_with_gas_limit(parent.gas_limit - 5);

        assert_eq!(
            EthBeaconConsensus::new(Arc::new(ChainSpec::default()))
                .validate_against_parent_gas_limit(&child, &parent),
            Ok(())
        );
    }

    #[test]
    fn test_invalid_gas_limit_decrease_exceeding_limit() {
        let parent = header_with_gas_limit(GAS_LIMIT_BOUND_DIVISOR * 10);
        let child = header_with_gas_limit(
            parent.gas_limit - parent.gas_limit / GAS_LIMIT_BOUND_DIVISOR - 1,
        );

        assert_eq!(
            EthBeaconConsensus::new(Arc::new(ChainSpec::default()))
                .validate_against_parent_gas_limit(&child, &parent),
            Err(ConsensusError::GasLimitInvalidDecrease {
                parent_gas_limit: parent.gas_limit,
                child_gas_limit: child.gas_limit,
            })
        );
    }

    #[test]
    fn shanghai_block_zero_withdrawals() {
        // ensures that if shanghai is activated, and we include a block with a withdrawals root,
        // that the header is valid
        let chain_spec = Arc::new(ChainSpecBuilder::mainnet().shanghai_activated().build());

        let header = Header {
            base_fee_per_gas: Some(1337u64),
            withdrawals_root: Some(proofs::calculate_withdrawals_root(&[])),
            ..Default::default()
        }
        .seal_slow();

        assert_eq!(EthBeaconConsensus::new(chain_spec).validate_header(&header), Ok(()));
    }
}