use safe_arith::SafeArith;
use std::mem;
use types::{
    BeaconState, BeaconStateElectra, BeaconStateError as Error, ChainSpec, EpochCache, EthSpec,
    Fork,
};

/// Transform a `Deneb` state into an `Electra` state.
pub fn upgrade_to_electra<E: EthSpec>(
    pre_state: &mut BeaconState<E>,
    spec: &ChainSpec,
) -> Result<(), Error> {
    let epoch = pre_state.current_epoch();

    let earliest_exit_epoch = pre_state
        .validators()
        .iter()
        .filter(|v| v.exit_epoch != spec.far_future_epoch)
        .map(|v| v.exit_epoch)
        .max()
        .unwrap_or(epoch)
        .safe_add(1)?;

    // The total active balance cache must be built before the consolidation churn limit
    // is calculated.
    pre_state.build_total_active_balance_cache(spec)?;
    let earliest_consolidation_epoch = spec.compute_activation_exit_epoch(epoch)?;

    let pre = pre_state.as_deneb_mut()?;
    // Where possible, use something like `mem::take` to move fields from behind the &mut
    // reference. For other fields that don't have a good default value, use `clone`.
    //
    // Fixed size vectors get cloned because replacing them would require the same size
    // allocation as cloning.
    let mut post = BeaconState::Electra(BeaconStateElectra {
        // Versioning
        genesis_time: pre.genesis_time,
        genesis_validators_root: pre.genesis_validators_root,
        slot: pre.slot,
        fork: Fork {
            previous_version: pre.fork.current_version,
            current_version: spec.electra_fork_version,
            epoch,
        },
        // History
        latest_block_header: pre.latest_block_header.clone(),
        block_roots: pre.block_roots.clone(),
        state_roots: pre.state_roots.clone(),
        historical_roots: mem::take(&mut pre.historical_roots),
        // Eth1
        eth1_data: pre.eth1_data.clone(),
        eth1_data_votes: mem::take(&mut pre.eth1_data_votes),
        eth1_deposit_index: pre.eth1_deposit_index,
        // Registry
        validators: mem::take(&mut pre.validators),
        balances: mem::take(&mut pre.balances),
        // Randomness
        randao_mixes: pre.randao_mixes.clone(),
        // Slashings
        slashings: pre.slashings.clone(),
        // `Participation
        previous_epoch_participation: mem::take(&mut pre.previous_epoch_participation),
        current_epoch_participation: mem::take(&mut pre.current_epoch_participation),
        // Finality
        justification_bits: pre.justification_bits.clone(),
        previous_justified_checkpoint: pre.previous_justified_checkpoint,
        current_justified_checkpoint: pre.current_justified_checkpoint,
        finalized_checkpoint: pre.finalized_checkpoint,
        // Inactivity
        inactivity_scores: mem::take(&mut pre.inactivity_scores),
        // Sync committees
        current_sync_committee: pre.current_sync_committee.clone(),
        next_sync_committee: pre.next_sync_committee.clone(),
        // Execution
        latest_execution_payload_header: pre.latest_execution_payload_header.upgrade_to_electra(),
        // Capella
        next_withdrawal_index: pre.next_withdrawal_index,
        next_withdrawal_validator_index: pre.next_withdrawal_validator_index,
        historical_summaries: pre.historical_summaries.clone(),
        // Electra
        deposit_requests_start_index: spec.unset_deposit_requests_start_index,
        deposit_balance_to_consume: 0,
        exit_balance_to_consume: 0,
        earliest_exit_epoch,
        consolidation_balance_to_consume: 0,
        earliest_consolidation_epoch,
        pending_balance_deposits: Default::default(),
        pending_partial_withdrawals: Default::default(),
        pending_consolidations: Default::default(),
        // Caches
        total_active_balance: pre.total_active_balance,
        progressive_balances_cache: mem::take(&mut pre.progressive_balances_cache),
        committee_caches: mem::take(&mut pre.committee_caches),
        pubkey_cache: mem::take(&mut pre.pubkey_cache),
        exit_cache: mem::take(&mut pre.exit_cache),
        slashings_cache: mem::take(&mut pre.slashings_cache),
        epoch_cache: EpochCache::default(),
    });
    *post.exit_balance_to_consume_mut()? = post.get_activation_exit_churn_limit(spec)?;
    *post.consolidation_balance_to_consume_mut()? = post.get_consolidation_churn_limit(spec)?;

    // Add validators that are not yet active to pending balance deposits
    let validators = post.validators().clone();
    let mut pre_activation = validators
        .iter()
        .enumerate()
        .filter(|(_, validator)| validator.activation_epoch == spec.far_future_epoch)
        .collect::<Vec<_>>();

    // Sort the indices by activation_eligibility_epoch and then by index
    pre_activation.sort_by(|(index_a, val_a), (index_b, val_b)| {
        if val_a.activation_eligibility_epoch == val_b.activation_eligibility_epoch {
            index_a.cmp(index_b)
        } else {
            val_a
                .activation_eligibility_epoch
                .cmp(&val_b.activation_eligibility_epoch)
        }
    });

    // Process validators to queue entire balance and reset them
    for (index, _) in pre_activation {
        post.queue_entire_balance_and_reset_validator(index, spec)?;
    }

    // Ensure early adopters of compounding credentials go through the activation churn
    for (index, validator) in validators.iter().enumerate() {
        if validator.has_compounding_withdrawal_credential(spec) {
            post.queue_excess_active_balance(index, spec)?;
        }
    }

    *pre_state = post;

    Ok(())
}
