use crate::per_epoch_processing::single_pass::{SinglePassConfig, process_epoch_single_pass};
use crate::{common::initiate_validator_exit, per_epoch_processing::Error};
use safe_arith::SafeArith;
use types::{BeaconState, ChainSpec, EthSpec, Validator};

/// Performs a validator registry update, if required.
///
/// NOTE: unchanged in Altair
pub fn process_registry_updates<E: EthSpec>(
    state: &mut BeaconState<E>,
    spec: &ChainSpec,
) -> Result<(), Error> {
    // Process activation eligibility and ejections.
    // Collect eligible and exiting validators (we need to avoid mutating the state while iterating).
    // We assume it's safe to re-order the change in eligibility and `initiate_validator_exit`.
    // Rest assured exiting validators will still be exited in the same order as in the spec.
    let current_epoch = state.current_epoch();
    let is_ejectable = |validator: &Validator| {
        validator.is_active_at(current_epoch)
            && validator.effective_balance <= spec.ejection_balance
    };
    let fork_name = state.fork_name_unchecked();
    let indices_to_update: Vec<_> = state
        .validators()
        .iter()
        .enumerate()
        .filter(|(_, validator)| {
            validator.is_eligible_for_activation_queue(spec, fork_name) || is_ejectable(validator)
        })
        .map(|(idx, _)| idx)
        .collect();

    for index in indices_to_update {
        let validator = state.get_validator_mut(index)?;
        if validator.is_eligible_for_activation_queue(spec, fork_name) {
            validator.activation_eligibility_epoch = current_epoch.safe_add(1)?;
        }
        if is_ejectable(validator) {
            initiate_validator_exit(state, index, spec)?;
        }
    }

    // Queue validators eligible for activation and not dequeued for activation prior to finalized epoch
    // Dequeue validators for activation up to churn limit
    let churn_limit = state.get_activation_churn_limit(spec)? as usize;

    let epoch_cache = state.epoch_cache();
    let activation_queue = epoch_cache
        .activation_queue()?
        .get_validators_eligible_for_activation(state.finalized_checkpoint().epoch, churn_limit);

    let delayed_activation_epoch = state.compute_activation_exit_epoch(current_epoch, spec)?;
    for index in activation_queue {
        state.get_validator_mut(index)?.activation_epoch = delayed_activation_epoch;
    }

    Ok(())
}

pub fn process_registry_updates_slow<E: EthSpec>(
    state: &mut BeaconState<E>,
    spec: &ChainSpec,
) -> Result<(), Error> {
    process_epoch_single_pass(
        state,
        spec,
        SinglePassConfig {
            registry_updates: true,
            ..SinglePassConfig::disable_all()
        },
    )?;
    Ok(())
}