/// Returns `true` if the given `store` should be updated to set

/// `state.current_justified_checkpoint` its `justified_checkpoint`.

///

/// ## Specification

///

/// Is equivalent to:

///

/// https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/fork-choice.md#should_update_justified_checkpoint

fn should_update_justified_checkpoint(

&mut self,

new_justified_checkpoint: Checkpoint,

slots: UpdateJustifiedCheckpointSlots,

spec: &ChainSpec,

) -> Result<bool, Error<T::Error>> {

self.update_time(slots.current_slot(), spec)?;

if compute_slots_since_epoch_start::<E>(self.fc_store.get_current_slot())

< spec.safe_slots_to_update_justified

{

return Ok(true);

}

let justified_slot =

compute_start_slot_at_epoch::<E>(self.fc_store.justified_checkpoint().epoch);

// This sanity check is not in the spec, but the invariant is implied.

if let Some(state_slot) = slots.state_slot() {

if justified_slot >= state_slot {

return Err(Error::AttemptToRevertJustification {

store: justified_slot,

state: state_slot,

});

}

}

// We know that the slot for `new_justified_checkpoint.root` is not greater than

// `state.slot`, since a state cannot justify its own slot.

//

// We know that `new_justified_checkpoint.root` is an ancestor of `state`, since a `state`

// only ever justifies ancestors.

//

// A prior `if` statement protects against a justified_slot that is greater than

// `state.slot`

let justified_ancestor =

self.get_ancestor(new_justified_checkpoint.root, justified_slot)?;

if justified_ancestor != Some(self.fc_store.justified_checkpoint().root) {

return Ok(false);

}

Ok(true)

}

if justified_checkpoint.epoch > self.fc_store.best_justified_checkpoint().epoch {

self.fc_store

.set_best_justified_checkpoint(justified_checkpoint);

}

if self.should_update_justified_checkpoint(justified_checkpoint, slots, spec)? {

self.fc_store

.set_justified_checkpoint(justified_checkpoint)

.map_err(Error::UnableToSetJustifiedCheckpoint)?;

}

self.fc_store

.set_justified_checkpoint(justified_checkpoint)

.map_err(Error::UnableToSetJustifiedCheckpoint)?;