nnary_snowball.go

// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package snowball

import (
	"fmt"

	"github.com/ava-labs/avalanchego/ids"
)

var _ NnarySnowball = (*nnarySnowball)(nil)

func newNnarySnowball(betaVirtuous, betaRogue int, choice ids.ID) nnarySnowball {
	return nnarySnowball{
		nnarySnowflake:     newNnarySnowflake(betaVirtuous, betaRogue, choice),
		preference:         choice,
		preferenceStrength: make(map[ids.ID]int),
	}
}

// nnarySnowball is a naive implementation of a multi-color snowball instance
type nnarySnowball struct {
	// wrap the n-nary snowflake logic
	nnarySnowflake

	// preference is the choice with the largest number of polls which preferred
	// it. Ties are broken by switching choice lazily
	preference ids.ID

	// maxPreferenceStrength is the maximum value stored in [preferenceStrength]
	maxPreferenceStrength int

	// preferenceStrength tracks the total number of network polls which
	// preferred that choice
	preferenceStrength map[ids.ID]int
}

func (sb *nnarySnowball) Preference() ids.ID {
	// It is possible, with low probability, that the snowflake preference is
	// not equal to the snowball preference when snowflake finalizes. However,
	// this case is handled for completion. Therefore, if snowflake is
	// finalized, then our finalized snowflake choice should be preferred.
	if sb.Finalized() {
		return sb.nnarySnowflake.Preference()
	}
	return sb.preference
}

func (sb *nnarySnowball) RecordSuccessfulPoll(choice ids.ID) {
	sb.increasePreferenceStrength(choice)
	sb.nnarySnowflake.RecordSuccessfulPoll(choice)
}

func (sb *nnarySnowball) RecordPollPreference(choice ids.ID) {
	sb.increasePreferenceStrength(choice)
	sb.nnarySnowflake.RecordPollPreference(choice)
}

func (sb *nnarySnowball) String() string {
	return fmt.Sprintf("SB(Preference = %s, PreferenceStrength = %d, %s)",
		sb.preference, sb.maxPreferenceStrength, &sb.nnarySnowflake)
}

func (sb *nnarySnowball) increasePreferenceStrength(choice ids.ID) {
	preferenceStrength := sb.preferenceStrength[choice] + 1
	sb.preferenceStrength[choice] = preferenceStrength

	if preferenceStrength > sb.maxPreferenceStrength {
		sb.preference = choice
		sb.maxPreferenceStrength = preferenceStrength
	}
}