package p2p

import (
	"fmt"
	"math"
	"time"

	pubsub "github.com/libp2p/go-libp2p-pubsub"
	"github.com/libp2p/go-libp2p/core/peer"
)

// DecayToZero is the decay factor for a peer's score to zero.
const DecayToZero = 0.01

// ScoreDecay returns the decay factor for a given duration.
func ScoreDecay(duration time.Duration, slot time.Duration) float64 {
	numOfTimes := duration / slot
	return math.Pow(DecayToZero, 1/float64(numOfTimes))
}

// LightPeerScoreParams is an instantiation of [pubsub.PeerScoreParams] with light penalties.
// See [PeerScoreParams] for detailed documentation.
//
// [PeerScoreParams]: https://pkg.go.dev/github.com/libp2p/go-libp2p-pubsub@v0.8.1#PeerScoreParams
var LightPeerScoreParams = func(blockTime uint64) pubsub.PeerScoreParams {
	slot := time.Duration(blockTime) * time.Second
	if slot == 0 {
		slot = 2 * time.Second
	}
	// We initialize an "epoch" as 6 blocks suggesting 6 blocks,
	// each taking ~ 2 seconds, is 12 seconds
	epoch := 6 * slot
	tenEpochs := 10 * epoch
	oneHundredEpochs := 100 * epoch
	return pubsub.PeerScoreParams{
		Topics:        make(map[string]*pubsub.TopicScoreParams),
		TopicScoreCap: 34,
		AppSpecificScore: func(p peer.ID) float64 {
			return 0
		},
		AppSpecificWeight:           1,
		IPColocationFactorWeight:    -35,
		IPColocationFactorThreshold: 10,
		IPColocationFactorWhitelist: nil,
		BehaviourPenaltyWeight:      -16,
		BehaviourPenaltyThreshold:   6,
		BehaviourPenaltyDecay:       ScoreDecay(tenEpochs, slot),
		DecayInterval:               slot,
		DecayToZero:                 DecayToZero,
		RetainScore:                 oneHundredEpochs,
	}
}

// DisabledPeerScoreParams is an instantiation of [pubsub.PeerScoreParams] where all scoring is disabled.
// See [PeerScoreParams] for detailed documentation.
//
// [PeerScoreParams]: https://pkg.go.dev/github.com/libp2p/go-libp2p-pubsub@v0.8.1#PeerScoreParams
var DisabledPeerScoreParams = func(blockTime uint64) pubsub.PeerScoreParams {
	slot := time.Duration(blockTime) * time.Second
	if slot == 0 {
		slot = 2 * time.Second
	}
	// We initialize an "epoch" as 6 blocks suggesting 6 blocks,
	// each taking ~ 2 seconds, is 12 seconds
	epoch := 6 * slot
	tenEpochs := 10 * epoch
	oneHundredEpochs := 100 * epoch
	return pubsub.PeerScoreParams{
		Topics: make(map[string]*pubsub.TopicScoreParams),
		// 0 represent no cap
		TopicScoreCap: 0,
		AppSpecificScore: func(p peer.ID) float64 {
			return 0
		},
		AppSpecificWeight: 1,
		// ignore colocation scoring
		IPColocationFactorWeight:    0,
		IPColocationFactorWhitelist: nil,
		// 0 disables the behaviour penalty
		BehaviourPenaltyWeight: 0,
		BehaviourPenaltyDecay:  ScoreDecay(tenEpochs, slot),
		DecayInterval:          slot,
		DecayToZero:            DecayToZero,
		RetainScore:            oneHundredEpochs,
	}
}

// PeerScoreParamsByName is a map of name to function that returns a [pubsub.PeerScoreParams] based on the provided [rollup.Config].
var PeerScoreParamsByName = map[string](func(blockTime uint64) pubsub.PeerScoreParams){
	"light": LightPeerScoreParams,
	"none":  DisabledPeerScoreParams,
}

// AvailablePeerScoreParams returns a list of available peer score params.
// These can be used as an input to [GetPeerScoreParams] which returns the
// corresponding [pubsub.PeerScoreParams].
func AvailablePeerScoreParams() []string {
	var params []string
	for name := range PeerScoreParamsByName {
		params = append(params, name)
	}
	return params
}

// GetPeerScoreParams returns the [pubsub.PeerScoreParams] for the given name.
func GetPeerScoreParams(name string, blockTime uint64) (pubsub.PeerScoreParams, error) {
	params, ok := PeerScoreParamsByName[name]
	if !ok {
		return pubsub.PeerScoreParams{}, fmt.Errorf("invalid params %s", name)
	}

	return params(blockTime), nil
}

// NewPeerScoreThresholds returns a default [pubsub.PeerScoreThresholds].
// See [PeerScoreThresholds] for detailed documentation.
//
// [PeerScoreThresholds]: https://pkg.go.dev/github.com/libp2p/go-libp2p-pubsub@v0.8.1#PeerScoreThresholds
func NewPeerScoreThresholds() pubsub.PeerScoreThresholds {
	return pubsub.PeerScoreThresholds{
		SkipAtomicValidation:        false,
		GossipThreshold:             -10,
		PublishThreshold:            -40,
		GraylistThreshold:           -40,
		AcceptPXThreshold:           20,
		OpportunisticGraftThreshold: 0.05,
	}
}