package routing

import (
	"math"
	"sync"
	"time"

	"github.com/btcsuite/btcd/btcec"
	"github.com/coreos/bbolt"
	"github.com/lightningnetwork/lnd/channeldb"
	"github.com/lightningnetwork/lnd/lnwire"
	"github.com/lightningnetwork/lnd/routing/route"
	"github.com/lightningnetwork/lnd/zpay32"
)

const (
	// DefaultPenaltyHalfLife is the default half-life duration. The
	// half-life duration defines after how much time a penalized node or
	// channel is back at 50% probability.
	DefaultPenaltyHalfLife = time.Hour
)

// MissionControl contains state which summarizes the past attempts of HTLC
// routing by external callers when sending payments throughout the network. It
// acts as a shared memory during routing attempts with the goal to optimize the
// payment attempt success rate.
//
// Failed payment attempts are reported to mission control. These reports are
// used to track the time of the last node or channel level failure. The time
// since the last failure is used to estimate a success probability that is fed
// into the path finding process for subsequent payment attempts.
type MissionControl struct {
	history map[route.Vertex]*nodeHistory

	graph *channeldb.ChannelGraph

	selfNode *channeldb.LightningNode

	queryBandwidth func(*channeldb.ChannelEdgeInfo) lnwire.MilliSatoshi

	// now is expected to return the current time. It is supplied as an
	// external function to enable deterministic unit tests.
	now func() time.Time

	cfg *MissionControlConfig

	sync.Mutex

	// TODO(roasbeef): further counters, if vertex continually unavailable,
	// add to another generation

	// TODO(roasbeef): also add favorable metrics for nodes
}

// A compile time assertion to ensure MissionControl meets the
// PaymentSessionSource interface.
var _ PaymentSessionSource = (*MissionControl)(nil)

// MissionControlConfig defines parameters that control mission control
// behaviour.
type MissionControlConfig struct {
	// PenaltyHalfLife defines after how much time a penalized node or
	// channel is back at 50% probability.
	PenaltyHalfLife time.Duration

	// PaymentAttemptPenalty is the virtual cost in path finding weight
	// units of executing a payment attempt that fails. It is used to trade
	// off potentially better routes against their probability of
	// succeeding.
	PaymentAttemptPenalty lnwire.MilliSatoshi

	// MinProbability defines the minimum success probability of the
	// returned route.
	MinRouteProbability float64

	// AprioriHopProbability is the assumed success probability of a hop in
	// a route when no other information is available.
	AprioriHopProbability float64
}

// nodeHistory contains a summary of payment attempt outcomes involving a
// particular node.
type nodeHistory struct {
	// lastFail is the last time a node level failure occurred, if any.
	lastFail *time.Time

	// channelLastFail tracks history per channel, if available for that
	// channel.
	channelLastFail map[uint64]*channelHistory
}

// channelHistory contains a summary of payment attempt outcomes involving a
// particular channel.
type channelHistory struct {
	// lastFail is the last time a channel level failure occurred.
	lastFail time.Time

	// minPenalizeAmt is the minimum amount for which to take this failure
	// into account.
	minPenalizeAmt lnwire.MilliSatoshi
}

// MissionControlSnapshot contains a snapshot of the current state of mission
// control.
type MissionControlSnapshot struct {
	// Nodes contains the per node information of this snapshot.
	Nodes []MissionControlNodeSnapshot
}

// MissionControlNodeSnapshot contains a snapshot of the current node state in
// mission control.
type MissionControlNodeSnapshot struct {
	// Node pubkey.
	Node route.Vertex

	// Lastfail is the time of last failure, if any.
	LastFail *time.Time

	// Channels is a list of channels for which specific information is
	// logged.
	Channels []MissionControlChannelSnapshot

	// OtherChanSuccessProb is the success probability for channels not in
	// the Channels slice.
	OtherChanSuccessProb float64
}

// MissionControlChannelSnapshot contains a snapshot of the current channel
// state in mission control.
type MissionControlChannelSnapshot struct {
	// ChannelID is the short channel id of the snapshot.
	ChannelID uint64

	// LastFail is the time of last failure.
	LastFail time.Time

	// MinPenalizeAmt is the minimum amount for which the channel will be
	// penalized.
	MinPenalizeAmt lnwire.MilliSatoshi

	// SuccessProb is the success probability estimation for this channel.
	SuccessProb float64
}

// NewMissionControl returns a new instance of missionControl.
//
// TODO(roasbeef): persist memory
func NewMissionControl(g *channeldb.ChannelGraph, selfNode *channeldb.LightningNode,
	qb func(*channeldb.ChannelEdgeInfo) lnwire.MilliSatoshi,
	cfg *MissionControlConfig) *MissionControl {

	log.Debugf("Instantiating mission control with config: "+
		"PenaltyHalfLife=%v, PaymentAttemptPenalty=%v, "+
		"MinRouteProbability=%v, AprioriHopProbability=%v",
		cfg.PenaltyHalfLife,
		int64(cfg.PaymentAttemptPenalty.ToSatoshis()),
		cfg.MinRouteProbability, cfg.AprioriHopProbability)

	return &MissionControl{
		history:        make(map[route.Vertex]*nodeHistory),
		selfNode:       selfNode,
		queryBandwidth: qb,
		graph:          g,
		now:            time.Now,
		cfg:            cfg,
	}
}

// NewPaymentSession creates a new payment session backed by the latest prune
// view from Mission Control. An optional set of routing hints can be provided
// in order to populate additional edges to explore when finding a path to the
// payment's destination.
func (m *MissionControl) NewPaymentSession(routeHints [][]zpay32.HopHint,
	target route.Vertex) (PaymentSession, error) {

	edges := make(map[route.Vertex][]*channeldb.ChannelEdgePolicy)

	// Traverse through all of the available hop hints and include them in
	// our edges map, indexed by the public key of the channel's starting
	// node.
	for _, routeHint := range routeHints {
		// If multiple hop hints are provided within a single route
		// hint, we'll assume they must be chained together and sorted
		// in forward order in order to reach the target successfully.
		for i, hopHint := range routeHint {
			// In order to determine the end node of this hint,
			// we'll need to look at the next hint's start node. If
			// we've reached the end of the hints list, we can
			// assume we've reached the destination.
			endNode := &channeldb.LightningNode{}
			if i != len(routeHint)-1 {
				endNode.AddPubKey(routeHint[i+1].NodeID)
			} else {
				targetPubKey, err := btcec.ParsePubKey(
					target[:], btcec.S256(),
				)
				if err != nil {
					return nil, err
				}
				endNode.AddPubKey(targetPubKey)
			}

			// Finally, create the channel edge from the hop hint
			// and add it to list of edges corresponding to the node
			// at the start of the channel.
			edge := &channeldb.ChannelEdgePolicy{
				Node:      endNode,
				ChannelID: hopHint.ChannelID,
				FeeBaseMSat: lnwire.MilliSatoshi(
					hopHint.FeeBaseMSat,
				),
				FeeProportionalMillionths: lnwire.MilliSatoshi(
					hopHint.FeeProportionalMillionths,
				),
				TimeLockDelta: hopHint.CLTVExpiryDelta,
			}

			v := route.NewVertex(hopHint.NodeID)
			edges[v] = append(edges[v], edge)
		}
	}

	// We'll also obtain a set of bandwidthHints from the lower layer for
	// each of our outbound channels. This will allow the path finding to
	// skip any links that aren't active or just don't have enough
	// bandwidth to carry the payment.
	sourceNode, err := m.graph.SourceNode()
	if err != nil {
		return nil, err
	}
	bandwidthHints, err := generateBandwidthHints(
		sourceNode, m.queryBandwidth,
	)
	if err != nil {
		return nil, err
	}

	return &paymentSession{
		additionalEdges:      edges,
		bandwidthHints:       bandwidthHints,
		errFailedPolicyChans: make(map[nodeChannel]struct{}),
		mc:                   m,
		pathFinder:           findPath,
	}, nil
}

// NewPaymentSessionForRoute creates a new paymentSession instance that is just
// used for failure reporting to missioncontrol.
func (m *MissionControl) NewPaymentSessionForRoute(preBuiltRoute *route.Route) PaymentSession {
	return &paymentSession{
		errFailedPolicyChans: make(map[nodeChannel]struct{}),
		mc:                   m,
		preBuiltRoute:        preBuiltRoute,
	}
}

// NewPaymentSessionEmpty creates a new paymentSession instance that is empty,
// and will be exhausted immediately. Used for failure reporting to
// missioncontrol for resumed payment we don't want to make more attempts for.
func (m *MissionControl) NewPaymentSessionEmpty() PaymentSession {
	return &paymentSession{
		errFailedPolicyChans: make(map[nodeChannel]struct{}),
		mc:                   m,
		preBuiltRoute:        &route.Route{},
		preBuiltRouteTried:   true,
	}
}

// generateBandwidthHints is a helper function that's utilized the main
// findPath function in order to obtain hints from the lower layer w.r.t to the
// available bandwidth of edges on the network. Currently, we'll only obtain
// bandwidth hints for the edges we directly have open ourselves. Obtaining
// these hints allows us to reduce the number of extraneous attempts as we can
// skip channels that are inactive, or just don't have enough bandwidth to
// carry the payment.
func generateBandwidthHints(sourceNode *channeldb.LightningNode,
	queryBandwidth func(*channeldb.ChannelEdgeInfo) lnwire.MilliSatoshi) (map[uint64]lnwire.MilliSatoshi, error) {

	// First, we'll collect the set of outbound edges from the target
	// source node.
	var localChans []*channeldb.ChannelEdgeInfo
	err := sourceNode.ForEachChannel(nil, func(tx *bbolt.Tx,
		edgeInfo *channeldb.ChannelEdgeInfo,
		_, _ *channeldb.ChannelEdgePolicy) error {

		localChans = append(localChans, edgeInfo)
		return nil
	})
	if err != nil {
		return nil, err
	}

	// Now that we have all of our outbound edges, we'll populate the set
	// of bandwidth hints, querying the lower switch layer for the most up
	// to date values.
	bandwidthHints := make(map[uint64]lnwire.MilliSatoshi)
	for _, localChan := range localChans {
		bandwidthHints[localChan.ChannelID] = queryBandwidth(localChan)
	}

	return bandwidthHints, nil
}

// ResetHistory resets the history of MissionControl returning it to a state as
// if no payment attempts have been made.
func (m *MissionControl) ResetHistory() {
	m.Lock()
	defer m.Unlock()

	m.history = make(map[route.Vertex]*nodeHistory)

	log.Debugf("Mission control history cleared")
}

// getEdgeProbability is expected to return the success probability of a payment
// from fromNode along edge.
func (m *MissionControl) getEdgeProbability(fromNode route.Vertex,
	edge EdgeLocator, amt lnwire.MilliSatoshi) float64 {

	m.Lock()
	defer m.Unlock()

	// Get the history for this node. If there is no history available,
	// assume that it's success probability is a constant a priori
	// probability. After the attempt new information becomes available to
	// adjust this probability.
	nodeHistory, ok := m.history[fromNode]
	if !ok {
		return m.cfg.AprioriHopProbability
	}

	return m.getEdgeProbabilityForNode(nodeHistory, edge.ChannelID, amt)
}

// getEdgeProbabilityForNode estimates the probability of successfully
// traversing a channel based on the node history.
func (m *MissionControl) getEdgeProbabilityForNode(nodeHistory *nodeHistory,
	channelID uint64, amt lnwire.MilliSatoshi) float64 {

	// Calculate the last failure of the given edge. A node failure is
	// considered a failure that would have affected every edge. Therefore
	// we insert a node level failure into the history of every channel.
	lastFailure := nodeHistory.lastFail

	// Take into account a minimum penalize amount. For balance errors, a
	// failure may be reported with such a minimum to prevent too aggresive
	// penalization. We only take into account a previous failure if the
	// amount that we currently get the probability for is greater or equal
	// than the minPenalizeAmt of the previous failure.
	channelHistory, ok := nodeHistory.channelLastFail[channelID]
	if ok && channelHistory.minPenalizeAmt <= amt {

		// If there is both a node level failure recorded and a channel
		// level failure is applicable too, we take the most recent of
		// the two.
		if lastFailure == nil ||
			channelHistory.lastFail.After(*lastFailure) {

			lastFailure = &channelHistory.lastFail
		}
	}

	if lastFailure == nil {
		return m.cfg.AprioriHopProbability
	}

	timeSinceLastFailure := m.now().Sub(*lastFailure)

	// Calculate success probability. It is an exponential curve that brings
	// the probability down to zero when a failure occurs. From there it
	// recovers asymptotically back to the a priori probability. The rate at
	// which this happens is controlled by the penaltyHalfLife parameter.
	exp := -timeSinceLastFailure.Hours() / m.cfg.PenaltyHalfLife.Hours()
	probability := m.cfg.AprioriHopProbability * (1 - math.Pow(2, exp))

	return probability
}

// createHistoryIfNotExists returns the history for the given node. If the node
// is yet unknown, it will create an empty history structure.
func (m *MissionControl) createHistoryIfNotExists(vertex route.Vertex) *nodeHistory {
	if node, ok := m.history[vertex]; ok {
		return node
	}

	node := &nodeHistory{
		channelLastFail: make(map[uint64]*channelHistory),
	}
	m.history[vertex] = node

	return node
}

// reportVertexFailure reports a node level failure.
func (m *MissionControl) reportVertexFailure(v route.Vertex) {
	log.Debugf("Reporting vertex %v failure to Mission Control", v)

	now := m.now()

	m.Lock()
	defer m.Unlock()

	history := m.createHistoryIfNotExists(v)
	history.lastFail = &now
}

// reportEdgeFailure reports a channel level failure.
//
// TODO(roasbeef): also add value attempted to send and capacity of channel
func (m *MissionControl) reportEdgeFailure(failedEdge edge,
	minPenalizeAmt lnwire.MilliSatoshi) {

	log.Debugf("Reporting channel %v failure to Mission Control",
		failedEdge.channel)

	now := m.now()

	m.Lock()
	defer m.Unlock()

	history := m.createHistoryIfNotExists(failedEdge.from)
	history.channelLastFail[failedEdge.channel] = &channelHistory{
		lastFail:       now,
		minPenalizeAmt: minPenalizeAmt,
	}
}

// GetHistorySnapshot takes a snapshot from the current mission control state
// and actual probability estimates.
func (m *MissionControl) GetHistorySnapshot() *MissionControlSnapshot {
	m.Lock()
	defer m.Unlock()

	log.Debugf("Requesting history snapshot from mission control: "+
		"node_count=%v", len(m.history))

	nodes := make([]MissionControlNodeSnapshot, 0, len(m.history))

	for v, h := range m.history {
		channelSnapshot := make([]MissionControlChannelSnapshot, 0,
			len(h.channelLastFail),
		)

		for id, lastFail := range h.channelLastFail {
			// Show probability assuming amount meets min
			// penalization amount.
			prob := m.getEdgeProbabilityForNode(
				h, id, lastFail.minPenalizeAmt,
			)

			channelSnapshot = append(channelSnapshot,
				MissionControlChannelSnapshot{
					ChannelID:      id,
					LastFail:       lastFail.lastFail,
					MinPenalizeAmt: lastFail.minPenalizeAmt,
					SuccessProb:    prob,
				},
			)
		}

		otherProb := m.getEdgeProbabilityForNode(h, 0, 0)

		nodes = append(nodes,
			MissionControlNodeSnapshot{
				Node:                 v,
				LastFail:             h.lastFail,
				OtherChanSuccessProb: otherProb,
				Channels:             channelSnapshot,
			},
		)
	}

	snapshot := MissionControlSnapshot{
		Nodes: nodes,
	}

	return &snapshot
}