package manager

import (
	"context"
	"sync"
	"time"

	log "github.com/sirupsen/logrus"

	"github.com/netbirdio/netbird/management/internals/modules/peers"
	"github.com/netbirdio/netbird/management/internals/modules/peers/ephemeral"
	"github.com/netbirdio/netbird/management/server/activity"
	nbpeer "github.com/netbirdio/netbird/management/server/peer"
	"github.com/netbirdio/netbird/management/server/telemetry"

	"github.com/netbirdio/netbird/management/server/store"
)

const (
	// cleanupWindow is the time window to wait after nearest peer deadline to start the cleanup procedure.
	cleanupWindow = 1 * time.Minute
)

var (
	timeNow = time.Now
)

type ephemeralPeer struct {
	id        string
	accountID string
	deadline  time.Time
	next      *ephemeralPeer
}

// todo: consider to remove peer from ephemeral list when the peer has been deleted via API. If we do not do it
// in worst case we will get invalid error message in this manager.

// EphemeralManager keep a list of ephemeral peers. After EphemeralLifeTime inactivity the peer will be deleted
// automatically. Inactivity means the peer disconnected from the Management server.
type EphemeralManager struct {
	store        store.Store
	peersManager peers.Manager

	headPeer  *ephemeralPeer
	tailPeer  *ephemeralPeer
	peersLock sync.Mutex
	timer     *time.Timer

	lifeTime      time.Duration
	cleanupWindow time.Duration

	// metrics is nil-safe; methods on telemetry.EphemeralPeersMetrics
	// no-op when the receiver is nil so deployments without an app
	// metrics provider work unchanged.
	metrics *telemetry.EphemeralPeersMetrics
}

// NewEphemeralManager instantiate new EphemeralManager
func NewEphemeralManager(store store.Store, peersManager peers.Manager) *EphemeralManager {
	return &EphemeralManager{
		store:        store,
		peersManager: peersManager,

		lifeTime:      ephemeral.EphemeralLifeTime,
		cleanupWindow: cleanupWindow,
	}
}

// SetMetrics attaches a metrics collector. Safe to call once before
// LoadInitialPeers; later attachment is fine but earlier loads won't be
// reflected in the gauge. Pass nil to detach.
func (e *EphemeralManager) SetMetrics(m *telemetry.EphemeralPeersMetrics) {
	e.peersLock.Lock()
	e.metrics = m
	e.peersLock.Unlock()
}

// LoadInitialPeers load from the database the ephemeral type of peers and schedule a cleanup procedure to the head
// of the linked list (to the most deprecated peer). At the end of cleanup it schedules the next cleanup to the new
// head.
func (e *EphemeralManager) LoadInitialPeers(ctx context.Context) {
	e.peersLock.Lock()
	defer e.peersLock.Unlock()

	e.loadEphemeralPeers(ctx)
	if e.headPeer != nil {
		e.timer = time.AfterFunc(e.lifeTime, func() {
			e.cleanup(ctx)
		})
	}
}

// Stop timer
func (e *EphemeralManager) Stop() {
	e.peersLock.Lock()
	defer e.peersLock.Unlock()

	if e.timer != nil {
		e.timer.Stop()
	}
}

// OnPeerConnected remove the peer from the linked list of ephemeral peers. Because it has been called when the peer
// is active the manager will not delete it while it is active.
func (e *EphemeralManager) OnPeerConnected(ctx context.Context, peer *nbpeer.Peer) {
	if !peer.Ephemeral {
		return
	}

	log.WithContext(ctx).Tracef("remove peer from ephemeral list: %s", peer.ID)

	e.peersLock.Lock()
	defer e.peersLock.Unlock()

	if e.removePeer(peer.ID) {
		e.metrics.DecPending(1)
	}

	// stop the unnecessary timer
	if e.headPeer == nil && e.timer != nil {
		e.timer.Stop()
		e.timer = nil
	}
}

// OnPeerDisconnected add the peer to the linked list of ephemeral peers. Because of the peer
// is inactive it will be deleted after the EphemeralLifeTime period.
func (e *EphemeralManager) OnPeerDisconnected(ctx context.Context, peer *nbpeer.Peer) {
	if !peer.Ephemeral {
		return
	}

	log.WithContext(ctx).Tracef("add peer to ephemeral list: %s", peer.ID)

	e.peersLock.Lock()
	defer e.peersLock.Unlock()

	if e.isPeerOnList(peer.ID) {
		return
	}

	e.addPeer(peer.AccountID, peer.ID, e.newDeadLine())
	e.metrics.IncPending()
	if e.timer == nil {
		delay := e.headPeer.deadline.Sub(timeNow()) + e.cleanupWindow
		if delay < 0 {
			delay = 0
		}
		e.timer = time.AfterFunc(delay, func() {
			e.cleanup(ctx)
		})
	}
}

func (e *EphemeralManager) loadEphemeralPeers(ctx context.Context) {
	peers, err := e.store.GetAllEphemeralPeers(ctx, store.LockingStrengthNone)
	if err != nil {
		log.WithContext(ctx).Debugf("failed to load ephemeral peers: %s", err)
		return
	}

	t := e.newDeadLine()
	for _, p := range peers {
		e.addPeer(p.AccountID, p.ID, t)
	}
	e.metrics.AddPending(int64(len(peers)))

	log.WithContext(ctx).Debugf("loaded ephemeral peer(s): %d", len(peers))
}

func (e *EphemeralManager) cleanup(ctx context.Context) {
	log.Tracef("on ephemeral cleanup")
	deletePeers := make(map[string]*ephemeralPeer)

	e.peersLock.Lock()
	now := timeNow()
	for p := e.headPeer; p != nil; p = p.next {
		if now.Before(p.deadline) {
			break
		}

		deletePeers[p.id] = p
		e.headPeer = p.next
		if p.next == nil {
			e.tailPeer = nil
		}
	}

	if e.headPeer != nil {
		delay := e.headPeer.deadline.Sub(timeNow()) + e.cleanupWindow
		if delay < 0 {
			delay = 0
		}
		e.timer = time.AfterFunc(delay, func() {
			e.cleanup(ctx)
		})
	} else {
		e.timer = nil
	}

	e.peersLock.Unlock()

	// Drop the gauge by the number of entries we just took off the list,
	// regardless of whether the subsequent DeletePeers call succeeds. The
	// list invariant is what the gauge tracks; failed delete batches are
	// counted separately via CountCleanupError so we can still see them.
	if len(deletePeers) > 0 {
		e.metrics.CountCleanupRun()
		e.metrics.DecPending(int64(len(deletePeers)))
	}

	peerIDsPerAccount := make(map[string][]string)
	for id, p := range deletePeers {
		peerIDsPerAccount[p.accountID] = append(peerIDsPerAccount[p.accountID], id)
	}

	for accountID, peerIDs := range peerIDsPerAccount {
		log.WithContext(ctx).Debugf("cleanup: deleting %d ephemeral peers for account %s: %s", len(peerIDs), accountID, peerIDs)
		err := e.peersManager.DeletePeers(ctx, accountID, peerIDs, activity.SystemInitiator, true)
		if err != nil {
			log.WithContext(ctx).Errorf("failed to delete ephemeral peers: %s", err)
			e.metrics.CountCleanupError()
			continue
		}
		e.metrics.CountPeersCleaned(int64(len(peerIDs)))
	}
}

func (e *EphemeralManager) addPeer(accountID string, peerID string, deadline time.Time) {
	ep := &ephemeralPeer{
		id:        peerID,
		accountID: accountID,
		deadline:  deadline,
	}

	if e.headPeer == nil {
		e.headPeer = ep
	}
	if e.tailPeer != nil {
		e.tailPeer.next = ep
	}
	e.tailPeer = ep
}

// removePeer drops the entry from the linked list. Returns true if a
// matching entry was found and removed so callers can keep the pending
// metric gauge in sync.
func (e *EphemeralManager) removePeer(id string) bool {
	if e.headPeer == nil {
		return false
	}

	if e.headPeer.id == id {
		e.headPeer = e.headPeer.next
		if e.tailPeer.id == id {
			e.tailPeer = nil
		}
		return true
	}

	for p := e.headPeer; p.next != nil; p = p.next {
		if p.next.id == id {
			// if we remove the last element from the chain then set the last-1 as tail
			if e.tailPeer.id == id {
				e.tailPeer = p
			}
			p.next = p.next.next
			return true
		}
	}
	return false
}

func (e *EphemeralManager) isPeerOnList(id string) bool {
	for p := e.headPeer; p != nil; p = p.next {
		if p.id == id {
			return true
		}
	}
	return false
}

func (e *EphemeralManager) newDeadLine() time.Time {
	return timeNow().Add(e.lifeTime)
}