package holepunch

import (
	"context"
	"fmt"
	"sync"
	"time"

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

	ma "github.com/multiformats/go-multiaddr"
)

const (
	tracerGCInterval    = 2 * time.Minute
	tracerCacheDuration = 5 * time.Minute
)

// WithTracer is a Service option that enables hole punching tracing
func WithTracer(tr EventTracer) Option {
	return func(hps *Service) error {
		t := &tracer{
			tr:   tr,
			self: hps.host.ID(),
			peers: make(map[peer.ID]struct {
				counter int
				last    time.Time
			}),
		}
		t.refCount.Add(1)
		t.ctx, t.ctxCancel = context.WithCancel(context.Background())
		go t.gc()
		hps.tracer = t
		return nil
	}
}

type tracer struct {
	tr   EventTracer
	self peer.ID

	refCount  sync.WaitGroup
	ctx       context.Context
	ctxCancel context.CancelFunc

	mutex sync.Mutex
	peers map[peer.ID]struct {
		counter int
		last    time.Time
	}
}

type EventTracer interface {
	Trace(evt *Event)
}

type Event struct {
	Timestamp int64       // UNIX nanos
	Peer      peer.ID     // local peer ID
	Remote    peer.ID     // remote peer ID
	Type      string      // event type
	Evt       interface{} // the actual event
}

// Event Types
const (
	DirectDialEvtT       = "DirectDial"
	ProtocolErrorEvtT    = "ProtocolError"
	StartHolePunchEvtT   = "StartHolePunch"
	EndHolePunchEvtT     = "EndHolePunch"
	HolePunchAttemptEvtT = "HolePunchAttempt"
)

// Event Objects
type DirectDialEvt struct {
	Success      bool
	EllapsedTime time.Duration
	Error        string `json:",omitempty"`
}

type ProtocolErrorEvt struct {
	Error string
}

type StartHolePunchEvt struct {
	RemoteAddrs []string
	RTT         time.Duration
}

type EndHolePunchEvt struct {
	Success      bool
	EllapsedTime time.Duration
	Error        string `json:",omitempty"`
}

type HolePunchAttemptEvt struct {
	Attempt int
}

// tracer interface
func (t *tracer) DirectDialSuccessful(p peer.ID, dt time.Duration) {
	if t == nil {
		return
	}

	t.tr.Trace(&Event{
		Timestamp: time.Now().UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      DirectDialEvtT,
		Evt: &DirectDialEvt{
			Success:      true,
			EllapsedTime: dt,
		},
	})
}

func (t *tracer) DirectDialFailed(p peer.ID, dt time.Duration, err error) {
	if t == nil {
		return
	}

	t.tr.Trace(&Event{
		Timestamp: time.Now().UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      DirectDialEvtT,
		Evt: &DirectDialEvt{
			Success:      false,
			EllapsedTime: dt,
			Error:        err.Error(),
		},
	})
}

func (t *tracer) ProtocolError(p peer.ID, err error) {
	if t == nil {
		return
	}

	t.tr.Trace(&Event{
		Timestamp: time.Now().UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      ProtocolErrorEvtT,
		Evt: &ProtocolErrorEvt{
			Error: err.Error(),
		},
	})
}

func (t *tracer) StartHolePunch(p peer.ID, obsAddrs []ma.Multiaddr, rtt time.Duration) {
	if t == nil {
		return
	}

	addrs := make([]string, 0, len(obsAddrs))
	for _, a := range obsAddrs {
		addrs = append(addrs, a.String())
	}

	t.tr.Trace(&Event{
		Timestamp: time.Now().UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      StartHolePunchEvtT,
		Evt: &StartHolePunchEvt{
			RemoteAddrs: addrs,
			RTT:         rtt,
		},
	})
}

func (t *tracer) EndHolePunch(p peer.ID, dt time.Duration, err error) {
	if t == nil {
		return
	}

	evt := &EndHolePunchEvt{
		Success:      err == nil,
		EllapsedTime: dt,
	}
	if err != nil {
		evt.Error = err.Error()
	}

	t.tr.Trace(&Event{
		Timestamp: time.Now().UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      EndHolePunchEvtT,
		Evt:       evt,
	})
}

func (t *tracer) HolePunchAttempt(p peer.ID) {
	if t == nil {
		return
	}

	now := time.Now()
	t.mutex.Lock()
	attempt := t.peers[p]
	attempt.counter++
	counter := attempt.counter
	attempt.last = now
	t.peers[p] = attempt
	t.mutex.Unlock()

	t.tr.Trace(&Event{
		Timestamp: now.UnixNano(),
		Peer:      t.self,
		Remote:    p,
		Type:      HolePunchAttemptEvtT,
		Evt:       &HolePunchAttemptEvt{Attempt: counter},
	})
}

func (t *tracer) gc() {
	defer func() {
		fmt.Println("done")
		t.refCount.Done()
	}()

	timer := time.NewTicker(tracerGCInterval)
	defer timer.Stop()

	for {
		select {
		case now := <-timer.C:
			t.mutex.Lock()
			for id, entry := range t.peers {
				if entry.last.Before(now.Add(-tracerCacheDuration)) {
					delete(t.peers, id)
				}
			}
			t.mutex.Unlock()
		case <-t.ctx.Done():
			return
		}
	}
}

func (t *tracer) Close() error {
	if t == nil {
		return nil
	}

	t.ctxCancel()
	t.refCount.Wait()
	return nil
}