package router

import (
	"context"
	sync "sync"

	"github.com/xtls/xray-core/common/dice"
	"github.com/xtls/xray-core/features/extension"
	"github.com/xtls/xray-core/features/outbound"
)

type BalancingStrategy interface {
	PickOutbound([]string) string
}

type RandomStrategy struct{}

func (s *RandomStrategy) PickOutbound(tags []string) string {
	n := len(tags)
	if n == 0 {
		panic("0 tags")
	}

	return tags[dice.Roll(n)]
}

type RoundRobinStrategy struct {
	mu    sync.Mutex
	index int
}

func (s *RoundRobinStrategy) PickOutbound(tags []string) string {
	n := len(tags)
	if n == 0 {
		panic("0 tags")
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	tag := tags[s.index%n]
	s.index = (s.index + 1) % n
	return tag
}

type Balancer struct {
	selectors []string
	strategy  BalancingStrategy
	ohm       outbound.Manager
}

func (b *Balancer) PickOutbound() (string, error) {
	hs, ok := b.ohm.(outbound.HandlerSelector)
	if !ok {
		return "", newError("outbound.Manager is not a HandlerSelector")
	}
	tags := hs.Select(b.selectors)
	if len(tags) == 0 {
		return "", newError("no available outbounds selected")
	}
	tag := b.strategy.PickOutbound(tags)
	if tag == "" {
		return "", newError("balancing strategy returns empty tag")
	}
	return tag, nil
}

func (b *Balancer) InjectContext(ctx context.Context) {
	if contextReceiver, ok := b.strategy.(extension.ContextReceiver); ok {
		contextReceiver.InjectContext(ctx)
	}
}