package channel

import (
	"context"
	"math/rand"
	"opencatd-open/internal/dao"
	"opencatd-open/internal/store"
	"opencatd-open/internal/pkg/crypto"
	"sync"
	"time"
)

type Service struct {
	channelDAO *dao.ChannelDAO
	modelDAO   *dao.ModelDAO

	// Health tracking
	mu           sync.RWMutex
	healthStatus map[uint64]*channelHealth

	// Concurrency control per channel
	sems map[uint64]chan struct{}
}

type channelHealth struct {
	status      string
	consecutive int
	lastCheck   time.Time
	cooldown    time.Time
}

func NewService(channelDAO *dao.ChannelDAO, modelDAO *dao.ModelDAO) *Service {
	return &Service{
		channelDAO:  channelDAO,
		modelDAO:    modelDAO,
		healthStatus: make(map[uint64]*channelHealth),
		sems:         make(map[uint64]chan struct{}),
	}
}

// SelectedRoute 一次路由决策的完整结果：渠道 + 命中的模型绑定。
// Binding 可能为 nil（渠道经回退路径选中、无绑定记录）。
type SelectedRoute struct {
	Channel *store.Channel
	Binding *store.ChannelModelBinding
}

// Candidates 返回可用渠道候选：健康 + 启用。
// model 非空时优先取绑定该模型的渠道（携带 upstream_model 映射，权重降序）；
// 无绑定则回退到未绑定模型路径：按权重升序（闲置渠道优先探活）。
func (s *Service) Candidates(model string) []Candidate {
	if model != "" {
		var b []store.ChannelModelBinding
		var modelIDs []uint64
		s.modelDAO.DB().Model(&store.Model{}).Where("name = ? AND enabled = ?", model, true).Pluck("id", &modelIDs)
		if len(modelIDs) > 0 {
			s.channelDAO.DB().Where("model_id IN ?", modelIDs).Find(&b)
			if cands := s.loadBound(b); len(cands) > 0 {
				return cands
			}
		}
	}
	// 未绑定模型回退：取优先级最低的空闲健康渠道作为"备用渠道"承接搭车流量
	// （排序与绑定候选一致：priority ASC, weight DESC, id ASC，取末位）。
	// weight=0 的渠道不被加权随机选中，但可作为最后备用承接 unbound 流量。
	var chs []store.Channel
	s.channelDAO.DB().Where("enabled = ?", true).
		Order("priority ASC, weight DESC, id ASC").Find(&chs)
	all := make([]Candidate, 0, len(chs))
	for i := range chs {
		all = append(all, Candidate{Channel: &chs[i]})
	}
	healthy := s.FilterHealthy(all)
	if len(healthy) == 0 {
		return nil
	}
	return healthy[len(healthy)-1:]
}

// loadBound 按绑定顺序加载渠道候选，过滤健康/启用，携带 upstream_model 映射。
func (s *Service) loadBound(bindings []store.ChannelModelBinding) []Candidate {
	if len(bindings) == 0 {
		return nil
	}
	// channel_id -> 绑定（取该渠道对该模型的映射）
	byChannel := map[uint64]store.ChannelModelBinding{}
	ids := make([]uint64, 0, len(bindings))
	for _, b := range bindings {
		if _, ok := byChannel[b.ChannelID]; !ok {
			ids = append(ids, b.ChannelID)
		}
		byChannel[b.ChannelID] = b
	}
	var chs []store.Channel
	s.channelDAO.DB().Where("id IN ? AND enabled = ? AND health_status = ?", ids, true, store.ChannelHealthHealthy).
		Order("priority ASC, weight DESC, id ASC").Find(&chs)
	byID := map[uint64]*store.Channel{}
	for i := range chs {
		byID[chs[i].ID] = &chs[i]
	}
	out := make([]Candidate, 0, len(ids))
	for _, id := range ids {
		if ch, ok := byID[id]; ok {
			b := byChannel[id]
			out = append(out, Candidate{Channel: ch, Binding: &b})
		}
	}
	return out
}

// GetChannelByKeyID decrypts the API key for a channel
func (s *Service) GetChannelByKeyID(ctx context.Context, channelID uint64) (*store.Channel, error) {
	ch, err := s.channelDAO.GetByID(channelID)
	if err != nil {
		return nil, err
	}
	return ch, nil
}

// GetAPIKey decrypts the channel's API key
func (s *Service) GetAPIKey(ch *store.Channel) (string, error) {
	return crypto.Decrypt(ch.APIKeyEnc)
}

// RecordSuccess records a successful request to a channel
func (s *Service) RecordSuccess(channelID uint64) {
	s.mu.Lock()
	defer s.mu.Unlock()

	h := s.getOrCreateHealth(channelID)
	h.consecutive = 0
	h.status = store.ChannelHealthHealthy
	h.lastCheck = time.Now()
}

// RecordFailure records a failed request to a channel.
// 连续 2 次失败进入 degraded（快速熔断）：失败过的渠道让位给健康渠道，
// 健康检查成功或冷却过期后复位。
func (s *Service) RecordFailure(channelID uint64) {
	s.mu.Lock()
	defer s.mu.Unlock()

	h := s.getOrCreateHealth(channelID)
	h.consecutive++
	h.lastCheck = time.Now()

	if h.consecutive >= 2 {
		h.status = store.ChannelHealthDegraded
		h.cooldown = time.Now().Add(5 * time.Minute)
	}
	if h.consecutive >= 5 {
		h.status = store.ChannelHealthCooldown
		h.cooldown = time.Now().Add(15 * time.Minute)
	}
}

// RecordTimeout records a timeout to a channel
func (s *Service) RecordTimeout(channelID uint64) {
	s.RecordFailure(channelID)
}

func (s *Service) getOrCreateHealth(channelID uint64) *channelHealth {
	h, ok := s.healthStatus[channelID]
	if !ok {
		h = &channelHealth{
			status: store.ChannelHealthHealthy,
		}
		s.healthStatus[channelID] = h
	}
	return h
}

func (s *Service) filterHealthy(channels []*store.Channel) []*store.Channel {
	s.mu.RLock()
	defer s.mu.RUnlock()

	var healthy []*store.Channel
	now := time.Now()

	for _, ch := range channels {
		h, ok := s.healthStatus[ch.ID]
		if !ok {
			healthy = append(healthy, ch)
			continue
		}

		// Check if cooldown has expired
		if now.After(h.cooldown) && h.cooldown.IsZero() == false {
			h.consecutive = 0
			h.status = store.ChannelHealthHealthy
			healthy = append(healthy, ch)
			continue
		}

		if h.status == store.ChannelHealthHealthy || h.status == store.ChannelHealthDegraded {
			healthy = append(healthy, ch)
		}
	}

	return healthy
}

// GetHealthStatus returns the health status of a channel
func (s *Service) GetHealthStatus(channelID uint64) string {
	s.mu.RLock()
	defer s.mu.RUnlock()

	h, ok := s.healthStatus[channelID]
	if !ok {
		return store.ChannelHealthHealthy
	}
	return h.status
}

// Candidate 一个候选渠道 + 该模型的映射关系。
type Candidate struct {
	Channel *store.Channel
	Binding *store.ChannelModelBinding // 全局模型在此渠道的映射（无绑定则 nil）
}

// Pick 按权重加权随机选一个候选渠道（负载均衡；weight<=0 按 1 计）。
func (s *Service) Pick(cands []Candidate) *Candidate {
	if len(cands) == 0 {
		return nil
	}
	total := 0
	for _, c := range cands {
		w := c.Channel.Weight
		if w <= 0 {
			w = 1
		}
		total += w
	}
	r := rand.Intn(total)
	acc := 0
	for i := range cands {
		w := cands[i].Channel.Weight
		if w <= 0 {
			w = 1
		}
		acc += w
		if r < acc {
			return &cands[i]
		}
	}
	return &cands[len(cands)-1]
}

// FilterHealthy 过滤掉内存健康状态异常的渠道候选（degraded/cooldown 均排除，
// 冷却/降级过期后复位放行）。degraded 由单次请求失败触发，作为快速熔断：
// 后续请求先走其他渠道，健康检查成功后恢复。
func (s *Service) FilterHealthy(cands []Candidate) []Candidate {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]Candidate, 0, len(cands))
	now := time.Now()
	for _, c := range cands {
		h, ok := s.healthStatus[c.Channel.ID]
		if !ok || h.status == store.ChannelHealthHealthy {
			out = append(out, c)
			continue
		}
		// 冷却/降级已过期：复位并放行
		if !h.cooldown.IsZero() && now.After(h.cooldown) {
			h.status = store.ChannelHealthHealthy
			h.consecutive = 0
			out = append(out, c)
		}
	}
	return out
}

// TryAcquire 尝试获取渠道并发槽；渠道满载返回 false（调用方可溢出到其他渠道）。
// MaxConcurrency<=0 视为不限制。
func (s *Service) TryAcquire(ch *store.Channel) (func(), bool) {
	if ch.MaxConcurrency <= 0 {
		return func() {}, true
	}
	s.mu.Lock()
	sem, ok := s.sems[ch.ID]
	if !ok {
		sem = make(chan struct{}, ch.MaxConcurrency)
		s.sems[ch.ID] = sem
	}
	s.mu.Unlock()
	select {
	case sem <- struct{}{}:
		return func() { <-sem }, true
	default:
		return nil, false
	}
}