package channel

import (
	"errors"
	"math/rand"
	"sort"
	"sync"

	"go.uber.org/zap"
	"gorm.io/gorm"

	"openteam/server/internal/config"
	"openteam/server/internal/pkg/crypto"
	"openteam/server/internal/store"
)

var ErrNoChannel = errors.New("no available channel for model")

// Service manages channels, model bindings and load-balanced selection.
type Service struct {
	db  *gorm.DB
	cfg *config.Config
	log *zap.Logger

	mu     sync.RWMutex
	sem    map[int64]chan struct{} // per-channel concurrency limiter
	master string
}

func NewService(db *gorm.DB, cfg *config.Config, log *zap.Logger) *Service {
	return &Service{
		db: db, cfg: cfg, log: log,
		sem:    map[int64]chan struct{}{},
		master: cfg.MasterKey,
	}
}

// DecryptKey decrypts a channel's stored upstream API key.
func (s *Service) DecryptKey(enc string) (string, error) {
	return crypto.Decrypt(enc, s.master)
}

// Acquire takes a concurrency slot for a channel (blocks if saturated).
func (s *Service) Acquire(channelID int64) (func(), error) {
	s.mu.Lock()
	lim, ok := s.sem[channelID]
	if !ok {
		var rec store.Channel
		if err := s.db.First(&rec, channelID).Error; err != nil {
			s.mu.Unlock()
			return nil, err
		}
		limit := rec.MaxConcurrency
		if limit <= 0 {
			limit = 100
		}
		lim = make(chan struct{}, limit)
		s.sem[channelID] = lim
	}
	s.mu.Unlock()
	lim <- struct{}{}
	return func() { <-lim }, nil
}

// ResolveModel returns the model registry record.
func (s *Service) ResolveModel(name string) (*store.Model, error) {
	var m store.Model
	if err := s.db.Where("name = ? AND enabled = ?", name, true).First(&m).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, errors.New("model not found: " + name)
		}
		return nil, err
	}
	return &m, nil
}

// SelectChannel picks a healthy channel bound to the given model.
// Channels with higher priority (lower number) and higher weight win;
// cooldown channels are skipped, degraded channels are deprioritized.
// Channels in exclude (already tried in this request) are skipped.
func (s *Service) SelectChannel(modelID int64, exclude map[int64]bool) (*store.Channel, *store.ChannelModelBinding, error) {
	var bindings []store.ChannelModelBinding
	if err := s.db.Preload("Channel").Where("model_id = ?", modelID).Find(&bindings).Error; err != nil {
		return nil, nil, err
	}
	var candidates []struct {
		ch *store.Channel
		b  *store.ChannelModelBinding
		score float64
	}
	for i := range bindings {
		ch := &bindings[i].Channel
		if !ch.Enabled {
			continue
		}
		if ch.HealthStatus == "cooldown" {
			continue
		}
		if exclude[ch.ID] {
			continue
		}
		score := float64(bindings[i].Weight)
		if ch.HealthStatus == "degraded" {
			score *= 0.1
		}
		candidates = append(candidates, struct {
			ch *store.Channel
			b  *store.ChannelModelBinding
			score float64
		}{ch: ch, b: &bindings[i], score: score})
	}
	if len(candidates) == 0 {
		return nil, nil, ErrNoChannel
	}
	// Sort by priority asc, then weight desc.
	sort.SliceStable(candidates, func(i, j int) bool {
		if candidates[i].ch.Priority != candidates[j].ch.Priority {
			return candidates[i].ch.Priority < candidates[j].ch.Priority
		}
		return candidates[i].score > candidates[j].score
	})
	// Weighted random pick among the top priority group.
	total := 0.0
	for _, c := range candidates {
		total += c.score
	}
	if total <= 0 {
		return candidates[0].ch, candidates[0].b, nil
	}
	pick := rand.Float64() * total
	for _, c := range candidates {
		pick -= c.score
		if pick <= 0 {
			return c.ch, c.b, nil
		}
	}
	return candidates[0].ch, candidates[0].b, nil
}

// ListModelsForChannel returns the model names a channel serves.
func (s *Service) ListModelsForChannel(channelID int64) ([]string, error) {
	var names []string
	err := s.db.Table("channel_model_bindings").
		Joins("JOIN models ON models.id = channel_model_bindings.model_id").
		Where("channel_model_bindings.channel_id = ? AND models.enabled = ?", channelID, true).
		Order("models.sort ASC, models.id ASC").
		Pluck("models.name", &names).Error
	return names, err
}

// ListEnabledModels returns all enabled models for GET /v1/models.
func (s *Service) ListEnabledModels() ([]store.Model, error) {
	var models []store.Model
	err := s.db.Where("enabled = ?", true).Order("sort ASC, id ASC").Find(&models).Error
	return models, err
}