// Package channel 渠道仓储：选择、加解密、健康过滤。
// M1 阶段实现最小选择逻辑（按优先级+权重取第一个健康启用的渠道），
// 负载均衡/健康检查/故障转移在 M4 完善。
package channel

import (
	"errors"

	"github.com/openteam/server/internal/pkg/crypto"
	"github.com/openteam/server/internal/store"
	"gorm.io/gorm"
)

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

type Service struct {
	db  *gorm.DB
	enc *crypto.Encryptor
}

func NewService(db *gorm.DB, enc *crypto.Encryptor) *Service {
	return &Service{db: db, enc: enc}
}

// Select 选择处理请求的渠道：启用 + 健康，按 priority 升序、weight 降序。
func (s *Service) Select() (*store.Channel, error) {
	var chs []store.Channel
	if err := s.db.Where("enabled = ? AND health_status = ?", true, store.ChannelHealthHealthy).
		Order("priority ASC, weight DESC, id ASC").Find(&chs).Error; err != nil {
		return nil, err
	}
	if len(chs) == 0 {
		return nil, ErrNoChannel
	}
	return &chs[0], nil
}

// UpstreamKey 解密渠道上游密钥。
func (s *Service) UpstreamKey(ch *store.Channel) (string, error) {
	return s.enc.Decrypt(ch.APIKeyEnc)
}

// ResolveModel 按全局模型名找到绑定渠道；M1 简化：返回绑定该模型的第一个健康渠道。
func (s *Service) ResolveModel(modelName string) (*store.Channel, *store.ChannelModelBinding, error) {
	var m store.Model
	if err := s.db.Where("name = ? AND enabled = ?", modelName, true).First(&m).Error; err != nil {
		return nil, nil, err
	}
	var b store.ChannelModelBinding
	if err := s.db.Where("model_id = ?", m.ID).
		Joins("JOIN channels ON channels.id = channel_model_bindings.channel_id AND channels.enabled = ? AND channels.health_status = ?", true, store.ChannelHealthHealthy).
		Order("channel_model_bindings.weight DESC").
		First(&b).Error; err != nil {
		return nil, nil, err
	}
	ch, err := s.Select()
	if err != nil {
		return nil, nil, err
	}
	// 用绑定里的渠道（如果健康），否则回退默认渠道
	if b.ChannelID != ch.ID {
		var bound store.Channel
		if err := s.db.First(&bound, b.ChannelID).Error; err == nil && bound.Enabled && bound.HealthStatus == store.ChannelHealthHealthy {
			return &bound, &b, nil
		}
	}
	return ch, &b, nil
}