You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: api_removeChannel.go
    path of file: ./repos/databag/net/server/internal
    
    the code of the file until where you have to start completion: package databag

import (
	"databag/internal/store"
	"errors"
	"github.com/gorilla/mux"
	"gorm.io/gorm"
	"net/http"
)

//RemoveChannel removes channel from account
func RemoveChannel(w http.ResponseWriter, r *http.Request) {
	var err error
	var code int

	// scan parameters
	params := mux.Vars(r)
	channelID := params["channelID"]

	// validate contact access
	var account *store.Account
	var contact *store.Card
	tokenType := ParamTokenType(r)
	if tokenType == APPTokenAgent {
		account, code, err = ParamAgentToken(r, false)
		if err != nil {
			ErrResponse(w, code, err)
			return
		}
	} else if tokenType == APPTokenContact {
		contact, code, err = ParamContactToken(r, true)
		if err != nil {
			ErrResponse(w, code, err)
			return
		}
		account = &contact.Account
	} else {
		err = errors.New("unknown token type")
		code = http.StatusBadRequest
		ErrResponse(w, code, err)
		return
	}

	// load channel
	var slot store.ChannelSlot
	if err = store.DB.Preload("Channel.Members.Card").Preload("Channel.Groups.Cards").Where("account_id = ? AND channel_slot_id = ?", account.ID, channelID).First(&slot).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			ErrResponse(w, http.StatusNotFound, err)
		} else {
			ErrResponse(w, http.StatusInternalServerError, err)
		}
		return
	}
	if slot.Channel == nil {
		ErrResponse(w, http.StatusNotFound, errors.New("referenced empty channel"))
		return
	}

	// determine affected contact list
	cards := make(map[string]store.Card)
	for _, member := range slot.Channel.Members {
		cards[member.Card.GUID] = member.Card
	}
	for _, group := range slot.Channel.Groups {
		for _, card := range group.Cards {
			cards[card.GUID] = card
		}
	}

	if contact == nil {
		err = store.DB.Transaction(func(tx *gorm.DB) error {
			if res := tx.Model(&slot.Channel).Association("Groups").Clear(); res != nil {
				return res
			}
			slot.Channel.Groups = []store.Group{}
      if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Member{}).Error; res != nil {
        return res
      }
			slot.Channel.Members = []store.Member{}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Tag{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.TagSlot{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Asset{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Topic{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.TopicSlot{}).Error; res != nil {
				return res
			}
			slot.Channel.Topics = []store.Topic{}
			if res := tx.Delete(&slot.Channel).Error; res != nil {
				return res
			}
			slot.Channel = nil
			if res := tx.Model(&slot).Update("channel_id", -1).Error; res != nil {
				return res
			}
			if res := tx.Model(&slot).Update("revision", account.ChannelRevision+1).Error; res != nil {
				return res
			}
			if res := tx.Model(account).Update("channel_revisi
    
func RemoveChannel(w http.ResponseWriter, r *http.Request) {
	var err error
	var code int

	// scan parameters
	params := mux.Vars(r)
	channelID := params["channelID"]

	// validate contact access
	var account *store.Account
	var contact *store.Card
	tokenType := ParamTokenType(r)
	if tokenType == APPTokenAgent {
		account, code, err = ParamAgentToken(r, false)
		if err != nil {
			ErrResponse(w, code, err)
			return
		}
	} else if tokenType == APPTokenContact {
		contact, code, err = ParamContactToken(r, true)
		if err != nil {
			ErrResponse(w, code, err)
			return
		}
		account = &contact.Account
	} else {
		err = errors.New("unknown token type")
		code = http.StatusBadRequest
		ErrResponse(w, code, err)
		return
	}

	// load channel
	var slot store.ChannelSlot
	if err = store.DB.Preload("Channel.Members.Card").Preload("Channel.Groups.Cards").Where("account_id = ? AND channel_slot_id = ?", account.ID, channelID).First(&slot).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			ErrResponse(w, http.StatusNotFound, err)
		} else {
			ErrResponse(w, http.StatusInternalServerError, err)
		}
		return
	}
	if slot.Channel == nil {
		ErrResponse(w, http.StatusNotFound, errors.New("referenced empty channel"))
		return
	}

	// determine affected contact list
	cards := make(map[string]store.Card)
	for _, member := range slot.Channel.Members {
		cards[member.Card.GUID] = member.Card
	}
	for _, group := range slot.Channel.Groups {
		for _, card := range group.Cards {
			cards[card.GUID] = card
		}
	}

	if contact == nil {
		err = store.DB.Transaction(func(tx *gorm.DB) error {
			if res := tx.Model(&slot.Channel).Association("Groups").Clear(); res != nil {
				return res
			}
			slot.Channel.Groups = []store.Group{}
      if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Member{}).Error; res != nil {
        return res
      }
			slot.Channel.Members = []store.Member{}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Tag{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.TagSlot{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Asset{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.Topic{}).Error; res != nil {
				return res
			}
			if res := tx.Where("channel_id = ?", slot.Channel.ID).Delete(&store.TopicSlot{}).Error; res != nil {
				return res
			}
			slot.Channel.Topics = []store.Topic{}
			if res := tx.Delete(&slot.Channel).Error; res != nil {
				return res
			}
			slot.Channel = nil
			if res := tx.Model(&slot).Update("channel_id", -1).Error; res != nil {
				return res
			}
			if res := tx.Model(&slot).Update("revision", account.ChannelRevision+1).Error; res != nil {
				return res
			}
			if res := tx.Model(account).Update("channel_revision", account.ChannelRevision+1).Error; res != nil {
				return res
			}
			return nil
		})
		if err != nil {
			ErrResponse(w, http.StatusInternalServerError, err)
			return
		}

		// cleanup file assets
		go garbageCollect(account)
	} else {
		if _, member := cards[contact.GUID]; !member {
			ErrResponse(w, http.StatusNotFound, errors.New("member channel not found"))
			return
		}
		err = store.DB.Transaction(func(tx *gorm.DB) error {
      if res := tx.Where("channel_id = ? AND card_id = ?", slot.Channel.ID, contact.ID).Delete(&store.Member{}).Error; res != nil {
				return res
			}
      if res := tx.Model(&store.Channel{}).Where("id = ?", slot.Channel.ID).Update("detail_revision", account.ChannelRevision+1).Error; res != nil {
        return res
      }
      if res := tx.Model(&store.ChannelSlot{}).Where("id = ?", slot.ID).Update("revision", account.ChannelRevision+1).Error; res != nil {
        return res
      }
			if res := tx.Model(&account).Update("channel_revision", account.ChannelRevision+1).Error; res != nil {
				return res
			}
			return nil
		})
		if err != nil {
			ErrResponse(w, http.StatusInternalServerError, err)
			return
		}
	}

	SetStatus(account)
	for _, card := range cards {
		SetContactChannelNotification(account, &card)
	}
	WriteResponse(w, nil)
}