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_addChannelTopicBlock.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/google/uuid"
	"github.com/gorilla/mux"
	"gorm.io/gorm"
	"net/http"
)

//AddChannelTopicBlock adds a file block asset to a topic
func AddChannelTopicBlock(w http.ResponseWriter, r *http.Request) {

	// scan parameters
	params := mux.Vars(r)
	topicID := params["topicID"]
  body := r.FormValue("body")

	channelSlot, guid, code, err := getChannelSlot(r, true)
	if err != nil {
		ErrResponse(w, code, err)
		return
	}
	act := &channelSlot.Account

	// check storage
	if full, err := isStorageFull(act); err != nil {
		ErrResponse(w, http.StatusInternalServerError, err)
		return
	} else if full {
		ErrResponse(w, http.StatusNotAcceptable, errors.New("storage limit reached"))
		return
	}

	// load topic
	var topicSlot store.TopicSlot
	if err = store.DB.Preload("Topic").Where("channel_id = ? AND topic_slot_id = ?", channelSlot.Channel.ID, topicID).First(&topicSlot).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			ErrResponse(w, http.StatusNotFound, err)
		} else {
			ErrResponse(w, http.StatusInternalServerError, err)
		}
		return
	}
	if topicSlot.Topic == nil {
		ErrResponse(w, http.StatusNotFound, errors.New("referenced empty topic"))
		return
	}

	// can only update topic if creator
	if topicSlot.Topic.GUID != guid {
		ErrResponse(w, http.StatusUnauthorized, errors.New("topic not created by you"))
		return
	}

	// avoid async cleanup of file before record is created
	garbageSync.Lock()
	defer garbageSync.Unlock()

  // save new file
  var crc uint32
  var size int64
  id := uuid.New().String()
  path := getStrConfigValue(CNFAssetPath, APPDefaultPath) + "/" + channelSlot.Account.GUID + "/" + id
  if body == "multipart" {
    if err := r.ParseMultipartForm(32 << 20); err != nil {
      ErrResponse(w, http.StatusBadRequest, err)
      return
    }

    file, _, err := r.FormFile("asset")
    if err != nil {
      ErrResponse(w, http.StatusBadRequest, err)
      return
    }
    defer file.Close()
    crc, size, err = saveAsset(file, path)
    if err != nil {
      ErrResponse(w, http.StatusInternalServerError, err)
      return
    }
  } else {
    crc, size, err = saveAsset(r.Body, path)
    if err != nil {
      ErrResponse(w, http.StatusInternalServerError, err)
      return
    }
  }

	asset := &store.Asset{}
	asset.AssetID = id
	asset.AccountID = channelSlot.Account.ID
	asset.ChannelID = channelSlot.Channel.ID
	asset.TopicID = topicSlot.Topic.ID
	asset.Status = APPAssetReady
  asset.Transform = APPTransformCopy
  asset.TransformID = id
	asset.Size = size
	asset.Crc = crc
	err = store.DB.Transaction(func(tx *gorm.DB) error {
		if res := tx.Save(asset).Error; res != nil {
			return res
		}
		if res := tx.Model(&topicSlot.Topic).Update("detail_revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&topicSlot).Update("revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&channelSlot.Channel).Update("topic_revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&channelSlot).Update("
    
func AddChannelTopicBlock(w http.ResponseWriter, r *http.Request) {

	// scan parameters
	params := mux.Vars(r)
	topicID := params["topicID"]
  body := r.FormValue("body")

	channelSlot, guid, code, err := getChannelSlot(r, true)
	if err != nil {
		ErrResponse(w, code, err)
		return
	}
	act := &channelSlot.Account

	// check storage
	if full, err := isStorageFull(act); err != nil {
		ErrResponse(w, http.StatusInternalServerError, err)
		return
	} else if full {
		ErrResponse(w, http.StatusNotAcceptable, errors.New("storage limit reached"))
		return
	}

	// load topic
	var topicSlot store.TopicSlot
	if err = store.DB.Preload("Topic").Where("channel_id = ? AND topic_slot_id = ?", channelSlot.Channel.ID, topicID).First(&topicSlot).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			ErrResponse(w, http.StatusNotFound, err)
		} else {
			ErrResponse(w, http.StatusInternalServerError, err)
		}
		return
	}
	if topicSlot.Topic == nil {
		ErrResponse(w, http.StatusNotFound, errors.New("referenced empty topic"))
		return
	}

	// can only update topic if creator
	if topicSlot.Topic.GUID != guid {
		ErrResponse(w, http.StatusUnauthorized, errors.New("topic not created by you"))
		return
	}

	// avoid async cleanup of file before record is created
	garbageSync.Lock()
	defer garbageSync.Unlock()

  // save new file
  var crc uint32
  var size int64
  id := uuid.New().String()
  path := getStrConfigValue(CNFAssetPath, APPDefaultPath) + "/" + channelSlot.Account.GUID + "/" + id
  if body == "multipart" {
    if err := r.ParseMultipartForm(32 << 20); err != nil {
      ErrResponse(w, http.StatusBadRequest, err)
      return
    }

    file, _, err := r.FormFile("asset")
    if err != nil {
      ErrResponse(w, http.StatusBadRequest, err)
      return
    }
    defer file.Close()
    crc, size, err = saveAsset(file, path)
    if err != nil {
      ErrResponse(w, http.StatusInternalServerError, err)
      return
    }
  } else {
    crc, size, err = saveAsset(r.Body, path)
    if err != nil {
      ErrResponse(w, http.StatusInternalServerError, err)
      return
    }
  }

	asset := &store.Asset{}
	asset.AssetID = id
	asset.AccountID = channelSlot.Account.ID
	asset.ChannelID = channelSlot.Channel.ID
	asset.TopicID = topicSlot.Topic.ID
	asset.Status = APPAssetReady
  asset.Transform = APPTransformCopy
  asset.TransformID = id
	asset.Size = size
	asset.Crc = crc
	err = store.DB.Transaction(func(tx *gorm.DB) error {
		if res := tx.Save(asset).Error; res != nil {
			return res
		}
		if res := tx.Model(&topicSlot.Topic).Update("detail_revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&topicSlot).Update("revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&channelSlot.Channel).Update("topic_revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(&channelSlot).Update("revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		if res := tx.Model(act).Update("channel_revision", act.ChannelRevision+1).Error; res != nil {
			return res
		}
		return nil
	})
	if err != nil {
		ErrResponse(w, http.StatusInternalServerError, err)
		return
	}

  WriteResponse(w, &Asset{AssetID: asset.AssetID, Transform: "_", Status: APPAssetReady})
}