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: import.go
    path of file: ./repos/photoprism/internal/photoprism
    
    the code of the file until where you have to start completion: package photoprism

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"runtime/debug"
	"sort"
	"sync"

	"github.com/karrick/godirwalk"

	"github.com/photoprism/photoprism/internal/config"
	"github.com/photoprism/photoprism/internal/entity"
	"github.com/photoprism/photoprism/internal/event"
	"github.com/photoprism/photoprism/internal/mutex"
	"github.com/photoprism/photoprism/pkg/clean"
	"github.com/photoprism/photoprism/pkg/fs"
	"github.com/photoprism/photoprism/pkg/media"
)

// Import represents an importer that can copy/move MediaFiles to the originals directory.
type Import struct {
	conf    *config.Config
	index   *Index
	convert *Convert
}

// NewImport returns a new importer and expects its dependencies as arguments.
func NewImport(conf *config.Config, index *Index, convert *Convert) *Import {
	instance := &Import{
		conf:    conf,
		index:   index,
		convert: convert,
	}

	return instance
}

// 
    
func (imp *Import) DestinationFilename(mainFile *MediaFile, mediaFile *MediaFile, folder string) (string, error) {
	fileName := mainFile.CanonicalName()
	fileExtension := mediaFile.Extension()
	dateCreated := mainFile.DateCreated()

	if !mediaFile.IsSidecar() {
		if f, err := entity.FirstFileByHash(mediaFile.Hash()); err == nil {
			existingFilename := FileName(f.FileRoot, f.FileName)
			if fs.FileExists(existingFilename) {
				return existingFilename, fmt.Errorf("%s is identical to %s (sha1 %s)", clean.Log(filepath.Base(mediaFile.FileName())), clean.Log(f.FileName), mediaFile.Hash())
			} else {
				return existingFilename, nil
			}
		}
	}

	// Find and return available filename.
	iteration := 0
	pathName := filepath.Join(imp.originalsPath(), folder, dateCreated.Format("2006/01"))
	result := filepath.Join(pathName, fileName+fileExtension)

	for fs.FileExists(result) {
		if mediaFile.Hash() == fs.Hash(result) {
			return result, fmt.Errorf("%s already exists", clean.Log(fs.RelName(result, imp.originalsPath())))
		}

		iteration++

		result = filepath.Join(pathName, fileName+"."+fmt.Sprintf("%05d", iteration)+fileExtension)
	}

	return result, nil
}