func prepareTargetDirectory()

in cmd/gomodgen/main.go [134:183]
45 lines of code
15 McCabe index (conditional complexity)

func prepareTargetDirectory(path string, buildManifest manifest.Manifest) error {
	if _, err := os.Stat(path); err != nil && os.IsNotExist(err) {
		return os.MkdirAll(path, 0755)
	} else if err != nil {
		return err
	}

	targetManifest, err := manifest.LoadManifest(filepath.Join(path, manifestFileName))
	var notFoundErr *manifest.NoManifestFound
	if err != nil && !errors.As(err, &notFoundErr) {
		return err
	}

	var (
		targetModule string
		cleanupList  []string
	)
	if err == nil {
		targetModule = targetManifest.Module
		cleanupList = targetManifest.Files
	} else {
		log.Printf("[WARN] target directory %v is missing generated.json, will only remove files present in build artifact", path)
		if ok, err := gomod.IsGoModPresent(path); err != nil {
			return err
		} else if ok {
			moduleFile, err := gomod.LoadModuleFile(path, nil, true)
			if err != nil {
				return err
			}
			targetModule, err = gomod.GetModulePath(moduleFile)
			if err != nil {
				return err
			}

			if targetModule != buildManifest.Module {
				return fmt.Errorf("target module %v does not match build artifact %v", targetModule, buildManifest.Module)
			}
		}
		cleanupList = buildManifest.Files
	}

	for _, fileName := range cleanupList {
		filePath := filepath.Join(path, fileName)
		if err := os.Remove(filePath); err != nil && !os.IsNotExist(err) {
			return fmt.Errorf("failed to remove %v: %w", filePath, err)
		}
	}

	return nil
}