def flatten_hash(hash, results = {}, parent_key = '')
  return results unless hash.kind_of?(Hash)

  hash.keys.each do |key|
    # current_key = "#{parent_key}[#{key}]" # uncomment this if you want to keep parent key as a partof key for flattened hash (csv column name)
    current_key = key
    if hash[key].kind_of?(Hash)
      results = flatten_hash(hash[key], results, current_key)
    else
      if hash[key].kind_of?(Array)
        results[current_key] = hash[key].reject(&:empty?).join("; ")
      else
        results[current_key] = hash[key]
      end
    end
  end

  results
end