class BatchExportShixunReportService
  Error = Class.new(StandardError)

  MAX_BATCH_LIMIT = 20

  attr_reader :homework, :student_work_ids

  def initialize(homework, student_work_ids)
    @homework         = homework
    @student_work_ids = student_work_ids
  end

  def filename
    @_filename ||= "#{Time.now.strftime('%Y%m%d%H%M%S')}-#{homework.name}.zip"
  end

  def zip
    validate!
    student_works = homework.student_works.where(id: student_work_ids).includes(:myshixun, user: :user_extension)

    if student_works.count.zero?
      raise Error, '请选择要导出的学生实训报告'
    end
    pdfs = []
    zip_file = Tempfile.new(filename)
    Zip::File.open(zip_file.path, Zip::File::CREATE) do |zip|
      student_works.find_each.map do |student_work|
        export = ExportShixunReportService.new(homework, student_work)
        pdf = export.to_pdf
        pdfs << pdf
        begin
          zip.add(export.filename, pdf.path)
        rescue => ex
          Rails.logger.error(ex.message)

          zip.get_output_stream('FILE_NOTICE.txt'){|os| os.write('文件重复') }
          next
        end
      end
      zip_file
    end
  end

  private

  def validate!
    if student_work_ids.size.zero?
      raise Error, '请选择学生实训作业'
    end

    if student_work_ids.size > MAX_BATCH_LIMIT
      raise Error, '导出实训报告太多，请分批导出'
    end
  end
end