#  Copyright (c) 2017, Jungwacht Blauring Schweiz. This file is part of
#  hitobito and licensed under the Affero General Public License version 3
#  or later. See the COPYING file at the top-level directory or at
#  https://github.com/hitobito/hitobito.

class Invoice::PaymentSlip
  # Defined at http://www.pruefziffernberechnung.de/E/Einzahlungsschein-CH.shtml
  ESR9_TABLE = [0, 9, 4, 6, 8, 2, 7, 1, 3, 5].freeze
  BCS = {esr: "01", esr_plus: "04"}.freeze

  attr_reader :invoice

  def self.format_as_esr(string)
    string.reverse.gsub(/(.{5})/, '\1 ').reverse
  end

  def initialize(invoice = nil)
    @invoice = invoice
  end

  def esr_number
    Invoice::PaymentSlip.format_as_esr(number_string_with_check)
  end

  def check_digit(string)
    number = string.each_char.inject(0) do |digit, char|
      current_digit = digit + char.to_i
      ESR9_TABLE[current_digit % 10]
    end
    (10 - number) % 10
  end

  def code_line
    "#{code_line_prefix}>#{number_string_with_check}+ #{code_line_suffix}>"
  end

  def padded_number
    return zero_padded(invoice.group_id.to_s, 13) if invoice.invoice_config.reference_prefix.nil? || invoice.qr_without_qr_iban?

    if invoice.group_id <= 999999
      "#{invoice.invoice_config.reference_prefix.to_s.ljust(7, "0")}#{zero_padded(invoice.group_id.to_s, 6)}"
    else
      raise "HighlyUnlikelyError: Prefixing the reference number is not possible for this invoice, sequence number (group_id, invoice count) is too long. This error will only occur for invoices created in groups with an id higher than 999'999"
    end
  end

  private

  def number_string
    [padded_number, zero_padded(index, 13)].join
  end

  def code_line_prefix
    block = ""
    block << BCS[calculate_bc.to_sym]
    block << format("%011.2f", invoice.total).delete(".") if calculate_bc == "esr" && show_total?
    block << check_digit(block).to_s
  end

  def code_line_suffix
    participant_number_parts.each_with_index.inject("") do |block, (nr, i)|
      block << ((i != 1) ? nr : zero_padded(nr, 6))
    end
  end

  def calculate_bc
    invoice.invoice_items.present? ? "esr" : "esr_plus"
  end

  def number_string_with_check
    number_string + check_digit(number_string).to_s
  end

  def index
    invoice.sequence_number.split("-")[1]
  end

  def participant_number_parts
    invoice.participant_number.split("-")
  end

  def zero_padded(string, length)
    format("%0#{length}d", string[0..(length - 1)].to_i)
  end

  def show_total?
    !@invoice.hide_total?
  end
end
