template_creation.rb

# frozen_string_literal: true

# The Creation service is responsible for creating a template from a given PDF file.
#
# It extracts instructions from the PDF, converts the PDF to HTML, and prepares parameters
# for template creation.
#
# @see Templates::Invoices::CreateInput for the expected input structure.
class Templates::Templates::Contexts::Creation < BaseService
  performs_checks
  # Initializes a new Creation service instance.
  #
  # @param [Templates::Invoices::CreateInput] input The input data containing file details and other attributes.
  # @return [void]
  def initialize(input:)
    @input = input
    @pages_instructions_map = {}
  end

  # Processes the PDF file, extracting instructions and converting it to HTML.
  #
  # @return [String] The HTML string content of the PDF.
  def call
    safely_execute do
      after_extracting_pdf_instructions do
        succeed(::Templates::Template.create!(**template_create_params))
      end
    ensure
      tmpfile.close
    end
  end

  private

  attr_reader :pages_instructions_map

  # Prepares parameters for creating a template.
  #
  # @return [Hash] A hash containing parameters for template creation.
  def template_create_params
    {
      reference_file_name: input.file_name,
      title: input.title,
      html_content: template_html_content,
      instructions: pages_instructions_map,
      user_id: input.user_id
    }
  end

  # Converts the PDF content to HTML using MuPDF.
  #
  # @return [String] The converted HTML content of the PDF.
  def template_html_content
    output_file = "#{File.basename(tmpfile.path, '.pdf')}.html"
    system("mutool convert -o #{output_file} #{tmpfile.path}")
    File.read(output_file)
  ensure
    File.delete(output_file)
  end

  # Extracts instructions from the PDF pages and yields to the block.
  #
  # @yield [void] Yields control to the block after extraction is complete.
  def after_extracting_pdf_instructions
    reader.pages.each.with_index do |page, index|
      receiver = ::PDF::Reader::RegisterReceiver.new
      page.walk(receiver)
      pages_instructions_map[index + 1] =
        # the first entry specifies the page number, redundant to save it.
        receiver.callbacks[1..receiver.callbacks.length].to_s
    end
    yield
  end

  # Initializes a PDF reader for the provided file.
  #
  # @return [PDF::Reader] The PDF reader instance.
  def reader
    @reader ||= ::PDF::Reader.new(tmpfile.path)
  end

  # Creates a temporary file to hold the decoded PDF content.
  #
  # @return [Tempfile] The temporary file containing the PDF content.
  def tmpfile
    @tmpfile ||= begin
      tmp = Tempfile.new(input.file_name)
      tmp.binmode
      tmp.write(Base64.decode64(input.file_base64))
      tmp
    end
  end
end