require 'open3'
require 'tmpdir'

module NewspaperWorks
  # Adapter class composes a PDF derivative for issue, if it requires one.
  class IssuePDFComposer
    attr_accessor :issue, :page_pdfs

    CMD_BASE = "gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite".freeze

    # @param issue [NewspaperIssue] adapts issue work object
    def initialize(issue)
      @issue = issue
      # paths to page PDFs
      @page_pdfs = []
    end

    def compose
      # we will not step on any existing PDF
      return if issue_pdf_exists?
      # we can not compose a multi-page issue PDF if constituent page PDFs
      #   do not exist (yet == not ready, possibly waiting on an async job).
      @page_pdfs = validated_page_pdfs
      # Compose a Ghostscript command to merge all paths in @page_pdfs into
      #   a single output document, execute:
      compose_from_pages
    end

    def compose_from_pages
      outfile = File.join(Dir.mktmpdir, output_filename)
      sources = @page_pdfs.join(' ')
      cmd = "#{CMD_BASE} -sOutputFile=#{outfile} #{sources}"
      # rubocop:disable Lint/UnusedBlockArgument
      Open3.popen3(cmd) do |stdin, stdout, stderr, wait_thr|
        unless wait_thr.value.success?
          e = "Ghostscript Error: \n#{stderr.read}"
          raise NewspaperWorks::DataError, e
        end
      end
      # rubocop:enable Lint/UnusedBlockArgument
      # at this point, something should exist and validate at path `outfile`:
      raise NewspaperWorks::DataError, "Generated PDF invalid" unless validate_pdf(outfile)
      # Assign for attachment to issue, commit:
      attach_to_issue(outfile)
    end

    def output_filename
      "#{@issue.id}_full-issue.pdf"
    end

    # Validate PDF with poppler `pdfinfo` command, which will detect
    #   error conditions in cases like truncated PDF, and only in those
    #   error conditions will write to stderr.
    # @param path [String] path to PDF file
    # @return [Boolean] true or false
    def validate_pdf(path)
      return false if path.nil? || !File.exist?(path)
      return false if File.size(path).zero?
      result = ''
      cmd = "pdfinfo #{path}"
      # rubocop:disable Lint/UnusedBlockArgument
      Open3.popen3(cmd) do |stdin, stdout, stderr, wait_thr|
        result = stderr.read
      end
      # rubocop:enable Lint/UnusedBlockArgument
      # only zero bytes stderr output from `pdfinfo` considered valid PDF:
      result.size.zero?
    end

    private

      # @return [Array] list of paths to page PDFs, in page order
      # @raises [NewspaperWorks::PagesNotReady] if any page has invalid
      #   or non-ready PDF source.
      def validated_page_pdfs
        result = []
        # if any page PDF invalid, raise; otherwise append to result:
        issue.pages.to_a.each_with_index do |page, idx|
          e = "Page PDFs not ready for issue "\
            "(Issue id: #{issue.id}, Page index: #{idx})"
          path = derivatives_of(page).path('pdf')
          raise NewspaperWorks::PagesNotReady, e unless validate_pdf(path)
          result.push(path)
        end
        result
      end

      def issue_pdf_exists?
        derivatives_of(@issue).exist?('pdf')
      end

      def derivatives_of(work)
        NewspaperWorks::Data::WorkDerivatives.of(work)
      end

      def ensure_whitelist
        whitelist = Hyrax.config.whitelisted_ingest_dirs
        whitelist.push(Dir.tmpdir) unless whitelist.include?(Dir.tmpdir)
      end

      def attach_to_issue(path)
        ensure_whitelist
        # We rely upon WorkFiles to create fileset, and by consequence of
        #   running primary file attachment through actor stack,
        #   visibility of the FileSet is copied from the work:
        attachment = NewspaperWorks::Data::WorkFiles.of(@issue)
        attachment.assign(path)
        attachment.commit!
      end
  end
end