require 'digest/sha2'
require 'time'
require 'fileutils'
require 'pty'
require 'expect'
require 'pdf-reader'

class P3
  BASE_URL = "https://arxiv.org"
  REFERENCE_START_REGEXP = Regexp.new('\n*[rR][eE][fF][eE][rR][eE][nN][cC][eE][sS]?( +|\n+)?$')
  REFERENCE_REGEXP = Regexp.new('(\[[0-9]?[0-9]\]|\[.+?\])')
  def self.makeId
    return Digest::SHA256.hexdigest Time.now.strftime("%F %H:%M:%S")
  end

  def self.makeDir(id, work_dir)
    Dir.mkdir("#{work_dir}/#{id}") 
  end

  def self.removeDir(id, work_dir)
    FileUtils.rm_rf("#{work_dir}/#{id}")
  end

  def self.makeFile(id, work_dir, use_dir)
    if use_dir
      return "#{work_dir}/#{id}/output.pdf"
    else
      return "#{work_dir}/#{id}-output.pdf"
    end
  end

  def self. getK2Pdf(id, work_dir, use_dir)
    if use_dir
      return "#{work_dir}/#{id}/output_k2opt.pdf"
    else
      return "#{work_dir}/#{id}-output_k2opt.pdf"
    end
  end

  def self.removeFile(id, work_dir)
    File.delete("#{work_dir}/#{id}-output.pdf")
    File.delete("#{work_dir}/#{id}-output_k2opt.pdf")
  end
  def self.fetchPdfFile(pdfUrl,file_name) 
    open(file_name, 'wb') do |o|
      open(pdfUrl) do |data|
        o.write(data.read)
      end
    end
  end

  def self.convertSingleColPdf(job_id, work_dir,file_name, use_dir)
    cmd = "k2pdfopt -dev kpw #{file_name}"
    PTY.spawn(cmd) do |i,o|
      o.sync = true
      i.expect(/\S.*Enter option above \(h=help, q=quit\):/,10){
        o.puts "\n"
        o.flush
      }
      while( i.eof? == false )
        res = i.gets
        print res
        break unless res.index('written').nil?
      end
    end
    return getK2Pdf(job_id, work_dir, use_dir)
  end

  def self.fetchReference(file_name)
    reader = PDF::Reader.new(file_name)
    page_no = reader.
      pages.
      reject{|i|
        i.text.index(REFERENCE_START_REGEXP).nil?
      }.
      map(&:number).
      sort.
      shift

      ref_page = reader.
        pages.
        select{|i|
          i.number >= page_no
        }.
        map{|i|
          i.text.gsub(/\n\n+/,"\n").gsub(/ +/,' ').gsub(/-\n +/,'')
        }

        ref_page.shift

        ref_page = ref_page.
        join(' ').
        gsub(REFERENCE_REGEXP,"\n\\1")

        ref_page = ref_page.
        split(/\n *\n/).
        map{|i| i.gsub("\n",'')}.
        select{|i| i.length > 15}
      return ref_page
  end

  def self.fetchFromPdfUrl(pdfUrl, work_dir=true, use_dir=true)
    job_id = makeId
    makeDir(job_id, work_dir) if use_dir
    file_name = makeFile(job_id, work_dir, use_dir)

    fetchPdfFile(pdfUrl, file_name)
    executed_pdf = convertSingleColPdf(job_id, work_dir, file_name, use_dir)
    references = fetchReference(executed_pdf)
    if use_dir
      removeDir(job_id, work_dir) 
    else
      removeFile(job_id, work_dir)
    end
    return references
  end
end