class LatexToPdf
  def self.config
    @config||={:command => 'pdflatex', :arguments => [], :parse_twice => false}
  end

  # Converts a string of LaTeX +code+ into a binary string of PDF.
  #
  # pdflatex is used to convert the file and creates the directory +#{Rails.root}/tmp/rails-latex/+ to store intermediate
  # files.
  #
  # The config argument defaults to LatexToPdf.config but can be overridden using @latex_config.
  #
  # The parse_twice argument is deprecated in favor of using config[:parse_twice] instead.
  def self.generate_pdf(code,config,parse_twice=nil)
    parse_twice=config[:parse_twice] if parse_twice.nil?
    config=self.config.merge(config)
    dir=File.join(Rails.root,'tmp','rails-latex',"#{Process.pid}-#{Thread.current.hash}")
    input=File.join(dir,'input.tex')
    FileUtils.mkdir_p(dir)
    File.open(input,'wb') {|io| io.write(code) }
    Process.waitpid(fork do
                      begin
                        Dir.chdir dir
                        STDOUT.reopen("input.log","a")
                        STDERR.reopen(STDOUT)
                        args=config[:arguments] + ['-shell-escape','-interaction','batchmode',"input.tex"]
                        system config[:command],'-draftmode',*args if parse_twice
                        exec config[:command],*args
                      rescue
                        File.open("input.log",'a') {|io|
                          io.write("#{$!.message}:\n#{$!.backtrace.join("\n")}\n")
                        }
                      ensure
                        Process.exit! 1
                      end
                    end)
    if File.exist?(pdf_file=input.sub(/\.tex$/,'.pdf'))
      FileUtils.mv(input.sub(/\.tex$/,'.log'),File.join(dir,'..','input.log'))
      result=File.read(pdf_file)
      FileUtils.rm_rf(dir)
    else
      raise "pdflatex failed: See #{input.sub(/\.tex$/,'.log')} for details"
    end
    result
  end

  # Escapes LaTex special characters in text so that they wont be interpreted as LaTex commands.
  #
  # This method will use RedCloth to do the escaping if available.
  def self.escape_latex(text)
    # :stopdoc:
    unless @latex_escaper
      if defined?(RedCloth::Formatters::LATEX)
        class << (@latex_escaper=RedCloth.new(''))
          include RedCloth::Formatters::LATEX
        end
      else
        class << (@latex_escaper=Object.new)
          ESCAPE_RE=/([{}_$&%#])|([\\^~|<>])/
          ESC_MAP={
            '\\' => 'backslash',
            '^' => 'asciicircum',
            '~' => 'asciitilde',
            '|' => 'bar',
            '<' => 'less',
            '>' => 'greater',
          }

          def latex_esc(text)   # :nodoc:
            text.gsub(ESCAPE_RE) {|m|
              if $1
                "\\#{m}"
              else
                "\\text#{ESC_MAP[m]}{}"
              end
            }
          end
        end
      end
      # :startdoc:
    end

    @latex_escaper.latex_esc(text.to_s).html_safe
  end
end