require 'pdf/reader'
require 'json'
require 'forwardable'

class JsonTextReceiver
  extend Forwardable

  SPACE = " "

  attr_reader :state, :options, :characters

  ########## BEGIN FORWARDERS ##########
  # Graphics State Operators
  def_delegators :@state, :save_graphics_state, :restore_graphics_state

  # Matrix Operators
  def_delegators :@state, :concatenate_matrix

  # Text Object Operators
  def_delegators :@state, :begin_text_object, :end_text_object

  # Text State Operators
  def_delegators :@state, :set_character_spacing, :set_horizontal_text_scaling
  def_delegators :@state, :set_text_font_and_size, :font_size
  def_delegators :@state, :set_text_leading, :set_text_rendering_mode
  def_delegators :@state, :set_text_rise, :set_word_spacing

  # Text Positioning Operators
  def_delegators :@state, :move_text_position, :move_text_position_and_set_leading
  def_delegators :@state, :set_text_matrix_and_text_line_matrix, :move_to_start_of_next_line
  ##########  END FORWARDERS  ##########

  # starting a new page
  def page=(page)
    @state = PDF::Reader::PageState.new(page)
    @content = []
    @characters = []
    @mediabox = page.objects.deref(page.attributes[:MediaBox])
  end

  #####################################################
  # Text Showing Operators
  #####################################################
  # record text that is drawn on the page
  def show_text(string) # Tj (AWAY)
    internal_show_text(string)
  end

  def show_text_with_positioning(params) # TJ [(A) 120 (WA) 20 (Y)]
    params.each do |arg|
      if arg.is_a?(String)
        internal_show_text(arg)
      else
        @state.process_glyph_displacement(0, arg, false)
      end
    end
  end

  def move_to_next_line_and_show_text(str) # '
    @state.move_to_start_of_next_line
    show_text(str)
  end

  def set_spacing_next_line_show_text(aw, ac, string) # "
    @state.set_word_spacing(aw)
    @state.set_character_spacing(ac)
    move_to_next_line_and_show_text(string)
  end

  #####################################################
  # XObjects
  #####################################################
  def invoke_xobject(label)
    @state.invoke_xobject(label) do |xobj|
      case xobj
      when PDF::Reader::FormXObject then
        xobj.walk(self)
      end
    end
  end

  private

  def internal_show_text(string)
    if @state.current_font.nil?
      raise PDF::Reader::MalformedPDFError, "current font is invalid"
    end
    glyphs = @state.current_font.unpack(string)
    glyphs.each_with_index do |glyph_code, index|
      # paint the current glyph
      newx, newy = @state.trm_transform(0,0)
      utf8_chars = @state.current_font.to_utf8(glyph_code)

      # apply to glyph displacment for the current glyph so the next
      # glyph will appear in the correct position
      glyph_width = @state.current_font.glyph_width(glyph_code) / 1000.0
      th = 1
      scaled_glyph_width = glyph_width * @state.font_size * th
      unless utf8_chars == SPACE
        @characters << {x: newx, y: newy, scaled_font_size: scaled_glyph_width, font_size: @state.font_size, character: utf8_chars}
      end
      @state.process_glyph_displacement(glyph_width, 0, utf8_chars == SPACE)
    end
  end

end

PDF::Reader.open("WFD_I15_VCQM2D.pdf") do |reader|
  reader.pages.each do |page|
    receiver = JsonTextReceiver.new
    page.walk(receiver)
    puts JSON.pretty_generate(receiver.characters)
  end
end