oo_headlines.rb

require 'open-uri'

class Webpage

  attr_reader :address

  def initialize(address)
    @address = address
  end

  def headlines
    HeadlineFinder.new(page_content).results
  end

  private

  def page_content
    @content ||= open(address).read
  end

end

class HeadlineFinder

  attr_reader :text

  TAG_NAMES = ["h1", "h2", "h3", "h4"]

  def initialize(text)
    @text = text
  end

  def results
    TAG_NAMES.map do |tag_name|
      TagBuilder.all_content_for(tag_name, text)
    end.flatten.compact
  end

end

class TagBuilder

  class << self

    def all_content_for(name, context)

      headlines = []
      offset = 0
      until offset == "at the end"
        headline = new(name, context, offset)
        headlines << headline
        offset = headline.next_offset
      end
      headlines
    end

  end

  attr_reader :name, :context, :opening, :closing

  def initialize(name, context, offset = 0)
    @name = name
    @context = context
    @opening = OpeningTag.new(name, context, offset)
    @closing = ClosingTag.new(name, context, offset)
  end

  def content
    return nil unless content_available?

    if context.index(name) != nil
      context[content_start..content_finish]
    else
      "Could not find any #{name} tags."
    end
  end

  def content_start
    opening.finish + 1
  end

  def content_finish
    closing.start - 1
  end

  def next_offset
    if opening.start != nil
      closing.final_position
    else
      "at the end"
    end
  end

  def content_available?
    opening.present? && closing.present?
  end

end

class OpeningTag

  attr_reader :name, :context, :offset

  def initialize(name, context, offset = 0)
    @name = name
    @context = context
    @offset = offset
  end

  def present?
    start != nil && finish != nil
  end

  def start
    context.index("<#{name}", offset)
  end

  def finish
    context.index(">", start)
  end

end

class ClosingTag

  attr_reader :name, :context, :offset

  def initialize(name, context, offset = 0)
    @name = name
    @context = context
    @offset = offset
  end

  def present?
    start != nil
  end

  def start
    context.index("</#{name}>", offset)
  end

  def final_position
    # 3 for the <, /, and >
    start + 3 + name.length
  end

end