require 'csv'

class StripStats

  attr_accessor :output_file
  attr_accessor :rows
  attr_accessor :fields

  def initialize(html_source, output_file='out.csv', fields=nil)
    @output_file = output_file
    @rows = []
    data_hashes = self.strip_data(html_source)
    if fields.nil?
      @fields = data_hashes.first.keys #field order determined by interpreter
    else
      @fields = fields #field order specified by user
    end
    data_hashes.each do |data_hash|
      row = []
      @fields.each do |field|
        row<< data_hash[field]
      end
      @rows<< row
    end
  end

  # Abstract method - override this in derived class. Should return an array of hashes
  def strip_data
    nil
  end

  # Actions
  def write_data
    raise StandardError if @rows.nil? #TODO: raise better exception when no data

    write_headers = false
    headers = nil
    if output_file_contains_only_whitespace?
      File.open(@output_file, 'w') {} #remove any whitespace in otherwise empty file
      write_headers = true
      headers = @fields
    end
    
    CSV.open(@output_file, 'ab',
      write_headers: write_headers,
      headers: headers,
      row_sep: "\r\n"
    ) do |csv|
      @rows.each { |row| csv<< row }
    end
  end

  # Utility
  def output_file_contains_only_whitespace?
    begin
      return true if File.zero?(@output_file)
      File.foreach(@output_file) do |line|
        return false unless line.strip.empty?
      end
    rescue Exception => e
      puts e.message
    end
    return true
  end
end