report_card.rb

class ReportCard
  def initialize(print_strategy)
    @print_strategy = print_strategy.new
    @grades = Hash.new
  end

  def add_grade(subject, grade)
    @grades[subject] = grade
  end

  def print
    puts @print_strategy.print(@grades)
  end
end

class CSVStrategy
  def print(grades)
    output = ["Subject,Grade"]
    for subject in grades.keys
      output << "#{subject},#{grades[subject]}"
    end
    output.join("\n")
  end
end

class HTMLStrategy
  def print(grades)
    output = ["<table>"]
    output << "<th><td>Subject</td><td>Grade</td></th>"
    for subject in grades.keys
      output << "<tr><td>#{subject}</td><td>#{grades[subject]}</td></tr>"
    end
    output << "</table>"
    output.join("\n")
  end
end

csv_report_card = ReportCard.new(CSVStrategy)
csv_report_card.add_grade("English", "A")
csv_report_card.add_grade("Maths", "B+")
csv_report_card.add_grade("French", "C")

csv_report_card.print #=> will print out the above in CSV format

html_report_card = ReportCard.new(HTMLStrategy)
html_report_card.add_grade("English", "A")
html_report_card.add_grade("Maths", "B+")
html_report_card.add_grade("French", "C")

html_report_card.print #=> will print out the above in HTML format