Students and Courses

_grade_students.rb

class GradeStudents
  def self.call(teacher_name, course_name, grade_list)
    course = CourseRegistry.lookup(course_name)
    teacher = TeacherRegistry.lookup(teacher_name)
    course.for_each_student do |student|
      if grade = grade_list[student.name]
        student.complete_course(course, grade)
      end
    end
  end
end

_register_course.rb

class RegisterCourse
  def self.call(student_name, course_name)
    course = CourseRegistry.lookup(course_name)
    student = StudentRegistry.lookup(student_name)
    course.add_student(student)
    student.add_course(course)
  end
end
class CourseRegistry
  def self.lookup(course_name)
    Course.new(course_name)
  end
end

class StudentRegistry
  def self.lookup(student_name)
    Student.new(student_name)
  end
end

course.rb

class Course

  attr_accessor :title, :location

  private
  attr_accessor :teachers, :students

  def initialize(params = {}); end
  def add_teacher(teacher); end
  def add_student(student); end
  def for_each_student; end

  def initialize(params = {})
    self.title = params[:title] || ""
    self.location = params[:location] || ""
    self.teachers = params[:teachers] || []
    self.courses = params[:courses] || []
  end

  def add_teacher(teacher)
    self.teachers << teacher
  end

  def add_student(student)
    self.students << student
  end

  def for_each_student
    students.each { |student| yield student }
  end
end

person.rb

class Person
  attr_accessor :name, :age

  def initialize(params = {}); end

  def initialize(params = {})
    self.name = params[:name] || ""
    self.age = params[:age] || 0
  end
end

student.rb

class Student < Person
  protected
  attr_accessor :gpa
  def initialize(params = {}); end
  def add_course(course); end
  def complete_course(course, gpa); end

  private
  attr_accessor :courses
  attr_accessor :grades
  def calculate_gpa; end

  public

  def initialize(params={})
    self.gpa = params[:gpa] || 0.0
    self.courses = params[:courses] || []
    self.grades = params[:grades] || {}
    super
  end

  def add_course(course)
    courses << course
  end

  def complete_course(course, grade)
    grades[course] = grade
    calculate_cpa
  end

  private

  def calculate_gpa
    self.gpa = grades.values.inject(0.0) {|gpa, grade| gpa += grade } / grades.size
  end
end

teacher.rb

class Teacher  < Person
  attr_accessor :description

  private
  attr_accessor :courses

  def initialize(params={}); end
  def add_course(course); end

  def initialize(params={})
    self.description = params[:description] || ""
    self.courses = params[:courses] || []
    super
  end

  def add_course(course)
    courses << course
  end

end