app.rb

require './todo'
require './todos_list'

todo1 = Todo.new("View RailsGuides", true, :high)
todo2 = Todo.new("Check out the Stack Overflow ruby-on-rails tag", false, :high)
todo3 = Todo.new("Watch 'Game of Thrones' because the books are just too long", true)
todo4 = Todo.new("Read 'Hitchhiker's Guide to the Galaxy'", false)

todos = [todo1, todo2, todo3, todo4]

todo_list = TodosList.new(todos)
todo_list.high_priority_todos
puts "\n"
todo_list.low_priority_todos

todo.rb

class Todo
  attr_accessor :content, :complete, :priority

  def initialize(content, complete, priority=:low) # Here, we are defaulting the priority argument to :low and making it optional
    @content = content
    @complete = complete
    @priority = priority
  end

  def show_content
    puts "I really need to #{@content}"
  end
  
  def complete?
    @complete
  end
end

todos_list.rb

class TodosList
  attr_accessor :todos
  
  def initialize(todos)
    @todos = todos
  end
  
  def list_all_todos
    @todos.each do |todo|
      puts todo.content
    end
  end
  
  def list_complete_todos
    puts "I have already accomplished:"
    @todos.each do |todo|
      if todo.complete? == true
        puts todo.content
      end
    end
  end
  
  def list_incomplete_todos
    puts "I still need to:"
    @todos.each do |todo|
      if todo.complete? == false
        puts todo.content
      end
    end    
  end
  
  def high_priority_todos
    puts "High priorities:"
    @todos.each do |todo|
      if todo.priority == :high
        
        if todo.complete?
          status = "complete"
        else
          status = "incomplete"
        end
        
        puts "#{todo.content} - #{status}"
      end
    end
  end
  
  def low_priority_todos
    puts "Low priorities:"
    @todos.each do |todo|
      if todo.priority == :low
        
        if todo.complete?
          status = "complete"
        else
          status = "incomplete"
        end
        
        puts "#{todo.content} - #{status}"
      end
    end
  end
end