interface.rb

require_relative "xmas_list"

puts "Welcome to your Christmas gift list"

gifts = [
  { name: "Necklace", bought: true },    # 0
  { name: "Teddy Bear", bought: false }, # 1
  { name: "Ring", bought: false }        # 2
]

loop do
  puts "What do you want to do? (list / add / delete / mark)"
  action = gets.chomp

  case action
  when "list"
    display_gifts(gifts)
  when "add"
    puts "What's the name of the gift you want to add?"
    gift_name = gets.chomp

    new_gift = { name: gift_name, bought: false }
    gifts << new_gift
  when "delete"
    display_gifts(gifts)

    puts "What do you want do delete? (pick by number)"
    gift_index = gets.chomp.to_i - 1
    gifts.delete_at(gift_index)
  when "mark"
    # Display all gifts
    display_gifts(gifts)

    # Ask user for the index of the gift to be marked
    puts "Which gift you want to mark as bought?"
    gift_index = gets.chomp.to_i - 1 # 2 will mean index 1, and so on...

    # Get the gift of the given index --- gift => { name: "Teddy Bear", bought: false }
    bought_gift = gifts[gift_index] # => a gift (a Hash)
    # Update (remember CRUD) the :bought value to true
    # { name: "Teddy Bear", bought: false }
    bought_gift[:bought] = true
    # { name: "Teddy Bear", bought: true }
  when "quit"
    puts "Goodbye"
    break
  end
end

xmas_list.rb

def display_gifts(gifts_array)
  gifts_array.each_with_index do |gift, index|
    checkbox = gift[:bought] ? "[x]" : "[ ]"
    puts "#{index + 1}. #{checkbox} #{gift[:name]}"
  end
end