[Solved] `add_contact': undefined method `push'

require "./contact"
require "yaml"

class AddressBook
    attr_reader :contacts

    def initialize
        @contacts = []
        open()
    end

    def open
        if File.exist?("contacts.yml")
            @contacts = YAML.load_file("contacts.yml")
        end
    end

    def save
        File.open("contacts.yml", "w") do |file|
            file.write(contacts.to_yaml)
        end
    end

    def run
        loop do
            puts "Address Book"
            puts "a: Add Contact"
            puts "p: Print Address Book"
            puts "s: Search"
            puts "e: Exit"
            print "Enter your choice: "
            input = gets.chomp.downcase
            case input
            when 'a'
                add_contact
            when 'p'
                print_contact_list
            when 's'
                print "Search term: "
                search = gets.chomp
                find_by_name(search)
                find_by_phone_number(search)
                find_by_address(search)
            when 'e'
                save()
                break  
            end
            puts "\n"
        end
    end

    def add_contact
        contact = Contact.new
        print "First name: "
        contact.first_name = gets.chomp
        print "Middle name: "
        contact.middle_name = gets.chomp
        print "Last name: "
        contact.last_name = gets.chomp

        loop do
            puts "Add phone number or address? "
            puts "p: Add phone number"
            puts "a: Add address"
            puts "(Any other key to go back)"
            response = gets.chomp.downcase
            case response
            when 'p'
                phone = PhoneNumber.new
                print "Phone number kind (Home, Work, etc): "
                phone.kind = gets.chomp
                print "Number: "
                phone.number = gets.chomp
                contact.phone_numbers.push(phone)
            when 'a'
                address = Address.new
                print "Address Kind (Home, Work, etc): "
                address.kind = gets.chomp
                print "Address line 1: "
                address.street_1 = gets.chomp
                print "Address line 2: "
                address.street_2 = gets.chomp
                print "City: "
                address.city = gets.chomp
                print "State: "
                address.state = gets.chomp
                print "Postal Code: "
                address.postal_code = gets.chomp
                contact.addresses.push(address)
            else
                print "\n"
                break
            end
        end

        contacts.push(contact)
    end

    def print_results(search, results)
        puts search
        results.each do |contact|
            puts contact.to_s('full_name')
            contact.print_phone_numbers
            contact.print_addresses
            puts "\n"
        end
    end

    def find_by_name(name)
        results = []
        search = name.downcase
        contacts.each do |contact|
            if contact.full_name.downcase.include?(search)
                results.push(contact)
            end
        end
        print_results("Name search results (#{search})", results)
    end

    def find_by_phone_number(number)
        results = []
        search = number.gsub("-", "")
        contacts.each do |contact|
            contact.phone_numbers.each do |phone_number|
                if phone_number.number.gsub("-", "").include?(search)
                    results.push(contact) unless results.include?(contact)
                end
            end
        end
        print_results("Phone search results (#{search})", results)
    end

    def find_by_address(query)
        results = []
        search = query.downcase
        contacts.each do |contact|
            contact.addresses.each do |address|
                if address.to_s('long').downcase.include?(search)
                    results.push(contact) unless results.include?(contact)
                end
            end
        end
        print_results("Address search results (#{search})", results)
    end

    def print_contact_list
        puts "Contact List"
        contacts.each do |contact|
            puts contact.to_s('last_first')
        end
    end
end

address_book = AddressBook.new
address_book.run