class CreateFriendships < ActiveRecord::Migration[6.0]
  def change
    create_table :friendships do |t|
      t.references :user, null: false, foreign_key: { to_table: :users }
      t.references :friend, null: false, foreign_key: { to_table: :users }
      t.integer :status, default: 0, limit: 1

      t.timestamps
    end
  end
end

2.7.0 :033 > user4.contact_request(user5)
  Connection Exists? (0.3ms)  SELECT 1 AS one FROM "connections" WHERE "connections"."user_id" = ? AND "connections"."contact_id" = ? LIMIT ?  [["user_id", 7], ["contact_id", 8], ["LIMIT", 1]]
  TRANSACTION (0.1ms)  begin transaction
  Connection Create (1.1ms)  INSERT INTO "connections" ("user_id", "contact_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["user_id", 7], ["contact_id", 8], ["created_at", "2021-04-19 23:45:32.553041"], ["updated_at", "2021-04-19 23:45:32.553041"]]
  TRANSACTION (0.1ms)  rollback transaction
Traceback (most recent call last):
        4: from (irb):32
        3: from (irb):33:in `rescue in irb_binding'
        2: from app/models/user.rb:49:in `contact_request'
        1: from app/models/user.rb:50:in `block in contact_request'
ActiveRecord::StatementInvalid (SQLite3::SQLException: no such table: main.contacts)

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :validatable
	has_many :developments, dependent: :destroy
	has_many :connections
	has_many :connections, dependent: :destroy
	has_many :contacts, -> { where connections: { status: :accepted }}, through: :connections
	has_many :requested_contacts, -> { where connections: {status: :requested}}, through: :connections, source: :contact
	has_many :pending_contacts, -> { where connections: { status: :pending }}, through: :connections, source: :contact	
        has_many :blocked_contacts, -> { where connections: { status: :blocked }}, through: :connections, source: :contact

class Connection < ApplicationRecord
  belongs_to :user
  belongs_to :contact, class_name: 'User'
  enum status: {pending: 0, requested: 1, accepted: 2, blocked: 3}
  # id: 1
  # contact: 2

  # user_id: 1, contact_id: 2, status: :requested
  # user_id: 2, contact_id: 1, status: :pending
end

➜  155-friend-requests-from-scratch-master bin/rails c
Loading development environment (Rails 5.2.5)
2.7.3 :001 > user = User.first
  User Load (0.1ms)  SELECT  "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ?  [["LIMIT", 1]]
 => #<User id: 1, email: "john@example.com", created_at: "2021-04-20 01:30:35", updated_at: "2021-04-20 01:30:35"> 
2.7.3 :002 > user2 = User.last
  User Load (0.3ms)  SELECT  "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT ?  [["LIMIT", 1]]
 => #<User id: 4, email: "eve@example.com", created_at: "2021-04-20 01:30:35", updated_at: "2021-04-20 01:30:35"> 
2.7.3 :003 > user.friend_request(user2)
  Friendship Exists (0.1ms)  SELECT  1 AS one FROM "friendships" WHERE "friendships"."user_id" = ? AND "friendships"."friend_id" = ? LIMIT ?  [["user_id", 1], ["friend_id", 4], ["LIMIT", 1]]
   (0.0ms)  begin transaction
  Friendship Create (0.6ms)  INSERT INTO "friendships" ("user_id", "friend_id", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["user_id", 1], ["friend_id", 4], ["created_at", "2021-04-20 01:30:59.662695"], ["updated_at", "2021-04-20 01:30:59.662695"]]
  Friendship Create (0.1ms)  INSERT INTO "friendships" ("user_id", "friend_id", "status", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["user_id", 4], ["friend_id", 1], ["status", 1], ["created_at", "2021-04-20 01:30:59.664399"], ["updated_at", "2021-04-20 01:30:59.664399"]]
   (0.7ms)  commit transaction
 => #<Friendship id: 2, user_id: 4, friend_id: 1, status: "requested", created_at: "2021-04-20 01:30:59", updated_at: "2021-04-20 01:30:59"> 
2.7.3 :004 > 

def contact_request(contact)
		unless self == contact || Connection.where(user: self, contact: contact).exists?
			transaction do
			Connection.create(user: self, contact: contact, status: :pending)
			Connection.create(user: contact, contact: self, status: :requested)
			end
		end
	end

	def accept_request(contact)
		transaction do
			Connection.find_by(user: self, contact: contact, status: [:requested])&.accepted!
			Connection.find_by(user: contact, contact: self, status: [:pending])&.accepted!
		end
	end

create_table "connections", force: :cascade do |t|
    t.integer "user_id", null: false
    t.integer "contact_id", null: false
    t.integer "status", limit: 1, default: 0
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["contact_id"], name: "index_connections_on_contact_id"
    t.index ["user_id"], name: "index_connections_on_user_id"
  end

create_table "users", force: :cascade do |t|
    t.string "email", default: "", null: false
    t.string "encrypted_password", default: "", null: false
    t.string "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.boolean "admin", default: false
    t.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end

  add_foreign_key "connections", "contacts"
  add_foreign_key "connections", "users"
end

class CreateConnections < ActiveRecord::Migration[6.1]
  def change
    create_table :connections do |t|
      t.references :user, null: false, foreign_key: { to_table: :users}
      t.references :contact, null: false, foreign_key: {to_table: :users}
      t.integer :status, default: 0, limit: 1

      t.timestamps
    end
  end
end