Chore: Enable Users to create multiple accounts (#440)

Addresses: #402
- migrations to split roles and other attributes from users table
- make changes in code to accommodate this change

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Pranav Raj Sreepuram <pranavrajs@gmail.com>

db/migrate/20200121190901_create_account_users.rb

@@ -0,0 +1,42 @@
+class CreateAccountUsers < ActiveRecord::Migration[6.0]
+  def change
+    create_table :account_users do |t|
+      t.references :account, foreign_key: true, index: true
+      t.references :user, foreign_key: true, index: true
+      t.integer :role, default: 0
+      t.bigint :inviter_id
+      t.timestamps
+    end
+
+    migrate_to_account_users
+
+    remove_column :users, :account_id, :bigint
+    remove_column :users, :role, :integer
+    remove_column :users, :inviter_id, :bigint
+  end
+
+  def migrate_to_account_users
+    ::User.find_in_batches.each do |users|
+      users.each do |user|
+        account_user = ::AccountUser.find_by(account_id: user.account_id, user_id: user.id, role: user.role)
+
+        notification_setting = ::NotificationSetting.find_by(account_id: user.account_id, user_id: user.id)
+        selected_email_flags = notification_setting.selected_email_flags
+        notification_setting.destroy!
+
+        next if account_user.present?
+
+        ::AccountUser.create!(
+          account_id: user.account_id,
+          user_id: user.id,
+          role: user[:role], # since we are overriding role method, lets fetch value from attribute
+          inviter_id: user.inviter_id
+        )
+
+        updated_notification_setting = ::NotificationSetting.find_by(account_id: user.account_id, user_id: user.id)
+        updated_notification_setting.selected_email_flags = selected_email_flags
+        updated_notification_setting.save!
+      end
+    end
+  end
+end

db/migrate/20200121220431_add_uniqueness_constraint_to_account_users.rb

@@ -0,0 +1,5 @@
+class AddUniquenessConstraintToAccountUsers < ActiveRecord::Migration[6.0]
+  def change
+    add_index :account_users, [:account_id, :user_id], unique: true, name: 'uniq_user_id_per_account_id'
+  end
+end