Add consumable invites (#5814)

* Add consumable invites

* Add UI for generating invite codes

* Add tests

* Display max uses and expiration in invites table, delete invite

* Remove unused column and redundant validator

- Default follows not used, probably bad idea
- InviteCodeValidator is redundant because RegistrationsController
  checks invite code validity

* Add admin setting to disable invites

* Add admin UI for invites, configurable role for invite creation

- Admin UI that lists everyone's invites, always available
- Admin setting min_invite_role to control who can invite people
- Non-admin invite UI only visible if users are allowed to

* Do not remove invites from database, expire them instantly

spec/fabricators/invite_fabricator.rb

@@ -0,0 +1,6 @@
+Fabricator(:invite) do
+  user
+  expires_at nil
+  max_uses   nil
+  uses       0
+end

spec/models/invite_spec.rb

@@ -0,0 +1,30 @@
+require 'rails_helper'
+
+RSpec.describe Invite, type: :model do
+  describe '#valid_for_use?' do
+    it 'returns true when there are no limitations' do
+      invite = Invite.new(max_uses: nil, expires_at: nil)
+      expect(invite.valid_for_use?).to be true
+    end
+
+    it 'returns true when not expired' do
+      invite = Invite.new(max_uses: nil, expires_at: 1.hour.from_now)
+      expect(invite.valid_for_use?).to be true
+    end
+
+    it 'returns false when expired' do
+      invite = Invite.new(max_uses: nil, expires_at: 1.hour.ago)
+      expect(invite.valid_for_use?).to be false
+    end
+
+    it 'returns true when uses still available' do
+      invite = Invite.new(max_uses: 250, uses: 249, expires_at: nil)
+      expect(invite.valid_for_use?).to be true
+    end
+
+    it 'returns false when maximum uses reached' do
+      invite = Invite.new(max_uses: 250, uses: 250, expires_at: nil)
+      expect(invite.valid_for_use?).to be false
+    end
+  end
+end

spec/models/user_spec.rb

@@ -273,4 +273,47 @@ RSpec.describe User, type: :model do
       expect(user.token_for_app(app)).to be_nil
     end
   end
+
+  describe '#role' do
+    it 'returns admin for admin' do
+      user = User.new(admin: true)
+      expect(user.role).to eq 'admin'
+    end
+
+    it 'returns moderator for moderator' do
+      user = User.new(moderator: true)
+      expect(user.role).to eq 'moderator'
+    end
+
+    it 'returns user otherwise' do
+      user = User.new
+      expect(user.role).to eq 'user'
+    end
+  end
+
+  describe '#role?' do
+    it 'returns false when invalid role requested' do
+      user = User.new(admin: true)
+      expect(user.role?('disabled')).to be false
+    end
+
+    it 'returns true when exact role match' do
+      user  = User.new
+      mod   = User.new(moderator: true)
+      admin = User.new(admin: true)
+
+      expect(user.role?('user')).to be true
+      expect(mod.role?('moderator')).to be true
+      expect(admin.role?('admin')).to be true
+    end
+
+    it 'returns true when role higher than needed' do
+      mod   = User.new(moderator: true)
+      admin = User.new(admin: true)
+
+      expect(mod.role?('user')).to be true
+      expect(admin.role?('user')).to be true
+      expect(admin.role?('moderator')).to be true
+    end
+  end
 end