Make sign up Magic Links work across devices

Previously if someone started signing in on their phone, but finished it on their laptop, they'd end up on the menu screen with no account. Bu tracking the purpose of a Magic Link we can always direct the user to sign up if they requested a magic link through sign up. This also makes the logic for changing the copy in the email more robust.

app/controllers/sessions/magic_links_controller.rb

@@ -9,9 +9,9 @@ class Sessions::MagicLinksController < ApplicationController
   end
 
   def create
-    if identity = MagicLink.consume(code)
+    if magic_link = MagicLink.consume(code)
-      start_new_session_for identity
+      start_new_session_for magic_link.identity
-      redirect_to after_authentication_url
+      redirect_to after_sign_in_url(magic_link)
     else
       redirect_to session_magic_link_path, alert: "Try another code."
     end
@@ -21,4 +21,12 @@ class Sessions::MagicLinksController < ApplicationController
     def code
       params.expect(:code)
     end
+
+    def after_sign_in_url(magic_link)
+      if magic_link.for_sign_up?
+        new_signup_completion_path
+      else
+        after_authentication_url
+      end
+    end
 end

app/models/identity.rb

@@ -12,8 +12,10 @@ class Identity < ApplicationRecord
 
   normalizes :email_address, with: ->(value) { value.strip.downcase.presence }
 
-  def send_magic_link
+  def send_magic_link(**attributes)
-    magic_links.create!.tap do |magic_link|
+    attributes[:purpose] = attributes.delete(:for) if attributes.key?(:for)
+
+    magic_links.create!(attributes).tap do |magic_link|
       MagicLinkMailer.sign_in_instructions(magic_link).deliver_later
     end
   end

app/models/magic_link.rb

@@ -4,6 +4,8 @@ class MagicLink < ApplicationRecord
 
   belongs_to :identity
 
+  enum :purpose, %w[ sign_in sign_up ], prefix: :for, default: :sign_in
+
   scope :active, -> { where(expires_at: Time.current...) }
   scope :stale, -> { where(expires_at: ..Time.current) }
 
@@ -24,7 +26,7 @@ class MagicLink < ApplicationRecord
 
   def consume
     destroy
-    identity
+    self
   end
 
   private

app/models/signup.rb

@@ -18,7 +18,7 @@ class Signup
 
   def create_identity
     @identity = Identity.find_or_create_by!(email_address: email_address)
-    @identity.send_magic_link
+    @identity.send_magic_link for: :sign_up
   end
 
   def complete

app/views/mailers/magic_link_mailer/sign_in_instructions.html.erb

@@ -1,5 +1,5 @@
 
-<% if @identity.users.any? %>
+<% if @magic_link.for_sign_in? %>
   <h1 class="title">Fizzy verification code</h1>
   <p class="subtitle">Please enter this 6-character verification code on the Fizzy sign-in page:</p>
 <% else %>

app/views/mailers/magic_link_mailer/sign_in_instructions.text.erb

@@ -1,4 +1,4 @@
-<% if @identity.users.any? %>
+<% if @magic_link.for_sign_in? %>
 Please enter this 6-character verification code on the Fizzy sign-in page:
 <% else %>
 Please enter this 6-character verification code on the Fizzy sign-up page to create your new account:

db/migrate/20251129110120_add_purpose_to_magic_links.rb

@@ -0,0 +1,11 @@
+class AddPurposeToMagicLinks < ActiveRecord::Migration[8.2]
+  def change
+    add_column :magic_links, :purpose, :integer, null: true
+
+    execute <<-SQL
+      UPDATE magic_links SET purpose = 0
+    SQL
+
+    change_column_null :magic_links, :purpose, false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2025_11_27_000001) do
+ActiveRecord::Schema[8.2].define(version: 2025_11_29_110120) do
   create_table "accesses", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.datetime "accessed_at"
     t.uuid "account_id", null: false
@@ -315,6 +315,7 @@ ActiveRecord::Schema[8.2].define(version: 2025_11_27_000001) do
     t.datetime "created_at", null: false
     t.datetime "expires_at", null: false
     t.uuid "identity_id"
+    t.integer "purpose", null: false
     t.datetime "updated_at", null: false
     t.index ["code"], name: "index_magic_links_on_code", unique: true
     t.index ["expires_at"], name: "index_magic_links_on_expires_at"

test/controllers/sessions/magic_links_controller_test.rb

@@ -9,17 +9,32 @@ class Sessions::MagicLinksControllerTest < ActionDispatch::IntegrationTest
     end
   end
 
-  test "create" do
+  test "create with sign in code" do
     identity = identities(:kevin)
     magic_link = MagicLink.create!(identity: identity)
 
     untenanted do
       post session_magic_link_url, params: { code: magic_link.code }
-    end
 
-    assert_response :redirect
+      assert_response :redirect
-    assert cookies[:session_token].present?
+      assert cookies[:session_token].present?
-    assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+      assert_redirected_to landing_path, "Should redirect to after authentication path"
+      assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+    end
+  end
+
+  test "create with sign up code" do
+    identity = identities(:kevin)
+    magic_link = MagicLink.create!(identity: identity, purpose: :sign_up)
+
+    untenanted do
+      post session_magic_link_url, params: { code: magic_link.code }
+
+      assert_response :redirect
+      assert cookies[:session_token].present?
+      assert_redirected_to new_signup_completion_path, "Should redirect to signup completion"
+      assert_not MagicLink.exists?(magic_link.id), "The magic link should be consumed"
+    end
   end
 
   test "create with invalid code" do

test/models/magic_link_test.rb

@@ -32,8 +32,8 @@ class MagicLinkTest < ActiveSupport::TestCase
     magic_link = MagicLink.create!(identity: identities(:kevin))
     code_with_spaces = magic_link.code.downcase.chars.join(" ")
 
-    identity = MagicLink.consume(code_with_spaces)
+    consumed_magic_link = MagicLink.consume(code_with_spaces)
-    assert_equal identities(:kevin), identity
+    assert_equal magic_link, consumed_magic_link
     assert_not MagicLink.exists?(magic_link.id)
 
     expired_link = MagicLink.create!(identity: identities(:kevin))