feat: add custom field slug

lib/membership/custom_field.ex

@@ -9,6 +9,7 @@ defmodule Mv.Membership.CustomField do
 
   ## Attributes
   - `name` - Unique identifier for the custom field (e.g., "phone_mobile", "birthday")
+  - `slug` - URL-friendly, immutable identifier automatically generated from name (e.g., "phone-mobile")
   - `value_type` - Data type constraint (`:string`, `:integer`, `:boolean`, `:date`, `:email`)
   - `description` - Optional human-readable description
   - `immutable` - If true, custom field values cannot be changed after creation
@@ -54,8 +55,14 @@ defmodule Mv.Membership.CustomField do
   end
 
   actions do
-    defaults [:create, :read, :update, :destroy]
+    defaults [:read, :update, :destroy]
     default_accept [:name, :value_type, :description, :immutable, :required]
+
+    create :create do
+      accept [:name, :value_type, :description, :immutable, :required]
+      change Mv.Membership.CustomField.Changes.GenerateSlug
+      validate string_length(:slug, min: 1)
+    end
   end
 
   attributes do
@@ -69,6 +76,15 @@ defmodule Mv.Membership.CustomField do
         trim?: true
       ]
 
+    attribute :slug, :string,
+      allow_nil?: false,
+      public?: true,
+      writable?: false,
+      constraints: [
+        max_length: 100,
+        trim?: true
+      ]
+
     attribute :value_type, :atom,
       constraints: [one_of: [:string, :integer, :boolean, :date, :email]],
       allow_nil?: false,
@@ -97,5 +113,6 @@ defmodule Mv.Membership.CustomField do
 
   identities do
     identity :unique_name, [:name]
+    identity :unique_slug, [:slug]
   end
 end

lib/membership/custom_field/changes/generate_slug.ex

@@ -0,0 +1,118 @@
+defmodule Mv.Membership.CustomField.Changes.GenerateSlug do
+  @moduledoc """
+  Ash Change that automatically generates a URL-friendly slug from the `name` attribute.
+
+  ## Behavior
+
+  - **On Create**: Generates a slug from the name attribute using slugify
+  - **On Update**: Slug remains unchanged (immutable after creation)
+  - **Slug Generation**: Uses the `slugify` library to convert name to slug
+    - Converts to lowercase
+    - Replaces spaces with hyphens
+    - Removes special characters
+    - Handles UTF-8 characters (e.g., ä → a, ß → ss)
+    - Trims leading/trailing hyphens
+    - Truncates to max 100 characters
+
+  ## Examples
+
+      # Create with automatic slug generation
+      CustomField.create!(%{name: "Mobile Phone"})
+      # => %CustomField{name: "Mobile Phone", slug: "mobile-phone"}
+
+      # German umlauts are converted
+      CustomField.create!(%{name: "Café Müller"})
+      # => %CustomField{name: "Café Müller", slug: "cafe-muller"}
+
+      # Slug is immutable on update
+      custom_field = CustomField.create!(%{name: "Original"})
+      CustomField.update!(custom_field, %{name: "New Name"})
+      # => %CustomField{name: "New Name", slug: "original"}  # slug unchanged!
+
+  ## Implementation Note
+
+  This change only runs on `:create` actions. The slug is immutable by design,
+  as changing slugs would break external references (e.g., CSV imports/exports).
+  """
+  use Ash.Resource.Change
+
+  @doc """
+  Generates a slug from the changeset's `name` attribute.
+
+  Only runs on create actions. Returns the changeset unchanged if:
+  - The action is not :create
+  - The name is not being changed
+  - The name is nil or empty
+
+  ## Parameters
+
+  - `changeset` - The Ash changeset
+
+  ## Returns
+
+  The changeset with the `:slug` attribute set to the generated slug.
+  """
+  def change(changeset, _opts, _context) do
+    # Only generate slug on create, not on update (immutability)
+    if changeset.action_type == :create do
+      case Ash.Changeset.get_attribute(changeset, :name) do
+        nil ->
+          changeset
+
+        name when is_binary(name) ->
+          slug = generate_slug(name)
+          Ash.Changeset.force_change_attribute(changeset, :slug, slug)
+      end
+    else
+      # On update, don't touch the slug (immutable)
+      changeset
+    end
+  end
+
+  @doc """
+  Generates a URL-friendly slug from a given string.
+
+  Uses the `slugify` library to create a clean, lowercase slug with:
+  - Spaces replaced by hyphens
+  - Special characters removed
+  - UTF-8 characters transliterated (ä → a, ß → ss, etc.)
+  - Multiple consecutive hyphens reduced to single hyphen
+  - Leading/trailing hyphens removed
+  - Maximum length of 100 characters
+
+  ## Examples
+
+      iex> generate_slug("Mobile Phone")
+      "mobile-phone"
+
+      iex> generate_slug("Café Müller")
+      "cafe-muller"
+
+      iex> generate_slug("TEST NAME")
+      "test-name"
+
+      iex> generate_slug("E-Mail & Address!")
+      "e-mail-address"
+
+      iex> generate_slug("Multiple   Spaces")
+      "multiple-spaces"
+
+      iex> generate_slug("-Test-")
+      "test"
+
+      iex> generate_slug("Straße")
+      "strasse"
+
+  """
+  def generate_slug(name) when is_binary(name) do
+    slug = Slug.slugify(name)
+
+    case slug do
+      nil -> ""
+      "" -> ""
+      slug when is_binary(slug) -> String.slice(slug, 0, 100)
+    end
+  end
+
+  def generate_slug(_), do: ""
+end