chore: adds settings ressource and migration

lib/membership/membership.ex

@@ -6,12 +6,14 @@ defmodule Mv.Membership do
   - `Member` - Club members with personal information and custom field values
   - `CustomFieldValue` - Dynamic custom field values attached to members
   - `CustomField` - Schema definitions for custom fields
+  - `Setting` - Global application settings (singleton)
 
   ## Public API
   The domain exposes these main actions:
   - Member CRUD: `create_member/1`, `list_members/0`, `update_member/2`, `destroy_member/1`
   - Custom field value management: `create_custom_field_value/1`, `list_custom_field_values/0`, etc.
   - Custom field management: `create_custom_field/1`, `list_custom_fields/0`, etc.
+  - Settings management: `get_settings/0`, `update_settings/2`
 
   ## Admin Interface
   The domain is configured with AshAdmin for management UI.
@@ -45,5 +47,80 @@ defmodule Mv.Membership do
       define :destroy_custom_field, action: :destroy_with_values
       define :prepare_custom_field_deletion, action: :prepare_deletion, args: [:id]
     end
+
+    resource Mv.Membership.Setting do
+      # Note: create action exists but is not exposed via code interface
+      # It's only used internally as fallback in get_settings/0
+      # Settings should be created via seed script
+      define :update_settings, action: :update
+    end
+  end
+
+  # Singleton pattern: Get the single settings record
+  @doc """
+  Gets the global settings.
+
+  Settings should normally be created via the seed script (`priv/repo/seeds.exs`).
+  If no settings exist, this function will create them as a fallback using the
+  `ASSOCIATION_NAME` environment variable or "Mitgliederverwaltung" as default.
+
+  ## Returns
+
+    - `{:ok, settings}` - The settings record
+    - `{:ok, nil}` - No settings exist (should not happen if seeds were run)
+    - `{:error, error}` - Error reading settings
+
+  ## Examples
+
+      iex> {:ok, settings} = Mv.Membership.get_settings()
+      iex> settings.club_name
+      "My Club"
+
+  """
+  def get_settings do
+    # Try to get the first (and only) settings record
+    case Ash.read_one(Mv.Membership.Setting, domain: __MODULE__) do
+      {:ok, nil} ->
+        # No settings exist - create as fallback (should normally be created via seed script)
+        default_club_name = System.get_env("ASSOCIATION_NAME") || "Mitgliederverwaltung"
+
+        Mv.Membership.Setting
+        |> Ash.Changeset.for_create(:create, %{club_name: default_club_name})
+        |> Ash.create!(domain: __MODULE__)
+        |> then(fn settings -> {:ok, settings} end)
+
+      {:ok, settings} ->
+        {:ok, settings}
+
+      {:error, error} ->
+        {:error, error}
+    end
+  end
+
+  @doc """
+  Updates the global settings.
+
+  ## Parameters
+
+    - `settings` - The settings record to update
+    - `attrs` - A map of attributes to update (e.g., `%{club_name: "New Name"}`)
+
+  ## Returns
+
+    - `{:ok, updated_settings}` - Successfully updated settings
+    - `{:error, error}` - Validation or update error
+
+  ## Examples
+
+      iex> {:ok, settings} = Mv.Membership.get_settings()
+      iex> {:ok, updated} = Mv.Membership.update_settings(settings, %{club_name: "New Club"})
+      iex> updated.club_name
+      "New Club"
+
+  """
+  def update_settings(settings, attrs) do
+    settings
+    |> Ash.Changeset.for_update(:update, attrs)
+    |> Ash.update(domain: __MODULE__)
   end
 end

lib/membership/setting.ex

@@ -0,0 +1,80 @@
+defmodule Mv.Membership.Setting do
+  @moduledoc """
+  Ash resource representing global application settings.
+
+  ## Overview
+  Settings is a singleton resource that stores global configuration for the association,
+  such as the club name and branding information. There should only ever be one settings
+  record in the database.
+
+  ## Attributes
+  - `club_name` - The name of the association/club (required, cannot be empty)
+
+  ## Singleton Pattern
+  This resource uses a singleton pattern - there should only be one settings record.
+  The resource is designed to be read and updated, but not created or destroyed
+  through normal CRUD operations. Initial settings should be seeded.
+
+  ## Environment Variable Support
+  The `club_name` can be set via the `ASSOCIATION_NAME` environment variable.
+  If set, the environment variable value is used as a fallback when no database
+  value exists. Database values always take precedence over environment variables.
+
+  ## Examples
+
+      # Get current settings
+      {:ok, settings} = Mv.Membership.get_settings()
+      settings.club_name  # => "My Club"
+
+      # Update club name
+      {:ok, updated} = Mv.Membership.update_settings(settings, %{club_name: "New Name"})
+  """
+  use Ash.Resource,
+    domain: Mv.Membership,
+    data_layer: AshPostgres.DataLayer
+
+  postgres do
+    table "settings"
+    repo Mv.Repo
+  end
+
+  resource do
+    description "Global application settings (singleton resource)"
+  end
+
+  actions do
+    defaults [:read]
+
+    # Internal create action - not exposed via code interface
+    # Used only as fallback in get_settings/0 if settings don't exist
+    # Settings should normally be created via seed script
+    create :create do
+      accept [:club_name]
+    end
+
+    update :update do
+      primary? true
+      accept [:club_name]
+    end
+  end
+
+  attributes do
+    uuid_primary_key :id
+
+    attribute :club_name, :string,
+      allow_nil?: false,
+      public?: true,
+      description: "The name of the association/club",
+      constraints: [
+        trim?: true,
+        min_length: 1
+      ]
+
+    timestamps()
+  end
+
+  validations do
+    validate present(:club_name), on: [:create, :update]
+    validate string_length(:club_name, min: 1), on: [:create, :update]
+  end
+end