feat: add Role resource with validations

Create Role resource with name, description, permission_set_name,
and is_system_role fields. Add validations for permission_set_name
and system role deletion protection.

lib/mv/authorization/role.ex

@@ -0,0 +1,152 @@
+defmodule Mv.Authorization.Role do
+  @moduledoc """
+  Represents a user role that references a permission set.
+
+  Roles are stored in the database and link users to permission sets.
+  Each role has a `permission_set_name` that references one of the four
+  hardcoded permission sets defined in `Mv.Authorization.PermissionSets`.
+
+  ## Fields
+
+  - `name` - Unique role name (e.g., "Vorstand", "Admin")
+  - `description` - Human-readable description of the role
+  - `permission_set_name` - Must be one of: "own_data", "read_only", "normal_user", "admin"
+  - `is_system_role` - If true, role cannot be deleted (protects critical roles like "Mitglied")
+
+  ## Relationships
+
+  - `has_many :users` - Users assigned to this role
+
+  ## Validations
+
+  - `permission_set_name` must be a valid permission set (checked against PermissionSets.all_permission_sets/0)
+  - `name` must be unique
+  - System roles cannot be deleted (enforced via validation)
+
+  ## Examples
+
+      # Create a new role
+      {:ok, role} = Mv.Authorization.create_role(%{
+        name: "Vorstand",
+        description: "Board member with read access",
+        permission_set_name: "read_only"
+      })
+      
+      # List all roles
+      {:ok, roles} = Mv.Authorization.list_roles()
+  """
+  use Ash.Resource,
+    domain: Mv.Authorization,
+    data_layer: AshPostgres.DataLayer
+
+  postgres do
+    table "roles"
+    repo Mv.Repo
+  end
+
+  code_interface do
+    define :create_role
+    define :list_roles, action: :read
+    define :update_role
+    define :destroy_role, action: :destroy
+  end
+
+  actions do
+    defaults [:read]
+
+    create :create_role do
+      primary? true
+      accept [:name, :description, :permission_set_name, :is_system_role]
+      # Note: In Ash 3.0, require_atomic? is not available for create actions
+      # Custom validations will still work
+    end
+
+    update :update_role do
+      primary? true
+      accept [:name, :description, :permission_set_name, :is_system_role]
+      # Required because custom validation functions cannot be executed atomically
+      require_atomic? false
+    end
+
+    destroy :destroy do
+      # Required because custom validation functions cannot be executed atomically
+      require_atomic? false
+    end
+  end
+
+  validations do
+    validate fn changeset, _context ->
+      permission_set_name = Ash.Changeset.get_attribute(changeset, :permission_set_name)
+
+      if permission_set_name do
+        valid_sets =
+          Mv.Authorization.PermissionSets.all_permission_sets()
+          |> Enum.map(&Atom.to_string/1)
+
+        if permission_set_name in valid_sets do
+          :ok
+        else
+          valid_sets_string = Enum.join(valid_sets, ", ")
+
+          {:error,
+           field: :permission_set_name,
+           message: "Invalid permission set name. Must be one of: #{valid_sets_string}"}
+        end
+      else
+        :ok
+      end
+    end
+
+    validate fn changeset, _context ->
+               if changeset.action_type == :destroy do
+                 if changeset.data.is_system_role do
+                   {:error,
+                    message:
+                      "Cannot delete system role. System roles are required for the application to function."}
+                 else
+                   :ok
+                 end
+               else
+                 :ok
+               end
+             end,
+             on: [:destroy]
+  end
+
+  attributes do
+    uuid_primary_key :id
+
+    attribute :name, :string do
+      allow_nil? false
+      public? true
+    end
+
+    attribute :description, :string do
+      allow_nil? true
+      public? true
+    end
+
+    attribute :permission_set_name, :string do
+      allow_nil? false
+      public? true
+    end
+
+    attribute :is_system_role, :boolean do
+      allow_nil? false
+      default false
+      public? true
+    end
+
+    timestamps()
+  end
+
+  relationships do
+    has_many :users, Mv.Accounts.User do
+      destination_attribute :role_id
+    end
+  end
+
+  identities do
+    identity :unique_name, [:name]
+  end
+end