green_fairy

defmodule GreenFairy.Deferred.Interface do
  @moduledoc """
  Deferred GraphQL interface definition.

  Like `GreenFairy.Deferred.Type`, this stores definitions as pure data
  with no compile-time dependencies on implementing types.

  ## Usage

      defmodule MyApp.GraphQL.Interfaces.Node do
        use GreenFairy.Deferred.Interface

        @desc "An object with an ID"
        interface "Node" do
          field :id, non_null(:id)
        end
      end

  The resolve_type function is automatically generated based on registered
  implementations in the schema compiler.
  """

  alias GreenFairy.Deferred.Definition

  @doc false
  defmacro __using__(_opts) do
    quote do
      import GreenFairy.Deferred.Interface, only: [interface: 2, interface: 3]

      Module.register_attribute(__MODULE__, :desc, accumulate: false)
      Module.register_attribute(__MODULE__, :deferred_interface_def, accumulate: false)
      Module.register_attribute(__MODULE__, :deferred_fields, accumulate: true)

      @before_compile GreenFairy.Deferred.Interface
    end
  end

  @doc """
  Defines a GraphQL interface.

  ## Options

  - `:description` - Interface description (can also use @desc)
  - `:resolve_type` - Custom resolve_type function (optional, auto-generated by default)
  """
  defmacro interface(name, opts \\ [], do: block) do
    quote do
      @deferred_interface_def %{
        name: unquote(name),
        description: @desc || unquote(opts[:description]),
        resolve_type: unquote(Macro.escape(opts[:resolve_type]))
      }

      @desc nil

      import GreenFairy.Deferred.Interface, only: [field: 2, field: 3]

      unquote(block)
    end
  end

  @doc "Defines a field on the interface."
  defmacro field(name, type, opts \\ []) do
    quote do
      @deferred_fields %Definition.Field{
        name: unquote(name),
        type: unquote(Macro.escape(type)),
        description: @desc || unquote(opts[:description]),
        null: Keyword.get(unquote(opts), :null, true),
        args: unquote(Macro.escape(opts[:args])),
        deprecation_reason: unquote(opts[:deprecation_reason])
      }

      @desc nil
    end
  end

  @doc false
  defmacro __before_compile__(env) do
    interface_def = Module.get_attribute(env.module, :deferred_interface_def)
    fields = Module.get_attribute(env.module, :deferred_fields) || []

    identifier = GreenFairy.Naming.to_identifier(interface_def[:name])

    definition = %Definition.Interface{
      name: interface_def[:name],
      identifier: identifier,
      module: env.module,
      description: interface_def[:description],
      fields: Enum.reverse(fields),
      resolve_type: interface_def[:resolve_type]
    }

    quote do
      @doc false
      def __green_fairy_definition__ do
        unquote(Macro.escape(definition))
      end

      @doc false
      def __green_fairy_kind__, do: :interface

      @doc false
      def __green_fairy_identifier__, do: unquote(identifier)

      # Register with the deferred registry when module is loaded
      GreenFairy.Deferred.Registry.register(__MODULE__, :interface)
    end
  end
end