defmodule Grapix.SchemaBuilder do
  defp gen_quoted_preamble_block() do
    quote do
      use(Absinthe.Schema)
      import_types(Absinthe.Type.Custom)
    end
  end

  defp gen_types_block(api_list) do
    block =
      api_list
      |> Enum.map(fn api ->
        {decls, []} = Code.eval_string("#{to_string(api)}.QuotedDeclarations.types()")
        decls
      end)
      |> Enum.filter(&(&1 != {:__block__, [], []}))

    {:__block__, [], block}
  end

  defp gen_fields_block(api_list) do
    block =
      api_list
      |> Enum.map(fn api ->
        {decls, []} = Code.eval_string("#{to_string(api)}.QuotedDeclarations.fields()")
        decls
      end)
      |> Enum.filter(&(&1 != {:__block__, [], []}))

    {:__block__, [], block}
  end

  defp gen_root_imports_statements(root_operation, api_list) do
    api_list
    |> Enum.map(fn api ->
      {imports, []} =
        Code.eval_string(
          "#{to_string(api)}.QuotedDeclarations.root_field_imports(:#{root_operation})"
        )

      imports
    end)
    |> Enum.filter(&(&1 != {:__block__, [], []}))
  end

  defp gen_root_operation_block(root_operation, api_list) do
    case gen_root_imports_statements(root_operation, api_list) do
      [] -> nil
      block -> {root_operation, [], [[name: Macro.camelize(to_string(root_operation))], [do: {:__block__, [], block}]]}
    end
  end

  defmacro inject_schema_def(modules) do
    {api_list, []} = Code.eval_quoted(modules)

    block =
      [
        gen_quoted_preamble_block(),
        gen_types_block(api_list),
        gen_fields_block(api_list),
        gen_root_operation_block(:query, api_list),
        gen_root_operation_block(:mutation, api_list),
        gen_root_operation_block(:subscription, api_list)
      ]
      |> Enum.filter(&(not is_nil(&1)))

    ast = {:__block__, [], block}
    Macro.to_string(ast)
    ast
  end
end