module GraphQL::StaticValidation::FieldsHaveAppropriateSelections

def on_field(node, parent)
  field_defn = field_definition
  if validate_field_selections(node, field_defn.type.unwrap)
    super
  end
end

def on_operation_definition(node, _parent)
  if validate_field_selections(node, type_definition)
    super
  end
end

def validate_field_selections(ast_node, resolved_type)
  msg = if resolved_type.nil?
    nil
  elsif resolved_type.kind.scalar? && ast_node.selections.any?
    if ast_node.selections.first.is_a?(GraphQL::Language::Nodes::InlineFragment)
      "Selections can't be made on scalars (%{node_name} returns #{resolved_type.name} but has inline fragments [#{ast_node.selections.map(&:type).map(&:name).join(", ")}])"
    else
      "Selections can't be made on scalars (%{node_name} returns #{resolved_type.name} but has selections [#{ast_node.selections.map(&:name).join(", ")}])"
    end
  elsif resolved_type.kind.fields? && ast_node.selections.empty?
    "Field must have selections (%{node_name} returns #{resolved_type.name} but has no selections. Did you mean '#{ast_node.name} { ... }'?)"
  else
    nil
  end
  if msg
    node_name = case ast_node
    when GraphQL::Language::Nodes::Field
      "field '#{ast_node.name}'"
    when GraphQL::Language::Nodes::OperationDefinition
      if ast_node.name.nil?
        "anonymous query"
      else
        "#{ast_node.operation_type} '#{ast_node.name}'"
      end
    else
      raise("Unexpected node #{ast_node}")
    end
    extensions = {
      "rule": "StaticValidation::FieldsHaveAppropriateSelections",
      "name": node_name.to_s
    }
    unless resolved_type.nil?
      extensions["type"] = resolved_type.to_s
    end
    add_error(GraphQL::StaticValidation::FieldsHaveAppropriateSelectionsError.new(
      msg % { node_name: node_name },
      nodes: ast_node,
      node_name: node_name.to_s,
      type: resolved_type.nil? ? nil : resolved_type.to_s
    ))
    false
  else
    true
  end
end