Extract GraphQL possible types to support result validation and accurate fragment matching on unions and interfaces.

More info here: https://www.apollographql.com/docs/react/data/fragments/#defining-possibletypes-manually

Example usage in a mix task:

defmodule Mix.Tasks.ExtractPossibleTypes do
  use Mix.Task
  alias Fast.Absinthe.ExtractPossibleTypes
  alias Fast.Application.Schema
  require Logger

  @shortdoc "Extract GraphQL possible types"
  def run([schema_name, output_path]) do
    Logger.info("Extracting possible types...")
    schema =
      case schema_name do
        "api" -> Schema.Api
        "admin" -> Schema.Admin
      end

    json =
      schema
      |> ExtractPossibleTypes.run()
      |> Jason.encode!()

    File.write!(output_path, json)
    Logger.info("Done! (possible types written to " <> output_path <> ")")
  end
end