JSON.ex

defmodule Web.Graphql.Types.Scalars.JSON do
  @moduledoc """
  The Json scalar type allows arbitrary JSON values to be passed in and out.
  Requires `{ :jason, "~> 1.1" }` package: https://github.com/michalmuskala/jason
  """
  use Absinthe.Schema.Notation

  scalar :json_text, name: "Json" do
    description("""
    The `Json` scalar type represents arbitrary json string data, represented as UTF-8
    character sequences. The Json type is most often used to represent a free-form
    human-readable json string.
    """)

    serialize(&encode/1)
    parse(&decode/1)
  end

  @spec decode(Absinthe.Blueprint.Input.String.t()) :: {:ok, term()} | :error
  @spec decode(Absinthe.Blueprint.Input.Null.t()) :: {:ok, nil}
  defp decode(%Absinthe.Blueprint.Input.String{value: value}) do
    case Jason.decode(value) do
      {:ok, result} -> {:ok, result}
      _ -> :error
    end
  end

  defp decode(%Absinthe.Blueprint.Input.Null{}) do
    {:ok, nil}
  end

  defp decode(_) do
    :error
  end

  defp encode(value), do: value
end

scalars.ex

defmodule Web.Graphql.Types.Scalars do
  @moduledoc false

  use IziAPIWeb.Graphql, :graphql

  require Logger

  @desc """
  The `DateTime` scalar type represents full date and time in UTC.
  (e.g. "2017-06-19T22:06:37.205849Z").
  https://github.com/bitwalker/timex/blob/master/lib/format/datetime/formatters/default.ex
  """
  scalar :date_time, description: "ISOz time" do
    parse(fn input ->
      case Timex.parse(input.value, "{ISO:Extended:Z}") do
        {:error, _reason} -> :error
        result -> result
      end
    end)

    serialize(&Timex.format!(&1, "{ISO:Extended:Z}"))
  end

  scalar :short_time, description: "Time in HH:MM format" do
    parse(fn input ->
      case Timex.parse(input.value, "{h24}:{m}") do
        {:error, _reason} -> :error
        result -> result
      end
    end)

    serialize(&Timex.format!(&1, "{h24}:{m}"))
  end

  @desc """
  The `Date` scalar type represents a ISO date.
  (e.g. "2017-06-19").
  """
  scalar :date, description: "ISO date" do
    parse(fn input ->
      case Timex.parse(input.value, "{ISOdate}") do
        {:error, _reason} -> :error
        result -> result
      end
    end)

    serialize(&Timex.format!(&1, "{ISOdate}"))
  end
end

schema.ex

defmodule Web.Graphql.Schema do
  import_types(Web.Graphql.Types.Scalars)
  import_types(Web.Graphql.Types.Scalars.JSON)
end