ecto_postgres_enum

defmodule EctoPostgresEnum do
  @moduledoc false

  defmacro __using__(opts) do
    quote(bind_quoted: [opts: opts]) do
      schema = opts[:schema] || :public

      type = opts[:type] || raise "Option type (atom) is required"
      values = opts[:values] || raise "Option values (list) is required"
      values == Enum.uniq(values) || raise "Duplicates are not allowed in enum values"
      Enum.count(values) >= 2 || raise "Valid enums requires at least 2 different values"
      Enum.all?(values, &is_atom/1) || raise "All values must be atoms"
      is_atom(schema) || raise "Option schema must be atom"

      alias Ecto.Migration

      @behaviour Ecto.Type
      @__input_values__ Enum.map(values, &Atom.to_string/1)
      @__output_values__ values
      @__schema__ schema
      @__type__ if is_nil(@__schema__), do: type, else: :"#{@__schema__}.#{type}"
      @__valid_values__ @__input_values__ ++ @__output_values__

      types = Enum.map_join(values, ", ", &"'#{&1}'")
      @__create_sql__ "CREATE TYPE #{type} AS ENUM (#{types})"
      @__drop_sql__ "DROP TYPE #{@__type__}"

      @doc """
      Check if specifed argument is valid element of enum.
      """
      @spec valid_value?(term) :: boolean
      defmacro valid_value?(value) do
        quote do
          unquote(value) in unquote(@__valid_values__)
        end
      end

      @spec cast(value) :: value when value: atom
      def cast(atom) when is_atom(atom) and valid_value?(atom), do: {:ok, atom}

      @spec cast(String.t()) :: atom
      def cast(binary) when is_binary(binary) and valid_value?(binary),
        do: {:ok, String.to_existing_atom(binary)}

      @spec cast(term) :: :error
      def cast(_term), do: :error

      @doc """
      Creates database enum
      """
      @spec create_db_enum :: :ok
      def create_db_enum, do: Migration.execute(@__create_sql__)

      @doc """
      Drops database enum
      """
      @spec drop_db_enum :: :ok
      def drop_db_enum, do: Migration.execute(@__drop_sql__)

      @spec dump(atom) :: {:ok, String.t()}
      def dump(atom) when is_atom(atom) and valid_value?(atom), do: {:ok, Atom.to_string(atom)}
      @spec dump(value) :: value when value: String.t()
      def dump(string) when is_binary(string) and valid_value?(string), do: {:ok, string}
      @spec dump(term) :: :error
      def dump(_term), do: :error

      @spec load(value) :: {:ok, value} when value: atom
      def load(value) when is_binary(value) and valid_value?(value), do: {:ok, value}
      @spec load(term) :: :error
      def load(_value), do: :error

      @doc """
      Returns database enum type
      """
      @spec type :: atom
      def type, do: @__type__
    end
  end
end