defmodule EctoPostgresEnum do
  @moduledoc false

  defmacro __using__(opts) do
    quote(bind_quoted: [opts: opts], unquote: false) do
      default_type =
        __MODULE__
        |> Module.split()
        |> List.last()
        |> Macro.underscore()
        |> String.to_atom()

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

      list = Enum.zip(@__output_values__, @__input_values__)

      [head | tail] = Enum.reverse(@__output_values__)
      ast = Enum.reduce(tail, head, &{:|, [], [&1, &2]})

      @type t :: unquote(ast)

      @doc "Casts the given input to the custom type"
      @spec cast(value) :: value when value: t()
      @spec cast(String.t()) :: t() | :error
      @spec cast(term) :: :error
      for {atom, string} <- list do
        def cast(unquote(atom)), do: {:ok, unquote(atom)}
        def cast(unquote(string)), do: {:ok, unquote(atom)}
      end

      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__)

      @doc "Dumps the given term into an Ecto native type"
      @spec dump(t()) :: {:ok, String.t()}
      @spec dump(value) :: value | :error when value: String.t()
      @spec dump(term) :: :error
      for {atom, string} <- list do
        def dump(unquote(atom)), do: {:ok, unquote(string)}
        def dump(unquote(string)), do: {:ok, unquote(string)}
      end

      def dump(_term), do: :error

      @doc "Loads the given term into a custom type"
      @spec load(String.t()) :: {:ok, t()} | :error
      @spec load(term) :: :error
      for {atom, string} <- list do
        def load(unquote(string)), do: {:ok, unquote(atom)}
      end

      def load(_value), do: :error

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