compat_type.ex
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compat_type.ex
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	# FlakeId: Decentralized, k-ordered ID generation service
	# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
	# SPDX-License-Identifier: LGPL-3.0-only

	defmodule FlakeId.Ecto.CompatType do
	@moduledoc """
	Provides a compatibility Ecto type for someone wishes to migrate from integer ids to flakes.

	## Schema Example

	@primary_key {:id, FlakeId.Ecto.CompatType, autogenerate: true}

	schema "posts" do
	add :body, :string
	end

	"""

	import Kernel, except: [to_string: 1]

	@behaviour Ecto.Type

	def embed_as(_), do: :self

	def equal?(term1, term2), do: term1 == term2

	def type, do: :uuid

	defdelegate autogenerate, to: FlakeId, as: :get

	def cast(value) do
	{:ok, to_string(value)}
	end

	def load(value) do
	{:ok, to_string(value)}
	end

	def dump(value) do
	{:ok, from_string(value)}
	end

	defp to_string(<<0::integer-size(64), id::integer-size(64)>>), do: Kernel.to_string(id)
	defp to_string(binary_flake), do: FlakeId.to_string(binary_flake)

	# zero or -1 is a null flake
	for i <- [-1, 0] do
	defp from_string(unquote(i)), do: <<0::integer-size(128)>>
	defp from_string(unquote(Kernel.to_string(i))), do: <<0::integer-size(128)>>
	end

	defp from_string(int) when is_integer(int) do
	int
	\|> Kernel.to_string()
	\|> from_string()
	end

	defp from_string(<<_::integer-size(128)>> = flake), do: flake

	defp from_string(string) when is_binary(string) and byte_size(string) < 18 do
	case Integer.parse(string) do
	{id, ""} -> <<0::integer-size(64), id::integer-size(64)>>
	_ -> nil
	end
	end

	defp from_string(string), do: FlakeId.from_string(string)
	end