defmodule Mv.Membership.Member.Changes.SyncEmailToUser do
  @moduledoc """
  Synchronizes member email changes to the linked user.

  When a member's email is updated and the member is linked to a user,
  this change automatically updates the user's email to match.

  This ensures bidirectional email synchronization.

  Uses `around_transaction` to guarantee atomicity - both the member
  and user updates happen in the SAME database transaction.
  """
  use Ash.Resource.Change
  alias Mv.EmailSync.Helpers

  @impl true
  def change(changeset, _opts, context) do
    cond do
      # Skip if already syncing to avoid recursion
      Map.get(context, :syncing_email, false) ->
        changeset

      # Only proceed if email is actually changing
      not Ash.Changeset.changing_attribute?(changeset, :email) ->
        changeset

      # Apply the sync logic
      true ->
        new_email = Ash.Changeset.get_attribute(changeset, :email)

        # around_transaction receives the changeset (cs) from Ash
        # and a callback that executes the actual database operation
        Ash.Changeset.around_transaction(changeset, fn cs, callback ->
          result = callback.(cs)

          with {:ok, member} <- Helpers.extract_record(result),
               linked_user <- get_linked_user(member) do
            Helpers.sync_email_to_linked_record(result, linked_user, new_email)
          else
            _ -> result
          end
        end)
    end
  end

  # Load the linked user relationship (returns nil if not linked)
  defp get_linked_user(member) do
    case Ash.load(member, :user) do
      {:ok, %{user: user}} -> user
      {:error, _} -> nil
    end
  end
end