# SPDX-FileCopyrightText: 2019 ash contributors <https://github.com/ash-project/ash/graphs/contributors>
#
# SPDX-License-Identifier: MIT

defmodule Ash.Query.Function.IsDistinctFrom do
  @moduledoc """
  is_distinct_from(left, right)

  SQL's IS DISTINCT FROM operator.
  Unlike `!=`, this operator treats NULL as a comparable value.

  When both sides cannot return NULL, this simplifies to `!=` for better performance.
  """
  use Ash.Query.Function, name: :is_distinct_from, predicate?: true

  def args, do: [[:any, :same]]

  def returns, do: [:boolean]

  def evaluate_nil_inputs?, do: true

  def new([left, right]) do
    if Ash.Expr.can_return_nil?(left) || Ash.Expr.can_return_nil?(right) do
      {:ok, struct(__MODULE__, arguments: [left, right])}
    else
      Ash.Query.Operator.new(Ash.Query.Operator.NotEq, left, right)
    end
  end

  def evaluate(%{arguments: [left, right]}) do
    {:known, Comp.not_equal?(left, right)}
  end

  def can_return_nil?(_), do: false
end