defmodule Ash.Filter.Predicate do
@moduledoc """
Represents a predicate which can be simplified and/or compared with other predicates
Simplification and comparison will need more documentation, but ultimately it
is the logic that allows us to have a flexible and powerful authorization
system.
"""
@type predicate :: struct
@type comparison ::
:unknown
| :right_includes_left
| :left_includes_right
| :mutually_inclusive
| :mutually_exclusive
@doc "Compare two predicates. If possible, use `c:bulk_compare/1` instead"
@callback compare(predicate(), predicate()) :: comparison()
@doc """
As long as at least one predicate of the type defined in your module,
(and this callback is implemented), it will be called with all of the
other predicates present in a filter. The return value is relatively
complex, but it should be a list of boolean statements. E.g.
`{op, left, right}` and `{:not, predicate}` (nested as deep as necessary).
The best way to do it is to find lists of predicates that are mutually
exclusive or mutually inclusive, and pass those lists into
`Ash.SatSolver.mutually_exclusive/1` and `Ash.SatSolver.mutually_inclusive/1`
"""
@callback bulk_compare([predicate()]) :: term
@doc """
Simplify to a more primitive statement.
For example, `x in [1, 2]` simplifies to `x == 1 or x == 2`.
Simplifying to filter expressions that already have comparisons
lets you avoid writing that logic for a given predicate.
"""
@callback simplify(predicate()) :: term
@optional_callbacks compare: 2, bulk_compare: 1, simplify: 1
@doc """
Checks with each predicate module to see if it has a comparison
with
"""
def compare(same, same), do: :mutually_inclusive
def compare(left, right) do
if :erlang.function_exported(right.__struct__, :compare, 2) do
if left.__struct__ == right.__struct__ do
with :unknown <- left.__struct__.compare(left, right) do
right.__struct__.compare(left, right)
end
else
with :unknown <- left.__struct__.compare(left, right),
:unknown <- right.__struct__.compare(right, left),
:unknown <- right.__struct__.compare(left, right) do
left.__struct__.compare(right, left)
end
end
else
if :erlang.function_exported(left.__struct__, :compare, 2) do
left.__struct__.compare(left, right)
else
:unknown
end
end
end
end