lib/src/solver/assignment.dart

// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import '../package_name.dart';
import 'incompatibility.dart';
import 'partial_solution.dart';
import 'term.dart';

/// A term in a [PartialSolution] that tracks some additional metadata.
class Assignment extends Term {
  /// The number of decisions at or before this in the [PartialSolution] that
  /// contains it.
  final int decisionLevel;

  /// The index of this assignment in [PartialSolution._assignments].
  final int index;

  /// The incompatibility that caused this assignment to be derived, or `null`
  /// if the assignment isn't a derivation.
  final Incompatibility? cause;

  /// Whether this assignment is a decision, as opposed to a derivation.
  bool get isDecision => cause == null;

  /// Creates a decision: a speculative assignment of a single package version.
  Assignment.decision(PackageId package, this.decisionLevel, this.index)
    : cause = null,
      super(package.toRange(), true);

  /// Creates a derivation: an assignment that's automatically propagated from
  /// incompatibilities.
  Assignment.derivation(
    super.package,
    super.isPositive,
    this.cause,
    this.decisionLevel,
    this.index,
  );
}