read method

@override Future<ResourceState> read(ResolvedResource resource, FormulaContext context)

Looks at the node and reports what is there.

Never throws for "it is not there" — that is ResourceState with absent. Throwing is for "I could not look", and the planner turns it into ResourceState.unknown rather than letting it fail the whole plan: one unreadable resource should not blind the other thirty.

Implementation

@override
Future<ResourceState> read(
  ResolvedResource resource,
  FormulaContext context,
) async {
  final formula = registry.byId(resource.id.name);
  if (formula == null) {
    // Not absent. This node has never heard of the formula, which says
    // nothing about whether the software is on the machine — and reporting
    // `absent` would invite an install this node cannot perform anyway.
    return ResourceState.unknown(
      resource.id,
      context.now(),
      message: 'this node has no formula "${resource.id.name}"',
    );
  }

  final report = await formula.status(context);
  return ResourceState(
    id: resource.id,
    status: report.status,
    version: report.version,
    message: report.message,
    // The detected version is the fingerprint: for a formula, "the same" means
    // the same version, and there is nothing else to compare.
    fingerprint: report.version,
    checkedAt: report.checkedAt,
  );
}