;; lib/mod/engine.sx — decide a report by querying the policy program.
;;
;; build-program assembles the report's facts plus the compiled policy clauses;
;; decide-report runs the Prolog query and returns a decision. A decision is a
;; proof, not a bare keyword: it carries the matching rule, the conditions it
;; required, the evidence that satisfied them, and the report count — everything
;; Phase 2's audit trail needs to persist a "why".

(define
  mod/find-rule
  (fn
    (rules name)
    (reduce
      (fn
        (acc r)
        (if (nil? acc) (if (= (mod/rule-name r) name) r acc) acc))
      nil
      rules)))

(define
  mod/build-program
  (fn
    (r count rules)
    (str (mod/report-facts r count) "\n" (mod/rules->program rules))))

(define
  mod/decide-report
  (fn
    (r reports rules)
    (let
      ((count (mod/report-count (mod/report-about r) reports))
        (kinds (mod/classify-keywords r))
        (id (mod/report-id r)))
      (let
        ((program (mod/build-program r count rules)))
        (let
          ((db (pl-load program)))
          (let
            ((sol (pl-query-one db (str "policy_action(" id ", Action, Rule)"))))
            (if
              (nil? sol)
              {:action "keep" :proof {:evidence kinds :conditions (list) :rule "none" :count count} :report-id id :rule "none"}
              (let
                ((rname (dict-get sol "Rule")))
                (let ((rule (mod/find-rule rules rname))) {:action (mod/rule-action rule) :proof {:evidence kinds :conditions (mod/rule-when rule) :rule rname :count count} :report-id id :rule rname})))))))))