;; lib/prolog/hs-bridge.sx — Prolog↔Hyperscript bridge
;;
;; Creates SX functions backed by a Prolog DB, callable directly from
;; Hyperscript DSL conditions.  No parser/compiler changes needed:
;;   when allowed(user, action) then …
;; compiles to (allowed user action) — a plain SX call.
;;
;; Setup:
;;   (define pl-db (pl-load "role(alice,admin). permission(admin,edit). allowed(U,A) :- role(U,R), permission(R,A)."))
;;   (define allowed (pl-hs-predicate/2 pl-db "allowed"))
;;
;; Requires tokenizer.sx, parser.sx, runtime.sx, query.sx loaded first.

;; Test whether a ground Prolog goal succeeds against db.
;; Returns true/false (not a solution dict).
(define
  pl-hs-query
  (fn (db goal-str) (not (nil? (pl-query-one db goal-str)))))

;; Build a Prolog goal string from a predicate name and arg list.
;; SX values: strings/keywords (already strings in SX) pass through;
;; numbers are stringified via str.
(define
  pl-hs-build-goal
  (fn
    (pred-name args)
    (str pred-name "(" (join ", " (map (fn (a) (str a)) args)) ")")))

;; Return a 1-arg SX function that succeeds iff pred(a) holds in db.
(define
  pl-hs-predicate/1
  (fn
    (db pred-name)
    (fn (a) (pl-hs-query db (pl-hs-build-goal pred-name (list a))))))

;; Return a 2-arg SX function that succeeds iff pred(a, b) holds in db.
(define
  pl-hs-predicate/2
  (fn
    (db pred-name)
    (fn (a b) (pl-hs-query db (pl-hs-build-goal pred-name (list a b))))))

;; Return a 3-arg SX function that succeeds iff pred(a, b, c) holds in db.
(define
  pl-hs-predicate/3
  (fn
    (db pred-name)
    (fn (a b c) (pl-hs-query db (pl-hs-build-goal pred-name (list a b c))))))

;; Install every predicate in install-list as a named def in the caller's
;; environment.  install-list: list of (name arity) pairs.
;; Returns a dict {name → fn} for the caller to destructure.
(define
  pl-hs-install
  (fn
    (db install-list)
    (reduce
      (fn
        (acc entry)
        (let
          ((pred-name (first entry)) (arity (nth entry 1)))
          (dict-set!
            acc
            pred-name
            (cond
              ((= arity 1) (pl-hs-predicate/1 db pred-name))
              ((= arity 2) (pl-hs-predicate/2 db pred-name))
              ((= arity 3) (pl-hs-predicate/3 db pred-name))
              (true (fn (a b) false))))
          acc))
      {}
      install-list)))