;; lib/flow/store.sx — durable flow store + lifecycle (Phase 3).
;;
;; The store maps flow-id -> record. A record is a plain list:
;;   (flow input log status payload)
;;     flow    — the flow procedure (live; re-resolved by name on restart)
;;     input   — the original start input (plain data)
;;     log     — replay log: list of (tag value) entries (plain data)
;;     status  — done | suspended | cancelled
;;     payload — result (done) | waiting-tag (suspended) | #f (cancelled)
;;
;; Lifecycle (all use deterministic replay via flow-drive — see spec.sx):
;;   (flow/start flow input) — run from empty log. If it completes, return the raw
;;     result (backward compatible with Phases 1-2). If it suspends, register the
;;     record and return (flow-suspended id tag).
;;   (flow/resume id value)  — append (tag value) to the log and re-drive. Returns
;;     the raw result on completion, (flow-suspended id tag) on a further suspend,
;;     or (flow-error reason) if the id is unknown / not suspended.
;;   (flow/cancel id)        — mark cancelled; a later resume is rejected (the stale
;;     replay can never wake a cancelled flow).

(define
  flow-store-src
  "(define flow-store (list))\n   (define flow-next-id 0)\n   (define (flow-store-put! id rec) (set! flow-store (cons (list id rec) flow-store)))\n   (define (flow-store-find id store)\n     (if (null? store)\n         (list)\n         (if (= (car (car store)) id)\n             (car (cdr (car store)))\n             (flow-store-find id (cdr store)))))\n   (define (flow-store-get id) (flow-store-find id flow-store))\n   (define (flow-mk-rec flow input log status payload)\n     (list flow input log status payload))\n   (define (flow-rec-flow r) (car r))\n   (define (flow-rec-input r) (car (cdr r)))\n   (define (flow-rec-log r) (car (cdr (cdr r))))\n   (define (flow-rec-status r) (car (cdr (cdr (cdr r)))))\n   (define (flow-rec-payload r) (car (cdr (cdr (cdr (cdr r))))))\n   (define (flow-outcome id flow input log outcome)\n     (if (eq? (car outcome) (quote flow-done))\n         (begin\n           (flow-store-put! id (flow-mk-rec flow input log (quote done) (car (cdr outcome))))\n           (car (cdr outcome)))\n         (begin\n           (flow-store-put! id (flow-mk-rec flow input log (quote suspended) (car (cdr outcome))))\n           (list (quote flow-suspended) id (car (cdr outcome))))))\n   (define (flow/start flow input)\n     (set! flow-next-id (+ flow-next-id 1))\n     (flow-outcome flow-next-id flow input (list) (flow-drive flow input (list))))\n   (define (flow/resume id value)\n     (let ((rec (flow-store-get id)))\n       (if (null? rec)\n           (list (quote flow-error) (quote no-such-flow))\n           (if (eq? (flow-rec-status rec) (quote suspended))\n               (let ((newlog (cons (list (flow-rec-payload rec) value) (flow-rec-log rec))))\n                 (flow-outcome id (flow-rec-flow rec) (flow-rec-input rec) newlog\n                   (flow-drive (flow-rec-flow rec) (flow-rec-input rec) newlog)))\n               (list (quote flow-error) (quote not-suspended))))))\n   (define (flow/cancel id)\n     (let ((rec (flow-store-get id)))\n       (if (null? rec)\n           (list (quote flow-error) (quote no-such-flow))\n           (begin\n             (flow-store-put! id\n               (flow-mk-rec (flow-rec-flow rec) (flow-rec-input rec) (flow-rec-log rec) (quote cancelled) #f))\n             (list (quote flow-cancelled) id)))))")

(define
  flow-load-store!
  (fn
    (env)
    (begin (scheme-eval-program (scheme-parse-all flow-store-src) env) env)))