;;~ title    "Cost vs price · margin"
;;~ author   "lacuna"
;;~ version  1
;;~ mode     analysis
;;~ flavor   white
;;~ id       cost-vs-price-margin
;;~ touches  ()
;;~ summary  "Gross margin per listing."

;; Gross margin per listing.
;;
;; Read-only cart, architect-shape. The verb call lives inside (act ...)
;; with a SYMBOL on-result. The driver intercepts, makes the real Etsy
;; request, threads the response into ctx via 'last-result, then jumps
;; to the named result handler.

(cart 'cost-vs-price-margin
  '((author    . "lacuna")
    (version   . 1)
    (read-only . #t)))

(define (start ctx)
  (let ((connected (ctx-get 'shop-connected ctx)))
    (cond
      ((not connected)     (escalate 'shop-not-connected null))
      (else                (next 'fetch ctx)))))

(define (fetch ctx)
  (act 'etsy/listings (list 'cost-vs-price-margin) 'render))

(define (render ctx)
  (let ((rows (ctx-result ctx)))
    (cond
      ((null? rows)              (escalate 'no-data null))
      ((eq? rows 'rate-limited)  (after 30 'fetch ctx))
      (else                      (begin
                                   (table rows '(listing-id title metric value))
                                   (done))))))