;; lib/commerce/tests/stack.sx — stacking precedence, exclusivity, best price.
;; Uses (commerce-test name got expected) provided by conformance.sh.

(define
  pcat
  (make-catalog
    (list
      (list "widget" 1000 :standard)
      (list "book" 800 :zero-rated)
      (list "tea" 1000 :reduced))
    (list)
    (list)))

(define gctx (make-pricing-context pcat (list) :uk :guest))
(define mctx (make-pricing-context pcat (list) :uk :member))

(define
  cart
  (list
    (list "widget" :none 3)
    (list "book" :none 1)
    (list "tea" :none 6)))

(define
  ruleset
  (list
    (list :percent "TEN" :standard 1000)
    (list :percent "TWENTY" :standard 2000)
    (list :fixed "FIVER" 5000 500)
    (list :bundle "B3T" "tea" 3)
    (list :member "MEM" :standard 2500)))

;; The three standard-class discounts are mutually exclusive.
(define
  exclusions
  (list (list "TEN" "TWENTY") (list "TEN" "MEM") (list "TWENTY" "MEM")))

;; --- exclusivity predicates ---

(commerce-test
  "excluded-pair-direct"
  (excluded-pair? exclusions "TEN" "TWENTY")
  true)
(commerce-test
  "excluded-pair-symmetric"
  (excluded-pair? exclusions "TWENTY" "TEN")
  true)
(commerce-test
  "excluded-pair-none"
  (excluded-pair? exclusions "TEN" "FIVER")
  false)
(commerce-test
  "compatible-yes"
  (compatible? exclusions (list "FIVER" "B3T" "TWENTY"))
  true)
(commerce-test
  "compatible-no"
  (compatible? exclusions (list "TEN" "TWENTY" "B3T"))
  false)

;; --- powerset + valid stackings ---

(commerce-test
  "powerset-size"
  (len (powerset (list 1 2 3 4)))
  16)

(define gappl (applicable-promos gctx cart ruleset))

(commerce-test "applicable-guest-count" (len gappl) 4)

;; 16 subsets minus the 4 containing both TEN and TWENTY = 12 legal.
(commerce-test
  "valid-stackings-count"
  (len (valid-stackings exclusions gappl))
  12)

(commerce-test
  "stacking-total"
  (stacking-total (list (list "TWENTY" 600) (list "B3T" 2000)))
  2600)

;; --- best price (deterministic selection) ---

(commerce-test
  "best-discount-guest"
  (best-promo-discount gctx cart ruleset exclusions)
  3100)
(commerce-test
  "best-codes-guest"
  (best-promo-codes gctx cart ruleset exclusions)
  (list "TWENTY" "FIVER" "B3T"))

;; exclusivity holds: the cheaper conflicting code is dropped.
(commerce-test
  "best-excludes-ten"
  (some
    (fn (c) (= c "TEN"))
    (best-promo-codes gctx cart ruleset exclusions))
  false)

;; --- member vs guest ---

(commerce-test
  "best-discount-member"
  (best-promo-discount mctx cart ruleset exclusions)
  3250)
(commerce-test
  "best-codes-member"
  (best-promo-codes mctx cart ruleset exclusions)
  (list "FIVER" "B3T" "MEM"))

;; --- best price backward query (the showcase) ---

(commerce-test
  "stacking-by-total-backward"
  (run*
    codes
    (stacking-by-totalo (valid-stackings exclusions gappl) codes 3100))
  (list (list "TWENTY" "FIVER" "B3T")))

;; --- edge: no applicable promos ---

(commerce-test
  "best-empty"
  (best-promo-discount gctx empty-cart ruleset exclusions)
  0)