;; lib/flow/tests/railway.sx — Phase 6: railway-oriented composition (attempt).

(define flow-rail-pass 0)
(define flow-rail-fail 0)
(define flow-rail-fails (list))

(define
  flow-rail-test
  (fn
    (name actual expected)
    (if
      (= actual expected)
      (set! flow-rail-pass (+ flow-rail-pass 1))
      (begin
        (set! flow-rail-fail (+ flow-rail-fail 1))
        (append! flow-rail-fails {:name name :expected expected :actual actual})))))

(define flow-r (fn (src) (flow-run src)))

;; ── attempt — short-circuit on the first (fail ...) ─────────────
(flow-rail-test
  "attempt: threads like sequence when nothing fails"
  (flow-r
    "(flow/start (attempt (lambda (x) (+ x 1)) (lambda (x) (* x 10))) 4)")
  50)
(flow-rail-test
  "attempt: empty is identity"
  (flow-r "(flow/start (attempt) 7)")
  7)
(flow-rail-test
  "attempt: returns the first failure"
  (flow-r
    "(failed? (flow/start (attempt (lambda (x) (fail (quote bad))) (lambda (x) (* x 10))) 4))")
  true)
(flow-rail-test
  "attempt: the failure carries its reason"
  (flow-r
    "(fail-reason (flow/start (attempt (lambda (x) x) (lambda (x) (fail (quote rejected)))) 4))")
  "rejected")
(flow-rail-test
  "attempt: nodes after a failure do not run"
  (flow-r
    "(define ran 0) (flow/start (attempt (lambda (x) (fail (quote stop))) (lambda (x) (begin (set! ran (+ ran 1)) x))) 0) ran")
  0)
(flow-rail-test
  "attempt: a failed input short-circuits immediately"
  (flow-r
    "(define ran 0) (fail-reason (flow/start (attempt (lambda (x) (begin (set! ran (+ ran 1)) x))) (fail (quote pre))))")
  "pre")
(flow-rail-test
  "attempt: middle failure halts the chain"
  (flow-r
    "(define ran 0) (flow/start (attempt (lambda (x) (+ x 1)) (lambda (x) (fail (quote mid))) (lambda (x) (begin (set! ran (+ ran 1)) x))) 5) ran")
  0)

;; ── attempt + recover (rejoin the happy track) ──────────────────
(flow-rail-test
  "attempt + recover: recover turns a failure into a value"
  (flow-r
    "(flow/start (recover (attempt (lambda (x) (if (> x 0) x (fail (quote non-positive)))) (lambda (x) (* x 2))) (flow-const 0)) -5)")
  0)
(flow-rail-test
  "attempt + recover: happy path passes recover through"
  (flow-r
    "(flow/start (recover (attempt (lambda (x) (if (> x 0) x (fail (quote non-positive)))) (lambda (x) (* x 2))) (flow-const 0)) 5)")
  10)
(flow-rail-test
  "attempt: validation pipeline reports the failing stage"
  (flow-r
    "(defflow validate (attempt (lambda (s) (if (>= (string-length s) 3) s (fail (quote too-short)))) (lambda (s) (if (<= (string-length s) 8) s (fail (quote too-long)))) (lambda (s) (list (quote ok) (string-length s))))) (list (fail-reason (flow/start validate \"hi\")) (flow/start validate \"hello\"))")
  (list "too-short" (list "ok" 5)))

(define flow-rail-tests-run! (fn () {:total (+ flow-rail-pass flow-rail-fail) :passed flow-rail-pass :failed flow-rail-fail :fails flow-rail-fails}))