; lib/agentic/durable.sx — agentic-sx Phase 4: long agent sessions as
; DURABLE flow workflows. Deterministic replay IS the durability mechanism:
; every transition re-runs a self-contained flow program (the session's
; defflow source + flow/start + a replay of every recorded resume value),
; so the only durable state is a plain record {:flow :input :resumes ...}
; in the persist kv store — restart-safe by construction, and forking an
; agent run is literally copying the record (both replays then diverge).
; Effects are data: a suspended session exposes its suspend tag / typed
; (request kind payload) envelope to the host as plain SX values.
; Transitions also land in the agent's Phase-3 trace buffer, so the session
; history travels with the agent's next commit.
; Convention for session flows: suspend tags are quoted symbols, decision
; values are numbers/strings/lists of those (see agentic/scm-lit).
; Requires: lib/agentic/trace.sx (and its deps), lib/flow/* (+ scheme stack).

; ---- SX -> Scheme literal (numbers, strings, booleans, lists; nil = ()) ----
(define
  agentic/scm-lit
  (fn
    (v)
    (cond
      ((nil? v) "(list)")
      ((= v true) "#t")
      ((= v false) "#f")
      ((number? v) (str v))
      ((string? v) (str "\"" v "\""))
      ((list? v) (str "(list " (join " " (map agentic/scm-lit v)) ")"))
      (else "(list)"))))

; ---- Scheme -> SX: unbox {:scm-string ...} recursively ----
(define
  agentic/scm-out
  (fn
    (v)
    (cond
      ((and (dict? v) (has-key? v :scm-string)) (get v :scm-string))
      ((list? v) (map agentic/scm-out v))
      (else v))))

; ---- kv keys (namespaced under the repo prefix) ----
(define
  agentic/session-def-key
  (fn
    (sp name)
    (str (get (agentic/space-repo sp) :prefix) "/session-def/" name)))

(define
  agentic/session-key
  (fn
    (sp agent)
    (str (get (agentic/space-repo sp) :prefix) "/session/" agent)))

; ---- durable session flow definitions ----
(define
  agentic/defsession!
  (fn
    (sp name scheme-src)
    (begin
      (persist/kv-put
        (git/repo-db (agentic/space-repo sp))
        (agentic/session-def-key sp name)
        scheme-src)
      name)))

(define
  agentic/session-def
  (fn
    (sp name)
    (persist/kv-get
      (git/repo-db (agentic/space-repo sp))
      (agentic/session-def-key sp name))))

(define
  agentic/session-record
  (fn
    (sp agent)
    (persist/kv-get
      (git/repo-db (agentic/space-repo sp))
      (agentic/session-key sp agent))))

; ---- one self-contained replay program per transition ----
; a fresh flow-run resets the flow store, so the started flow is always id 1
(define
  agentic/session-program
  (fn
    (defs name input resumes)
    (str
      defs
      "\n"
      "(define s0 (flow/start "
      name
      " "
      (agentic/scm-lit input)
      "))\n"
      (join
        "\n"
        (map
          (fn (v) (str "(flow/resume 1 " (agentic/scm-lit v) ")"))
          resumes))
      "\n(list (flow/status 1) (flow/pending) (flow/result 1))")))

; replay the record, derive {:status :tag/:result}, persist record+state
(define
  agentic/session-transition!
  (fn
    (sp agent record)
    (let
      ((defs (agentic/session-def sp (get record :flow))))
      (if
        (nil? defs)
        {:flow (get record :flow) :error "no-such-session-flow"}
        (let
          ((out (flow-run (agentic/session-program defs (get record :flow) (get record :input) (get record :resumes)))))
          (let
            ((status (agentic/scm-out (nth out 0)))
              (pending (agentic/scm-out (nth out 1))))
            (let
              ((state (cond ((= status "done") {:status "done" :result (agentic/scm-out (nth out 2))}) ((= status "suspended") {:tag (nth (nth pending 0) 1) :status "suspended"}) (else {:status status}))))
              (begin
                (persist/kv-put
                  (git/repo-db (agentic/space-repo sp))
                  (agentic/session-key sp agent)
                  (merge {:flow (get record :flow) :resumes (get record :resumes) :input (get record :input)} state))
                state))))))))

; ---- lifecycle ----
(define
  agentic/session-start!
  (fn
    (sp agent flow-name input)
    (if
      (nil? (agentic/head sp agent))
      {:agent agent :error "no-such-agent"}
      (let
        ((state (agentic/session-transition! sp agent {:flow flow-name :resumes (list) :input input})))
        (begin
          (if
            (has-key? state :error)
            nil
            (agentic/trace! sp agent "session" (str "start " flow-name)))
          state)))))

(define
  agentic/session-resume!
  (fn
    (sp agent value)
    (let
      ((rec (agentic/session-record sp agent)))
      (cond
        ((nil? rec) {:agent agent :error "no-session"})
        ((not (= (get rec :status) "suspended")) {:agent agent :error "not-suspended"})
        (else
          (let
            ((state (agentic/session-transition! sp agent {:flow (get rec :flow) :resumes (append (get rec :resumes) (list value)) :input (get rec :input)})))
            (begin
              (if
                (has-key? state :error)
                nil
                (agentic/trace!
                  sp
                  agent
                  "session"
                  (str "resume " (agentic/scm-lit value))))
              state)))))))

(define
  agentic/session-status
  (fn
    (sp agent)
    (let
      ((r (agentic/session-record sp agent)))
      (if (nil? r) "none" (get r :status)))))

(define
  agentic/session-pending
  (fn
    (sp agent)
    (let
      ((r (agentic/session-record sp agent)))
      (if
        (and (dict? r) (= (get r :status) "suspended"))
        (get r :tag)
        nil))))

(define
  agentic/session-result
  (fn
    (sp agent)
    (let
      ((r (agentic/session-record sp agent)))
      (if (and (dict? r) (= (get r :status) "done")) (get r :result) nil))))

; ---- fork-an-agent-run: copy the record, replay rebuilds the run ----
; to-agent must already be spawned (branch fork) and session-free
(define
  agentic/session-fork!
  (fn
    (sp from-agent to-agent)
    (let
      ((rec (agentic/session-record sp from-agent)))
      (cond
        ((nil? rec) {:agent from-agent :error "no-session"})
        ((nil? (agentic/head sp to-agent)) {:agent to-agent :error "no-such-agent"})
        ((not (nil? (agentic/session-record sp to-agent))) {:agent to-agent :error "session-exists"})
        (else
          (let
            ((state (agentic/session-transition! sp to-agent {:flow (get rec :flow) :resumes (get rec :resumes) :input (get rec :input)})))
            (begin
              (if
                (has-key? state :error)
                nil
                (agentic/trace!
                  sp
                  to-agent
                  "session"
                  (str "fork " from-agent)))
              state)))))))

; ---- effect-as-data helpers over (request kind payload) envelopes ----
(define
  agentic/effect-request?
  (fn
    (tag)
    (and
      (list? tag)
      (= (len tag) 3)
      (= (nth tag 0) "flow-request"))))

(define
  agentic/effect-kind
  (fn (tag) (if (agentic/effect-request? tag) (nth tag 1) nil)))

(define
  agentic/effect-payload
  (fn (tag) (if (agentic/effect-request? tag) (nth tag 2) nil)))