; lib/agentic/branch.sx — agentic-sx Phase 2: one branch = one agent.
; spawn = branch-from-briefing: write the briefing, then a genesis "spawn"
; agent-commit whose parent is the fork point; the branch ref IS the agent.
; The commit verb snapshots a full worktree VALUE (path -> data) into a typed
; agent-commit and advances the branch by CAS — no shared index, multi-agent
; safe by construction. Branch topology = agent topology: fork points via
; git/merge-base, plus relations typed edges (sub-agent-of / reviews /
; merges) in a Datalog db carried on the space handle.
; Edge direction: (rel src dst kind) reads src=parent/actor, dst=child/object
;   (root child sub-agent-of), (reviewer reviewee reviews), (into from merges).
; Session merges are always recorded as a two-parent "session-merge" commit
; (no fast-forward) so the merge itself is an agent action with metadata.
; Requires: lib/agentic/schema.sx, lib/git/*, lib/relations/* (+ datalog).

; ---- space: repo + relations db ----
(define agentic/space (fn (db name) {:repo (git/repo-named db name) :rels (relations-build-db (list))}))

(define agentic/space-repo (fn (sp) (get sp :repo)))
(define agentic/space-rels (fn (sp) (get sp :rels)))

(define agentic/branch-name (fn (agent) (str "agents/" agent)))

; ---- typed edges over relations ----
(define
  agentic/relate!
  (fn
    (sp src dst kind)
    (begin
      (dl-assert! (agentic/space-rels sp) (relations-rel src dst kind))
      true)))

(define
  agentic/sub-agents
  (fn
    (sp agent)
    (sort
      (relations-children-of
        (agentic/space-rels sp)
        agent
        (quote sub-agent-of)))))

(define
  agentic/parent-agent
  (fn
    (sp agent)
    (let
      ((ps (relations-parents-of (agentic/space-rels sp) agent (quote sub-agent-of))))
      (if (= (len ps) 0) nil (nth ps 0)))))

(define
  agentic/agent-tree
  (fn
    (sp agent)
    (sort
      (relations-descendants
        (agentic/space-rels sp)
        agent
        (quote sub-agent-of)))))

(define
  agentic/reviews!
  (fn
    (sp reviewer reviewee)
    (agentic/relate! sp reviewer reviewee (quote reviews))))

(define
  agentic/reviewers
  (fn
    (sp agent)
    (sort
      (relations-parents-of (agentic/space-rels sp) agent (quote reviews)))))

(define
  agentic/reviewing
  (fn
    (sp agent)
    (sort
      (relations-children-of (agentic/space-rels sp) agent (quote reviews)))))

(define
  agentic/merged-sessions
  (fn
    (sp agent)
    (sort
      (relations-children-of (agentic/space-rels sp) agent (quote merges)))))

(define
  agentic/merged-into
  (fn
    (sp agent)
    (sort
      (relations-parents-of (agentic/space-rels sp) agent (quote merges)))))

; ---- spawn = branch-from-briefing ----
; base-cid nil => root agent over an empty tree; parent-agent nil => no edge.
; => {:agent :branch :briefing :genesis} | {:conflict true :actual cid}
(define
  agentic/spawn-at!
  (fn
    (sp agent briefing base-cid parent-agent)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((bcid (git/write repo briefing))
          (tree
            (if
              (nil? base-cid)
              (git/tree-from-files repo {})
              (git/commit-tree (git/read repo base-cid))))
          (parents (if (nil? base-cid) (list) (list base-cid))))
        (let
          ((g (agentic/agent-commit tree parents "spawn" {:message (str "spawn: " (agentic/briefing-title briefing)) :agent agent :briefing bcid})))
          (let
            ((gcid (git/write repo g)))
            (let
              ((res (git/branch-create! repo (agentic/branch-name agent) gcid)))
              (if
                (and (dict? res) (has-key? res :conflict))
                res
                (begin
                  (if
                    (nil? parent-agent)
                    nil
                    (agentic/relate!
                      sp
                      parent-agent
                      agent
                      (quote sub-agent-of)))
                  {:agent agent :briefing bcid :branch (agentic/branch-name agent) :genesis gcid})))))))))

(define
  agentic/spawn!
  (fn (sp agent briefing) (agentic/spawn-at! sp agent briefing nil nil)))

(define
  agentic/spawn-from!
  (fn
    (sp agent briefing parent-agent)
    (let
      ((h (agentic/head sp parent-agent)))
      (if
        (nil? h)
        {:agent parent-agent :error "no-such-agent"}
        (agentic/spawn-at! sp agent briefing h parent-agent)))))

; ---- heads / listing ----
(define
  agentic/head
  (fn
    (sp agent)
    (git/branch-get (agentic/space-repo sp) (agentic/branch-name agent))))

(define
  agentic/agents
  (fn (sp) (git/refs-under (agentic/space-repo sp) "heads/agents/")))

; ---- the commit verb: snapshot + typed agent-commit + CAS advance ----
; files = the agent's FULL worktree value (path -> data). Briefing and agent
; identity propagate from the branch head. => cid | {:error ...} | {:conflict ...}
(define
  agentic/commit!
  (fn
    (sp agent kind files meta)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((head (agentic/head sp agent)))
        (cond
          ((nil? head) {:agent agent :error "no-such-agent"})
          ((not (agentic/commit-kind? kind)) {:error "unknown-kind" :kind kind})
          (else
            (let
              ((tree (git/tree-from-files repo files))
                (b (agentic/commit-briefing (git/read repo head))))
              (let
                ((pm (if (nil? b) {:agent agent} {:agent agent :briefing b})))
                (let
                  ((cid (git/write repo (agentic/agent-commit tree (list head) kind (merge meta pm)))))
                  (let
                    ((res (git/branch-cas! repo (agentic/branch-name agent) head cid)))
                    (if (and (dict? res) (has-key? res :conflict)) res cid)))))))))))

; commits authored by this agent, newest first, from its branch head
(define
  agentic/session-log
  (fn
    (sp agent)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((head (agentic/head sp agent)))
        (if
          (nil? head)
          (list)
          (filter
            (fn (cid) (= (agentic/commit-agent (git/read repo cid)) agent))
            (git/log repo head)))))))

; the branch's genesis spawn commit (oldest spawn authored by this agent)
(define
  agentic/genesis
  (fn
    (sp agent)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((head (agentic/head sp agent)))
        (if
          (nil? head)
          nil
          (let
            ((hits (filter (fn (cid) (let ((c (git/read repo cid))) (and (= (agentic/commit-kind c) "spawn") (= (agentic/commit-agent c) agent)))) (git/log repo head))))
            (if (= (len hits) 0) nil (last hits))))))))

(define
  agentic/briefing-of
  (fn
    (sp agent)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((g (agentic/genesis sp agent)))
        (if
          (nil? g)
          nil
          (let
            ((bcid (agentic/commit-briefing (git/read repo g))))
            (if (nil? bcid) nil (git/read repo bcid))))))))

; ---- topology: fork points via the DAG ----
(define
  agentic/fork-point
  (fn
    (sp agent-a agent-b)
    (let
      ((ha (agentic/head sp agent-a)) (hb (agentic/head sp agent-b)))
      (if
        (or (nil? ha) (nil? hb))
        nil
        (git/merge-base (agentic/space-repo sp) ha hb)))))

; ---- session merge: always an explicit two-parent session-merge commit ----
(define
  agentic/merge-commit-at!
  (fn
    (sp into-agent from-agent ours theirs tree meta)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((b (agentic/commit-briefing (git/read repo ours))))
        (let
          ((pm (if (nil? b) {:agent into-agent :merged-agent from-agent} {:agent into-agent :briefing b :merged-agent from-agent})))
          (let
            ((cid (git/write repo (agentic/agent-commit tree (list ours theirs) "session-merge" (merge meta pm)))))
            (let
              ((res (git/branch-cas! repo (agentic/branch-name into-agent) ours cid)))
              (if
                (and (dict? res) (has-key? res :conflict))
                res
                (begin
                  (agentic/relate! sp into-agent from-agent (quote merges))
                  {:cid cid :result "merged"})))))))))

; => {:result "up-to-date"} | {:result "merged" :cid} |
;    {:result "conflicts" :tree :conflicts (paths)} | {:error ...}
; Conflicts commit nothing — resolve with agentic/merge-resolve!.
(define
  agentic/merge-session!
  (fn
    (sp into-agent from-agent meta)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((ours (agentic/head sp into-agent))
          (theirs (agentic/head sp from-agent)))
        (cond
          ((nil? ours) {:agent into-agent :error "no-such-agent"})
          ((nil? theirs) {:agent from-agent :error "no-such-agent"})
          (else
            (let
              ((m (git/merge-commits repo ours theirs)))
              (cond
                ((= (get m :result) "up-to-date") m)
                ((= (get m :result) "conflicts") m)
                (else
                  (let
                    ((tree (if (= (get m :result) "fast-forward") (git/commit-tree (git/read repo theirs)) (get m :tree))))
                    (agentic/merge-commit-at!
                      sp
                      into-agent
                      from-agent
                      ours
                      theirs
                      tree
                      meta)))))))))))

; conclude a conflicted session merge with resolved worktree files
(define
  agentic/merge-resolve!
  (fn
    (sp into-agent from-agent files meta)
    (let
      ((repo (agentic/space-repo sp)))
      (let
        ((ours (agentic/head sp into-agent))
          (theirs (agentic/head sp from-agent)))
        (if
          (or (nil? ours) (nil? theirs))
          {:error "no-such-agent"}
          (agentic/merge-commit-at!
            sp
            into-agent
            from-agent
            ours
            theirs
            (git/tree-from-files repo files)
            meta))))))