From 22f068f20d8203e8cb5db2f74d418a4c4785175b Mon Sep 17 00:00:00 2001
From: andersmurphy <andersmurphy@gmail.com>
Date: Fri, 26 Dec 2025 10:58:27 +0000
Subject: [PATCH] Implement session changeset undo

---
 src/sqlite4clj/impl/api.clj |   4 ++
 src/sqlite4clj/session.clj  | 134 ++++++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100644 src/sqlite4clj/session.clj

diff --git a/src/sqlite4clj/impl/api.clj b/src/sqlite4clj/impl/api.clj
index 3893e9a..a4f2050 100644
--- a/src/sqlite4clj/impl/api.clj
+++ b/src/sqlite4clj/impl/api.clj
@@ -64,6 +64,10 @@
 
 (defonce init-lib (initialize nil))
 
+(defcfn free
+  sqlite3_free
+  [::mem/pointer] ::mem/void)
+
 (defcfn errmsg
   sqlite3_errmsg
   [::mem/pointer] ::mem/c-string)
diff --git a/src/sqlite4clj/session.clj b/src/sqlite4clj/session.clj
new file mode 100644
index 0000000..98dd7e9
--- /dev/null
+++ b/src/sqlite4clj/session.clj
@@ -0,0 +1,134 @@
+(ns sqlite4clj.session
+  (:require
+   [coffi.ffi :as ffi :refer [defcfn]]
+   [coffi.mem :as mem]
+   [sqlite4clj.impl.api :as api]))
+
+;; ========= SESSION extension =========
+;; https://sqlite.org/session/changegroup.html
+
+(defcfn session-create
+  "sqlite3session_create"
+  [::mem/pointer ::mem/c-string ::mem/pointer] ::mem/int
+  sqlite3session-create-native
+  [pdb]
+  (with-open [arena (mem/confined-arena)]
+    (let [ppSession (mem/alloc-instance ::mem/pointer arena)
+          code      (sqlite3session-create-native pdb "main" ppSession)]
+      (if (api/sqlite-ok? code)
+        (mem/deserialize-from ppSession ::mem/pointer)
+        (throw (api/sqlite-ex-info pdb code {}))))))
+
+(defcfn session-attach
+  sqlite3session_attach
+  [::mem/pointer ::mem/c-string] ::mem/int)
+
+(defcfn session-delete
+  sqlite3session_delete
+  [::mem/pointer] ::mem/int)
+
+(defcfn session-changeset
+  "sqlite3session_changeset"
+  [::mem/pointer ::mem/pointer ::mem/pointer] ::mem/int
+  sqlite3session-patchset-native
+  [pdb pSession]
+  (with-open [arena (mem/confined-arena)]
+    (let [pnPatchset (mem/alloc-instance ::mem/int arena)
+          ppPatchset (mem/alloc-instance ::mem/pointer arena)
+          code       (sqlite3session-patchset-native pSession
+                       pnPatchset
+                       ppPatchset)]
+      (if (api/sqlite-ok? code)
+        [(mem/deserialize-from pnPatchset ::mem/int)
+         (mem/deserialize-from ppPatchset ::mem/pointer)]
+        (throw (api/sqlite-ex-info pdb code {}))))))
+
+(defcfn changeset-invert
+  "sqlite3changeset_invert"
+  [::mem/int ::mem/pointer
+   ::mem/pointer ::mem/pointer] ::mem/int
+  sqlite3changeset-invert-native
+  [pdb nInSet pInSet]
+  (with-open [arena (mem/confined-arena)]
+    (let [pnOutSet (mem/alloc-instance ::mem/int arena)
+          ppOutSet (mem/alloc-instance ::mem/pointer arena)
+          code     (sqlite3changeset-invert-native
+                     nInSet pInSet
+                     pnOutSet ppOutSet)]
+      (if (api/sqlite-ok? code)
+        [(mem/deserialize-from pnOutSet ::mem/int)
+         (mem/deserialize-from ppOutSet ::mem/pointer)]
+        (throw (api/sqlite-ex-info pdb code {}))))))
+
+(defcfn changeset-apply
+  sqlite3changeset_apply
+  [::mem/pointer ;; db
+   ::mem/int     ;; size of changeset
+   ::mem/pointer ;; changeset
+   ::mem/pointer ;; xFilter
+   ::mem/pointer ;; xConflict
+   ::mem/pointer ;; First arg to conflict
+   ] ::mem/int)
+
+(defn new-session
+  "Creates a session and attaches it to the database."
+  [conn]
+  (let [pdb      (:pdb conn)
+        pSession (session-create pdb)]
+    (session-attach pSession nil)
+    (atom pSession)))
+
+(defn cancel-session
+  "Cancels session without undoing changes."
+  [session]
+  (when-let [session @session]
+    (session-delete session)))
+
+(defn undo-session
+  "Undoes the current session and deletes it."
+  [conn session]
+  (when-let [pSession @session]
+    (let [pdb                     (:pdb conn)
+          [nSet pSet]             (session-changeset pdb pSession)
+          _                       (session-delete pSession)
+          [nInvertSet pInvertSet] (changeset-invert pdb nSet pSet)]
+      (with-open [arena (mem/confined-arena)]
+        (let [x-conflict
+              ;; Fails if there's a conflict (there should never be a conflict)
+              ;; when using undo-session correctly.
+              (mem/serialize (fn [_ _ _] (int 0))
+                [::ffi/fn
+                 [::mem/pointer ::mem/int ::mem/pointer]
+                 ::mem/int
+                 :raw-fn? true]
+                arena)]
+          (changeset-apply pdb nInvertSet pInvertSet nil x-conflict nil)))
+      (api/free pSet)
+      (api/free pInvertSet)
+      (reset! session nil))))
+
+(comment
+  (require '[sqlite4clj.core :as d])
+
+  (defonce db
+    (d/init-db! "database.db"
+      {:read-only true
+       :pool-size 4
+       :pragma    {:foreign_keys false}}))
+
+  (def reader  (db :reader))
+  (def writer (db :writer))
+
+  (d/q writer
+    ["CREATE TABLE IF NOT EXISTS bar(id INT PRIMARY KEY, data BLOB)"])
+
+  (let [session (d/with-conn [conn (:writer db)]
+                  (new-session conn))]
+    (println (d/q (:reader db) ["select count(*) from bar"]))
+    (d/q (:writer db)
+      ["insert into bar (id, data) VALUES (?, ?)"
+       (str (random-uuid)) 34])
+    (println (d/q (:reader db) ["select count(*) from bar"]))
+    (d/with-conn [conn (:writer db)]
+      (undo-session conn session))
+    (println (d/q (:reader db) ["select count(*) from bar"]))))