From 51c83537bacf9d6c07b57b7f5817660bd8a41ca8 Mon Sep 17 00:00:00 2001
From: Martin Varga <martin.varga@lutraconsulting.co.uk>
Date: Tue, 31 Mar 2026 15:12:35 +0200
Subject: [PATCH] Fix issue with gpkg reconstruction from merged diffs

---
 server/mergin/sync/models.py             |  5 ++-
 server/mergin/tests/test_file_restore.py | 47 +++++++++++++++++++++---
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/server/mergin/sync/models.py b/server/mergin/sync/models.py
index cc7779d2..1b99735b 100644
--- a/server/mergin/sync/models.py
+++ b/server/mergin/sync/models.py
@@ -1017,8 +1017,9 @@ def construct_checkpoint(self) -> bool:
         )
 
         for item in cached_items:
-            # basefile is a start of the diff chain
-            if item.start <= basefile.project_version_name:
+            # basefile is a start of the diff chain, item cannot cross over it,
+            # but merged diffs can start with basefile version containing changes since then
+            if item.start < basefile.project_version_name:
                 continue
 
             # find diff in table and on disk
diff --git a/server/mergin/tests/test_file_restore.py b/server/mergin/tests/test_file_restore.py
index 42ee2446..8025d7de 100644
--- a/server/mergin/tests/test_file_restore.py
+++ b/server/mergin/tests/test_file_restore.py
@@ -4,6 +4,7 @@
 import os
 import pytest
 import shutil
+from sqlalchemy import tuple_
 from sqlalchemy.orm.attributes import flag_modified
 
 from ..app import db
@@ -15,6 +16,7 @@
     Project,
     GeodiffActionHistory,
 )
+from ..sync.utils import Checkpoint
 from . import test_project_dir, TMP_DIR
 from .utils import (
     create_project,
@@ -250,11 +252,46 @@ def test_version_file_restore(diff_project):
     test_file = os.path.join(diff_project.storage.project_dir, "v30", "test.gpkg")
     os.rename(test_file, test_file + "_backup")
     diff_project.storage.restore_versioned_file("test.gpkg", 30)
+    checkpoints = Checkpoint.get_checkpoints(9, 30)
     assert os.path.exists(test_file)
     assert gpkgs_are_equal(test_file, test_file + "_backup")
-    assert (
-        FileDiff.query.filter_by(file_path_id=file_path_id)
-        .filter(FileDiff.rank > 0)
-        .count()
-        > 0
+    assert FileDiff.query.filter_by(file_path_id=file_path_id).filter(
+        tuple_(FileDiff.rank, FileDiff.version).in_(
+            [(item.rank, item.end) for item in checkpoints]
+        )
+    ).count() == len(checkpoints)
+
+    # let's create new project with basefile at v1 (which can be start of multiple checkpoints)
+    working_dir = os.path.join(TMP_DIR, "restore_from_diffs")
+    basefile = os.path.join(working_dir, "base.gpkg")
+    project = _prepare_restore_project(working_dir)
+    file_path_id = (
+        ProjectFilePath.query.filter_by(project_id=project.id, path="base.gpkg")
+        .first()
+        .id
     )
+
+    for i in range(17):
+        sql = "INSERT INTO simple (geometry, name) VALUES (GeomFromText('POINT(24.5, 38.2)', 4326), 'insert_test')"
+        execute_query(basefile, sql)
+        pv_latest = push_change(project, "updated", "base.gpkg", working_dir)
+        assert project.latest_version == pv_latest.name
+        assert os.path.exists(
+            os.path.join(
+                project.storage.project_dir,
+                ProjectVersion.to_v_name(pv_latest.name),
+                "base.gpkg",
+            )
+        )
+
+    test_file = os.path.join(project.storage.project_dir, "v17", "base.gpkg")
+    os.rename(test_file, test_file + "_backup")
+    project.storage.restore_versioned_file("base.gpkg", 17)
+    checkpoints = Checkpoint.get_checkpoints(1, 17)
+    assert os.path.exists(test_file)
+    assert gpkgs_are_equal(test_file, test_file + "_backup")
+    assert FileDiff.query.filter_by(file_path_id=file_path_id).filter(
+        tuple_(FileDiff.rank, FileDiff.version).in_(
+            [(item.rank, item.end) for item in checkpoints]
+        )
+    ).count() == len(checkpoints)