Flatten budget-app contents into repo root

backend/app/preupgrade.py

@@ -0,0 +1,59 @@
+"""Run before `alembic upgrade`: when there are database changes to apply, ask the backup container for a
+fresh dump and wait for it, so every upgrade can be rolled back to the moment just before it.
+
+The api stops (and Docker retries it) if the backup fails, unless SKIP_PRE_UPGRADE_BACKUP=true.
+"""
+import os
+import sys
+import time
+import uuid
+from pathlib import Path
+
+from alembic.config import Config
+from alembic.runtime.migration import MigrationContext
+from alembic.script import ScriptDirectory
+
+from .db import engine
+
+REQUESTS = Path(os.getenv("BACKUP_REQUEST_DIR", "/requests"))
+TIMEOUT = int(os.getenv("PRE_UPGRADE_BACKUP_TIMEOUT", "900"))
+
+
+def pending() -> tuple[str | None, str]:
+    head = ScriptDirectory.from_config(Config("alembic.ini")).get_current_head()
+    with engine.connect() as conn:
+        current = MigrationContext.configure(conn).get_current_revision()
+    return current, head
+
+
+def main() -> int:
+    current, head = pending()
+    if current is None or current == head:
+        return 0  # new database, or nothing to migrate
+    if os.getenv("SKIP_PRE_UPGRADE_BACKUP", "").lower() == "true":
+        print(f"pre-upgrade backup skipped ({current} -> {head})", flush=True)
+        return 0
+    if not REQUESTS.is_dir():
+        print(f"pre-upgrade backup: {REQUESTS} not mounted, cannot ask the backup container", file=sys.stderr, flush=True)
+        return 1
+    rid = time.strftime("%Y%m%d%H%M%S") + "-" + uuid.uuid4().hex[:6]
+    (REQUESTS / f"{rid}.request").write_text(f"database upgrade {current} -> {head}\n")
+    print(f"database upgrade {current} -> {head}: waiting for the backup container to take a backup", flush=True)
+    done = REQUESTS / f"{rid}.done"
+    deadline = time.time() + TIMEOUT
+    while time.time() < deadline:
+        if done.exists():
+            answer = done.read_text().strip()  # the backup container clears old answers itself
+            if answer == "ok":
+                print("pre-upgrade backup written", flush=True)
+                return 0
+            print("pre-upgrade backup FAILED; not upgrading. See: docker compose logs backup", file=sys.stderr, flush=True)
+            return 1
+        time.sleep(2)
+    print("pre-upgrade backup did not answer in time; not upgrading. Is the backup container running?",
+          file=sys.stderr, flush=True)
+    return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())