backup: If a database exists write an intial snapshot

backup/backup-cli

@@ -1,8 +1,10 @@
 #!/usr/bin/env python3
-from backup import FileBackend, get_backend
+from backup import FileBackend, get_backend, Change
 import os
 import click
 import json
+import sqlite3
+import sys
 
 
 @click.command()
@@ -17,6 +19,7 @@ def init(lightning_dir, backend_url):
     backend.write_metadata()
 
     lock_file = os.path.join(lightning_dir, "backup.lock")
+    db_file = os.path.join(lightning_dir, "lightningd.sqlite3")
 
     with open(lock_file, "w") as f:
         f.write(json.dumps({
@@ -25,6 +28,28 @@ def init(lightning_dir, backend_url):
 
     # TODO Take a snapshot
 
+    data_version = 0
+    if os.path.exists(db_file):
+        print("Found an existing database at {db_file}, initializing the backup with a snapshot".format(db_file=db_file))
+        # Peek into the DB to see if we have
+        db = sqlite3.connect(db_file)
+        cur = db.cursor()
+        rows = cur.execute("SELECT intval FROM vars WHERE name = 'data_version'")
+        data_version = rows.fetchone()[0]
+
+        snapshot = Change(
+            version=data_version,
+            snapshot=open(db_file, 'rb').read(),
+            transaction=None
+        )
+        if not backend.add_change(snapshot):
+            print("Could not write snapshot to backend")
+            sys.exit(1)
+        else:
+            print("Successfully written initial snapshot to {destination}".format(destination=destination))
+    else:
+        print("Database does not exist yet, created an empty backup file")
+
     print("Initialized backup backend {destination}, you can now start c-lightning".format(
         destination=destination,
     ))