Check that there are enough snapshots before diff (#144)

* Check that there are enough snapshots before diff

* Implement review feedback

Delete duplicate code and pull usage of the calculated stats into the
conditional block.

Author: johnmaguire

bin/restic_backup.sh

@@ -170,14 +170,20 @@ if [[ -n "$RESTIC_BACKUP_STATS_DIR" || -n "$RESTIC_BACKUP_NOTIFICATION_FILE" ]];
 		| awk '{print $1}' \
 		| tail -2 \
 		| tr '\n' ' ')
-	latest_snapshot_diff=$(echo "$latest_snapshots"	| xargs restic diff)
-	added=$(echo "$latest_snapshot_diff" | grep -i 'added:' | awk '{print $2 " " $3}')
-	removed=$(echo "$latest_snapshot_diff" | grep -i 'removed:' | awk '{print $2 " " $3}')
-	snapshot_size=$(restic stats latest --tag "$RESTIC_BACKUP_TAG" | grep -i 'total size:' | cut -d ':' -f2 | xargs)  # xargs acts as trim
-	snapshotId=$(echo "$latest_snapshots" | cut -d ' ' -f2)
-	statsMsg="Added: ${added}. Removed: ${removed}. Snap size: ${snapshot_size}"
-
-	echo "$statsMsg"
-	test -n "$RESTIC_BACKUP_STATS_DIR"         && logBackupStatsCsv "$snapshotId" "$added" "$removed" "$snapshot_size"
-	test -n "$RESTIC_BACKUP_NOTIFICATION_FILE" && notifyBackupStats "$statsMsg"
+
+	snapshot_count=$(echo "$latest_snapshots" | wc -l)
+	if [[ $snapshot_count -lt 2 ]]; then
+		echo "Warning: $snapshot_count snapshot(s) found. Skipping diff stats (need at least 2 snapshots)."
+	else
+		latest_snapshot_diff=$(echo "$latest_snapshots" | xargs restic diff)
+		added=$(echo "$latest_snapshot_diff" | grep -i 'added:' | awk '{print $2 " " $3}')
+		removed=$(echo "$latest_snapshot_diff" | grep -i 'removed:' | awk '{print $2 " " $3}')
+		snapshot_size=$(restic stats latest --tag "$RESTIC_BACKUP_TAG" | grep -i 'total size:' | cut -d ':' -f2 | xargs)  # xargs acts as trim
+		snapshotId=$(echo "$latest_snapshots" | cut -d ' ' -f2)
+		statsMsg="Added: ${added}. Removed: ${removed}. Snap size: ${snapshot_size}"
+
+		echo "$statsMsg"
+		test -n "$RESTIC_BACKUP_STATS_DIR"         && logBackupStatsCsv "$snapshotId" "$added" "$removed" "$snapshot_size"
+		test -n "$RESTIC_BACKUP_NOTIFICATION_FILE" && notifyBackupStats "$statsMsg"
+	fi
 fi