nixos/open-webui: add backwards compatability migration (#432897)

nixos/modules/services/misc/open-webui.nix

@@ -97,6 +97,23 @@ in
       }
       // cfg.environment;
 
+      # backwards compatability migration
+      preStart = ''
+        if [ -d "${cfg.stateDir}/data" ] && [ -n "$(ls -A "${cfg.stateDir}/data" 2>/dev/null)" ]; then
+          exit 0
+        fi
+
+        mkdir -p "${cfg.stateDir}/data"
+
+        [ -f "${cfg.stateDir}/webui.db" ] && mv "${cfg.stateDir}/webui.db" "${cfg.stateDir}/data/"
+
+        for dir in cache uploads vector_db; do
+          [ -d "${cfg.stateDir}/$dir" ] && mv "${cfg.stateDir}/$dir" "${cfg.stateDir}/data/"
+        done
+
+        exit 0
+      '';
+
       serviceConfig = {
         ExecStart = "${lib.getExe cfg.package} serve --host \"${cfg.host}\" --port ${toString cfg.port}";
         EnvironmentFile = lib.optional (cfg.environmentFile != null) cfg.environmentFile;