nixos/librenms: regenerate caches after every package change

The LibreNMS cache may contain paths to the old package and may break
when the old package is removed. So it is not enough to clear the cache
only on version updates, as the package will also change when build
inputs change.

This commit updates the setup script to regenerate the cache on every
package change. In addition, it now only performs migrations when the
package version has changed, since the migrations only change on version
updates and don't need to be applied on every package change.

Author: NetaliDev

nixos/modules/services/monitoring/librenms.nix

@@ -603,9 +603,10 @@ in
         ''
       )
       + ''
-        # clear cache after update (before migrations)
-        OLD_VERSION=$(cat ${cfg.dataDir}/version)
-        if [[ $OLD_VERSION != "${package.version}" ]]; then
+        # clear cache if package has changed (cache may contain cached paths
+        # to the old package)
+        OLD_PACKAGE=$(cat ${cfg.dataDir}/package)
+        if [[ $OLD_PACKAGE != "${package}" ]]; then
           rm -r ${cfg.dataDir}/cache/*
         fi
 
@@ -616,16 +617,21 @@ in
           echo "${lib.boolToString cfg.enableOneMinutePolling}" > ${cfg.dataDir}/one_minute_enabled
         fi
 
-        # migrate db
-        ${artisanWrapper}/bin/librenms-artisan migrate --force --no-interaction
-
-        # regenerate cache after migrations after update
+        # migrate db if package version has changed
+        # not necessary for every package change
+        OLD_VERSION=$(cat ${cfg.dataDir}/version)
         if [[ $OLD_VERSION != "${package.version}" ]]; then
+          ${artisanWrapper}/bin/librenms-artisan migrate --force --no-interaction
+          echo "${package.version}" > ${cfg.dataDir}/version
+        fi
+
+        # regenerate cache if package has changed
+        if [[ $OLD_PACKAGE != "${package}" ]]; then
           ${artisanWrapper}/bin/librenms-artisan view:clear
           ${artisanWrapper}/bin/librenms-artisan optimize:clear
           ${artisanWrapper}/bin/librenms-artisan view:cache
           ${artisanWrapper}/bin/librenms-artisan optimize
-          echo "${package.version}" > ${cfg.dataDir}/version
+          echo "${package}" > ${cfg.dataDir}/package
         fi
       '';
     };
@@ -693,6 +699,7 @@ in
       "d ${cfg.dataDir}                              0750 ${cfg.user} ${cfg.group} - -"
       "f ${cfg.dataDir}/.env                         0600 ${cfg.user} ${cfg.group} - -"
       "f ${cfg.dataDir}/version                      0600 ${cfg.user} ${cfg.group} - -"
+      "f ${cfg.dataDir}/package                      0600 ${cfg.user} ${cfg.group} - -"
       "f ${cfg.dataDir}/one_minute_enabled           0600 ${cfg.user} ${cfg.group} - -"
       "f ${cfg.dataDir}/config.json                  0600 ${cfg.user} ${cfg.group} - -"
       "d ${cfg.dataDir}/storage                      0700 ${cfg.user} ${cfg.group} - -"