Monitor media directory sizes with node exporter

machines/lewis/configuration.nix

@@ -2,6 +2,7 @@
   self,
   config,
   pkgs,
+  lib,
   ...
 }: {
   config = {
@@ -22,5 +23,48 @@
       data-sharing.enable = true;
       backups.enable = true;
     };
+
+    systemd.timers.read-dir-sizes = {
+      wantedBy = ["timers.target"];
+      timerConfig = {
+        OnBootSec = "5m";
+        OnUnitActiveSec = "5m";
+        Unit = "read-dir-sizes.service";
+      };
+    };
+
+    systemd.services."read-dir-sizes" = {
+      script = let
+        script = pkgs.writeShellScriptBin "read-dir-sizes.sh" ''
+          DIRS=(
+            "/mnt/longhorn/persistent/media/movies"
+            "/mnt/longhorn/persistent/media/shows"
+          )
+
+          temp_file=$(mktemp)
+          trap 'rm -f "$temp_file"' EXIT
+
+          for DIR_PATH in "''${DIRS[@]}"; do
+              # Find all top-level subdirectories and calculate their size
+              find "$DIR_PATH" -mindepth 1 -maxdepth 1 -type d | while read -r subdir; do
+                  # Calculate the size of the top-level subdirectory
+                  du --block-size=1 -s "$subdir" | while read -r size path; do
+                      # Print size in Prometheus format
+                      echo "directory_size_bytes{dir=\"$path\"} $size" >> $temp_file
+                  done
+              done
+          done
+          mkdir -p /var/lib/node_exporter/textfile_collector
+          cp $temp_file /var/lib/node_exporter/textfile_collector/dir_sizes.prom
+          chmod o=r /var/lib/node_exporter/textfile_collector/dir_sizes.prom
+        '';
+      in "${lib.getExe script}";
+      serviceConfig = {
+        Type = "oneshot";
+        User = "root";
+      };
+    };
+
+    services.prometheus.exporters.node.extraFlags = ["--collector.textfile.directory=/var/lib/node_exporter/textfile_collector"];
   };
 }