os/mixin/radicle-stats: Collect rad stats

A systemd timer unit that will just take the output of `rad stats` and
timestamp it.

os/host/iris/radicle.nix

@@ -8,6 +8,7 @@ in {
   imports = [
     ../../mixin/radicle.nix
     ../../mixin/radicle-permissive.nix
+    ../../mixin/radicle-stats.nix
   ];
 
   fileSystems."/var/lib/radicle" = {

os/host/rosa/radicle.nix

@@ -8,6 +8,7 @@ in {
   imports = [
     ../../mixin/radicle.nix
     ../../mixin/radicle-permissive.nix
+    ../../mixin/radicle-stats.nix
   ];
 
   fileSystems."/var/lib/radicle" = {

os/host/seed/radicle.nix

@@ -3,7 +3,10 @@
   pkgs,
   ...
 }: {
-  imports = [../../mixin/radicle.nix];
+  imports = [
+    ../../mixin/radicle.nix
+    ../../mixin/radicle-stats.nix
+  ];
 
   fileSystems."/var/lib/radicle" = {
     device = "/dev/disk/by-id/scsi-0HC_Volume_30473554";

os/mixin/radicle-stats.nix

@@ -0,0 +1,40 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}: let
+  name = "radicle-stats";
+in {
+  systemd = {
+    timers.${name} = {
+      wantedBy = ["timers.target"];
+      timerConfig = {
+        OnBootSec = "1m";
+        OnUnitActiveSec = "6h";
+        Unit = "${name}.service";
+      };
+    };
+    services = {
+      ${name} = let
+        cmd = "rad-system";
+        rad =
+          lib.findFirst (x: x.name == cmd) (throw "could not find `${cmd}`") config.environment.systemPackages;
+      in {
+        script = ''
+          set -xeu
+          mkdir -p /tmp/radicle
+          ${lib.getExe rad} stats | ${lib.getExe pkgs.jq} --compact-output '. * { timestamp: now | strftime("%s") }' >> /tmp/radicle/stats.jsonl
+        '';
+        serviceConfig = {
+          Type = "oneshot";
+          User = "root";
+        };
+      };
+      nginx.serviceConfig.BindReadOnlyPaths = [
+        "/tmp/radicle/stats.jsonl:/tmp/radicle/stats.jsonl"
+      ];
+    };
+  };
+  services.nginx.virtualHosts.${config.networking.fqdn}.locations."/tmp/".alias = "/tmp/radicle/";
+}