gerrit: factor more configuration in the NixOS module for external consumption

Other modules may require information to configure themselves from the
Gerrit module.

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>

hosts/gerrit01/default.nix

@@ -35,6 +35,7 @@
     domains = [
       "cl.forkos.org"
     ];
+    canonicalDomain = "cl.forkos.org";
     data = "/gerrit-data";
   };
 

services/gerrit/default.nix

@@ -3,7 +3,7 @@
 { pkgs, config, lib, ... }:
 
 let
-  inherit (lib) mkEnableOption mkIf mkOption types;
+  inherit (lib) mkEnableOption mkIf mkOption types head;
   cfgGerrit = config.services.gerrit;
   cfg = config.bagel.services.gerrit;
 
@@ -16,11 +16,22 @@ in
       type = types.listOf types.str;
       description = "List of domains that Gerrit will answer to";
     };
+    canonicalDomain = mkOption {
+      type = types.str;
+      description = "Canonical domain for this Gerrit instance";
+      default = head cfg.domains;
+    };
     data = mkOption {
       type = types.path;
       default = "/var/lib/gerrit";
       description = "Root of data directory for the Gerrit";
     };
+    port = mkOption {
+      type = types.port;
+      default = 29418;
+      readOnly = true;
+      description = "Port for the Gerrit SSH server";
+    };
   };
 
   imports = [
@@ -28,7 +39,7 @@ in
   ];
 
   config = mkIf cfg.enable {
-    networking.firewall.allowedTCPPorts = [ 29418 ];
+    networking.firewall.allowedTCPPorts = [ cfg.port ];
 
     environment.systemPackages = [ jdk ];
 
@@ -58,7 +69,7 @@ in
         "webhooks"
       ];
 
-      plugins = with pkgs.gerritPlugins; [ 
+      plugins = with pkgs.gerritPlugins; [
         oauth
         metrics-reporter-prometheus
       ];
@@ -115,7 +126,7 @@ in
         # Other settings
         log.jsonLogging = true;
         log.textLogging = false;
-        sshd.advertisedAddress = "cl.forkos.org:29418";
+        sshd.advertisedAddress = "${cfg.canonicalDomain}:${cfg.port}";
         cache.web_sessions.maxAge = "3 months";
         plugins.allowRemoteAdmin = false;
         change.enableAttentionSet = true;
@@ -130,7 +141,7 @@ in
         # Configures gerrit for being reverse-proxied by nginx as per
         # https://gerrit-review.googlesource.com/Documentation/config-reverseproxy.html
         gerrit = {
-          canonicalWebUrl = "https://cl.forkos.org";
+          canonicalWebUrl = "https://${cfg.canonicalDomain}";
           docUrl = "/Documentation";
           defaultBranch = "refs/heads/main";
         };
@@ -147,7 +158,7 @@ in
         # Auto-link other CLs
         commentlink.gerrit = {
           match = "cl/(\\d+)";
-          link = "https://cl.forkos.org/$1";
+          link = "https://${cfg.canonicalDomain}/$1";
         };
 
         # Configures integration with Keycloak, which then integrates with a