feat(reverse-proxy): add Pikachu reverse proxy guest

modules/reverse-proxy.nix

@@ -0,0 +1,82 @@
+{ config, lib, my, ... }:
+let
+  cfg = config.modules.reverse-proxy;
+  inherit (my) reverseProxyRoutes;
+
+  enabledRoutes = lib.filterAttrs (_: route: route.enable) cfg.routes;
+  routesByHost = lib.groupBy (route: route.host) (lib.attrValues enabledRoutes);
+
+  rootRoutesByHost = lib.mapAttrs (
+    host: routes:
+    let
+      roots = builtins.filter (route: route.path == "/") routes;
+    in
+    if roots == [ ] then null else builtins.head roots
+  ) routesByHost;
+
+  hasDuplicatePaths = routes:
+    let
+      paths = map (route: route.path) routes;
+    in
+    lib.length paths != lib.length (lib.unique paths);
+
+  mkLocation = route: {
+    proxyPass = route.backend;
+    proxyWebsockets = route.websockets;
+  };
+
+  mkVirtualHost = host: routes:
+    let
+      rootRoute = rootRoutesByHost.${host};
+    in
+    lib.mkIf (rootRoute != null) {
+      forceSSL = rootRoute.tls;
+      enableACME = rootRoute.tls;
+      serverAliases = rootRoute.aliases;
+      locations = lib.listToAttrs (
+        map (route: lib.nameValuePair route.path (mkLocation route)) routes
+      );
+    };
+in
+{
+  options.modules.reverse-proxy = {
+    enable = lib.mkEnableOption "the Nginx reverse proxy route realizer";
+
+    routes = lib.mkOption {
+      type = lib.types.attrsOf reverseProxyRoutes.routeType;
+      default = { };
+      description = "Reverse-proxy route declarations keyed by stable route name.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions =
+      lib.mapAttrsToList (host: rootRoute: {
+        assertion = rootRoute != null;
+        message = "modules.reverse-proxy.routes for ${host} must include a primary / route.";
+      }) rootRoutesByHost
+      ++ lib.mapAttrsToList (host: routes: {
+        assertion = !hasDuplicatePaths routes;
+        message = "modules.reverse-proxy.routes for ${host} must not declare the same path more than once.";
+      }) routesByHost;
+
+    networking.firewall.allowedTCPPorts = [
+      80
+      443
+    ];
+
+    security.acme = {
+      acceptTerms = true;
+      defaults.email = "contact@alexion.dev";
+    };
+
+    services.nginx = {
+      enable = true;
+      recommendedGzipSettings = true;
+      recommendedOptimisation = true;
+      recommendedProxySettings = true;
+      recommendedTlsSettings = true;
+      virtualHosts = lib.mapAttrs mkVirtualHost routesByHost;
+    };
+  };
+}