feat(defzone): Add an Emacs package for generating zone files

This currently only supports a small subset of available records, but
I actually kind of like the nesting.

tools/emacs-pkgs/defzone/defzone.el

@@ -0,0 +1,48 @@
+;;; defzone.el --- Generate zone files from Elisp  -*- lexical-binding: t; -*-
+
+(require 'dash)
+(require 'dash-functional)
+(require 's)
+
+(defun record-to-record (zone record &optional subdomain)
+  "Evaluate a record definition and turn it into a zone file
+  record in ZONE, optionally prefixed with SUBDOMAIN."
+
+  (declare (indent defun))             ; TODO(tazjin): remove
+  (let ((name (if subdomain (s-join "." (list subdomain zone)) zone)))
+    (pcase record
+      (`(SOA . (,ttl . (,mname ,rname ,serial ,refresh ,retry ,expire ,min)))
+       (format "%s %s IN SOA %s %s %s %s %s %s %s"
+               name ttl mname rname serial refresh retry expire min))
+
+      (`(NS . (,ttl . ,targets))
+       (->> targets
+            (-map (lambda (target) (format "%s %s IN NS %s" name ttl target)))
+            (s-join "\n")))
+
+      (`(MX . (,ttl . ,pairs))
+       (->> pairs
+            (-map (-lambda ((preference . exchange))
+                    (format "%s %s IN MX %s %s" name ttl preference exchange)))
+            (s-join "\n")))
+
+      (`(TXT ,ttl ,text) (format "%s %s IN TXT %s" name ttl (prin1-to-string text)))
+
+      (`(A . (,ttl . ,ips))
+       (->> ips
+            (-map (lambda (ip) (format "%s %s IN A %s" name ttl ip)))
+            (s-join "\n")))
+
+      (`(CNAME ,ttl ,target) (format "%s %s IN CNAME %s" name ttl target))
+
+      ((and `(,sub . ,records)
+            (guard (stringp sub)))
+       (s-join "\n" (-map (lambda (r) (record-to-record zone r sub)) records)))
+
+      (_ (error "Invalid record definition: %s" record)))))
+
+(defmacro defzone (fqdn &rest records)
+  "Generate zone file for the zone at FQDN from a simple DSL."
+  (declare (indent defun))
+
+  `(s-join "\n" (-map (lambda (r) (record-to-record ,fqdn r)) (quote ,records))))