Add update-nixpkgs.rb

update-nixpkgs.rb

@@ -0,0 +1,36 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -p curl cacert ruby -i ruby --pure
+
+require 'time'
+
+CHANNEL = "nixos-22.05"
+AT_LEAST_DAYS_OLD = 21
+HASH_FILE = "nixpkgs.hash"
+
+threshold = (DateTime.now - AT_LEAST_DAYS_OLD).to_time.to_i
+
+# Download history
+history_lines = `curl -s https://channels.nix.gsc.io/#{CHANNEL}/history`.split("\n")
+
+class Release
+  attr_reader :sha, :epoch
+  def initialize(s)
+    @sha, epoch_str = s.split(" ")
+    @epoch = epoch_str.to_i
+  end
+  def to_s
+    [@sha, @epoch].to_s
+  end
+end
+
+release = history_lines
+       .map { |line| Release.new(line) }
+       .sort_by { |t|  t.epoch }
+       .reverse
+       .find { |t| t.epoch < threshold }
+
+puts "Picked first release older than #{AT_LEAST_DAYS_OLD} days: #{release.sha} (#{Time.at(release.epoch)})"
+
+File.open(HASH_FILE, "w") do |file|
+  file.print release.sha
+end