#!/usr/bin/env ruby

require 'rack'
require 'prometheus/middleware/exporter'
require 'socket'
require 'rack/handler/webrick'
require 'logger'

prometheus = Prometheus::Client.registry

mailq = prometheus.gauge(:postfix_queue_size, "Number of messages in the mail queue")

Thread.abort_on_exception = true

Thread.new do
	loop do
		begin
			%w{incoming active corrupt hold}.each do |q|
				mailq.set({ queue: q }, Dir["/var/spool/postfix/#{q}/*"].size)
			end

			# deferred is special, because it's often hueg it gets sharded into
			# multiple subdirectories
			mailq.set({ queue: 'deferred' }, Dir["/var/spool/postfix/deferred/*/*"].size)

			sleep 5
		rescue StandardError => ex
			$stderr.puts "Error while monitoring queue sizes: #{ex.message} (#{ex.class})"
			$stderr.puts ex.backtrace.map { |l| "  #{l}" }.join("\n")
			sleep 1
		end
	end
end

if ENV["SYSLOG_SOCKET"]
	delays   = prometheus.summary(:postfix_delivery_delays, "Distribution of time taken to deliver (or bounce) messages")

	Thread.new do
		begin
			s = Socket.new(Socket::AF_UNIX, Socket::SOCK_DGRAM, 0)
			s.bind(Socket.pack_sockaddr_un(ENV["SYSLOG_SOCKET"]))
		rescue Errno::EEXIST, Errno::EADDRINUSE
			File.unlink ENV["SYSLOG_SOCKET"]
			retry
		end

		loop do
			begin
				msg = s.recvmsg.first
				if msg =~ %r{postfix/.* delay=(\d+(\.\d+)?), .* dsn=(\d+\.\d+\.\d+), status=(\w+)}
					delay  = $1.to_f
					dsn    = $3
					status = $4

					if status == "bounced" or status == "sent"
						delays.observe({dsn: dsn, status: status}, delay)
					end
				end
			rescue StandardError => ex
				$stderr.puts "Error while receiving postfix logs: #{ex.message} (#{ex.class})"
				$stderr.puts ex.backtrace.map { |l| "  #{l}" }.join("\n")
				sleep 1
			end
		end
	end
end

app = Rack::Builder.new
app.use Rack::Deflater, if: ->(_, _, _, body) { body.any? && body[0].length > 512 }
app.use Prometheus::Middleware::Exporter
app.run ->(env) { [404, {'Content-Type' => 'text/plain'}, ['NOPE NOPE NOPE NOPE']] }

logger = Logger.new($stderr)
logger.level = Logger::INFO
logger.formatter = proc { |s, t, p, m| "WEBrick: #{m}\n" }

# This is the only way to get the Rack-mediated webrick to listen on both
# INADDR_ANY and IN6ADDR_ANY on libcs that don't support getaddrinfo("*")
# (ie musl-libc).  Setting `Host: '*'` barfs on the above-mentioned buggy(?)
# libcs, `Host: '::'` fails on newer rubies (because they use
# setsockopt(V6ONLY) by default), and with RACK_ENV at its default of
# "development", it only listens on localhost.  And even *this* only works
# on Rack 2, because before that the non-development default listen address
# was "0.0.0.0"!
ENV['RACK_ENV'] = "none"
Rack::Handler::WEBrick.run app, Port: 9154, Logger: logger, AccessLog: []