class Collector
	attr_reader :journal, :prometheus, :settings

	class PrefixProxy
		attr_reader :prometheus, :prefix
		def initialize prometheus, prefix
			@prometheus, @prefix = prometheus, prefix.dup.freeze
		end

		def counter name, **options
			@prometheus.counter :"#{prefix}_#{name}", **options
		end

		def gauge name, **options
			@prometheus.gauge :"#{prefix}_#{name}", **options
		end

		def histogram name, **options
			@prometheus.histogram :"#{prefix}_#{name}", **options
		end

		def summary name, **options
			@prometheus.summary :"#{prefix}_#{name}", **options
		end

		def prefix_proxy prefix
			PrefixProxy.new @prometheus, "#{@prefix}_#{prefix}"
		end
	end

	def self.start prometheus: nil, journal: nil
		self.new( prometheus: prometheus, journal: journal).start
	end

	def initialize prometheus: nil, journal: nil, settings: nil
		@settings = settings
		@journal = journal || Systemd::Journal.new( flags: Systemd::Journal::Flags::SYSTEM_ONLY)
		@prometheus = prometheus || Prometheus::Client.registry
		def @prometheus.prefix_proxy prefix
			PrefixProxy.new self, prefix
		end
		@store = {}

		@errors     = @prometheus.counter :postfix_exporter_errors_total, docstring: 'Count internal errors/exceptions'
		@dovecot    = Dovecot.new @store, PrefixProxy.new( @prometheus, :dovecot)
		@postfix    = Postfix.new @store, PrefixProxy.new( @prometheus, :postfix)
	end

	def run
		@journal.seek :tail
		@journal.move_previous
		@journal.watch do |entry|
			case entry._systemd_unit
			when 'dovecot.service'
				@dovecot.collect entry
			when 'postfix@-.service'
				@postfix.collect entry
			else
				if @settings.nil? or @settings.development?
					STDERR.puts "# unit: #{entry._systemd_unit}: #{entry.syslog_identifier} #{entry.message}"
				end
			end
		end
	end

	def start
		Thread.abort_on_exception = true
		Thread.new do
			begin
				run
			rescue SystemExit, Interrupt
				raise
			rescue Object
				@errors.increment
				STDERR.puts "#$! (#{$!.class})", $!.backtrace.map {|x| "  in #{x}"}
				retry
			end
		end
	end
end

require_relative 'collector/postfix'
require_relative 'collector/dovecot'