# frozen_string_literal: true

require 'prometheus/client/support/unicorn'

module Gitlab
  module Metrics
    module Samplers
      class RubySampler < BaseSampler
        DEFAULT_SAMPLING_INTERVAL_SECONDS = 60
        GC_REPORT_BUCKETS = [0.01, 0.05, 0.1, 0.2, 0.3, 0.5, 1].freeze

        def initialize(*)
          GC::Profiler.clear

          metrics[:process_start_time_seconds].set(labels, Time.now.to_i)

          super
        end

        def metrics
          @metrics ||= init_metrics
        end

        def with_prefix(prefix, name)
          "ruby_#{prefix}_#{name}".to_sym
        end

        def to_doc_string(name)
          name.to_s.humanize
        end

        def labels
          {}
        end

        def init_metrics
          metrics = {
            file_descriptors:                  ::Gitlab::Metrics.gauge(with_prefix(:file, :descriptors), 'File descriptors used', labels),
            process_cpu_seconds_total:         ::Gitlab::Metrics.gauge(with_prefix(:process, :cpu_seconds_total), 'Process CPU seconds total'),
            process_max_fds:                   ::Gitlab::Metrics.gauge(with_prefix(:process, :max_fds), 'Process max fds'),
            process_resident_memory_bytes:     ::Gitlab::Metrics.gauge(with_prefix(:process, :resident_memory_bytes), 'Memory used (RSS)', labels),
            process_unique_memory_bytes:       ::Gitlab::Metrics.gauge(with_prefix(:process, :unique_memory_bytes), 'Memory used (USS)', labels),
            process_proportional_memory_bytes: ::Gitlab::Metrics.gauge(with_prefix(:process, :proportional_memory_bytes), 'Memory used (PSS)', labels),
            process_start_time_seconds:        ::Gitlab::Metrics.gauge(with_prefix(:process, :start_time_seconds), 'Process start time seconds'),
            sampler_duration:                  ::Gitlab::Metrics.counter(with_prefix(:sampler, :duration_seconds_total), 'Sampler time', labels),
            gc_duration_seconds:               ::Gitlab::Metrics.histogram(with_prefix(:gc, :duration_seconds), 'GC time', labels, GC_REPORT_BUCKETS)
          }

          GC.stat.keys.each do |key|
            metrics[key] = ::Gitlab::Metrics.gauge(with_prefix(:gc_stat, key), to_doc_string(key), labels)
          end

          metrics
        end

        def sample
          start_time = System.monotonic_time

          metrics[:file_descriptors].set(labels, System.file_descriptor_count)
          metrics[:process_cpu_seconds_total].set(labels, ::Gitlab::Metrics::System.cpu_time)
          metrics[:process_max_fds].set(labels, ::Gitlab::Metrics::System.max_open_file_descriptors)
          set_memory_usage_metrics
          sample_gc

          metrics[:sampler_duration].increment(labels, System.monotonic_time - start_time)
        end

        private

        def sample_gc
          # Observe all GC samples
          sample_gc_reports.each do |report|
            metrics[:gc_duration_seconds].observe(labels, report[:GC_TIME])
          end

          # Collect generic GC stats
          GC.stat.each do |key, value|
            metrics[key].set(labels, value)
          end
        end

        def sample_gc_reports
          GC::Profiler.enable
          GC::Profiler.raw_data
        ensure
          GC::Profiler.clear
        end

        def set_memory_usage_metrics
          metrics[:process_resident_memory_bytes].set(labels, System.memory_usage_rss)

          if Gitlab::Utils.to_boolean(ENV['enable_memory_uss_pss'] || '1')
            memory_uss_pss = System.memory_usage_uss_pss
            metrics[:process_unique_memory_bytes].set(labels, memory_uss_pss[:uss])
            metrics[:process_proportional_memory_bytes].set(labels, memory_uss_pss[:pss])
          end
        end
      end
    end
  end
end