# frozen_string_literal: true

require 'socket'

module Intranet
  module System
    # Provides system statistics for a Linux system.
    class LinuxStatsProvider
      # @!visibility protected
      CPUINFO_FILE = '/proc/cpuinfo'
      # @!visibility protected
      LOADAVG_FILE = '/proc/loadavg'
      # @!visibility protected
      MEMINFO_FILE = '/proc/meminfo'
      # @!visibility protected
      SWAPS_FILE   = '/proc/swaps'

      # The system statistics refresh delay, in seconds.
      # Under Linux, it is not necessary to refresh statistics more frequently than 5s since this is
      # the refresh rate of the load average.
      STATS_REFRESH_DELAY_S = 5

      # Initializes a new Linux statistics provider.
      def initialize
        @stats = Hash[
          hostname: Socket.gethostname,
          loadavg: nil,
          cpu: { model: cpu_model, nb_cores: nb_cores },
          ram: { total: ram_available },
          swaps: {},
          partitions: {}]
        @stats_date = Time.now - STATS_REFRESH_DELAY_S
      end

      # Returns the latest system statistics. System statistics are updated if they are outdated.
      # @return [Hash] The system statistics, see {Responder#generate_page} for the structure.
      def stats
        now = Time.now
        if outdated?(now)
          @stats[:loadavg] = load_average
          @stats[:ram][:used] = ram_used
          @stats[:swaps] = swaps_usage
          @stats[:partitions] = partitions_usage
          @stats_date = now
        end
        @stats
      end

      private

      def outdated?(at)
        (at - @stats_date) >= STATS_REFRESH_DELAY_S
      end

      def cpu_model
        File.readlines(CPUINFO_FILE).grep(/model name/)[0].split(/:/)[1].strip
      end

      def nb_cores
        File.readlines(CPUINFO_FILE).grep(/^processor/).size
      end

      def load_average
        File.read(LOADAVG_FILE).split.first(3).map(&:to_f)
      end

      def ram_available
        # /proc/meminfo & /proc/swaps display Kib values despite indicating 'Kb'.
        File.readlines(MEMINFO_FILE).grep(/^MemTotal/)[0].split[1].to_i * 1024
      end

      def ram_used
        free = File.readlines(MEMINFO_FILE).grep(/^MemAvailable/)[0].split[1].to_i * 1024
        @stats[:ram][:total] - free
      end

      def swaps_usage
        File.readlines(SWAPS_FILE).grep(%r{^/}).map do |swap|
          infos = swap.split
          { infos[0] => { total: infos[2].to_i * 1024, used: infos[3].to_i * 1024 } }
        end.reduce({}, :update)
      end

      def partitions_usage
        `df -lB1`.lines.grep(%r{^/}).sort.map do |partition|
          infos = partition.split
          { infos[5] => { total: infos[1].to_i, used: infos[2].to_i } }
        end.reduce({}, :update)
      end
    end
  end
end