#! /usr/bin/env ruby
#
#   check-es-heap
#
# DESCRIPTION:
#   This plugin checks ElasticSearch's Java heap usage using its API.
#
# OUTPUT:
#   plain text
#
# PLATFORMS:
#   Linux
#
# DEPENDENCIES:
#   gem: sensu-plugin
#   gem: rest-client
#   gem: json
#
# USAGE:
#   example commands
#
# NOTES:
#
# LICENSE:
#  Copyright 2012 Sonian, Inc <chefs@sonian.net>
#   Released under the same terms as Sensu (the MIT license); see LICENSE
#   for details.
#

require 'sensu-plugin/check/cli'
require 'rest-client'
require 'json'

#
# ES Heap
#
class ESHeap < Sensu::Plugin::Check::CLI
  option :host,
         description: 'Elasticsearch host',
         short: '-h HOST',
         long: '--host HOST',
         default: 'localhost'

  option :port,
         description: 'Elasticsearch port',
         short: '-p PORT',
         long: '--port PORT',
         proc: proc(&:to_i),
         default: 9200

  option :warn,
         short: '-w N',
         long: '--warn N',
         description: 'Heap used in bytes WARNING threshold',
         proc: proc(&:to_i),
         default: 0

  option :timeout,
         description: 'Sets the connection timeout for REST client',
         short: '-t SECS',
         long: '--timeout SECS',
         proc: proc(&:to_i),
         default: 30

  option :crit,
         short: '-c N',
         long: '--crit N',
         description: 'Heap used in bytes CRITICAL threshold',
         proc: proc(&:to_i),
         default: 0

  option :percentage,
         short: '-P',
         long: '--percentage',
         description: 'Use the WARNING and CRITICAL threshold numbers as percentage indicators of the total heap available',
         default: false

  def acquire_es_version
    info = acquire_es_resource('/')
    info['version']['number']
  end

  def acquire_es_resource(resource)
    r = RestClient::Resource.new("http://#{config[:host]}:#{config[:port]}/#{resource}", timeout: config[:timeout])
    JSON.parse(r.get)
  rescue Errno::ECONNREFUSED
    warning 'Connection refused'
  rescue RestClient::RequestTimeout
    warning 'Connection timed out'
  rescue JSON::ParserError
    warning 'Elasticsearch API returned invalid JSON'
  end

  def acquire_heap_data(return_max = false) # rubocop:disable all
    if Gem::Version.new(acquire_es_version) >= Gem::Version.new('1.0.0')
      stats = acquire_es_resource('_nodes/_local/stats?jvm=true')
      node = stats['nodes'].keys.first
    else
      stats = acquire_es_resource('_cluster/nodes/_local/stats?jvm=true')
      node = stats['nodes'].keys.first
    end
    begin
      if return_max
        return stats['nodes'][node]['jvm']['mem']['heap_used_in_bytes'], stats['nodes'][node]['jvm']['mem']['heap_max_in_bytes']
      else
        stats['nodes'][node]['jvm']['mem']['heap_used_in_bytes']
      end
    rescue
      warning 'Failed to obtain heap used in bytes'
    end
  end

  def run # rubocop:disable all
    if config[:percentage]
      heap_used, heap_max = acquire_heap_data(true)
      heap_used_ratio = ((100 * heap_used) / heap_max).to_i
      message "Heap used in bytes #{heap_used} (#{heap_used_ratio}% full)"
      if heap_used_ratio >= config[:crit]
        critical
      elsif heap_used_ratio >= config[:warn]
        warning
      else
        ok
      end
    else
      heap_used = acquire_heap_data(false)
      message "Heap used in bytes #{heap_used}"
      if heap_used >= config[:crit]
        critical
      elsif heap_used >= config[:warn]
        warning
      else
        ok
      end
    end
  end
end