volume.rb

require 'json'
require 'open-uri'
require 'open3'

STREAMS_URL = 'https://mixlr-codetest.herokuapp.com/stations/netil-radio/streams'

def fetch_streams(url = STREAMS_URL)
  body = URI.open(url).read
  json = JSON.parse(body)
  json.dig('data', 'attributes', 'streams')
end

def analyze_stream_volume(stream_url)
  # ffmpeg outputs all the relevant information to stderr, nothing
  # interesting on stdout
  _, stderr, process_info = Open3.capture3('ffmpeg', '-t', '3', '-i', stream_url, '-af', 'volumedetect', '-f', 'null', '/dev/null')

  mean_volume = stderr.match(/mean_volume: (.*) dB/)[1].to_f
  max_volume = stderr.match(/max_volume: (.*) dB/)[1].to_f

  {mean_volume:, max_volume:}
end

def run!
  fetch_streams.each do |stream_name, stream_url|
    volumes = analyze_stream_volume(stream_url)
    puts "#{stream_name} - mean volume: #{volumes[:mean_volume]} dB, max volume: #{volumes[:max_volume]} dB"
  end
end

# do not run the script if it's been required by other scripts
run! if __FILE__ == $0

volume_test.rb

require 'rubygems'
require 'bundler/setup'
require 'webmock/minitest'
require 'minitest/autorun'
require_relative '../volume'

class VolumeTest < Minitest::Test
  def test_fetch_streams_works_properly
    body = {
      data: {
        attributes: {
          streams: {
            first: "first_stream_url",
            second: "second_stream_url"
          }
        }
      }
    }

    stub_request(:get, 'https://mixlr-codetest.herokuapp.com/stations/netil-radio/streams')
      .to_return(body: JSON.generate(body))

    streams = fetch_streams
    assert_equal 2, streams.size
    assert_equal "first_stream_url", streams["first"]
    assert_equal "second_stream_url", streams["second"]
  end

  def test_analyze_stream_volume_works_properly
    volumes = analyze_stream_volume('test/fixtures/test.mp3')

    assert_equal -23.1, volumes[:mean_volume]
    assert_equal -7.2, volumes[:max_volume]
  end
end