google_analytics.rb

# frozen_string_literal: true

require 'google/apis/analytics_v3'
require 'google/api_client/auth/key_utils'

module GoogleServices
  class Analytics
    attr_reader :start_date, :end_date

    def initialize(start_date: nil, end_date: nil)
      @end_date   = end_date || Time.zone.today
      @start_date = start_date || @end_date - 1.week
    end

    def execute
      result
    end

    private

    def authorization
      @authorization ||=
        Signet::OAuth2::Client.new(
          token_credential_uri: 'https://accounts.google.com/o/oauth2/token',
          audience: 'https://accounts.google.com/o/oauth2/token',
          scope: Google::Apis::AnalyticsV3::AUTH_ANALYTICS_READONLY,
          issuer: issuer,
          signing_key: signing_key
        )
    end

    def client
      @client ||=
        Google::Apis::AnalyticsV3::AnalyticsService.new.tap do |c|
          c.client_options.application_name = 'My App'
          c.client_options.application_version = '0.1'
          c.authorization = authorization
        end
    end

    def column_headers
      raw_response.column_headers
    end

    def header_keys
      column_headers.map { |header| header.name.sub('ga:', '') }
    end

    def issuer
      Settings.google_analytics.issuer
    end

    def key_file
      Rails.root.join(Settings.google_analytics.key_file).to_s
    end

    def key_secret
      Settings.google_analytics.key_secret
    end

    def profile_id
      "ga:#{Settings.google_analytics.profile_id}"
    end

    # https://github.com/google/google-api-ruby-client/blob/0.9.11/generated/google/apis/analytics_v3/service.rb#L113
    def raw_response
      @raw_response ||=
        client.get_ga_data(
          profile_id,
          start_date.strftime('%Y-%m-%d'),
          end_date.strftime('%Y-%m-%d'),
          'ga:sessions,ga:pageviews',
          dimensions: 'ga:date',
          filters: 'ga:pagePath==/',
          sort: 'ga:date'
        )
    end

    def result
      return @result if @result
      return @result = {} if column_headers.nil?
      @result =
        rows.each_with_object({}) do |row, result|
          date_key = Date.parse(row.first).strftime('%Y-%m-%d')
          result[date_key] = Hash[[header_keys[1..-1], row[1..-1]].transpose]
        end
    end

    def rows
      raw_response.rows
    end

    def signing_key
      Google::APIClient::KeyUtils.load_from_pkcs12(
        key_file,
        key_secret
      )
    end
  end
end