require 'aws-sdk-ssm'
require 'timeout'

module Docker
  module Pipeline
    class ExcessiveThrottlingError < StandardError; end

    class SsmParameters
      CLIENT = Aws::SSM::Client.new

      def self.at(path)
        new(path).to_h
      end

      def to_h
        env
      end

      private

      attr_reader :path
      attr_reader :env

      def initialize(path)
        @path = path
        @env = {}
        @pages = 0

        next_token = nil

        Timeout::timeout(60) do
          loop do
            next_token = read_page next_page(next_token)
            break unless next_token
          end
        end
      end

      def read_page(page)
        page.parameters.each do |parameter|
          key = parameter.name.split('/').last
          value = parameter.value
          env[key] = value
        end

        page.next_token
      end

      def next_page(next_token)
        @pages += 1

        with_exponential_backoff do
          CLIENT.get_parameters_by_path(
            path: path,
            with_decryption: true,
            next_token: next_token
          )
        end
      end

      def with_exponential_backoff(max_attempts = 10, backoff = 0.5)
        max_attempts.times do |try|
          begin
            return yield
          rescue Aws::SSM::Errors::ThrottlingException
            raise ExcessiveThrottlingError unless try < (max_attempts - 1)
            puts 'Backing off and retrying due to API throttling'
            sleep (try ** backoff) + (rand * 1.5)
          end
        end
      end
    end
  end
end