Purchases Checker

checker_test.rb

require 'test/unit'
require 'digest'
require 'date'

class PurchasesChecker
  attr_reader :authorizations

  def initialize
    @authorizations = []
    @purchases_idx = {}
  end

  def authorize!(customer, store, requested_at, amount)
    body = "#{customer} #{store}"
    md5 = Digest::MD5.hexdigest(body)
    timestamp = requested_at.to_time.to_i

    return if duplicate?(md5, timestamp)

    @authorizations.append({
      customer: customer,
      store: store,
      requested_at: requested_at.to_time,
      amount: amount
    })

    @purchases_idx[md5] = timestamp
  end

  def duplicate?(md5, timestamp)
    return false unless @purchases_idx[md5]

    timestamp - @purchases_idx[md5] < 900
  end
end

class AuthorizationsTest < Test::Unit::TestCase
  def test_idempotence
    checker = PurchasesChecker.new

    checker.authorize!('leandro', 'cafe sao paulo', DateTime.new(2022, 12, 20, 06, 00), 8)
    checker.authorize!('john', 'cafe sao paulo', DateTime.new(2022, 12, 20, 06, 00), 12)
    checker.authorize!('leandro', 'mesbla', DateTime.new(2022, 12, 20, 06, 05), 120)
    checker.authorize!('leandro', 'cafe sao paulo', DateTime.new(2022, 12, 20, 06, 31), 10)
    checker.authorize!('mary', 'mesbla', DateTime.new(2022, 12, 20, 10, 30), 100)
    checker.authorize!('mary', 'mesbla', DateTime.new(2022, 12, 20, 10, 32), 150)
    checker.authorize!('mary', 'mesbla', DateTime.new(2022, 12, 20, 10, 52), 100)

    expected = [
      { customer: 'leandro', store: 'cafe sao paulo', requested_at: DateTime.new(2022, 12, 20, 06, 00).to_time, amount: 8 },
      { customer: 'john', store: 'cafe sao paulo', requested_at: DateTime.new(2022, 12, 20, 06, 00).to_time, amount: 12 },
      { customer: 'leandro', store: 'mesbla', requested_at: DateTime.new(2022, 12, 20, 06, 05).to_time, amount: 120 },
      { customer: 'leandro', store: 'cafe sao paulo', requested_at: DateTime.new(2022, 12, 20, 06, 31).to_time, amount: 10 },
      { customer: 'mary', store: 'mesbla', requested_at: DateTime.new(2022, 12, 20, 10, 30).to_time, amount: 100 },
      { customer: 'mary', store: 'mesbla', requested_at: DateTime.new(2022, 12, 20, 10, 52).to_time, amount: 100 }
    ]

    assert_equal expected, checker.authorizations
  end
end