Debouncing API payloads

example.rb

class TalksController
  def create
    talk = Talk.new(talk_params)

    # handle creation
  end

  def update
    @talk.update_attributes(talk_params)
     # handle update
  end
end


class Talk < ApplicationRecord
  before_save :send_create_to_external_service, on: :create
  before_save :send_update_to_external_service, on: :update

  private

  def send_create_to_external_service
    SendTalkToApiService.new(self, changes, "create").call
  end

  def send_update_to_external_service
    SendTalkToApiService.new(self, changes, "update").call
  end
end

# NOTE: It might be worth breaking this out into two services, one for
# creation, one for updating, as the guard logic and whitelists might be
# different.

class SendTalkToApiService
  WHITELISTED_ATTRIBUTES = %w(foo bar baz).freeze
  # NOTE: This might need to be tuned
  DEBOUNCE_SECONDS = 10

  def initialize(talk, changes, action)
    @talk, @changes, @action = talk, changes, action
  end

  def call
    return unless changes_in_whitelist?
    return if payload_already_fired?
    ApiPayload.create(payload_hash: payload_hash, action: action)
    # fire update
  end

  private
  attr_accessor :talk, :changes, :action

  def changes_in_whitelist?
    talk.keys & WHITELISTED_ATTRIBUTES
  end

  def debounce_range
    (DEBOUNCE_SECONDS.seconds.ago..Time.now)
  end

  def payload_already_fired?
    ApiPayload.where(payload_hash: payload_digest, created_at: debounce_range, action: action).present?
  end

  def payload_digest
    Digest::SHA256.digest(changes.sort.to_yaml)
  end
end

class ApiPayload < ApplicationRecord
  # schema notes:
  #
  #  compound index payload_hash, created_at and action
  #  NOTE: we need to sort, serialize and hash the payload above as a
  #  workaround to MySQL not supporting indexable JSON columns. I'm not sure if
  #  Postgres' indexable JSONB column type allows for indexing the whole
  #  document. Sorting also might bite us here.
  #
end