Request deduplication with idempotency keys

                  module Idempotency
  extend ActiveSupport::Concern

  included do
    before_action :check_idempotency_key, only: [:create, :update]
    after_action :store_idempotent_response, only: [:create, :update]
  end

  private

  def check_idempotency_key
    return unless idempotency_key.present?

    cached = Rails.cache.read(idempotency_cache_key)
    return unless cached

    request_hash = compute_request_hash

    if cached[:request_hash] != request_hash
      render json: {
        error: 'IDEMPOTENCY_KEY_MISMATCH',
        message: 'Idempotency key was used with different request body'
      }, status: :conflict
      return
    end

    # Return cached response
    render json: cached[:response_body], status: cached[:status]
  end

  def store_idempotent_response
    return unless idempotency_key.present?
    return unless response.successful?

    Rails.cache.write(
      idempotency_cache_key,
      {
        request_hash: compute_request_hash,
        response_body: JSON.parse(response.body),
        status: response.status
      },
      expires_in: 24.hours
    )
  end

  def idempotency_key
    @idempotency_key ||= request.headers['Idempotency-Key']
  end

  def idempotency_cache_key
    "idempotency:#{idempotency_key}"
  end

  def compute_request_hash
    Digest::SHA256.hexdigest(request.raw_post)
  end
end