Export User Data As CSV and Send An Email with Ruby on Rails

# frozen_string_literal: true

# app/services/export_services/export_transaction_service.rb
# Example:
#   ExportServices::ExportTransactionService.new({ user: User.last}).call
#   ExportServices::ExportTransactionService.new({ user: User.last, from_date: '2022-01-01', to_date: '2022-09-01'}).call
module ExportServices
  # ExportTransactionService
  class ExportTransactionService
    # initialize the service with user, from_date and to_date and setting transactions accordingly
    def initialize(params) # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
      @user = params[:user]
      @from_date = params[:from_date] ? params[:from_date].to_date : 10.years.ago # -Infinity
      @to_date = params[:to_date] ? params[:to_date].to_date : Time.zone.now
      @transactions = @user.transactions.where(transaction_date: @from_date..@to_date)
                           .joins(:account, :category).kept.order(transaction_date: :desc)
    end

    # service work when call method is called
    def call
      return if @transactions.length.zero?

      generate_csv_file
      # export_to_storage
      send_email
    end

    # This method creates a temp CSV file and fills data based on initialized transactions
    def generate_csv_file # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
      @tempfile = Tempfile.new(["export_#{Time.zone.now.strftime('%Y%m%d%H%M%S')}_#{@user.id}", '.csv']).tap do |file|
        CSV.open(file, 'wb') do |csv|
          # CSV Header Row
          csv << %w[Date Description Type Amount Currency Category Account]

          # CSV Rows, each row representing a transaction
          @transactions.find_each do |transaction|
            csv << [
              transaction.transaction_date.to_date.to_s,
              transaction.description,
              transaction.transaction_type == 'income' ? 'Income' : 'Expense',
              transaction.value.to_f.round(2),
              transaction.account.currency.code,
              transaction.category.name,
              transaction.account.name,
            ]
          end
        end
      end
    end

    # Thios method adds the tempfile to ActiveStorage and hence to S3 service if attached
    # I have attached s3 to production environment
    # returns url of the uploaded CSV File
    def export_to_storage # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
      # Document Model `has_attached_file :doc` and `user has_many :documents` and `document belongs_to :user`
      document = Document.new(user: @user)
      document.doc.attach(
        io: @tempfile,
        filename: @tempfile.path.split('/').last,
        content_type: 'application/csv'
      )
      document.save!
      @file_url = if Rails.env.production?
                    # returns s3 public url
                    Rails.application.routes.url_helpers.rails_public_blob_url(@document.doc)
                  else
                    # return local url
                    Rails.application.routes.url_helpers.rails_blob_url(@document.doc)
                  end
    end

    # This method sends email with temp file attached
    # https://gist.github.com/sulmanweb/eab697301cf8209572c5a95af6543b3a
    # https://sulmanweb.com/send-emails-using-sendgrid-sdk-for-ruby-on-rails-using-dynamic-sendgrid-email-templates/
    def send_email # rubocop:disable Metrics/MethodLength
      EmailJob.new.perform(
        @user.id,
        { name: @user.name },
        ENV.fetch('EXPORT_TEMPLATE', nil),
        [
          {
            file: @tempfile.path,
            type: 'application/csv',
            name: @tempfile.path.split('/').last,
            content_id: 'export_file'
          }
        ]
      )
    end
  end
end

ExportServices::ExportTransactionService.new({ user: User.last}).call

ExportServices::ExportTransactionService.new({ user: User.last, from_date: '2022-01-01', to_date: '2022-09-01'}).call