csv_import.rb

require 'csv'
module Extensions
  module Csv
    module ClassMethods

      # Public: import a csv file
      #
      # file_path - the filepath of the csv file
      #
      # Yields a hash of the values of the row
      #
      # Examples
      #
      #   CSV.import("/foo.csv")
      def import(file_path)
        csv_text = File.read(file_path)
        CSV.parse(csv_text, headers: true).map(&:to_hash).each do |row|
          yield(row)
        end
      end

      # Public: Build a csv file out of an array
      #
      # collection - (ActiveRelation ||Enumerable) The collection of elements to build the rows
      # columns    - (Hash) the columns's headers and methods to build the rows
      # meta       - (Hash) meta info about the file we want to generate
      #
      # Examples
      #
      #   columns = {
      #     'Name' => :name,
      #     'Number of friends' => ->(user) { |user| user.friends.single.sexy.count },
      #     'empty line' => nil
      #   }
      #   meta = { filename: 'foo' }
      #   Csv.export(collection, columns, meta)
      #   # => new file in your tmp/exports/csv/foo.csv
      #
      # Create a csv file in tmp/exports/csv/ and return the array
      def export(collection, columns, meta={})
        path = File.join(Rails.root, 'private', 'exports', 'csv')
        fname = "#{meta[:filename]}" if meta[:filename].present?
        fname ||= "#{meta[:prefix] || ""}#{Date.today.strftime("%m-%d-%Y")}-#{Time.now.to_i}.csv"
        fmode = meta[:filemode] || 'wb'

        FileUtils.mkdir_p(path, mode: 0700)

        filename = File.join(path, fname)
        CSV.open(filename, fmode) do |csv|
          if block_given?
            csv << [*columns].flatten
            collection.each do |element|
              yield(csv, element)
            end
          else
            raise 'Expecting columns to be a Hash' unless columns.is_a?(Hash)

            csv << columns.keys

            collection.each do |element|
              csv << columns.values.map do |method|
                if method.is_a?(Proc)
                  method.call(element)
                elsif method.is_a?(Symbol)
                  element.send(method)
                else
                  method
                end
              end
            end
          end

        end
        filename
      end
    end
  end
end
CSV.send(:extend, Extensions::Csv::ClassMethods)