Using Prawn in your Rails App to download and attach the pdf in your email

mime_types.rb

# This file exists in your initializers folder
# Insert this line

Mime::Type.register "application/pdf", :pdf

pdf_generator.rb

# Create a folder named in the app/pdfs and create this file.

class PdfGenerator < Prawn::Document
  def initialize
    # Default state of the pdf would state to this code
    super
    # Uncomment the below line if you wish for some custom rearrangements in the default state. like for ex
    # super(top_margin: 100)  
  end
  
  # Now start defining methods and perform operations for your PDF.
  def header
    move_down 30  # This will move down the start of pdf by 30 pixels.
    text "My Header" , :style => :bold , :size => 14 # obviously, the size and style can be customized.
    text "#{Date.today}" , :style => :bold , :size => 5 # You can use Interpolation and rails as is, obviously.
  end
  
  def design_a_table( table_header , table_data )
    @header = table_header
    @data   = table_data
    
    # I will try and show as many operations for a table as i can.
    # 1st method to draw a table.
    table [ [ @header ] , [ @data ] ]
    
    # another method is : 
    # create a array object which has to be two dimensional no matter what.
    data_to_draw_a_table = [ [ @header ] , [ @data ] ]
    table( data_to_draw_a_table )
   
    # Some beautiful customization you can do before you call table to draw a table is 
    data.each do |data|
      table(data) do
        column(0).background_color = "b7b5b0"
        column(0).width = 120
        column(1).width = 180
      end
    end
  end

  # I used this method to draw a table as well. Here you can see how you can set width of a particular column. Dont worry the Height would be set automatically.
  # In order to DRY my code , i have a defined a method for width_of_table_columns.

  def tasks_table( tasks )
    move_down 30
    @tasks = tasks
    table [["#" , "Title" , "Rate" , "Hours" , "Cost" ]] , :column_widths => width_of_table_columns , :row_colors => ["b7b5b0"]

    @tasks.each_with_index do | task , index |
      table [[index + 1 , task.title , task.price_per_hour , task.hours_taken_to_complete_task , task.cost_by_hour_basis]] , :column_widths => width_of_table_columns
  end 
  
  def width_of_table_columns
    width = { 0 => 35 , 1 => 300 , 2=> 40 , 3 => 39 , 4 => 60 }
  end
end

pdf_generator_in_lib.rb

# This file is a library and thus it would be in lib/ folder of your rails app

module PdfGenerator
  extends ActiveSupport::Concern
  module ClassMethods
  end
  
  module InstanceMethods
    def pdf_generator( download = nil )
      pdf = InvoicePdf.new
      pdf.header
      pdf.design_a_table( "header" , "corresponding_data")
      pdf.tasks_table( "tasks" ) 
      
      # To download this pdf, write this down
      # Basically send_data would download the file in obviously a pdf format.
      if download
        send_data pdf.render , :filename => file_name_here , :type => "application/pdf"
      else
        pdf.render , :filename => file_name_here , :type => "application/pdf"
      end
    end
  end  
end

SomeController.rb

require 'pdf_generator'
class TasksController < ApplicationController
  include PdfGenerator
  def some_action
    pdf_generator( download = true )
  end
end

SomeMailer.rb

# A sample code of how to send the generated pdf as an attachment to your email.

require "pdf_generator"
class InvoiceMailer < ActionMailer::Base

  include PdfGenerator

  def your_mailer_method

   # mail.attachments api is the new way to do it since Rails 3.1, i guess.

    mail.attachments["invoice.pdf"] = {:mime_type => "application/pdf" , :content => pdf_generator }

   # mailing configurations
    mail(
      :to => "to_email@abc.com",
      :from => "from_email@abc.com",
      :subject => "the pdf has been attached with this email"
      )
  end
end

Thanks for taking the time man.