How to call image_tag and number_to_currency in dynamcially created html from ERB

I am trying to create an html file from ERB, as I want to save a copy of invoice of a very complicated calculation. My ERB template is using many different calculation and using heavily number_to_currency and image_tag

Following is my action method

def save_invoice
    erb_file = 'app/views/orders/invoice.html.erb'
    html_file = File.basename(erb_file, '.erb')
    erb_str = File.read(erb_file)
    renderer = ERB.new(erb_str)
    @order = Order.find(params[:id]).to_i
    result = renderer.result(binding)

      File.open(html_file, 'w') do |f|
        f.write(result)
      end
    end

My invoice.html.erb

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Invoice</title>
 </head>
<body>
<header>
    <%= image_tag 'logo_new.png', width: '110',height: '100' %>
</header>
<h1>Invoice # <%= @order.id %></h1>
<p>Client : <%= @order.user.first_name %>, <%= @order.user.last_name %></p>
<p>Amount : <%= number_to_currency(@order.totals) %></p>

It is making html file but if I remove all image_tag (viewer helper) and number_to_currency function. So how can I use those function in my ERB. I understand it is because I am creating ERB string I really don't understand this code much than a reference which is working when I remove all those functions. Please suggest me what should I include in method. I put here very condense codes, actually codes are a lot mess with thousands lines.

Solution

I just realised that I have used bindings, so why not call view helper as an object and use its function inside my view. that way it will automatically send helper to ERB file. I added following line on top after def save_invoice in my save_invoice method

    @views_helper = ActionView::Base.new

Now in my erb file I have replace my image_tag with adding this object like following

<%= @views_helper.image_tag 'logo_new.png', width: '110',height: '100' %>

and for my number_to_currency I did same thing


<p>Amount : <%= @views_helper.number_to_currency(@order.totals) %></p>

And it resolve my issue, currently working fine, I am sure I am making full object and then forwarding it to view may have consequences of heavy request but that is working fine for me.

As for explanation I create object and binding will show all local variables in my ERB file so this object will be also accessible and do job.