Prevent ActionMailer to strip repeating spaces in plain message - ruby-on-rails

Question

I'm trying to have an table in text mail, so I write some helpers:
module MailerHelper
def field_width(text, width)
' ' * (width - text.length) + text
end
def cell(text, width)
output = '| ' + field_width(text, width-2) + " |\n"
output << '+-' + '-'*(width-2) + '-+'
end
end
Then in view I write it like this:
<%= cell 'Test', 10 %>
But that what I get (according to letter_opener) is:
| Test |
+----------+
As can you see, the spaces that are repeating before Test. My question is how to prevent ActionMailer (or anything else what is destroying my beautiful table) from doing that.
Mailer code:
def remind(client, invoices)
#client = client
#company = #client.company
#invoices = invoices.to_a
days_left = #invoices.first.pay_date - Date.today
message = #client.group.messages.find_by_period days_left.to_i
raise 'No messages for this invoices.' if message.nil?
#template = message.template || if days_left < 0
t 'message.before'
elsif days_left > 0
t 'message.after'
else
t 'message.today'
end
#text = liquid_parse #template
#html = markdown_parse #text
mail(:to => #client.email, :subject => t('message.title'))
end
private
def markdown_parse(text)
markdown = Redcarpet::Markdown.new Redcarpet::Render::HTML,
:autolink => true, :space_after_headers => true
markdown.render text
end
def liquid_parse(text)
renderer = Liquid::Template.parse text
renderer.render 'company' => #company, 'invoice' => #invoice, 'client' => #client
end

Answer 1

I've found bug. It was caused by Premailer what I use to inline CSS in HTML part.
class InlineCSSInterceptor
def self.delivering_email(message)
#message.text_part.body = Premailer.new(message.text_part.body.to_s, with_html_string: true).to_plain_text # this is line causing the problem.
message.html_part.body = Premailer.new(message.html_part.body.to_s, with_html_string: true).to_inline_css
end
end
Mailer.register_interceptor InlineCSSInterceptor