How to apply additional inline style to html tags in ruby? - ruby-on-rails

Question

I have a html string. In that string I want to parse all <p> tags and apply additional inline style.
Additional Style: style="margin:0px;padding:0px;" or it could be something else
Case1:
input string: <p>some string</p>
output string: <p style="margin:0px;padding:0px;">some string</p>
Case2:
input string: <p style="text-align:right;" >some string</p>
output string: <p style="text-align:right;margin:0px;padding:0px;">some string</p>
Case3:
input string: <p align="justify">some string</p>
output string: <p style="margin:0px;padding:0px;" align="justify">some string</p>
Right now I am using regex like this
myHtmlString.gsub("<p", "<p style = \"margin:0px;padding:0px\"")
Which works fine except it removes previous styling. I am using Ruby (ROR).
I need help to tweak this a bit.

Answer 1

You can do this using Nokogiri, by setting [:style] on the relevant Nodes.
require "nokogiri"
inputs = [
'<p>some string</p>',
'<p style="text-align:right;" >some string</p>',
'<p align="justify">some string</p>'
]
inputs.each do |input|
noko = Nokogiri::HTML::fragment(input)
noko.css("p").each do |tag|
tag[:style] = (tag[:style] || "") + "margin:0px;padding:0px;"
end
puts noko.to_html
end
This will loop through all elements matching the css selector p, and set the style attribute like you want.
Output:
<p style="margin:0px;padding:0px;">some string</p>
<p style="text-align:right;margin:0px;padding:0px;">some string</p>
<p align="justify" style="margin:0px;padding:0px;">some string</p>

Answer 2

I recommend against using regex for this, as in general HTML can't be properly parsed by regex. That said, as long as your input data is consistent, regex will still work. You want to match whatever content is already in a p element's style attribute using parentheses, then insert it in the substitution string:
myHtmlString.gsub(/<p( style="(.*)")?/,
"<p style=\"#{$2};margin:0px;padding:0px\"")
Here's how the match pattern works:
/ #regex delimiter
<p #match start of p tag
( #open paren used to group, everything in this group gets saved in $1
style=" #open style attribute
(.*) #group contents of style attribute, gets saved to $2
" #close style attribute
)? #question mark makes everything in the paren group optional
/ #regex delimiter

Answer 3

I ended up doing something like this, I had to do this just before sending the email. I know this is not the best way to do it but worth sharing here. Solutions given by #sgroves and #Dobert are really good and helpful.
But I din't want to included Nokogiri, though I have picked the idea from above 2 solutions only. Thanks.
Here is my code ( I am new to ROR so nothing much fancy here, I used it in HAML block)
myString.gsub!(/<p[^>]*>/) do |match|
match1 = match
style1_arr = match1.scan(/style=".*"/)
unless style1_arr.blank?
style1 = style1_arr.first.sub("style=", "").gsub(/\"/, "").to_s
style2 = style1 + "margin:0px;padding:0px;"
match2 = match1.sub(/style=".*"/, "style=\"#{style2.to_s}\"")
else
match2 = match1.sub(/<p/, "<p style = \"margin:0px;padding:0px;\"")
end
end
Now myString will be updated string.(notice the ! after gsub)