Ruby/Rails: Determine variables from plain text to update via form - ruby-on-rails

Question

I'm creating an app where users can edit their own CSS (in SCSS syntax). That works fine, however, I eventually want these CSS files to be "programmable" so that users that don't know CSS can still edit them in a basic manner. How?
If I can mark certain things as editable, I don't have to make an impossible database schema. For example I have a scss file called style.scss:
// #type color
$header_bg_color: #555;
// #type image
$header_image: "http://someurl.com/image.jpg";
Then I can do this:
SomeParser.parse(contents of style.scss here)
This will return a hash or something similar of variables:
{:header_bg_color => {:type => "color", :value => "#555"}, :header_image => {:type => "image", :value => "http://someurl.com/image.jpg"} }
I can use the above hash to create a form which the novice user can use to change the data and submit. I believe I know how to do the GET and POST part.
What would be the best way to create / configure my own parser so that I could read the comments and extract the "variables" from this? And then, update the text file easily again?
Another possible way is something like this:
o = SomeParser.new(contents of style.scss here)
o.header_bg_color #returns "#555"
o.header_image = "http://anotherurl.com/image2.jpg" # "updates" or replaces the old header image variable with the new one
o.render # returns the text with the new values
Thanks in advance!

Answer 1

I haven't used it thoroughly, but my tests pass. I think it's enough to get the idea :) It took me several hours of study, then several more to implement it.
Btw, I did not do any optimization here. For me, it doesn't need to be quick
Look at my spec file:
require 'spec_helper'
describe StyleParser do
describe "given properly formatted input" do
it "should set and return variables properly" do
text = %{# #name Masthead Background Image
# #kind file
# #description Background image.
$mbc2: "http://someurl.com/image.jpg";
# #name Masthead BG Color
# #kind color
# #description Background color.
$mbc: #555;}
#s = StyleParser.new(text)
#s.mbc.name.should == "Masthead BG Color"
#s.mbc.kind.should == "color"
#s.mbc.description.should == "Background color."
#s.mbc.value.should == "#555"
#s.mbc2.name.should == "Masthead Background Image"
#s.mbc2.kind.should == "file"
#s.mbc2.description.should == "Background image."
#s.mbc2.value.should == %Q("http://someurl.com/image.jpg")
end
end
describe "when assigning values" do
it "should update its values" do
text = %{# #name Masthead Background Image
# #kind file
# #description Background image.
$mbc2: "http://someurl.com/image.jpg";}
#s = StyleParser.new(text)
#s.mbc2.value = %Q("Another URL")
#s.mbc2.value.should == %Q("Another URL")
rendered_text = #s.render
rendered_text.should_not match(/http:\/\/someurl\.com\/image\.jpg/)
rendered_text.should match(/\$mbc2: "Another URL";/)
#s.mbc2.value = %Q("Some third URL")
#s.mbc2.value.should == %Q("Some third URL")
rendered_text = #s.render
rendered_text.should_not match(/\$mbc2: "Another URL";/)
rendered_text.should match(/\$mbc2: "Some third URL";/)
end
it "should render the correct values" do
text_old = %{# #name Masthead Background Image
# #kind file
# #description Background image.
$mbc2: "http://someurl.com/image.jpg";}
text_new = %{# #name Masthead Background Image
# #kind file
# #description Background image.
$mbc2: "Another URL";}
#s = StyleParser.new(text_old)
#s.mbc2.value = %Q("Another URL")
#s.render.should == text_new
end
end
end
Then the following 2 files:
# Used to parse through an scss stylesheet to make editing of that stylesheet simpler
# Ex. Given a file called style.scss
#
# // #name Masthead Background Color
# // #type color
# // #description Background color of the masthead.
# $masthead_bg_color: #444;
#
# sp = StyleParser.new(contents of style.scss)
#
# # Reading
# sp.masthead_bg_color.value # returns "#444"
# sp.masthead_bg_color.name # returns "Masthead Background Color"
# sp.masthead_bg_color.type # returns "color"
# sp.masthead_bg_color.description # returns "Background color of the masthead."
#
# # Writing
# sp.masthead_bg_color.value = "#555"
# sp.render # returns all the text above except masthead_bg_color is now #555;
class StyleParser
def initialize(text)
#text = text
#variables = {}
#eol = '\n'
#context_lines = 3
#context = "((?:.*#{#eol}){#{#context_lines}})"
end
# Works this way: http://rubular.com/r/jWSYvfVrjj
# Derived from http://stackoverflow.com/questions/2760759/ruby-equivalent-to-grep-c-5-to-get-context-of-lines-around-the-match
def get_context(s)
regexp = /.*\${1}#{s}:.*;[#{#eol}]*/
#text =~ /^#{#context}(#{regexp})/
before, match = $1, $2
"#{before}#{match}"
end
def render
#variables.each do |key, var|
#text.gsub!(/^\$#{key}: .+;/, %Q($#{key}: #{var.value};))
end
#text
end
def method_missing(method_name)
if method_name.to_s =~ /[\w]+/
context = get_context(method_name)
#variables[method_name] ||= StyleVariable.new(method_name, context)
end
end
end
class StyleVariable
METADATA = %w(name kind description)
def initialize(var, text)
#var = var
#text = text
end
def method_missing(method_name)
if METADATA.include? method_name.to_s
content_of(method_name.to_s)
end
end
def value
#text.each do |string|
string =~ /^\${1}#{#var}: (.+);/
return $1 if $1
end
end
def value=(val)
#text.gsub!(/^\$#{#var}: .+;/, "$#{#var}: #{val};")
end
private
def content_of(variable)
#text.each do |string|
string =~ /^# #([\w]+[^\s]) (.+)/
return $2 if $1 == variable
end
end
end