URI Replacement

require 'URI'

# string to be parsed
rawString = 'This is the http://sameurl.com and a http://sameurl.com and yet another http://sameurl.com. Regardless, here\'s https://google.com and how much the Amazon Fire (http://arstechnica.com/gadgets/2014/04/amazon-fire-tv-misses-the-same-marks-as-ouya-other-media-boxes/) sucks'

puts "-- ORIGINAL --\n#{rawString}"

# extract an array of URLs from rawString
urls = URI.extract(rawString)

# with each URL, construct a hash {location,length,replacementString} and add it to replacements
replacements = Array.new
workingString = String.new(str=rawString)
urls.each { |url|
  location = workingString.index(url)
  replacements.push({'location' => location, 'length' => url.length, 'replacementString' => "<a href=\"#{url}\">#{url}</a>"})
  # replace this string in the workingString with XXXXXXX's of the same length as the original detected URL so that if subsequent URLs are exactly the same, they won't be found again
  xxxString = String.new
  for charPos in 0..url.length-1
    xxxString << 'X'
  end
  workingString[location..(location+url.length)-1] = xxxString
  }

# each time we replace a string in rawString, the length of rawString will change, and all locations we found in the last step past the first one will be wrong. We use the difference in length between each original URL and each replacementString to adjust the locations of the subsequent replacements
replacements.each_with_index { |replacement,index|
  
  # don't have to adjust anything in the first replacement (index 0)
  if index > 0
    # get the difference in length from previous replacement
    previousReplacement = replacements[index-1]
    diffLength = previousReplacement['replacementString'].length - previousReplacement['length']
    # adjust the current and all subsequent replacement locations
    remainder = replacements[index..replacements.length-1]
    remainder.each { |remainderReplacement|
      remainderReplacement['location'] = remainderReplacement['location'] + diffLength
      }
  end
  }
  
# perform each replacement
modifiedString = String.new(str=rawString)
replacements.each { |replacement|
  theStart = replacement['location']
  theEnd = (theStart + replacement['length']) - 1
  modifiedString[theStart..theEnd] = replacement['replacementString']
  }

puts "-- MODIFIED --\n#{modifiedString}"