This looks incredibly fragile and difficult to improve in the future. Some suggestions:

• Make the pattern match *all* markdown links. The exceptions being baked into the pattern make it incredibly difficult to decipher.
• Discard links you don't care about post-pattern-match (such as those starting with anchors #)
• Ignore ALL links that specify any protocol (://). While http(s) is common, they aren't the only ones.