I am pretty excited at the release of the new Coda plug-in SDK and I have been investigating it in preparation for building a Coda integration plugin for MenuMachine 3. As an exercise, I decided to try building a small, useful plug-in. I noticed that several people on the coda-users mailing list were bemoaning the fact that there was no “smart symbol wrapping” functionality in Coda, such as exists in TextMate.
Smart symbol wrapping is a neat feature for coders. The way it works is that you select some text in the editor and then press a particular symbol key, such as a square bracket. This key press is intercepted and the selected text is automatically wrapped in a pair of square brackets. Smart symbol wrapping handles all the various types of paired symbols, such as braces, parentheses and several other types of symbols such as quote marks.
I decided to write a Coda plug-in using the Cocoa API to implement this feature, which turned out to be reasonably straightforward. The resulting plugin, Wrapster, can be downloaded here.
Please note that you must be running Mac OS 10.5 (Leopard) in order to use this plugin.
The plug-in is open source and released under the MIT License. You can find the source in the plug-in’s bundle wrapper by selecting the plug-in in the Finder and choosing “Open Package Contents” from the Finder’s contextual menu.
The plugin uses a simple property list file (WrapOptions.plist, again in the wrapper) to configure the replacement characters so you can add to or modify the replacements that ship with it, which are:
{ } [ ] ( ) < > " ' “ ” ‘ ’ `
The WrapOptions.plist file contains a comment with instructions for how to edit the file.
You can enable and disable Wrapster in the Plug-Ins menu in Coda.
In terms of implementation, the only slightly tricky thing was finding a way to detect key events before Coda gets hold of them. It turns out that the only way to do this without having access to the internals of Coda is to use an Event Tap, which allows the plugin to capture the raw events posted from the keyboard before Coda’s NSApplication instance gets a chance to process those events. This does mean that in order to use the plug-in, you need to enable “Access for assistive devices” in the Universal Access System Preferences pane, as shown below. If you don’t do this, Wrapster cannot get access to any key events.
The Universal Access Preferences pane
I hope you find this plug-in useful. It certainly has served its purpose for me, I’m pretty familiar now with the Coda SDK and what can be done with it. The guys at Panic have done a great job with the API which is simple and well thought out.
I’d love to hear your feedback about the plug-in (good and bad!).
Update: It seems that Wrapster was preventing Command-] and Command-[ from working. I’ve updated it to version 1.1 and it will now not replace the text if either the Control or Command keys are down, it will just pass the key press through to Coda.
Update 2: Justin on the coda-users mailing list pointed out that Wrapster would activate if text was selected in the page and you entered one of the special characters in the search field. I’ve fixed this now with version 1.2, Wrapster will now only activate when you are actually editing text. Get the update here.
Update 3: Thanks to Rainer Brockerhoff who alerted me in the comments to a more efficient way of handling the Quartz Event Tap that Wrapster uses to capture key events. I’ve updated Wrapster to 1.2.1 and incorporated his suggestions. There is no real need to update to this latest version unless you just absolutely must have shiny new stuff 
.
Update 4:Thanks to Will Cosgrove from Panic who pointed out that one of the Apple methods I was using to intercept key press events is buggy and can cause a hang in the window server (this means a total UI lockup, very bad!). I have modified the code to make things safer. All users should update to the new version 1.3.