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delphirefactoring

How to refactor a Delphi unit with 10000 lines with no documentation?

I have been assigned the task to refactor a Delphi unit. Wow. 10000 lines of code, no documentation, tons of copy and paste code.

THere are many methods made with copy and paste that could be refactored, anyway I am lost in all those lines, I have the interface section where I can "find my way", but in general what do yuo suggest for tackling this kind of task?

Thanks.

Solution
    1. Get yourself a copy of Working Effectively with Legacy Code by Michael Feathers. It has all kinds of techniques for safely refactoring code to get it running under a test framework. Examples are mostly in Java and C++ but should be easy enough to figure out.
    2. Install a third-party refactoring tool (or multiple) such as CodeRush for Delphi(sadly no longer developed), Castalia or ModelMaker Code Explorer. Delphi has some refactoring support built in but in my experience it is too limited and tends to choke on very large code bases.
    3. Buy a copy of Simian. It doesn't have direct support for Object Pascal but its plain text parser works well enough. If enough people request support for Object Pascal I'm sure they'd add it. I haven't found any other code duplication detection tool as capable as Simian.

    I would also recommend bookmarking http://www.refactoring.com/catalog/ and http://www.industriallogic.com/xp/refactoring/catalog.html.

    It also wouldn't hurt to get a copy of Clean Code: A Handbook of Agile Software Craftsmanship by Robert "Uncle Bob" Martin et al. It's easy to recognize bad code. It's much harder know when you're writing good code.

    A word of caution: Focus on refactoring the code you need to work on. Its easy to start down the rabbit hole and wind up spending months refactoring code that wasn't immediately relevant to the task at hand.

    And save your self some trouble. Don't try to "fix" code and refactor it at the same time. Refactor first, then fix bugs or add that new feature. Remember, refactoring is modifying without changing external behavior.

    Resist the urge to attempt a complete rewrite. I learned the hard way that crappy code that meets the user's requirements is preferable to clean code that doesn't. Crappy code can always be incrementally improved until its something to be proud of.