Undo manager for Text Editor

Source code consists of a set of interfaces which form the model of an undo-manager for a text editor.

The exercise consists in implementing the interfaces UndoManager and UndoManagerFactory, including unit tests.

The other interfaces should be used "as is" - i.e. the implementation of UndoManager and UndoManagerFactory should not rely on any specific implementation of the other interfaces.

You are free to use third-party software libraries in your solution if you want.

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Solution description

Implemented UndoManager and UndoManagerFactory interfaces.

Created TextEditorModule which is the root module and in real application would consist of all submodules & configuration existing in the application.

Tested solution with unit tests.

Questions & Answers:

1. Why I chose CircularFifoQueue instead of Queue and Deque?
   • Queue, depending on implementation, could be faster than Deque as it is just "one-sided" and CircularFifoQueue perfectly fits DefaultUndoManager#registerChange requirements - when the queue is full, oldest element should be replaced.
2. Why Change and Document are moved to separate packages?
   • I believe that Change and Document are logically separate from UndoManager and can exist without it
3. Why use Guice Dependency Injection framework?
   • Because it is lightweight and helps to separate logical modules and that way introduces loose coupling
   • Easy to switch implementations
4. Why there are no comments in the code?
   • I believe that code should be self explanatory without the need of comments explaining what certain thing does. I usually try to write code in the way that a person without IT knowledge could read it and understand the concept of what is happening.

Possible improvements:

1. Clean up DefaultUndoManager by splitting Undo and Redo functionality into two different classes so each class does just one thing, however they would still be quite tightly coupled because of Undo<~>Redo connection.
2. Split functionality in the way that can help test values of Undo and Redo actions easily.