Design Patterns by PHP and JavaScript examples

After having your project fully tested, deployed and running, it seems the application architecture is pretty good enough. All the requirements met and everybody is happy. But then as it happens, the requirements change and you, all of sudden, find yourself in the time of troubles. It comes out that some modules easier to hack than to modify. Change of other ones brings endless changes in a cascade of dependent modules. Or you change one module and whole the application starts to collapse like a house of cards. And, of course, you find out that you can’t reuse already written modules for the new tasks, because the encapsulation of the desired parts would take too much risk and work. Robert C. Martin was very accurate naming those symptoms of rotting design as Viscosity, Rigidity, Fragility and Immobility