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I joined my current company recently, and I am on probation. The code I have inherited is brittle and has performance issues. I am not familiar with the system yet, but my manager told me to refactor this code, document it and set a hard deadline to do the first release by end of the next month.
I started working on this project last week. For a small refactoring in a simple component, I had to do many changes at various places. I fear that if I do a major refactoring, I would end up coding the project from scratch, and I will miss the deadline for sure. If I avoid doing this, the project is doomed to fail as code can break in multiple ways.
My manager made me sign a document that says I am supposed to complete all the tasks. Being nervous and confused, I signed the document. Now I fear that if I cannot complete the tasks, the whole blame will be on me. The project has already failed three times, and my manager is damned serious to make it work this time.
How should I professionally communicate to my manager that the issues with the code may cause me to miss the deadline?