Validate Deadline Eligibility Updates

MediumPython

Problem

Scale.ai task workflows may allow an annotator task to receive a later deadline, but only while the task remains eligible for modification. Implement update_deadline to validate all rules and return the updated task when the change is allowed.

A task is eligible only when:

Its status is exactly "pending".
The current time is strictly before its existing deadline.
The current time is no more than modification_window seconds after created_at.
The proposed new_deadline is strictly later than both the current time and the existing deadline.
The proposed deadline does not exceed created_at + max_lifetime.

If every rule passes, return a copy of the task with its deadline replaced by new_deadline. Otherwise, return None. Do not modify the input dictionary when the update is rejected.

Formal Specification

Input is a dictionary containing integer Unix timestamps for created_at, deadline, modification_window, and max_lifetime, plus a string status. The function also receives integer new_deadline and now values. Return a dictionary on success or None on failure.

Constraints

Timestamps are integers from 0 through 10^9.
0 <= created_at < deadline <= created_at + max_lifetime.
1 <= modification_window, max_lifetime <= 10^9.
status is a non-empty string.
The input task dictionary contains all required keys.

Function Signature

def update_deadline(task, new_deadline, now):

A task is eligible only when:

Its status is exactly "pending".
The current time is strictly before its existing deadline.
The current time is no more than modification_window seconds after created_at.
The proposed new_deadline is strictly later than both the current time and the existing deadline.
The proposed deadline does not exceed created_at + max_lifetime.

If every rule passes, return a copy of the task with its deadline replaced by new_deadline. Otherwise, return None. Do not modify the input dictionary when the update is rejected.