from typing import Dict


def swim_for_a_day(life_counts: Dict[int, int]):
    """Process the shoal, decrement the life_counts:
    any that get to -1 have procreated in the last day, their offspring are
    created with 8 day life_counts, whilst they get reset to 6 days… and are
    added to the count of any fish that moved down from 7 days.
    """
    new_counts = {d - 1: p for d, p in life_counts.items()}
    if -1 in new_counts.keys():
        new_counts[8] = new_counts[-1]
        new_counts[6] = new_counts[-1] + new_counts.get(6, 0)
        del new_counts[-1]

    return new_counts