Is there a dynamic way in BigQuery to select/create columns with pattern?

Question

Not sure how to sure how to best phrase it, but essentially I need ~50 columns x 12 weeks in BigQuery and was hoping there was a way to do it more efficiently using some sort of logic or function.

I can generate the script in Python, but the end output itself is long and unwieldy. Is there a cleaner way to do it within BigQuery itself?

Example code:

select id,
  sum(case when first_week_flag then visit else 0 end) as sum_visit_first_week,
  sum(case when second_week_flag then visit else 0 end) as sum_visit_second_week,
  ... for 12 weeks,
  avg(case when first_week_flag then gap else 0 end) as avg_gap_first_week,
  avg(case when second_week_flag then gap else 0 end) as avg_gap_second_week,
  ... for 12 weeks,
  etc. for 50 columns
from table
group by id

Potential for simplification:

select id,
  sum(case when {WEEK}_flag then visit else 0 end) as sum_visit_{WEEK},
  avg(case when {WEEK}_flag then gap else 0 end) as avg_gap_{WEEk},
  etc. for 50 columns
from table
group by id

Can anyone point me in the right direction of what to search for? Thanks!