Premier League Predictor: FastAPI & PostgreSQL — Chapter 10, Exercise 3
====================================================

TASK
Build the selector into a real page with at least two seasons and two
gameweeks to choose from, enter a fixture in one gameweek, switch to
the other gameweek and back, and confirm the previously-entered
fixture's own two teams are still shown as disabled after switching
back — without reloading the page.

SOLUTION

Steps to complete this exercise:

1. Ensure at least one season exists with two real gameweeks created
   (Chapter 4's POST /api/seasons/{id}/gameweeks) — gameweek 1 and
   gameweek 2, for this example.

2. Build a page combining static/selector.js, static/fixtures.js
   (updated in this chapter), and the HTML markup from both Chapter 4
   and this chapter — the season/gameweek <select> elements, the
   team-grid, and the fixture slots.

3. Load the page. initSelectors runs, populates both dropdowns,
   defaults to gameweek 1 (or whichever loads first), and
   selection-changed fires — triggering fixtures.js's own listener,
   which calls loadTeams() and seedUsedTeams(). Since no fixtures exist
   yet for gameweek 1, every team button should be enabled.

4. Click two teams into the Home/Away slots and click Add Fixture —
   confirming both teams' buttons become disabled, exactly as Chapter 4
   described.

5. Use the gameweek dropdown to switch to gameweek 2. selection-changed
   fires again with the new gameweekId; fixtures.js re-runs loadTeams()
   and seedUsedTeams() against gameweek 2's own (empty) fixture list —
   every team button should be enabled again, since gameweek 2 has no
   fixtures yet.

6. Switch the gameweek dropdown back to gameweek 1. selection-changed
   fires a third time; seedUsedTeams calls
   GET /api/gameweeks/1/fixtures again, which returns the real fixture
   entered in step 4, and disableUsedButtons() correctly grays out
   those same two teams' buttons — with no page reload involved
   anywhere in this sequence.

One-sentence confirmation: after switching away to gameweek 2 and back
to gameweek 1 entirely through the dropdown, the two teams used in the
step-4 fixture are shown disabled again, confirming seedUsedTeams
correctly re-fetches and re-applies the real server-side state on every
selection change, not just on a fresh page load.

WHY THIS WORKS AS AN ANSWER
----------------------------
It walks through the full real sequence step by step, explicitly
confirming the button-state changes at each gameweek switch (disabled
→ enabled → disabled again), and closes by directly verifying the
specific claim under test — that this all happens without any page
reload, which is exactly what distinguishes this chapter's fix from
Chapter 4's own original, reload-dependent behavior.