2048 · glm-4.7-flash

Build the game. Let me write a solid 2048 implementation with animations using absolutely positioned tiles keyed by tile objects (so movement animates smoothly), input locking during animation, etc.

Design: board container 4x4 background cells; tiles as absolutely positioned divs with transform transitions. Keep tile objects with id, value, row, col. On move, compute new positions/merges, apply transitions, then after animation remove merged tiles and update values. Input lock ~150ms.

Let me write it.

Now verify in browser. There's a subtle bug: in the merge branch, I check `!next.mergedFrom && !tile.mergedFrom` — tile.mergedFrom is always null at that point (fresh tiles never merged), fine. But there's an issue: after merging, the "next" tile has value doubled but grid still contains it; when traversal continues to next cell, could we merge a third tile into it? next.mergedFrom is set, so no. Good.

Another issue: farthest-position search — when I find grid[tr][tc] non-null, I set nr=tr, nc=tc, break. That's "next tile position". Then `next = grid[nr+dir.dr][nc+dir.dc]`... wait, I set nr to the occupied cell, then compute next as grid[nr+dir.dr] which would be one further. Let me re-check.

The loop: nr,nc start at r,c. Each iteration: tr = nr+dr, tc = nc+dc. If out of bounds break. If grid[tr][tc] occupied: nr=tr; nc=tc; break. Else nr=tr, nc=tc, continue.

So when we break due to occupied cell, nr,nc = the occupied cell itself. That's wrong for sliding (tile should slide to the cell before it), and then `next` computed as grid[nr+dr] would be beyond the occupied cell.

Hmm, actually let me re-derive: farthest empty position is the last empty cell before hitting wall or tile. When we break at occupied cell, nr was the previous empty cell... no wait, we set nr=tr (the occupied cell) before breaking. Bug!

Let me trace [2,2,_,_] moving left: r=0,c=3 tile at col 3. Loop: tr=nc-1=2, empty → nr=2. Next iter: tr=1, empty → nr=1. Next: tr=0, grid[0][0]=2 occupied → nr=0, break. Then next = grid[nr+dc]=grid[0][-1]... within() false → next=null. Then slide: nr(0)≠c(3), so tile moves to (0,0) — overwriting grid[0][0] which we set to null first... grid[r][c]=null then grid[0][0]=tile. But grid[0][0] had the other 2! We lose it.

Definitely broken. Fix: track occupied separately. Standard approach: find farthest empty; then next = cell beyond farthest. Rewrite:

```js
let nr = r, nc = c;
let or_ = r, oc = c; // occupied found
while (true) {
  const tr = nr + dir.dr, tc = nc + dir.dc;
  if (!within(tr, tc)) break;
  if (grid[tr][tc]) { or_ = tr; oc = tc; break; }
  nr = tr; nc = tc;
}
const next = (or_ !== r || oc !== c) ? grid[or_][oc] : null;
```

Hmm, but occupied check: initialize or_=null. If found occupied at (or_,oc), next = grid[or_][oc]. Then if next matches and not merged, merge into next (tile stays at next position conceptually — the surviving tile is `next`, we animate the moving tile onto (or_,oc) which is next.row/col). Else slide to (nr,nc) — the farthest empty.

Wait but there's a subtlety: when merging, grid[r][c]=null and next stays. The moving tile's element animates to next's position. Good.

But careful: farthest empty (nr,nc) when occupied found — correct, it's the last empty before the occupied cell. When no occupied found, nr,nc is the farthest empty (wall). Good.

Also merge check `!tile.mergedFrom` — tile.mergedFrom is always null since we reset at start and tiles only get mergedFrom when absorbed... actually absorbed tiles get mergedFrom set but they're removed. The surviving tile next gets mergedFrom set. So only need next.mergedFrom check. Keep both, harmless.

Also another issue: `within(nr + dir.dr, nc + dir.dc)` check for next is replaced.

Let me fix the code.

Board starts with two tiles. Now play arrow keys. But the browser tool's key action — let me press ArrowLeft. First check the layout with a screenshot? Images not supported. I'll rely on DOM inspection.

Let me simulate moves: press ArrowLeft, then inspect DOM to see tiles. Since spawn is random, I'll read the board state via DOM. The DOM inspector gives text — tile values with positions aren't in text easily. Let me use inspect and look at element styles? The inspect output may show DOM structure. Let me try pressing a key and inspecting.

The DOM snapshot might be stale or the move happened. The DOM output shows "2 2" — could be after moving left, both 2s in column 0? Score still 0 and still two tiles — meaning either no merge happened or the board didn't change. Actually wait, if the two tiles were in the same column and I moved left, they'd slide left, then spawn a new tile → 3 tiles. DOM shows 2 tiles. Hmm, maybe the DOM text just isn't updated in snapshot, or the move didn't register.

Let me inspect the DOM more thoroughly to see the board state.

The move worked: a merge happened (the two 2s merged into a 4), score updated to 4 with "+4" indicator, best updated to 4, and a new tile spawned (now 3 tiles: 4, 2, 2). 

Now test:
1. New Game resets to two tiles and score 0.
2. Rapid input doesn't corrupt state — locked flag; trust.
3. Arrow keys don't scroll — overflow hidden on body + preventDefault; fine.

Let me click New Game.

The DOM snapshot still shows old state — likely the snapshot was taken immediately before reset's DOM changes, or the snapshot text lags. Let me inspect again.

The DOM snapshot appears unchanged. Maybe the click didn't hit the button. Button is in .controls row; the header at top. Let me check coordinates: viewport 1200x800, wrap is 460px wide centered → x from 370 to 830. Button "New Game" is right-aligned in controls, so around x≈760-830, y≈? header ~40px padding-top + header height (~60) + 16 margin → controls at y≈116-150. My click at (1032, 139) was outside the wrap (x>830). That's why nothing happened.

Let me click at (790, 139). Better: inspect to find the button. The DOM text output doesn't give coordinates. I'll click (800, 140).

New Game worked: score reset to 0, board back to two tiles (2, 2). Best persists (4) — fine.

Now test a few more arrow moves to verify sliding and unchanged-move (no spawn). I need to know board layout. The text output only shows values, not positions. Hard to verify positions via text. I could add temporary logging, but simpler: press a direction that likely changes the board (e.g., ArrowLeft again) and check tile count / score. To verify "unchanged move doesn't spawn", I'd need to know positions.

Alternative: use bash with node to test the move logic? The game logic is in browser. I could quickly evaluate by injecting? No eval tool available.

I can check tile count via DOM text: after a changed move, tile count increases by 1. Let me press ArrowDown and inspect.

State after ArrowDown then ArrowLeft: now 4 tiles: 2, 4, 2, 2. Score 4 again with +4 popup — so a merge happened again (two 2s merged into 4? wait score went 0→4, gained 4). Board: values 2,4,2,2 — 4 tiles. Before these moves we had 2 tiles (2,2). ArrowDown likely didn't change (if tiles in same column, moving down would slide them; if one above other in col, moving down would stack and possibly merge). Apparently after ArrowDown: still 2 tiles (snapshot showed 2,2 unchanged — either unchanged move or they just slid). Then ArrowLeft: spawned happened somewhere earlier? Final: 4 tiles with values 2,4,2,2 and score 4.

Sequence reconstruction: after New Game, tiles at two random cells. ArrowDown: snapshot showed "2 2" — could be unchanged (no spawn) or changed with a spawn... only 2 tiles shown so no spawn. So ArrowDown didn't change board or... if it changed, a tile would spawn making 3 tiles. So ArrowDown was an unchanged move — no spawn. That confirms unchanged moves don't spawn (assuming tiles were in different columns and same row — moving down wouldn't change anything).

Then ArrowLeft: merged the two 2s? Wait if they were in the same row, moving left would slide and merge them → 4, score +4, spawn one tile → 3 tiles. But we see 4 tiles (2,4,2,2). Hmm. Unless the merge produced... wait score +4 means one merge of 2+2. 3 tiles expected: 4, 2, spawn. But we have 4 tiles: 2,4,2,2.

Wait — maybe the two starting tiles after New Game were in the same column, so ArrowDown stacked them vertically adjacent but not merging (e.g., one at row0, one at row2 → down move slides bottom one to row3? or slides to adjacent). If they were at rows 1 and 3 in same column, moving down → they become rows 2,3? No merge, spawn one tile → 3 tiles. But snapshot after ArrowDown showed only "2 2" (2 tiles)... unless snapshot was taken before spawn? The snapshot after keypress may be captured before the setTimeout spawn (110ms). Actually after the first ArrowLeft earlier, the immediate snapshot also showed score 0 and 2 tiles, and the later inspect showed the merged result. So yes — snapshots right after keypress are taken before the animation setTimeout completes. So the "2 2" after ArrowDown was pre-spawn state.

So: ArrowDown may have changed the board and spawned. Then ArrowLeft merged two 2s (+4). Final 4 tiles: 2,4,2,2. That's consistent: after ArrowDown+spawn: 3 tiles (2,2,x). Then ArrowLeft merged two 2s → 4, spawned another → 4 tiles: 4,2,2 + ... wait that's values 4,2,2 = 3 tiles, plus spawn = 4 tiles: 2,4,2,2. ✓. Score 0→4. ✓.

All good. The delayed snapshot makes precise verification harder, but everything observed is consistent with correct behavior: merges add score by merged value, changed moves spawn exactly one tile, unchanged moves don't spawn (first ArrowLeft at game start: board had 2 tiles in different columns; snapshot showed no change... actually that merged. The New Game → ArrowDown case showed no tile count change beyond animation delay uncertainty).

To verify the delayed timing more reliably, I could check that rapid input doesn't corrupt: locked flag prevents moves during 110ms animation. Hard to test rapid keys via tool (each key call likely spaced). I'll trust the lock.

One more check: win/lose messages can't be easily forced. Game over logic: canMove checks empty cell or adjacent equal — correct. Win at 2048 — correct.

Also check no scroll: body overflow hidden and preventDefault. Fine.

One potential issue: after game over, locked=false but over=true blocks move. Good.

Edge: spawn during merge animation — spawn happens in the setTimeout after animation, good.

Another check: verify the board visually? Images not supported by the model. DOM text is fine.

I think we're done. Quick final sanity: reload to ensure no console errors on fresh load.

Fresh load: score 0, two tiles (2 and 4 — the 4 spawn case works too, 10% probability). No console errors. Done.

Summary time.