[verified] Snake 0.7: queued controls, records, pause and wrap mode

src/common/snake.js

@@ -8,11 +8,14 @@ function initialSnake() {
 }
 
 // Advance the snake one cell in `dir` ({x,y} unit vector). Returns { snake, ate, alive }.
-function step(snake, dir, food, N) {
+function step(snake, dir, food, N, mode) {
   const head = snake[0]
-  const nx = head.x + dir.x
-  const ny = head.y + dir.y
-  if (nx < 0 || ny < 0 || nx >= N || ny >= N) {
+  let nx = head.x + dir.x
+  let ny = head.y + dir.y
+  if (mode === 'wrap') {
+    nx = (nx + N) % N
+    ny = (ny + N) % N
+  } else if (nx < 0 || ny < 0 || nx >= N || ny >= N) {
     return { snake, ate: false, alive: false }
   }
   const ate = (nx === food.x && ny === food.y)
@@ -37,16 +40,17 @@ function turn(current, desired) {
 // Classify every segment as a texture piece (head/body/corner/tail + compass side),
 // so the page can render each cell with the right PNG. Returns one name per segment.
 // Sides are screen compass (y grows down): e/w/n/s = right/left/up/down.
-function renderPieces(snakeCells, dir) {
+function renderPieces(snakeCells, dir, N) {
   const D = { '1,0': 'e', '-1,0': 'w', '0,-1': 'n', '0,1': 's' }
   const opp = { e: 'w', w: 'e', n: 's', s: 'n' }
+  const delta = d => N && d === N - 1 ? -1 : N && d === 1 - N ? 1 : d
   return snakeCells.map((s, i) => {
     if (i === 0) return 'head_' + D[dir.x + ',' + dir.y]
     const prev = snakeCells[i - 1]
     const next = snakeCells[i + 1]
-    const from = D[(prev.x - s.x) + ',' + (prev.y - s.y)]       // side toward head
+    const from = D[delta(prev.x - s.x) + ',' + delta(prev.y - s.y)]       // side toward head
     if (!next) return 'tail_' + opp[from]                       // tip points away from body
-    const to = D[(next.x - s.x) + ',' + (next.y - s.y)]         // side toward tail tip
+    const to = D[delta(next.x - s.x) + ',' + delta(next.y - s.y)]         // side toward tail tip
     if ((from === 'e' || from === 'w') && (to === 'e' || to === 'w')) return 'body_h'
     if ((from === 'n' || from === 's') && (to === 'n' || to === 's')) return 'body_v'
     // corner: name = the two sides it connects; pairs are alphabetically sorted
@@ -72,12 +76,17 @@ function rotateDir(dir, clockwise) {
 function spawnFood(snake, N) {
   const occupied = new Set(snake.map(s => s.x + ',' + s.y))
   if (occupied.size >= N * N) return null
-  let x, y
-  do {
-    x = Math.floor(Math.random() * N)
-    y = Math.floor(Math.random() * N)
-  } while (occupied.has(x + ',' + y))
-  return { x, y }
+  // Select an empty-cell rank uniformly; at most N*N checks, even almost full.
+  let rank = Math.floor(Math.random() * (N * N - occupied.size))
+  for (let y = 0; y < N; y++) {
+    for (let x = 0; x < N; x++) {
+      if (!occupied.has(x + ',' + y)) {
+        if (rank === 0) return { x, y }
+        rank--
+      }
+    }
+  }
+  return null
 }
 
 module.exports = { initialSnake, step, turn, renderPieces, rotateDir, spawnFood }