Adding first working version

backend/admin/src/caEngineSteps/outerTotalistic2d.ts

@@ -0,0 +1,45 @@
+import { resolveBoundaryCondition, resolveBoundaryIndex } from '../caRuntime.js'
+import type { Cells, SceneParams } from '../types.js'
+import { emptyCellsLike } from './cellGrid.js'
+
+function parseOuterTotalisticRule(ruleId: string) {
+  const match = /^B([0-8]*)\/S([0-8]*)$/i.exec(ruleId)
+  if (!match) return { birth: new Set([3]), survival: new Set([2, 3]) }
+
+  return {
+    birth: new Set(match[1].split('').map(Number)),
+    survival: new Set(match[2].split('').map(Number))
+  }
+}
+
+export function stepOuterTotalistic2d(cells: Cells, settings: SceneParams) {
+  const rule = parseOuterTotalisticRule(settings.simulation?.ruleId ?? 'B3/S23')
+  const next = emptyCellsLike(cells)
+  const height = cells.length
+  const width = cells[0]?.length ?? 0
+  const boundary = resolveBoundaryCondition(settings.simulation?.grid)
+
+  for (let y = 0; y < height; y += 1) {
+    for (let x = 0; x < width; x += 1) {
+      let neighbours = 0
+
+      for (let dy = -1; dy <= 1; dy += 1) {
+        for (let dx = -1; dx <= 1; dx += 1) {
+          if (dx === 0 && dy === 0) continue
+
+          const rawX = x + dx
+          const rawY = y + dy
+          const nx = resolveBoundaryIndex(rawX, width, boundary)
+          const ny = resolveBoundaryIndex(rawY, height, boundary)
+
+          if (nx === null || ny === null) continue
+          if (cells[ny][nx]) neighbours += 1
+        }
+      }
+
+      next[y][x] = cells[y][x] ? rule.survival.has(neighbours) : rule.birth.has(neighbours)
+    }
+  }
+
+  return next
+}