🔨 rename package compute -> solver

packages/solver/tunnel.ts

@@ -0,0 +1,81 @@
+import { getColor, isEmpty, isInside } from "@snk/types/grid";
+import { getHeadX, getHeadY, nextSnake } from "@snk/types/snake";
+import type { Snake } from "@snk/types/snake";
+import type { Grid } from "@snk/types/grid";
+import type { Point } from "@snk/types/point";
+
+/**
+ * get the sequence of snake to cross the tunnel
+ */
+export const getTunnelPath = (snake0: Snake, tunnel: Point[]) => {
+  const chain: Snake[] = [];
+  let snake = snake0;
+
+  for (let i = 1; i < tunnel.length; i++) {
+    const dx = tunnel[i].x - getHeadX(snake);
+    const dy = tunnel[i].y - getHeadY(snake);
+    snake = nextSnake(snake, dx, dy);
+    chain.unshift(snake);
+  }
+
+  return chain;
+};
+
+/**
+ * assuming the grid change and the colors got deleted, update the tunnel
+ */
+export const updateTunnel = (
+  grid: Grid,
+  tunnel: Point[],
+  toDelete: Point[]
+) => {
+  while (tunnel.length) {
+    const { x, y } = tunnel[0];
+    if (
+      isEmptySafe(grid, x, y) ||
+      toDelete.some((p) => p.x === x && p.y === y)
+    ) {
+      tunnel.shift();
+    } else break;
+  }
+
+  while (tunnel.length) {
+    const { x, y } = tunnel[tunnel.length - 1];
+    if (
+      isEmptySafe(grid, x, y) ||
+      toDelete.some((p) => p.x === x && p.y === y)
+    ) {
+      tunnel.pop();
+    } else break;
+  }
+};
+
+const isEmptySafe = (grid: Grid, x: number, y: number) =>
+  !isInside(grid, x, y) || isEmpty(getColor(grid, x, y));
+
+/**
+ * remove empty cell from start
+ */
+export const trimTunnelStart = (grid: Grid, tunnel: Point[]) => {
+  while (tunnel.length) {
+    const { x, y } = tunnel[0];
+    if (isEmptySafe(grid, x, y)) tunnel.shift();
+    else break;
+  }
+};
+
+/**
+ * remove empty cell from end
+ */
+export const trimTunnelEnd = (grid: Grid, tunnel: Point[]) => {
+  while (tunnel.length) {
+    const i = tunnel.length - 1;
+    const { x, y } = tunnel[i];
+    if (
+      isEmptySafe(grid, x, y) ||
+      tunnel.findIndex((p) => p.x === x && p.y === y) < i
+    )
+      tunnel.pop();
+    else break;
+  }
+};