feat: add drag direction enum and helpers

src/drag_direction.ts

@@ -0,0 +1,68 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export enum Direction {
+  Up = 1,
+  Down,
+  Left,
+  Right,
+}
+
+/**
+ * Convert a direction enum into an XY pair.
+ *
+ * @param dir The direction, or undefined.
+ * @returns An object containing x and y values corresponding to the input
+ *     direction.
+ */
+export function getXYFromDirection(dir: Direction | undefined): {
+  x: number;
+  y: number;
+} {
+  if (!dir) {
+    return {x: 0, y: 0};
+  }
+  switch (dir) {
+    case Direction.Up:
+      return {x: 0, y: -1};
+    case Direction.Down:
+      return {x: 0, y: 1};
+    case Direction.Left:
+      return {x: -1, y: 0};
+    case Direction.Right:
+      return {x: 1, y: 0};
+  }
+}
+
+/**
+ * Convert an XY pair into a direction enum.
+ *
+ * @param xy The input pair.
+ * @param xy.x The x direction, or undefined.
+ * @param xy.y The y direction, or undefined.
+ * @returns A direction corresponding to the XY pair, or null if they are invalid
+ *     or undefined.
+ */
+export function getDirectionFromXY(xy: {
+  x: number | undefined;
+  y: number | undefined;
+}): Direction | null {
+  const {x, y} = xy;
+  if (x == 0) {
+    if (y == -1) {
+      return Direction.Up;
+    } else if (y == 1) {
+      return Direction.Down;
+    }
+  } else if (y == 0) {
+    if (x == -1) {
+      return Direction.Left;
+    } else if (x == 1) {
+      return Direction.Right;
+    }
+  }
+  return null;
+}