feat(core): introduce Direction type and directional computation func…

…tion

Added the Direction type to define the four cardinal directions in the swiperia-core package. Also implemented a function to compute the direction between two points, supported by unit tests to ensure accurate direction determination across various scenarios.

packages/swiperia-core/src/lib/direction/Direction.type.ts

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+/**
+ * Represents the four cardinal directions: right, left, up, and down.
+ */
+export type Direction = 'right' | 'left' | 'up' | 'down';

packages/swiperia-core/src/lib/direction/direction.spec.ts

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+import { Point } from "../point/Point.type";
+import { direction } from "./direction";
+
+describe("direction", () => {
+  it("should return the correct direction for positive coordinates", () => {
+    const a: Point = [0, 0];
+    const b: Point = [3, 4];
+    expect(direction(a, b)).toEqual("down");
+  });
+
+  it("should return the correct direction for negative coordinates", () => {
+    const a: Point = [-2, 3];
+    const b: Point = [1, -1];
+    expect(direction(a, b)).toEqual("up");
+  });
+
+  it("should return null for the same point", () => {
+    const a: Point = [5, 5];
+    const b: Point = [5, 5];
+    expect(direction(a, b)).toBeNull();
+  });
+
+  it("should return the correct direction when x-coordinate is the same", () => {
+    const a: Point = [0, 0];
+    const b: Point = [0, 5];
+    expect(direction(a, b)).toEqual("down");
+  });
+
+  it("should return the correct direction when y-coordinate is the same", () => {
+    const a: Point = [0, 0];
+    const b: Point = [5, 0];
+    expect(direction(a, b)).toEqual("right");
+  });
+});

packages/swiperia-core/src/lib/direction/direction.ts

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+import type { Point } from '../point/Point.type';
+import type { Direction } from './Direction.type';
+
+/**
+ * Determines the direction between two points.
+ *
+ * @param a - The starting point.
+ * @param b - The ending point.
+ * @returns The direction between the two points, or `null` if the points are the same.
+ */
+export const direction = (a: Point, b: Point): Direction | null => {
+  const [ax, ay] = a;
+  const [bx, by] = b;
+  const dx = bx - ax;
+  const dy = by - ay;
+  const absX = Math.abs(dx);
+  const absY = Math.abs(dy);
+  // If the points are the same, return null.
+  if (absX === 0 && absY === 0) return null;
+  if (absX > absY) {
+    return dx > 0 ? 'right' : 'left';
+  }
+  return dy > 0 ? 'down' : 'up';
+};

packages/swiperia-core/src/lib/direction/index.ts

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+export type { Direction } from './Direction.type';
+export { direction } from './direction';