From c1ccc10a32fcbd18b9fdda32ec656791818f5856 Mon Sep 17 00:00:00 2001
From: Oleksandr Korneiko <oleksandr.korneiko@gmail.com>
Date: Fri, 23 Aug 2024 16:25:54 +0300
Subject: [PATCH] fix: prevent division by zero in bezier

---
 src/bezier.ts        |  2 +-
 tests/bezier.test.ts | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/bezier.ts b/src/bezier.ts
index 17ba5954..9fddfd2d 100644
--- a/src/bezier.ts
+++ b/src/bezier.ts
@@ -33,7 +33,7 @@ export class Bezier {
     const dxm = m1.x - m2.x;
     const dym = m1.y - m2.y;
 
-    const k = l2 / (l1 + l2);
+    const k = l1 + l2 == 0 ? 0 : l2 / (l1 + l2);
     const cm = { x: m2.x + dxm * k, y: m2.y + dym * k };
 
     const tx = s2.x - cm.x;
diff --git a/tests/bezier.test.ts b/tests/bezier.test.ts
index b95e1f26..b962b8f7 100644
--- a/tests/bezier.test.ts
+++ b/tests/bezier.test.ts
@@ -31,6 +31,25 @@ describe('.fromPoints', () => {
       expect(curve.endWidth).toBe(2);
     });
   });
+
+  it('returns a new Bézier when points are equal and division by zero may occur', () => {
+    const now = Date.now();
+
+    freezeTimeAt(now, () => {
+      const p1 = new Point(54.4, 10.9, 0.5);
+      const p2 = new Point(54.4, 10.9, 0.5);
+      const p3 = new Point(54.4, 10.9, 0.5);
+      const p4 = new Point(54.4, 10.9, 0.5);
+      const curve = Bezier.fromPoints([p1, p2, p3, p4], { start: 1, end: 1 });
+
+      expect(curve.startPoint).toEqual(p2);
+      expect(curve.control1).toEqual(new Point(54.4, 10.9));
+      expect(curve.control2).toEqual(new Point(54.4, 10.9));
+      expect(curve.endPoint).toBe(p3);
+      expect(curve.startWidth).toBe(1);
+      expect(curve.endWidth).toBe(1);
+    });
+  });
 });
 
 describe('#length', () => {