feat(slider): add pure value/position math helpers

src/shared/ui/Slider/slider-math.test.ts

@@ -0,0 +1,55 @@
+import {
+    pointerToValue,
+    snapToStep,
+} from './slider-math';
+
+describe('snapToStep', () => {
+    it('snaps a raw value to the nearest step on the grid', () => {
+        expect(snapToStep(53, { min: 0, max: 100, step: 10 })).toBe(50);
+        expect(snapToStep(56, { min: 0, max: 100, step: 10 })).toBe(60);
+    });
+
+    it('clamps below min and above max', () => {
+        expect(snapToStep(-20, { min: 0, max: 100, step: 1 })).toBe(0);
+        expect(snapToStep(200, { min: 0, max: 100, step: 1 })).toBe(100);
+    });
+
+    it('respects a non-zero min when snapping', () => {
+        expect(snapToStep(13, { min: 10, max: 90, step: 5 })).toBe(15);
+    });
+
+    it('preserves fractional step precision', () => {
+        expect(snapToStep(1.34, { min: 0, max: 2, step: 0.05 })).toBe(1.35);
+        expect(snapToStep(0.31, { min: 0, max: 1, step: 0.1 })).toBe(0.3);
+    });
+});
+
+describe('pointerToValue', () => {
+    const rect = { left: 100, right: 300, top: 50, bottom: 250, width: 200, height: 200 } as DOMRect;
+
+    it('maps horizontal pointer position left→min, right→max', () => {
+        const opts = { min: 0, max: 100, step: 1, orientation: 'horizontal' as const };
+        expect(pointerToValue({ clientX: 100, clientY: 0 }, rect, opts)).toBe(0);
+        expect(pointerToValue({ clientX: 200, clientY: 0 }, rect, opts)).toBe(50);
+        expect(pointerToValue({ clientX: 300, clientY: 0 }, rect, opts)).toBe(100);
+    });
+
+    it('inverts vertical: bottom→min, top→max', () => {
+        const opts = { min: 0, max: 100, step: 1, orientation: 'vertical' as const };
+        expect(pointerToValue({ clientX: 0, clientY: 250 }, rect, opts)).toBe(0);
+        expect(pointerToValue({ clientX: 0, clientY: 150 }, rect, opts)).toBe(50);
+        expect(pointerToValue({ clientX: 0, clientY: 50 }, rect, opts)).toBe(100);
+    });
+
+    it('clamps when pointer is outside the track', () => {
+        const opts = { min: 0, max: 100, step: 1, orientation: 'horizontal' as const };
+        expect(pointerToValue({ clientX: 0, clientY: 0 }, rect, opts)).toBe(0);
+        expect(pointerToValue({ clientX: 9999, clientY: 0 }, rect, opts)).toBe(100);
+    });
+
+    it('returns min for a zero-size track without NaN', () => {
+        const zero = { left: 0, right: 0, top: 0, bottom: 0, width: 0, height: 0 } as DOMRect;
+        const opts = { min: 5, max: 95, step: 1, orientation: 'horizontal' as const };
+        expect(pointerToValue({ clientX: 0, clientY: 0 }, zero, opts)).toBe(5);
+    });
+});