Fix(adjustHue): account for potential negative hue value

src/color/adjustHue.js

@@ -32,7 +32,7 @@ function adjustHue(degree: number | string, color: string): string {
   const hslColor = parseToHsl(color)
   return toColorString({
     ...hslColor,
-    hue: (hslColor.hue + parseFloat(degree)) % 360,
+    hue: hslColor.hue + parseFloat(degree),
   })
 }
 

src/internalHelpers/_hslToRgb.js

@@ -21,10 +21,10 @@ function hslToRgb(
     return convert(lightness, lightness, lightness)
   }
 
-  // formular from https://en.wikipedia.org/wiki/HSL_and_HSV
-  const huePrime = hue % 360 / 60
+  // formulae from https://en.wikipedia.org/wiki/HSL_and_HSV
+  const huePrime = (((hue % 360) + 360) % 360) / 60
   const chroma = (1 - Math.abs(2 * lightness - 1)) * saturation
-  const secondComponent = chroma * (1 - Math.abs(huePrime % 2 - 1))
+  const secondComponent = chroma * (1 - Math.abs((huePrime % 2) - 1))
 
   let red = 0
   let green = 0

src/internalHelpers/test/__snapshots__/_hslToRgb.test.js.snap

@@ -6,6 +6,24 @@ Object {
 }
 `;
 
+exports[`hslToRgb should convert correctly even when passed a "faulty" negative hue 1`] = `
+Object {
+  "background": "rgb(255,0,43)",
+}
+`;
+
+exports[`hslToRgb should convert correctly even when passed a "faulty" negative hue 2`] = `
+Object {
+  "background": "rgb(85,0,255)",
+}
+`;
+
+exports[`hslToRgb should convert correctly even when passed a "faulty" negative hue 3`] = `
+Object {
+  "background": "rgb(170,255,0)",
+}
+`;
+
 exports[`hslToRgb should convert numbers to a hex color 1`] = `
 Object {
   "background": "rgb(179,25,25)",

src/internalHelpers/test/_hslToRgb.test.js

@@ -34,4 +34,10 @@ describe('hslToRgb', () => {
   it('should convert black', () => {
     expect({ background: `rgb(${hslToRgb(360, 0, 0.4)})` }).toMatchSnapshot()
   })
+
+  it('should convert correctly even when passed a "faulty" negative hue', () => {
+    expect({ background: `rgb(${hslToRgb(-10, 1, 0.5)})` }).toMatchSnapshot()
+    expect({ background: `rgb(${hslToRgb(-100, 1, 0.5)})` }).toMatchSnapshot()
+    expect({ background: `rgb(${hslToRgb(-1000, 1, 0.5)})` }).toMatchSnapshot()
+  })
 })