feat: Add convertRGBtoHex (#17)

* feat: Add convertRGBtoHex

* chore: Add changeset log

.changeset/eleven-numbers-peel.md

@@ -0,0 +1,5 @@
+---
+"@sardine/colour": minor
+---
+
+Add convertRGBtoHex

src/converters.ts

@@ -50,8 +50,7 @@ export function convertXYZtoLab(colour: XYZColour): LabColour {
 
 /**
  * Indirectly converts RGB to Lab.
- * First converts RGB to XYZ,
- * Then converts XYZ to Lab
+ * First converts RGB to XYZ, then converts XYZ to Lab.
  * @param {RGBColour} colour sRGB colour
  * @return {LabColour} Lab colour
  */
@@ -60,6 +59,21 @@ export function convertRGBtoLab(colour: RGBColour): LabColour {
   return convertXYZtoLab(XYZColour);
 }
 
+/**
+ * Converts a colour in the RGB format to Hexadecimal.
+ * It accepts an option Alpha channel `A`
+ * @param {Object} colour - An object representing RGB Colour.
+ * @param {number} colour.R - A number between 0 and 255 to describe the Red colour channel
+ * @param {number} colour.G - A number between 0 and 255 to describe the Green colour channel
+ * @param {number} colour.B - A number between 0 and 255 to describe the Blue colour channel
+ * @param {number} colour.A - An optional number between 0 and 1 to describe the Alpha colour channel
+ * @returns - An hexadecimal string 
+ */
+export function convertRGBtoHex({R, G, B, A}: RGBColour): string {
+  const hex = (n: number) => n.toString(16).padStart(2, '0');
+  return '#'+hex(R)+hex(G)+hex(B)+(A ? hex(Math.round(A * 255)) : '');
+}
+
 export function convertHextoRGB(hex: string): RGBColour {
   if (typeof hex !== "string") {
     throw new Error(`convertHextoRGB expects a string but got a ${typeof hex}`);

src/index.ts

@@ -1,6 +1,7 @@
 export { ciede2000 } from "./CIEDE2000.js";
 export {
   convertHextoRGB,
+  convertRGBtoHex,
   convertRGBtoLab,
   convertRGBtoXYZ,
   convertXYZtoLab,

src/tests/converters.test.ts

@@ -1,9 +1,10 @@
 import test from "ava";
 import {
+  convertHextoRGB,
+  convertRGBtoHex,
+  convertRGBtoLab,
   convertRGBtoXYZ,
   convertXYZtoLab,
-  convertRGBtoLab,
-  convertHextoRGB,
 } from "../converters.js";
 import { ciede2000 } from "../CIEDE2000.js";
 import type { LabColour, RGBColour, XYZColour } from "../types";
@@ -153,3 +154,28 @@ test("throws an error if not passing a valid hexadecimal value", ({
     "convertHextoRGB expects an valid hexadecimal colour value but got HH77ZZs"
   );
 });
+
+test("converts RGB format to hexadecimal colour", ({
+  is
+}) => {
+  const expectedHex = "#ffffff";
+  const RGB: RGBColour = {
+    R: 255,
+    G: 255,
+    B: 255,
+  };
+  is(convertRGBtoHex(RGB), expectedHex);
+});
+
+test("converts RGBA format to hexadecimal colour with alpha channel", ({
+  is
+}) => {
+  const expectedHex = "#ffffff80";
+  const RGB: RGBColour = {
+    R: 255,
+    G: 255,
+    B: 255,
+    A: 0.5
+  };
+  is(convertRGBtoHex(RGB), expectedHex);
+});