From db3d318e256daa3de9a123159da09697a896ac34 Mon Sep 17 00:00:00 2001
From: Simon Bigelmayr <simon.bigelmayr@mll.com>
Date: Mon, 19 Aug 2024 12:44:56 +0200
Subject: [PATCH] feat: add stringToHslaColor

---
 src/stringToColor.test.ts | 34 +++++++++++++++++++++++++++++++
 src/stringToColor.ts      | 42 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 src/stringToColor.test.ts
 create mode 100644 src/stringToColor.ts

diff --git a/src/stringToColor.test.ts b/src/stringToColor.test.ts
new file mode 100644
index 0000000..3ec56fa
--- /dev/null
+++ b/src/stringToColor.test.ts
@@ -0,0 +1,34 @@
+import { uniq } from 'lodash';
+
+import { randomString, stringToHslaColor } from './stringToColor';
+
+describe('stringToHslaColor', () => {
+  it.each(['test', 'test'])(
+    'is a pure function returning the same hsla for the same string',
+    (testString) => {
+      expect(stringToHslaColor(testString)).toStrictEqual(
+        'hsla(58, 98%, 48%, 1)',
+      );
+    },
+  );
+
+  it('returns various hsla colors for various inputs', () => {
+    const testStrings = ['t', 'te', 'tes', 'test'];
+    expect(uniq(testStrings.map(stringToHslaColor)).length).toBe(
+      testStrings.length,
+    );
+  });
+
+  it('returns a valid color for a random string', () => {
+    expect(isValidColor(stringToHslaColor(randomString()))).toBe(true);
+  });
+});
+
+function isValidColor(color: string): boolean {
+  // Use the browser's validation. Create a dummy HTML element, assign the color and check if it's set.
+  const element = document.createElement('div');
+  element.style.borderColor = '';
+  element.style.borderColor = color;
+
+  return element.style.borderColor.length !== 0;
+}
\ No newline at end of file
diff --git a/src/stringToColor.ts b/src/stringToColor.ts
new file mode 100644
index 0000000..10d94e3
--- /dev/null
+++ b/src/stringToColor.ts
@@ -0,0 +1,42 @@
+function hashCode(string: string): number {
+  let hash = 0;
+  // eslint-disable-next-line no-plusplus
+  for (let i = 0; i < string.length; i++) {
+    // eslint-disable-next-line no-bitwise
+    hash = string.charCodeAt(i) + ((hash << 5) - hash);
+  }
+
+  return hash;
+}
+
+function getHslColor(hash: number): string {
+  const h = range(hash, 0, 360);
+  const s = range(hash, 50, 100);
+  const l = range(hash, 20, 50);
+
+  return `hsla(${h}, ${s}%, ${l}%, 1)`;
+}
+
+function range(hash: number, min: number, max: number): number {
+  const diff = max - min;
+  const x = ((hash % diff) + diff) % diff;
+
+  return x + min;
+}
+
+export function stringToHslaColor(string: string): string {
+  return getHslColor(hashCode(string));
+}
+
+/**
+ * Generates a random string with a length of 1-11 chars.
+ */
+export function randomString(): string {
+  // Cut off the constant 0. from the beginning
+  const fractionStart = 2;
+
+  // Unequal distribution at the edges, but sufficiently random for the purposes of this function
+  const randomLengthEnd = Math.round(Math.random() * 11) + 3;
+
+  return Math.random().toString(36).substring(fractionStart, randomLengthEnd);
+}