feat: support generating a color combination from a color palette

projects/common/src/color/color-palette.test.ts

@@ -31,4 +31,26 @@ describe('Color palette', () => {
     expect(() => new ColorPalette(['black'])).toThrow();
     expect(() => new ColorPalette(['white', 'black'])).not.toThrow();
   });
+
+  test('should return color combinations correctly', () => {
+    const palette = new ColorPalette(['#fffbeb', '#140300']);
+    expect(palette.getColorCombinations(2)).toEqual([
+      {
+        background: 'rgb(255, 251, 235)',
+        foreground: '#080909'
+      },
+      {
+        background: 'rgb(20, 3, 0)',
+        foreground: '#FFFFFF'
+      }
+    ]);
+  });
+
+  test('should generate color for a string as expected from a limited set', () => {
+    const palette = new ColorPalette(['#fffbeb', '#140300', '#789ab7']);
+    expect(palette.getColorCombinationForId(2, 'test')).toEqual({
+      background: 'rgb(255, 251, 235)',
+      foreground: '#080909'
+    });
+  });
 });

projects/common/src/color/color-palette.ts

@@ -1,5 +1,7 @@
 import { rgb } from 'd3-color';
 import { interpolateRgbBasis, quantize } from 'd3-interpolate';
+import { hashCode } from '../utilities/math/math-utilities';
+import { Color, ColorCombination } from './color';
 
 export class ColorPalette {
   private readonly basisColors: string[];
@@ -10,6 +12,25 @@ export class ColorPalette {
     this.basisColors = basisColors.map(color => rgb(color).toString());
   }
 
+  public getColorCombinations(count: number): ColorCombination[] {
+    return this.forNColors(count).map(color => ({ background: color, foreground: this.getContrast(color) }));
+  }
+
+  public getColorCombinationForId(colorCount: number, id: string): ColorCombination {
+    return this.getColorCombinations(colorCount)[Math.abs(hashCode(id)) % colorCount];
+  }
+
+  private getContrast(rgbColorString: string): string {
+    // Convert to RGB value
+    const rgbColor = rgb(rgbColorString);
+
+    // Get YIQ ratio
+    const yiq = (rgbColor.r * 299 + rgbColor.g * 587 + rgbColor.b * 114) / 1000;
+
+    // Check contrast
+    return yiq >= 128 ? Color.Gray9 : Color.White;
+  }
+
   public forNColors(count: number): string[] {
     if (count === this.basisColors.length) {
       // Use as is if palette size matches, don't interpolate

projects/common/src/color/color.ts

@@ -1,3 +1,5 @@
+import { hashCode } from '../utilities/math/math-utilities';
+
 export const enum Color {
   Blue1 = '#f0f6ff',
   Blue2 = '#b8d3ff',
@@ -58,3 +60,20 @@ export const enum Color {
   Yellow8 = '#6d5b00',
   Yellow9 = '#181400'
 }
+
+export interface ColorCombination {
+  background: string;
+  foreground: string;
+}
+
+export const getHexColorForString = (id: string): string => {
+  const hash = hashCode(id);
+  let rgb = '#';
+  for (let i = 0; i < 3; i++) {
+    // tslint:disable-next-line: no-bitwise
+    const value = (hash >> (i * 8)) & 0xff;
+    rgb += `00${value.toString(16)}`.substr(-2);
+  }
+
+  return rgb;
+};

projects/common/src/public-api.ts

@@ -124,3 +124,6 @@ export * from './time/page-time-range-preference.service';
 
 // Validators
 export * from './utilities/validators';
+
+// Color Palette
+export * from './color/color-palette';

projects/common/src/utilities/math/math-utilities.ts

@@ -110,6 +110,11 @@ export const getPercentage = (numerator: number | undefined, denominator: number
   return (numerator / denominator) * 100;
 };
 
+// Trying to recreate Java hashcode
+export const hashCode = (str: string): number =>
+  // tslint:disable-next-line: no-bitwise
+  Array.from(str).reduce((s, c) => (Math.imul(31, s) + c.charCodeAt(0)) | 0, 0);
+
 export interface Point {
   x: number;
   y: number;