Import/export chat styles

ts/util/hslToRGB.ts

@@ -0,0 +1,26 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+// https://en.wikipedia.org/wiki/HSL_and_HSV#HSL_to_RGB_alternative
+export function hslToRGB(
+  h: number,
+  s: number,
+  l: number
+): {
+  r: number;
+  g: number;
+  b: number;
+} {
+  const a = s * Math.min(l, 1 - l);
+
+  function f(n: number): number {
+    const k = (n + h / 30) % 12;
+    return l - a * Math.max(Math.min(k - 3, 9 - k, 1), -1);
+  }
+
+  return {
+    r: Math.round(255 * f(0)),
+    g: Math.round(255 * f(8)),
+    b: Math.round(255 * f(4)),
+  };
+}