Import/export chat styles

ts/util/rgbToHSL.ts

@@ -0,0 +1,45 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+// https://en.wikipedia.org/wiki/HSL_and_HSV#From_RGB
+export function rgbToHSL(
+  r: number,
+  g: number,
+  b: number
+): {
+  h: number;
+  s: number;
+  l: number;
+} {
+  // Normalize to [0, 1]
+  const rn = r / 255;
+  const gn = g / 255;
+  const bn = b / 255;
+
+  const xMax = Math.max(rn, gn, bn);
+  const xMin = Math.min(rn, gn, bn);
+  const v = xMax;
+  const c = xMax - xMin;
+  const l = v - c / 2;
+  let h: number;
+
+  if (c === 0) {
+    h = 0;
+  } else if (v === rn) {
+    h = 60 * (((gn - bn) / c) % 6);
+  } else if (v === gn) {
+    h = 60 * ((bn - rn) / c + 2);
+  } else {
+    // v === b
+    h = 60 * ((rn - gn) / c + 4);
+  }
+
+  let s: number;
+  if (l === 0 || l === 1) {
+    s = 0;
+  } else {
+    s = (v - l) / Math.min(l, 1 - l);
+  }
+
+  return { h, s, l };
+}