feat(xep): Provide an implementation of XEP-0392

packages/moxxmpp_color/lib/moxxmpp_color.dart

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+library moxxmpp_color;
+
+import 'dart:convert';
+import 'package:cryptography/cryptography.dart';
+import 'package:flutter/material.dart';
+import 'package:hsluv/extensions.dart';
+
+/// The default saturation to use.
+const _defaultSaturation = 50;
+
+/// The default lightness to use.
+const _defaultLightness = 50;
+
+/// Implementation of the algorithm in XEP-0392. [hashBytes] are the bytes
+/// of the SHA-1 hash of the input.
+Color _computeColor(
+  List<int> hashBytes, {
+  double? saturation,
+  double? lightness,
+}) {
+  final bytes = hashBytes.sublist(0, 2);
+  final angle = (bytes.last << 8 + bytes.first).toDouble() / 65565;
+  return hsluvToRGBColor([
+    angle * 360,
+    (saturation ?? _defaultSaturation).remainder(360),
+    (lightness ?? _defaultLightness).remainder(360),
+  ]);
+}
+
+/// Like [consistentColor], but synchronous.
+Color consistentColorSync(
+  String input, {
+  double? saturation,
+  double? lightness,
+}) {
+  return _computeColor(
+    Sha1().toSync().hashSync(utf8.encode(input)).bytes,
+    saturation: saturation,
+    lightness: lightness,
+  );
+}
+
+/// Compute the color based on the algorithm described in XEP-0392.
+/// [saturation] and [lightness] can be used to supply values to use
+/// instead of the default.
+Future<Color> consistentColor(
+  String input, {
+  double? saturation,
+  double? lightness,
+}) async {
+  return _computeColor(
+    (await Sha1().hash(utf8.encode(input))).bytes,
+    saturation: saturation,
+    lightness: lightness,
+  );
+}