use a function for textPatternStyle and add default to theme

packages/stream_chat_flutter/lib/src/message_input/message_input_controller.dart

@@ -17,7 +17,7 @@ class MessageInputController extends ValueNotifier<Message> {
   /// message.
   factory MessageInputController({
     Message? message,
-    Map<RegExp, TextStyle>? textPatternStyle,
+    Map<RegExp, TextStyleBuilder>? textPatternStyle,
   }) =>
       MessageInputController._(
         initialMessage: message ?? Message(),
@@ -27,7 +27,7 @@ class MessageInputController extends ValueNotifier<Message> {
   /// Creates a controller for an editable text field from an initial [text].
   factory MessageInputController.fromText(
     String? text, {
-    Map<RegExp, TextStyle>? textPatternStyle,
+    Map<RegExp, TextStyleBuilder>? textPatternStyle,
   }) =>
       MessageInputController._(
         initialMessage: Message(text: text),
@@ -38,7 +38,7 @@ class MessageInputController extends ValueNotifier<Message> {
   /// [attachments].
   factory MessageInputController.fromAttachments(
     List<Attachment> attachments, {
-    Map<RegExp, TextStyle>? textPatternStyle,
+    Map<RegExp, TextStyleBuilder>? textPatternStyle,
   }) =>
       MessageInputController._(
         initialMessage: Message(attachments: attachments),
@@ -47,7 +47,7 @@ class MessageInputController extends ValueNotifier<Message> {
 
   MessageInputController._({
     required Message initialMessage,
-    Map<RegExp, TextStyle>? textPatternStyle,
+    Map<RegExp, TextStyleBuilder>? textPatternStyle,
   })  : _textEditingController = MessageTextFieldController.fromValue(
           initialMessage.text == null
               ? const TextEditingValue()

packages/stream_chat_flutter/lib/src/message_input/message_text_field_controller.dart

@@ -1,4 +1,8 @@
 import 'package:flutter/material.dart';
+import 'package:stream_chat_flutter/stream_chat_flutter.dart';
+
+/// A function that takes a [BuildContext] and returns a [TextStyle].
+typedef TextStyleBuilder = TextStyle Function(BuildContext context);
 
 /// Controller for the [StreamTextField] widget.
 class MessageTextFieldController extends TextEditingController {
@@ -15,7 +19,7 @@ class MessageTextFieldController extends TextEditingController {
   }) : super.fromValue(value);
 
   /// A map of style to apply to the text matching the RegExp patterns.
-  final Map<RegExp, TextStyle>? textPatternStyle;
+  final Map<RegExp, TextStyleBuilder>? textPatternStyle;
 
   /// Builds a [TextSpan] from the current text,
   /// highlighting the matches for [textPatternStyle].
@@ -25,8 +29,14 @@ class MessageTextFieldController extends TextEditingController {
     TextStyle? style,
     required bool withComposing,
   }) {
-    final pattern = textPatternStyle;
-    if (pattern == null) {
+    final pattern = textPatternStyle ??
+        {
+          RegExp(r'(?:(?:https?|ftp):\/\/)?[\w/\-?=%.]+\.[\w/\-?=%.]+'):
+              (context) => TextStyle(
+                    color: MessageInputTheme.of(context).linkHighlightColor,
+                  ),
+        };
+    if (pattern.isEmpty) {
       return super.buildTextSpan(
         context: context,
         style: style,
@@ -41,7 +51,7 @@ class MessageTextFieldController extends TextEditingController {
         final key = pattern.keys.firstWhere((it) => it.hasMatch(text));
         return TextSpan(
           text: text,
-          style: pattern[key],
+          style: pattern[key]?.call(context),
         );
       },
     );

packages/stream_chat_flutter/lib/src/stream_chat_theme.dart

@@ -259,6 +259,7 @@ class StreamChatThemeData {
         sendButtonIdleColor: colorTheme.disabled,
         inputBackgroundColor: colorTheme.barsBg,
         inputTextStyle: textTheme.body,
+        linkHighlightColor: colorTheme.accentPrimary,
         idleBorderGradient: LinearGradient(
           colors: [
             colorTheme.disabled,

packages/stream_chat_flutter/lib/src/theme/message_input_theme.dart

@@ -65,6 +65,7 @@ class MessageInputThemeData with Diagnosticable {
     this.idleBorderGradient,
     this.borderRadius,
     this.expandButtonColor,
+    this.linkHighlightColor,
   });
 
   /// Duration of the [MessageInput] send button animation
@@ -73,6 +74,9 @@ class MessageInputThemeData with Diagnosticable {
   /// Background color of [MessageInput] send button
   final Color? sendButtonColor;
 
+  /// Color of a link
+  final Color? linkHighlightColor;
+
   /// Background color of [MessageInput] action buttons
   final Color? actionButtonColor;
 
@@ -110,6 +114,7 @@ class MessageInputThemeData with Diagnosticable {
     Color? actionButtonColor,
     Color? sendButtonColor,
     Color? actionButtonIdleColor,
+    Color? linkHighlightColor,
     Color? sendButtonIdleColor,
     Color? expandButtonColor,
     TextStyle? inputTextStyle,
@@ -133,6 +138,7 @@ class MessageInputThemeData with Diagnosticable {
         activeBorderGradient: activeBorderGradient ?? this.activeBorderGradient,
         idleBorderGradient: idleBorderGradient ?? this.idleBorderGradient,
         borderRadius: borderRadius ?? this.borderRadius,
+        linkHighlightColor: linkHighlightColor ?? this.linkHighlightColor,
       );
 
   /// Linearly interpolate from one [MessageInputThemeData] to another.
@@ -161,6 +167,8 @@ class MessageInputThemeData with Diagnosticable {
             Color.lerp(a.sendButtonIdleColor, b.sendButtonIdleColor, t),
         sendAnimationDuration: a.sendAnimationDuration,
         inputDecoration: a.inputDecoration,
+        linkHighlightColor:
+            Color.lerp(a.linkHighlightColor, b.linkHighlightColor, t),
       );
 
   /// Merges [this] [MessageInputThemeData] with the [other]
@@ -181,6 +189,7 @@ class MessageInputThemeData with Diagnosticable {
       idleBorderGradient: other.idleBorderGradient,
       borderRadius: other.borderRadius,
       expandButtonColor: other.expandButtonColor,
+      linkHighlightColor: other.linkHighlightColor,
     );
   }
 
@@ -200,7 +209,8 @@ class MessageInputThemeData with Diagnosticable {
           inputDecoration == other.inputDecoration &&
           idleBorderGradient == other.idleBorderGradient &&
           activeBorderGradient == other.activeBorderGradient &&
-          borderRadius == other.borderRadius;
+          borderRadius == other.borderRadius &&
+          linkHighlightColor == other.linkHighlightColor;
 
   @override
   int get hashCode =>
@@ -215,7 +225,8 @@ class MessageInputThemeData with Diagnosticable {
       inputDecoration.hashCode ^
       idleBorderGradient.hashCode ^
       activeBorderGradient.hashCode ^
-      borderRadius.hashCode;
+      borderRadius.hashCode ^
+      linkHighlightColor.hashCode;
 
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
@@ -232,6 +243,7 @@ class MessageInputThemeData with Diagnosticable {
       ..add(DiagnosticsProperty('activeBorderGradient', activeBorderGradient))
       ..add(DiagnosticsProperty('idleBorderGradient', idleBorderGradient))
       ..add(DiagnosticsProperty('borderRadius', borderRadius))
-      ..add(ColorProperty('expandButtonColor', expandButtonColor));
+      ..add(ColorProperty('expandButtonColor', expandButtonColor))
+      ..add(ColorProperty('linkHighlightColor', linkHighlightColor));
   }
 }