From f4aa686374a9e34ee8fa33a8e02ef09b45f0dc3b Mon Sep 17 00:00:00 2001
From: tamcy <tamcy@users.noreply.github.com>
Date: Mon, 25 Mar 2024 11:17:25 +0800
Subject: [PATCH] Add an optional offset argument to
 StringScanner.peekCodePoint to align with StringScanner.peekChar

---
 CHANGELOG.md                  |  4 +++-
 lib/src/string_scanner.dart   | 12 ++++++++----
 pubspec.yaml                  |  2 +-
 test/string_scanner_test.dart |  6 ++++++
 4 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa7af43..dacbfe0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
-## 1.2.1-wip
+## 1.3.0-wip
 
 * Require Dart 3.0.0
+* `StringScanner.peekCodePoint()` now accepts an optional `offset` argument like
+  `StringScanner.peekChar()`. 
 
 ## 1.2.0
 
diff --git a/lib/src/string_scanner.dart b/lib/src/string_scanner.dart
index 1466944..490727a 100644
--- a/lib/src/string_scanner.dart
+++ b/lib/src/string_scanner.dart
@@ -158,19 +158,23 @@ class StringScanner {
     return decodeSurrogatePair(first, next);
   }
 
-  /// Returns the Unicode code point immediately after [position].
+  /// Returns the Unicode code point [offset] away from [position].
   ///
   /// This works like [peekChar], except that it automatically handles UTF-16
   /// surrogate pairs. Specifically, if the next two code units form a surrogate
   /// pair, returns the corresponding Unicode code point.
   ///
+  /// [offset] defaults to zero, and may be negative to inspect already-consumed
+  /// characters.
+  ///
   /// If next two characters are not a surrogate pair, the next code unit is
   /// returned as-is, even if it's an unpaired surrogate.
-  int? peekCodePoint() {
-    final first = peekChar();
+  int? peekCodePoint([int? offset]) {
+    offset ??= 0;
+    final first = peekChar(offset);
     if (first == null || !isHighSurrogate(first)) return first;
 
-    final next = peekChar(1);
+    final next = peekChar(offset + 1);
     if (next == null || !isLowSurrogate(next)) return first;
 
     return decodeSurrogatePair(first, next);
diff --git a/pubspec.yaml b/pubspec.yaml
index 7ceb7d9..92a44cb 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: string_scanner
-version: 1.2.1-wip
+version: 1.3.0-wip
 description: A class for parsing strings using a sequence of patterns.
 repository: https://github.com/dart-lang/string_scanner
 
diff --git a/test/string_scanner_test.dart b/test/string_scanner_test.dart
index 36a737e..29f1199 100644
--- a/test/string_scanner_test.dart
+++ b/test/string_scanner_test.dart
@@ -154,6 +154,12 @@ void main() {
       expect(scanner.position, equals(0));
     });
 
+    test('peekCodePoint with an argument returns the nth character', () {
+      expect(scanner.peekCodePoint(4), equals(0x62));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
     test('a matching scanChar returns true moves forward', () {
       expect(scanner.scanChar($f), isTrue);
       expect(scanner.lastMatch, isNull);