Implement basic SNBT reader and testsuite

lib/nbt/Stream.dart

@@ -408,3 +408,124 @@ class StringBuilder {
     return "${_buffer}";
   }
 }
+
+class StringReader {
+  final String _buffer;
+  int _position = 0;
+  int _lastPostion = 0;
+
+  StringReader(this._buffer);
+
+  // Check if there's more to read
+  bool get canRead => _position < _buffer.length;
+
+  // Read the next character
+  String next() {
+    if (canRead) {
+      skipWhitespace();
+      return _buffer[_position++];
+    } else {
+      throw Exception("End of buffer reached");
+    }
+  }
+
+  // Peek the next character without advancing the position
+  String peek() {
+    skipWhitespace();
+    if (canRead) {
+      return _buffer[_position];
+    } else {
+      throw Exception("End of buffer reached");
+    }
+  }
+
+  // Skip any whitespace characters
+  void skipWhitespace() {
+    while (canRead && isWhitespace(_buffer[_position])) {
+      _position++;
+    }
+  }
+
+  // Check if a character is a whitespace
+  bool isWhitespace(String char) {
+    return char.trim().isEmpty;
+  }
+
+  // Read until a specific character is found
+  String readUntil(String stopChar) {
+    StringBuffer result = StringBuffer();
+    while (canRead && peek() != stopChar) {
+      result.write(next());
+    }
+    return result.toString();
+  }
+
+  // Read a string enclosed in double quotes
+  String readQuotedString() {
+    if (next() != '"') {
+      throw Exception('Expected double quotes at the start of a string');
+    }
+    StringBuffer result = StringBuffer();
+    while (canRead) {
+      String char = next();
+      if (char == '"') {
+        break;
+      }
+      result.write(char);
+    }
+    return result.toString();
+  }
+
+  // Read a number (int or double)
+  String readNumber() {
+    StringBuffer result = StringBuffer();
+    while (canRead && (isDigit(peek()) || peek() == '.' || peek() == '-')) {
+      result.write(next());
+    }
+    return result.toString();
+  }
+
+  // Check if a character is a digit
+  bool isDigit(String char) {
+    return int.tryParse(char) != null;
+  }
+
+  // Read an unquoted string (used for keys in SNBT)
+  String readUnquotedString() {
+    StringBuffer result = StringBuffer();
+    while (canRead &&
+        !isWhitespace(peek()) &&
+        peek() != ':' &&
+        peek() != ',' &&
+        peek() != '{' &&
+        peek() != '}' &&
+        peek() != '[' &&
+        peek() != ']') {
+      result.write(next());
+    }
+    return result.toString();
+  }
+
+  String readString() {
+    if (peek() == "\"") {
+      return readQuotedString();
+    } else
+      return readUnquotedString();
+  }
+
+  // Read a specific character and throw an exception if it's not found
+  void expect(String expectedChar) {
+    if (next().toLowerCase() != expectedChar.toLowerCase()) {
+      throw Exception('Expected $expectedChar');
+    }
+  }
+
+  void startSeek() {
+    _lastPostion = _position;
+  }
+
+  void endSeek() {
+    _position = _lastPostion;
+    _lastPostion = 0;
+  }
+}