feat(formula): add formula lexer

lib/src/lexer.dart

@@ -0,0 +1,219 @@
+import 'tokens.dart';
+import 'values.dart';
+
+class LexException implements Exception {
+  final String message;
+  const LexException(this.message);
+
+  @override
+  String toString() => 'LexException: $message';
+}
+
+class Lexer {
+  final String source;
+  int _pos = 0;
+
+  Lexer(this.source);
+
+  List<Token> tokenize() {
+    final tokens = <Token>[];
+    while (!_atEnd) {
+      final ch = _peek();
+      if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n') {
+        _pos++;
+        continue;
+      }
+      if (ch == '#') {
+        tokens.add(_readErrorLiteral());
+        continue;
+      }
+      if (_isDigit(ch) || (ch == '.' && _isDigit(_peekAt(1)))) {
+        tokens.add(_readNumber());
+        continue;
+      }
+      if (ch == '"') {
+        tokens.add(_readText());
+        continue;
+      }
+      if (ch == "'") {
+        tokens.add(_readQuotedName());
+        continue;
+      }
+      if (ch == r'$' || _isLetter(ch)) {
+        tokens.add(_readWord());
+        continue;
+      }
+      tokens.add(_readOperator());
+    }
+    tokens.add(const Token(TokenType.eof, ''));
+    return tokens;
+  }
+
+  Token _readErrorLiteral() {
+    for (final kind in ErrorKind.values) {
+      if (source.startsWith(kind.symbol, _pos)) {
+        _pos += kind.symbol.length;
+        return Token(TokenType.errorLit, kind.symbol, kind);
+      }
+    }
+    throw LexException('Unknown error literal at position $_pos');
+  }
+
+  Token _readNumber() {
+    final start = _pos;
+    while (!_atEnd && _isDigit(_peek())) {
+      _pos++;
+    }
+    if (!_atEnd && _peek() == '.') {
+      _pos++;
+      while (!_atEnd && _isDigit(_peek())) {
+        _pos++;
+      }
+    }
+    final lexeme = source.substring(start, _pos);
+    return Token(TokenType.number, lexeme, double.parse(lexeme));
+  }
+
+  Token _readText() {
+    _pos++;
+    final buffer = StringBuffer();
+    while (!_atEnd) {
+      final ch = _peek();
+      if (ch == '"') {
+        if (_peekAt(1) == '"') {
+          buffer.write('"');
+          _pos += 2;
+          continue;
+        }
+        _pos++;
+        return Token(TokenType.text, buffer.toString(), buffer.toString());
+      }
+      buffer.write(ch);
+      _pos++;
+    }
+    throw const LexException('Unterminated string literal');
+  }
+
+  Token _readQuotedName() {
+    _pos++;
+    final buffer = StringBuffer();
+    while (!_atEnd) {
+      final ch = _peek();
+      if (ch == "'") {
+        if (_peekAt(1) == "'") {
+          buffer.write("'");
+          _pos += 2;
+          continue;
+        }
+        _pos++;
+        return Token(TokenType.quotedName, buffer.toString(), buffer.toString());
+      }
+      buffer.write(ch);
+      _pos++;
+    }
+    throw const LexException('Unterminated sheet name');
+  }
+
+  Token _readWord() {
+    final start = _pos;
+    if (_peek() == r'$') _pos++;
+    while (!_atEnd && _isLetter(_peek())) {
+      _pos++;
+    }
+    final hasDollar = _peek() == r'$';
+    final afterLetters = hasDollar ? _peekAt(1) : _peek();
+    if (_isDigit(afterLetters)) {
+      if (hasDollar) _pos++;
+      while (!_atEnd && _isDigit(_peek())) {
+        _pos++;
+      }
+      final lexeme = source.substring(start, _pos);
+      if (_peek() == '!' || _peek() == '(') return Token(TokenType.identifier, lexeme);
+      return Token(TokenType.cellRef, lexeme);
+    }
+    final lexeme = source.substring(start, _pos);
+    return Token(TokenType.identifier, lexeme);
+  }
+
+  Token _readOperator() {
+    final ch = _peek();
+    switch (ch) {
+      case '+':
+        _pos++;
+        return const Token(TokenType.plus, '+');
+      case '-':
+        _pos++;
+        return const Token(TokenType.minus, '-');
+      case '*':
+        _pos++;
+        return const Token(TokenType.star, '*');
+      case '/':
+        _pos++;
+        return const Token(TokenType.slash, '/');
+      case '^':
+        _pos++;
+        return const Token(TokenType.caret, '^');
+      case '%':
+        _pos++;
+        return const Token(TokenType.percent, '%');
+      case '&':
+        _pos++;
+        return const Token(TokenType.amp, '&');
+      case '(':
+        _pos++;
+        return const Token(TokenType.lparen, '(');
+      case ')':
+        _pos++;
+        return const Token(TokenType.rparen, ')');
+      case ',':
+        _pos++;
+        return const Token(TokenType.comma, ',');
+      case ':':
+        _pos++;
+        return const Token(TokenType.colon, ':');
+      case '!':
+        _pos++;
+        return const Token(TokenType.bang, '!');
+      case '=':
+        _pos++;
+        return const Token(TokenType.eq, '=');
+      case '<':
+        _pos++;
+        if (_peek() == '=') {
+          _pos++;
+          return const Token(TokenType.lte, '<=');
+        }
+        if (_peek() == '>') {
+          _pos++;
+          return const Token(TokenType.neq, '<>');
+        }
+        return const Token(TokenType.lt, '<');
+      case '>':
+        _pos++;
+        if (_peek() == '=') {
+          _pos++;
+          return const Token(TokenType.gte, '>=');
+        }
+        return const Token(TokenType.gt, '>');
+      default:
+        throw LexException('Unexpected character "$ch" at position $_pos');
+    }
+  }
+
+  bool get _atEnd => _pos >= source.length;
+
+  String _peek() => _atEnd ? '' : source[_pos];
+
+  String _peekAt(int offset) {
+    final index = _pos + offset;
+    return index >= source.length ? '' : source[index];
+  }
+
+  bool _isDigit(String ch) => ch.length == 1 && ch.codeUnitAt(0) >= 0x30 && ch.codeUnitAt(0) <= 0x39;
+
+  bool _isLetter(String ch) {
+    if (ch.length != 1) return false;
+    final code = ch.codeUnitAt(0);
+    return (code >= 0x41 && code <= 0x5A) || (code >= 0x61 && code <= 0x7A) || code == 0x5F;
+  }
+}