feat(core): add cell value types and error kinds

lib/src/values.dart

@@ -0,0 +1,134 @@
+enum ErrorKind {
+  divZero('#DIV/0!'),
+  ref('#REF!'),
+  cycle('#CYCLE!'),
+  name('#NAME?'),
+  value('#VALUE!'),
+  numError('#NUM!'),
+  parse('#ERROR!'),
+  na('#N/A');
+
+  final String symbol;
+  const ErrorKind(this.symbol);
+
+  static ErrorKind? fromSymbol(String symbol) {
+    for (final kind in ErrorKind.values) {
+      if (kind.symbol == symbol) return kind;
+    }
+    return null;
+  }
+}
+
+sealed class CellValue {
+  const CellValue();
+
+  String display();
+}
+
+class NumberValue extends CellValue {
+  final double value;
+  const NumberValue(this.value);
+
+  @override
+  String display() => formatNumber(value);
+
+  @override
+  bool operator ==(Object other) => other is NumberValue && other.value == value;
+
+  @override
+  int get hashCode => value.hashCode;
+
+  @override
+  String toString() => 'NumberValue(${display()})';
+}
+
+class TextValue extends CellValue {
+  final String value;
+  const TextValue(this.value);
+
+  @override
+  String display() => value;
+
+  @override
+  bool operator ==(Object other) => other is TextValue && other.value == value;
+
+  @override
+  int get hashCode => value.hashCode;
+
+  @override
+  String toString() => 'TextValue($value)';
+}
+
+class BooleanValue extends CellValue {
+  final bool value;
+  const BooleanValue(this.value);
+
+  @override
+  String display() => value ? 'TRUE' : 'FALSE';
+
+  @override
+  bool operator ==(Object other) => other is BooleanValue && other.value == value;
+
+  @override
+  int get hashCode => value.hashCode;
+
+  @override
+  String toString() => 'BooleanValue($value)';
+}
+
+class BlankValue extends CellValue {
+  const BlankValue();
+
+  @override
+  String display() => '';
+
+  @override
+  bool operator ==(Object other) => other is BlankValue;
+
+  @override
+  int get hashCode => 0;
+
+  @override
+  String toString() => 'BlankValue()';
+}
+
+class ErrorValue extends CellValue {
+  final ErrorKind kind;
+  const ErrorValue(this.kind);
+
+  @override
+  String display() => kind.symbol;
+
+  @override
+  bool operator ==(Object other) => other is ErrorValue && other.kind == kind;
+
+  @override
+  int get hashCode => kind.hashCode;
+
+  @override
+  String toString() => 'ErrorValue(${kind.symbol})';
+}
+
+class EvalException implements Exception {
+  final ErrorValue error;
+  const EvalException(this.error);
+
+  ErrorKind get kind => error.kind;
+
+  @override
+  String toString() => 'EvalException(${error.kind.symbol})';
+}
+
+String formatNumber(double value) {
+  if (value.isNaN) return ErrorKind.numError.symbol;
+  if (value.isInfinite) return value.isNegative ? '-Infinity' : 'Infinity';
+  if (value == value.roundToDouble() && value.abs() < 1e15) {
+    return value.toInt().toString();
+  }
+  var text = value.toStringAsPrecision(12);
+  if (text.contains('.') && !text.contains('e') && !text.contains('E')) {
+    text = text.replaceFirst(RegExp(r'0+$'), '');
+    text = text.replaceFirst(RegExp(r'\.$'), '');
+  }
+  return text;
+}