Merge v2.0.0 - Rework serialization

 - Internals are reworked: now package is relying on a tree-like structure to improve maintainability and scalability.
 - Fixed `indentSize` validation (only values >=1 are allowed).
 - Resolved #6:
 ```yaml
 # BEFORE:
 field:
   - 
     - 5
     - 2
   - 
     a: 3
     b: 6

 # AFTER:
 field:
   - - 5
     - 2
   - a: 3
     b: 6
 ```
 - Update min Dart SDK version constraint from `2.12.0` to `3.0.0`
 - Update `lints: ^2.0.1` to `lints: ^3.0.0`

 BREAKING CHANGES:
 - `YAMLWriter` renamed to `YamlWriter` ([Effective Dart reference](https://dart.dev/effective-dart/style#do-capitalize-acronyms-and-abbreviations-longer-than-two-letters-like-words)).
 - Deprecated `identSize` property is removed. Use `indentSize` instead.
 - `toEncodable` property is removed. Use constructor parameter instead (`YamlWriter#toEncodable`).

CHANGELOG.md

@@ -1,3 +1,34 @@
+## 2.0.0
+
+- Internals are reworked: now package is relying on a tree-like structure to improve maintainability and scalability.
+- Fixed `indentSize` validation (only values >=1 are allowed).
+- Resolved https://github.com/gmpassos/yaml_writer/issues/6:
+```yaml
+# BEFORE:
+field:
+  - 
+    - 5
+    - 2
+  - 
+    a: 3
+    b: 6
+
+# AFTER:
+field:
+  - - 5
+    - 2
+  - a: 3
+    b: 6
+```
+- Update min Dart SDK version constraint from `2.12.0` to `3.0.0`
+- Update `lints: ^2.0.1` to `lints: ^3.0.0`
+
+BREAKING CHANGES:
+- `YAMLWriter` renamed to `YamlWriter` ([Effective Dart reference](https://dart.dev/effective-dart/style#do-capitalize-acronyms-and-abbreviations-longer-than-two-letters-like-words)).
+- Deprecated `identSize` property is removed. Use `indentSize` instead.
+- `toEncodable` property is removed. Use constructor parameter instead (`YamlWriter#toEncodable`).
+
+
 ## 1.0.3
 
 - `YAMLWriter`:

example/yaml_writer_example.dart

@@ -1,7 +1,7 @@
 import 'package:yaml_writer/yaml_writer.dart';
 
 void main() {
-  var yamlWriter = YAMLWriter();
+  var yamlWriter = YamlWriter();
 
   var yamlDoc = yamlWriter.write({
     'name': 'Joe',

lib/src/node.dart

@@ -0,0 +1,156 @@
+import 'dart:math';
+
+import 'yaml_context.dart';
+
+sealed class Node {
+  bool get requiresNewLine => false;
+
+  List<String> toYaml(YamlContext context);
+}
+
+class NullNode extends Node {
+  @override
+  List<String> toYaml(YamlContext context) => ['null'];
+}
+
+class NumNode extends Node {
+  final num number;
+
+  NumNode(this.number);
+
+  @override
+  List<String> toYaml(YamlContext context) => ['$number'];
+}
+
+class BoolNode extends Node {
+  final bool boolean;
+
+  BoolNode(this.boolean);
+
+  @override
+  List<String> toYaml(YamlContext context) => ['$boolean'];
+}
+
+class StringNode extends Node {
+  final String text;
+
+  StringNode(this.text);
+
+  @override
+  List<String> toYaml(YamlContext context) {
+    List<String> yamlLines = [];
+
+    if (text.contains('\n')) {
+      bool endsWithLineBreak = text.endsWith('\n');
+
+      List<String> lines;
+      if (endsWithLineBreak) {
+        yamlLines.add('|');
+        lines = text.substring(0, text.length - 1).split('\n');
+      } else {
+        yamlLines.add('|-');
+        lines = text.split('\n');
+      }
+
+      for (int index = 0; index < lines.length; index++) {
+        yamlLines.add(lines[index]);
+      }
+    } else {
+      var containsSingleQuote = text.contains("'");
+
+      if (context.allowUnquotedStrings &&
+          !containsSingleQuote &&
+          _isValidUnquotedString(text)) {
+        yamlLines.add(text);
+      } else if (!containsSingleQuote) {
+        yamlLines.add('\'$text\'');
+      } else {
+        var str = text.replaceAll('\\', '\\\\').replaceAll('"', '\\"');
+        yamlLines.add('"$str"');
+      }
+    }
+
+    return yamlLines;
+  }
+
+  static final _regexpInvalidUnquotedChars = RegExp(
+      r'[^0-9a-zA-ZàèìòùÀÈÌÒÙáéíóúýÁÉÍÓÚÝâêîôûÂÊÎÔÛãñõÃÑÕäëïöüÿÄËÏÖÜŸçÇßØøÅåÆæœ@/. \t-]');
+
+  bool _isValidUnquotedString(String s) =>
+      !_regexpInvalidUnquotedChars.hasMatch(s) &&
+      !s.startsWith('@') &&
+      !s.startsWith('-');
+}
+
+class ListNode extends Node {
+  final List<Node> subnodes;
+
+  ListNode(this.subnodes);
+
+  @override
+  bool get requiresNewLine => subnodes.isNotEmpty;
+
+  @override
+  List<String> toYaml(YamlContext context) {
+    if (subnodes.isEmpty) {
+      return ['[]'];
+    }
+
+    final List<String> lines = [];
+
+    for (final node in subnodes) {
+      final nodeYaml = node.toYaml(context);
+
+      final firstIndent = "-${' ' * max(1, context.indentSize - 1)}";
+      final subsequentIndent = ' ' * firstIndent.length;
+
+      lines.add("$firstIndent${nodeYaml.first}");
+      for (int i = 1; i < nodeYaml.length; i++) {
+        lines.add("$subsequentIndent${nodeYaml[i]}");
+      }
+    }
+
+    return lines;
+  }
+}
+
+class MapNode extends Node {
+  final Map<String, Node> subnodesMap;
+
+  MapNode(this.subnodesMap);
+
+  @override
+  bool get requiresNewLine => subnodesMap.isNotEmpty;
+
+  @override
+  List<String> toYaml(YamlContext context) {
+    if (subnodesMap.isEmpty) {
+      return ['{}'];
+    }
+
+    final List<String> lines = [];
+
+    for (final entry in subnodesMap.entries) {
+      final key = entry.key;
+      final node = entry.value;
+
+      final nodeYaml = node.toYaml(context);
+
+      final indent = ' ' * context.indentSize;
+
+      if (node.requiresNewLine) {
+        lines.add("$key: ");
+        for (final line in nodeYaml) {
+          lines.add("$indent$line");
+        }
+      } else {
+        lines.add("$key: ${nodeYaml.first}");
+        for (int i = 1; i < nodeYaml.length; i++) {
+          lines.add("$indent${nodeYaml[i]}");
+        }
+      }
+    }
+
+    return lines;
+  }
+}

lib/src/yaml_context.dart

@@ -0,0 +1,10 @@
+class YamlContext {
+  final int indentSize;
+
+  final bool allowUnquotedStrings;
+
+  YamlContext({
+    required this.indentSize,
+    required this.allowUnquotedStrings,
+  });
+}

lib/src/yaml_writer.dart

@@ -0,0 +1,71 @@
+import 'dart:convert';
+import 'dart:math';
+
+import 'package:yaml_writer/src/node.dart';
+
+import 'yaml_context.dart';
+
+@Deprecated('Use YamlWriter.')
+typedef YAMLWriter = YamlWriter;
+
+/// YAML Writer.
+class YamlWriter extends Converter<Object?, String> {
+  static dynamic _defaultToEncodable(dynamic object) => object.toJson();
+
+  /// The indentation size.
+  ///
+  /// Must be greater or equal to `1`.
+  ///
+  /// Defaults to `2`.
+  final int indentSize;
+
+  /// If `true` it will allow unquoted strings.
+  final bool allowUnquotedStrings;
+
+  /// Used to convert objects to an encodable version.
+  final Object? Function(dynamic object) toEncodable;
+
+  YamlWriter({
+    int indentSize = 2,
+    this.allowUnquotedStrings = false,
+    Object? Function(dynamic object)? toEncodable,
+  })  : indentSize = max(1, indentSize),
+        toEncodable = toEncodable ?? _defaultToEncodable;
+
+  /// Converts [input] to an YAML document as [String].
+  ///
+  /// This implements `dart:convert` [Converter].
+  ///
+  /// - Calls [write].
+  @override
+  String convert(Object? input) => write(input);
+
+  /// Writes [object] to an YAML document as [String].
+  String write(Object? object) {
+    final node = _parseNode(object);
+    final context = YamlContext(
+      indentSize: indentSize,
+      allowUnquotedStrings: allowUnquotedStrings,
+    );
+    final yaml = node.toYaml(context);
+    return '${yaml.join('\n')}\n';
+  }
+
+  Node _parseNode(Object? object) {
+    if (object == null) {
+      return NullNode();
+    } else if (object is num) {
+      return NumNode(object);
+    } else if (object is bool) {
+      return BoolNode(object);
+    } else if (object is String) {
+      return StringNode(object);
+    } else if (object is List) {
+      return ListNode(object.map(_parseNode).toList());
+    } else if (object is Map) {
+      return MapNode(object.map((k, v) => MapEntry(k, _parseNode(v))));
+    } else {
+      return _parseNode(toEncodable(object));
+    }
+  }
+}