Add dotenv configuration provider

.env

@@ -0,0 +1,2 @@
+app.name = 'CUBETIQ Solution'
+export NAME='Sambo Chea'

example/example.dart

@@ -0,0 +1,3 @@
+void main() {
+  print('Example');
+}

lib/dotenv/dotenv.dart

@@ -0,0 +1,54 @@
+/// Loads environment variables from a `.env` file.
+///
+/// ## usage
+///
+/// Once you call [load], the top-level [env] map is available.
+/// You may wish to prefix the import.
+///
+///     import 'package:dotenv/dotenv.dart' show load, env;
+///
+///     void main() {
+///       load();
+///       var x = env['foo'];
+///       // ...
+///     }
+///
+/// Verify required variables are present:
+///
+///     const _requiredEnvVars = const ['host', 'port'];
+///     bool get hasEnv => isEveryDefined(_requiredEnvVars);
+library dotenv;
+
+import 'dart:io';
+
+import 'package:meta/meta.dart';
+
+part 'parser.dart';
+
+var _env = Map<String, String>.from(Platform.environment);
+
+/// A copy of [Platform.environment](dart:io) including variables loaded at runtime from a file.
+Map<String, String> get env => _env;
+
+/// Overwrite [env] with a new writable copy of [Platform.environment](dart:io).
+Map clean() => _env = Map.from(Platform.environment);
+
+/// True if all supplied variables have nonempty value; false otherwise.
+/// Differs from [containsKey](dart:core) by excluding null values.
+/// Note [load] should be called first.
+bool isEveryDefined(Iterable<String> vars) =>
+    vars.every((k) => _env[k] != null && (_env[k]?.isNotEmpty ?? false));
+
+/// Read environment variables from [filename] and add them to [env].
+/// Logs to [stderr] if [filename] does not exist.
+void load([String filename = '.env', Parser psr = const Parser()]) {
+  var file = File.fromUri(Uri.file(filename));
+  var lines = _verify(file);
+  _env.addAll(psr.parse(lines));
+}
+
+List<String> _verify(File file) {
+  if (file.existsSync()) return file.readAsLinesSync();
+  stderr.writeln('[dotenv] Load failed: file not found: $file');
+  return [];
+}

lib/dotenv/parser.dart

@@ -0,0 +1,92 @@
+part of dotenv;
+
+/// Creates key-value pairs from strings formatted as environment
+/// variable definitions.
+class Parser {
+  static const _singleQuot = "'";
+  static const _keyword = 'export';
+
+  static final _comment = RegExp(r'''#.*(?:[^'"])$''');
+  static final _surroundQuotes = RegExp(r'''^(['"])(.*)\1$''');
+  static final _bashVar = RegExp(r'(?:\\)?(\$)(?:{)?([a-zA-Z_][\w]*)+(?:})?');
+
+  /// [Parser] methods are pure functions.
+  const Parser();
+
+  /// Creates a [Map](dart:core) suitable for merging into [Platform.environment](dart:io).
+  /// Duplicate keys are silently discarded.
+  Map<String, String> parse(Iterable<String> lines) {
+    var out = <String, String>{};
+    lines.forEach((line) {
+      var kv = parseOne(line, env: out);
+      if (kv.isEmpty) return;
+      out.putIfAbsent(kv.keys.single, () => kv.values.single);
+    });
+    return out;
+  }
+
+  /// Parses a single line into a key-value pair.
+  @visibleForTesting
+  Map<String, String> parseOne(String line,
+      {Map<String, String> env: const {}}) {
+    var stripped = strip(line);
+    if (!_isValid(stripped)) return {};
+
+    var idx = stripped.indexOf('=');
+    var lhs = stripped.substring(0, idx);
+    var k = swallow(lhs);
+    if (k.isEmpty) return {};
+
+    var rhs = stripped.substring(idx + 1, stripped.length).trim();
+    var quotChar = surroundingQuote(rhs);
+    var v = unquote(rhs);
+
+    if (quotChar == _singleQuot) {
+      return {k: v};
+    }
+
+    return {k: interpolate(v, env)};
+  }
+
+  /// Substitutes $bash_vars in [val] with values from [env].
+  @visibleForTesting
+  String interpolate(String val, Map<String, String> env) =>
+      val.replaceAllMapped(_bashVar, (m) {
+        var k = m.group(2)!;
+        return (!_has(env, k)) ? _tryPlatformEnv(k) ?? '' : env[k] ?? '';
+      });
+
+  /// If [val] is wrapped in single or double quotes, returns the quote character.
+  /// Otherwise, returns the empty string.
+  @visibleForTesting
+  String surroundingQuote(String val) {
+    if (!_surroundQuotes.hasMatch(val)) return '';
+    return _surroundQuotes.firstMatch(val)!.group(1)!;
+  }
+
+  /// Removes quotes (single or double) surrounding a value.
+  @visibleForTesting
+  String unquote(String val) =>
+      val.replaceFirstMapped(_surroundQuotes, (m) => m[2]!).trim();
+
+  /// Strips comments (trailing or whole-line).
+  @visibleForTesting
+  String strip(String line) => line.replaceAll(_comment, '').trim();
+
+  /// Omits 'export' keyword.
+  @visibleForTesting
+  String swallow(String line) => line.replaceAll(_keyword, '').trim();
+
+  bool _isValid(String s) => s.isNotEmpty && s.contains('=');
+
+  /// [null] is a valid value in a Dart map, but the env var representation is empty string, not the string 'null'
+  bool _has(Map<String, String> map, String key) =>
+      map.containsKey(key) && map[key] != null;
+
+  String? _tryPlatformEnv(String key) {
+    if (!_has(Platform.environment, key)) {
+      return '';
+    }
+    return Platform.environment[key];
+  }
+}

lib/dotenv_configuration_provider.dart

@@ -0,0 +1,20 @@
+import 'package:configurable/configuration_provider.dart';
+import 'package:configurable/dotenv/dotenv.dart' show env;
+
+class DotenvConfigurationProvider implements ConfigurationProvider {
+  @override
+  bool containsKey(String key) {
+    return env.containsKey(key);
+  }
+
+  @override
+  String? getOrNull(String key, {String? defaultValue}) {
+    var value = env[key];
+
+    if (value == null) {
+      return defaultValue;
+    }
+
+    return value;
+  }
+}

pubspec.lock

@@ -135,7 +135,7 @@ packages:
     source: hosted
     version: "0.12.10"
   meta:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: meta
       url: "https://pub.dartlang.org"

pubspec.yaml

@@ -8,6 +8,7 @@ environment:
 
 dependencies:
   test: ^1.16.8
+  meta: ^1.3.0
 
 dev_dependencies:
   pedantic: ^1.9.0

test/config_test.dart

@@ -10,4 +10,5 @@ void main() {
     expect(value, equals(result));
     expect(value, equals(SystemConfig.getOrNull(key)));
   });
+  
 }

test/dotenv_test.dart

@@ -0,0 +1,20 @@
+import 'package:configurable/dotenv/dotenv.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('just call env', () {
+    load();
+  
+    var result = env['app.name'];
+
+    expect('CUBETIQ Solution', equals(result));
+  });
+
+  test('get export variable', () {
+    load();
+
+    var result = env['NAME'];
+
+    expect('Sambo Chea', equals(result));
+  });
+}