feat: merge with platform environment

lib/src/dotenv.dart

@@ -1,16 +1,28 @@
+
+import 'dart:async';
+import 'dart:io';
+
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart' show rootBundle;
+import 'package:flutter/widgets.dart';
+import 'package:flutter_dotenv/src/parser.dart';
+
+import 'errors.dart';
+
 /// Loads environment variables from a `.env` file.
 ///
 /// ## usage
 ///
-/// Once you call [load] or the factory constructor with a valid env, the top-level [env] map is available.
+/// Once you call [load], the top-level [env] map is available.
 /// You may wish to prefix the import.
 ///
-///     import 'package:flutter_dotenv/flutter_dotenv.dart' show load, env;
+///     import 'package:dotenv/dotenv.dart' show load, env;
 ///
 ///     void main() {
-///       await DotEnv().load('.env');
-///       runApp(App());
-///       var x = DotEnv().env['foo'];
+///       load();
+///       var x = env['foo'];
 ///       // ...
 ///     }
 ///
@@ -18,77 +30,46 @@
 ///
 ///     const _requiredEnvVars = const ['host', 'port'];
 ///     bool get hasEnv => isEveryDefined(_requiredEnvVars);
-import 'dart:async';
-import 'dart:io';
-
-import 'package:flutter/foundation.dart';
-import 'package:flutter/material.dart';
-import 'package:flutter/services.dart' show rootBundle;
-import 'package:flutter/widgets.dart';
-
-import './parser.dart';
-
 ///
-/// ## usage
-///
-///   Future main() async {
-///     await DotEnv().load('.env');
-///     //...runapp
-///   }
-///
-/// Verify required variables are present:
-///
-///     const _requiredEnvVars = const ['host', 'port'];
-///     bool get hasEnv => isEveryDefined(_requiredEnvVars);
+var _isInitialized = false;
+var _envMap = Map<String, String>.from(Platform.environment);
 
-class DotEnv {
-  Map<String, String> _env = <String, String>{};
-  static DotEnv _singleton;
-
-  Map<String, String> get env {
-    if (_env.isEmpty) {
-      stderr.writeln(
-          '[flutter_dotenv] No env values found. Make sure you have called DotEnv.load()');
-    }
-    return _env;
+/// A copy of [Platform.environment](dart:io) including variables loaded at runtime from a file.
+Map<String, String> get env {
+  if(!_isInitialized) {
+    throw NotInitializedError();
+  }
+  return _envMap;
+}
+
+/// Clear [env] and optionally overwrite with a new writable copy of [Platform.environment](dart:io).
+Map clean({ bool retainPlatformEnvironment = true}) => _envMap = Map.from(retainPlatformEnvironment ? Platform.environment : {});
+
+/// Loads environment variables from the env file into a map
+Future load({String fileName = '.env', Parser parser = const Parser(), bool includePlatformEnvironment = true}) async {
+  clean(retainPlatformEnvironment: includePlatformEnvironment);
+  final allLines = await _getEntriesFromFile(fileName);
+  final envEntries = parser.parse(allLines);
+  _envMap.addAll(envEntries);
+  _isInitialized = true;
+}
+
+/// 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) => _envMap[k] != null && _envMap[k].isNotEmpty);
+
+
+Future<List<String>> _getEntriesFromFile(String filename) async {
+  try {
+    WidgetsFlutterBinding.ensureInitialized();
+    var envString = await rootBundle.loadString(filename);
+    if (envString.isEmpty) {
+      throw EmptyEnvFileError();
+    }
+    return envString.split('\n');
+  } on FlutterError {
+    throw FileNotFoundError();
   }
-
-  set env(Map<String, String> env) {
-    _env = env;
-  }
-
-  /// 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);
-
-  /// Read environment variables from [filename] and add them to [env].
-  /// Logs to [stderr] if [filename] does not exist.
-  Future load([String filename = '.env', Parser psr = const Parser()]) async {
-    var lines = await _verify(filename);
-    _env.addAll(psr.parse(lines));
-  }
-
-  Future<List<String>> _verify(String filename) async {
-    try {
-      WidgetsFlutterBinding.ensureInitialized();
-      var str = await rootBundle.loadString(filename);
-      if (str.isNotEmpty) return str.split('\n');
-      stderr.writeln('[flutter_dotenv] Load failed: file $filename was empty');
-    } on FlutterError {
-      stderr.writeln('[flutter_dotenv] Load failed: file not found');
-    }
-    return [];
-  }
-
-  factory DotEnv({Map<String, String> env}) {
-    if (_singleton == null) {
-      _singleton = DotEnv._internal(env: env);
-    }
-    return _singleton;
-  }
-
-  DotEnv._internal({Map<String, String> env})
-      : _env = env ?? <String, String>{};
 }

lib/src/errors.dart

@@ -0,0 +1,16 @@
+
+import 'dart:async';
+import 'dart:io';
+
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart' show rootBundle;
+import 'package:flutter/widgets.dart';
+
+import '../flutter_dotenv.dart';
+
+class NotInitializedError extends Error {}
+class ValueNotFound extends Error {}
+class FileNotFoundError extends Error {}
+class EmptyEnvFileError extends Error {}

lib/src/parser.dart

@@ -1,32 +1,35 @@
-import 'package:meta/meta.dart';
+import 'dart:io';
 
+import 'package:meta/meta.dart';
 /// 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)
+  /// 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>{};
-    for (var line in lines) {
+    lines.forEach((line) {
       var kv = parseOne(line, env: out);
-      if (kv.isEmpty) continue;
+      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 {}}) {
+      {Map<String, String> env: const {}}) {
     var stripped = strip(line);
     if (!_isValid(stripped)) return {};
 
@@ -36,11 +39,25 @@ class Parser {
     if (k.isEmpty) return {};
 
     var rhs = stripped.substring(idx + 1, stripped.length).trim();
+    var quotChar = surroundingQuote(rhs);
     var v = unquote(rhs);
 
-    return {k: v};
+    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);
+        if (!_has(env, k)) return _tryPlatformEnv(k);
+        return env[k];
+      });
+
   /// If [val] is wrapped in single or double quotes, returns the quote character.
   /// Otherwise, returns the empty string.
   @visibleForTesting
@@ -63,4 +80,13 @@ class Parser {
   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];
+  }
+}