feat(passkit): Work towards localizable pass files (#40)

* localization

* add translation file parsing

passkit/lib/src/passkit/pkpass.dart

@@ -6,6 +6,7 @@ import 'package:passkit/src/passkit/pass_data.dart';
 import 'package:passkit/src/passkit/pass_type.dart';
 import 'package:passkit/src/passkit/personalization.dart';
 import 'package:passkit/src/passkit/pk_pass_image.dart';
+import 'package:passkit/src/strings_parser/naive_strings_file_parser.dart';
 
 /// Dart uses a special fast decoder when using a fused [Utf8Decoder] and [JsonDecoder].
 /// This speeds up decoding.
@@ -48,6 +49,7 @@ class PkPass {
     this.personalizationLogo,
   });
 
+  /// Parses bytes to a [PkPass] file.
   static PkPass fromBytes(final List<int> bytes) {
     Map<String, dynamic>? manifestJson;
     Map<String, dynamic>? passJson;
@@ -94,12 +96,7 @@ class PkPass {
     final background = _loadImage(archive, 'background');
     final personalizationLogo = _loadImage(archive, 'personalizationLogo');
 
-    Map<String, Map<String, String>> availableTranslations = {};
-
-    for (final folder in archive.files.where((element) => !element.isFile)) {
-      final languageName = folder.name.split('.').first;
-      availableTranslations[languageName] = {};
-    }
+    final availableTranslations = _getTranslations(archive);
 
     return PkPass(
       pass: PassData.fromJson(passJson!),
@@ -115,6 +112,7 @@ class PkPass {
       personalization: personalizationJson == null
           ? null
           : Personalization.fromJson(personalizationJson),
+      languageData: availableTranslations,
     );
   }
 
@@ -149,6 +147,25 @@ class PkPass {
     );
   }
 
+  static Map<String, Map<String, String>> _getTranslations(Archive archive) {
+    final languageData = <String, Map<String, String>>{};
+
+    // The Archive object doesn't have APIs to work with folders.
+    // Instead the file name contains a `/` indicating the file is within a folder.
+    // Example: `file.name == en.lproj/pass.strings`
+    final translationFiles = archive.files
+        .where((element) => element.isFile)
+        .where((file) => file.name.endsWith('.lproj/pass.strings'));
+
+    for (final languageFile in translationFiles) {
+      final language = languageFile.name.split('.').first;
+
+      languageData[language] =
+          parseStringsFile(languageFile.content as List<int>);
+    }
+    return languageData;
+  }
+
   final PassData pass;
 
   final Map<String, dynamic> manifest;

passkit/lib/src/strings_parser/naive_strings_file_parser.dart

@@ -0,0 +1,41 @@
+import 'dart:convert';
+
+/// Parses [content] to a [Map<String, String>] which contains the
+/// key-value-pairs for translations.
+Map<String, String> parseStringsFile(List<int> content) {
+  final string = _stringsFileDecoder.convert(content);
+  return naiveStringsFileParser(string);
+}
+
+// TODO(ueman): `.strings` files should be read as UTF-16, not UTF-8.
+final Converter<List<int>, String> _stringsFileDecoder = const Utf8Decoder();
+
+/// Here's a breakdown of the pattern:
+/// - r'"((?:\"|[^"])*)"': This section matches the key, which is enclosed in
+///   double quotes. Inside the quotes, it captures any character sequence that
+///   is either a backslash-escaped double quote or any character that is not a
+///   double quote.
+/// - \s?=\s?: This part matches the equals sign with optional whitespace before
+///   and after it.
+/// - r'"((?:\"|[^"])*)"': This section matches the value, using a similar
+///   pattern to capture any character sequence within double quotes.
+/// - \s?;: This last part matches optional whitespace followed by a semicolon.
+final _stringsParserRegEx =
+    RegExp(r'"((?:\\"|[^"])*)"\s?=\s?"((?:\\"|[^"])*)"\s?;');
+
+/// This method uses a quite naive approach to parse Apples `strings` file
+/// format with a [RegExp]. It doesn't support placeholders.
+///
+/// The returned map has key value pairs.
+///
+/// See also:
+/// - https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/LoadingResources/Strings/Strings.html
+/// - https://localizely.com/apple-strings-file/
+Map<String, String> naiveStringsFileParser(String stringsFile) {
+  final matches = _stringsParserRegEx
+      .allMatches(stringsFile)
+      .where((match) => match.group(1) != null && match.group(2) != null)
+      .map((match) => MapEntry(match.group(1)!, match.group(2)!));
+
+  return Map.fromEntries(matches);
+}

passkit/test/strings_file_parser_test.dart

@@ -0,0 +1,34 @@
+import 'package:passkit/src/strings_parser/naive_strings_file_parser.dart';
+import 'package:test/test.dart';
+
+// Taken from https://developer.apple.com/library/archive/documentation/UserExperience/Conceptual/PassKit_PG/Creating.html
+final _testString = '''"origin_SVQ" = "Sevilla";
+"destination_LHR" = "Londres";
+''';
+
+// Taken from https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/LoadingResources/Strings/Strings.html
+final _testStringWithComments = '''/* Insert Element menu item */
+"Insert Element" = "Insert Element";
+/* Error string used for unknown error types. */
+"ErrorString_1" = "An unknown error occurred.";
+''';
+
+void main() {
+  test('naiveStringsFileParser() parses example correctly', () {
+    final keyValue = naiveStringsFileParser(_testString);
+    expect(keyValue, {
+      'origin_SVQ': 'Sevilla',
+      'destination_LHR': 'Londres',
+    });
+  });
+
+  test(
+      'naiveStringsFileParser() parsess example correctly despite comments in it',
+      () {
+    final keyValue = naiveStringsFileParser(_testStringWithComments);
+    expect(keyValue, {
+      'Insert Element': 'Insert Element',
+      'ErrorString_1': 'An unknown error occurred.',
+    });
+  });
+}