feat: Implement plaintext parsing

lib/matrix_api_lite.dart

@@ -80,6 +80,7 @@ export 'src/model/auth/authentication_token.dart';
 export 'src/model/auth/authentication_types.dart';
 export 'src/model/auth/authentication_user_identifier.dart';
 export 'src/model/events/forwarded_room_key_content.dart';
+export 'src/model/events/olm_plaintext_payload.dart';
 export 'src/model/events/room_encrypted_content.dart';
 export 'src/model/events/room_encryption_content.dart';
 export 'src/model/events/room_key_content.dart';

lib/src/model/events/olm_plaintext_payload.dart

@@ -0,0 +1,40 @@
+import '../../utils/try_get_map_extension.dart';
+
+class OlmPlaintextPayload {
+  String type;
+  Map<String, dynamic> content;
+  String sender;
+  String recipient;
+  Map<String, String> recipientKeys;
+  Map<String, String> keys;
+
+  OlmPlaintextPayload({
+    this.type,
+    this.content,
+    this.sender,
+    this.recipient,
+    this.recipientKeys,
+    this.keys,
+  }) : super();
+
+  factory OlmPlaintextPayload.fromJson(Map<String, dynamic> json) =>
+      OlmPlaintextPayload(
+        sender: json.tryGet<String>('sender'),
+        type: json.tryGet<String>('type'),
+        content: json.tryGetMap<String, dynamic>('content'),
+        recipient: json.tryGet<String>('recipient'),
+        recipientKeys: json.tryGetMap<String, String>('recipient_keys'),
+        keys: json.tryGetMap<String, String>('keys'),
+      );
+
+  Map<String, dynamic> toJson() {
+    final data = <String, dynamic>{};
+    if (type != null) data['type'] = type;
+    if (sender != null) data['sender'] = sender;
+    if (content != null) data['content'] = content;
+    if (recipient != null) data['recipient'] = recipient;
+    if (recipientKeys != null) data['recipient_keys'] = recipientKeys;
+    if (keys != null) data['keys'] = keys;
+    return data;
+  }
+}

lib/src/utils/try_get_map_extension.dart

@@ -20,7 +20,7 @@ extension TryGetMapExtension on Map<String, dynamic> {
     final value = this[key];
     if (value != null && !(value is List)) {
       Logs().w(
-          'Expected "${T.runtimeType}" in event content for the key "$key" but got "${value.runtimeType}".');
+          'Expected "List<${T.runtimeType}>" in event content for the key "$key" but got "${value.runtimeType}".');
       return fallbackValue;
     }
     if (value == null && fallbackValue != null) {
@@ -29,10 +29,31 @@ extension TryGetMapExtension on Map<String, dynamic> {
       return fallbackValue;
     }
     try {
-      return List<T>.from(value as List<dynamic>);
+      return List<T>.from(value);
     } catch (_) {
       Logs().w(
-          'Unable to create List<${T.runtimeType}> in event content for the key "$key');
+          'Unable to create "List<${T.runtimeType}>" in event content for the key "$key"');
+      return fallbackValue;
+    }
+  }
+
+  Map<A, B> tryGetMap<A, B>(String key, [Map<A, B> fallbackValue]) {
+    final value = this[key];
+    if (value != null && !(value is Map)) {
+      Logs().w(
+          'Expected "Map<${A.runtimeType},${B.runtimeType}>" in event content for the key "$key" but got "${value.runtimeType}".');
+      return fallbackValue;
+    }
+    if (value == null && fallbackValue != null) {
+      Logs().w(
+          'Required field in event content for the key "$key" is null. Set to "$fallbackValue".');
+      return fallbackValue;
+    }
+    try {
+      return Map<A, B>.from(value);
+    } catch (_) {
+      Logs().w(
+          'Unable to create "Map<${A.runtimeType},${B.runtimeType}>" in event content for the key "$key"');
       return fallbackValue;
     }
   }

test/event_content_test.dart

@@ -146,5 +146,20 @@ void main() {
       expect(BasicEvent.fromJson(json).parsedForwardedRoomKeyContent.toJson(),
           json['content']);
     });
+    test('OLM Plaintext Payload', () {
+      var json = <String, dynamic>{
+        'type': '<type of the plaintext event>',
+        'content': <String, dynamic>{
+          'msgtype': 'm.text',
+          'body': 'Hello world',
+        },
+        'sender': '<sender_user_id>',
+        'recipient': '<recipient_user_id>',
+        'recipient_keys': {'ed25519': '<our_ed25519_key>'},
+        'keys': {'ed25519': '<sender_ed25519_key>'}
+      };
+      json = jsonDecode(jsonEncode(json));
+      expect(OlmPlaintextPayload.fromJson(json).toJson(), json);
+    });
   });
 }