io utils; single favorite folder exporting and importing

lib/foundation/favorites.dart

@@ -1,5 +1,8 @@
+import 'dart:convert';
+
 import 'package:sqlite3/sqlite3.dart';
 import 'package:venera/foundation/appdata.dart';
+import 'package:venera/foundation/log.dart';
 import 'dart:io';
 
 import 'app.dart';
@@ -92,7 +95,39 @@ class FavoriteItem implements Comic {
 
   @override
   Map<String, dynamic> toJson() {
-    throw UnimplementedError();
+    return {
+      "name": name,
+      "author": author,
+      "type": type.value,
+      "tags": tags,
+      "id": id,
+      "coverPath": coverPath,
+    };
+  }
+
+  static FavoriteItem fromJson(Map<String, dynamic> json) {
+    var type = json["type"] as int;
+    if(type == 0 && json['coverPath'].toString().startsWith('http')) {
+      type = 'picacg'.hashCode;
+    } else if(type == 1) {
+      type = 'ehentai'.hashCode;
+    } else if(type == 2) {
+      type = 'jm'.hashCode;
+    } else if(type == 3) {
+      type = 'hitomi'.hashCode;
+    } else if(type == 4) {
+      type = 'wnacg'.hashCode;
+    } else if(type == 6) {
+      type = 'nhentai'.hashCode;
+    }
+    return FavoriteItem(
+      id: json["id"] ?? json['target'],
+      name: json["name"],
+      author: json["author"],
+      coverPath: json["coverPath"],
+      type: ComicType(type),
+      tags: List<String>.from(json["tags"] ?? []),
+    );
   }
 }
 
@@ -525,4 +560,39 @@ class LocalFavoritesManager {
       comic.type.value
     ]);
   }
+
+  String folderToJson(String folder) {
+    var res = _db.select("""
+      select * from "$folder";
+    """);
+    return jsonEncode({
+      "info": "Generated by Venera",
+      "name": folder,
+      "comics": res.map((e) => FavoriteItem.fromRow(e).toJson()).toList(),
+    });
+  }
+
+  void fromJson(String json) {
+    var data = jsonDecode(json);
+    var folder = data["name"];
+    if(folder == null || folder is! String) {
+      throw "Invalid data";
+    }
+    if (folderNames.contains(folder)) {
+      int i = 0;
+      while (folderNames.contains("$folder($i)")) {
+        i++;
+      }
+      folder = "$folder($i)";
+    }
+    createFolder(folder);
+    for (var comic in data["comics"]) {
+      try {
+        addComic(folder, FavoriteItem.fromJson(comic));
+      }
+      catch(e) {
+        Log.error("Import Data", e.toString());
+      }
+    }
+  }
 }