Initial KV API concept

Core/Option/CoreContextStorageService.cs

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+#nullable enable
+using System.Linq;
+using System.Threading.Tasks;
+using Kruzya.TelegramBot.Core.Data;
+using Kruzya.TelegramBot.Core.Extensions;
+using Microsoft.EntityFrameworkCore;
+
+namespace Kruzya.TelegramBot.Core.Option;
+
+public class CoreContextStorageService : IOptionStorageAdapter
+{
+    private CoreContext _db;
+    public CoreContextStorageService(CoreContext db)
+    {
+        _db = db;
+    }
+
+    public async Task<byte[]?> LoadValueAsync(IOptionKey key)
+    {
+        var entity = await BuildQueryForKey(key).FirstOrDefaultAsync();
+
+        return entity?.Value;
+    }
+
+    public async Task SaveValueAsync(IOptionKey key, byte[] value)
+    {
+         var entity = await BuildQueryForKey(key).FirstOrDefaultAsync();
+         if (entity == null)
+         {
+             entity = await CreateEntity(key);
+         }
+
+         entity.Value = value;
+         _db.AddOrUpdate(entity);
+    }
+
+    private IQueryable<BotUserValue> BuildQueryForKey(IOptionKey key)
+    {
+        var legacyUserId = key.UserId ?? 0;
+
+        return _db.UserValues.Where(e => e.BotUser.ChatId == key.ChatId && e.BotUser.UserId == legacyUserId
+                                                                        && e.Name == key.Identifier);
+    }
+
+    private async Task<BotUserValue> CreateEntity(IOptionKey key)
+    {
+        var entity = _db.UserValues.Create()!;
+        entity.BotUser = await _db.Users.FindOrCreate(key.ChatId, key.UserId ?? 0);
+        return entity;
+    }
+}