Refactor LastBlockDownloader to LastBlockSource and implement singlet…

…on pattern

src/DownloaderV2/Builders/DocumentBuilder/AbstractDocument.cs

@@ -0,0 +1,18 @@
+using Newtonsoft.Json.Linq;
+using DownloaderV2.Models.Covalent;
+
+namespace DownloaderV2.Builders.DocumentBuilder;
+
+public abstract class AbstractDocument(long savedLastBlock, long sourceLastBlock)
+{
+    public abstract string UrlSet { get; }
+    public abstract string GetUrl { get; }
+    public long SavedLastBlock { get; set; } = savedLastBlock;
+    public long SourceLastBlock { get; set; } = sourceLastBlock;
+
+    public abstract Task<InputData> FetchDataAsync();
+
+    protected abstract JToken? SendRequest(string url);
+
+    protected abstract InputData DeserializeResponse(JToken responseData);
+}

src/DownloaderV2/Builders/LastBlockBuilder/LastBlockSource.cs

@@ -0,0 +1,24 @@
+using DownloaderV2.Builders.LastBlockBuilder.SourcePage;
+
+namespace DownloaderV2.Builders.LastBlockBuilder;
+
+public class LastBlockSource
+{
+    private static LastBlockSource? _instance;
+    private static readonly object Lock = new object();
+    private Task<Dictionary<long, long>>? _lastBlockDictionary;
+    private readonly GetSourcePage _getLastBlock;
+
+    private LastBlockSource(GetSourcePage getLastBlock) => _getLastBlock = getLastBlock;
+
+    public static LastBlockSource GetInstance(GetSourcePage getLastBlock)
+    {
+        lock (Lock)
+        {
+            _instance ??= new LastBlockSource(getLastBlock);
+        }
+        return _instance;
+    }
+
+    public Task<Dictionary<long, long>> LastBlockDictionary => _lastBlockDictionary ??= _getLastBlock.FetchDataAsync();
+}

src/DownloaderV2/Builders/LastBlockBuilder/SourcePage/GetLastBlock.cs

@@ -7,8 +7,10 @@
 
 namespace DownloaderV2.Builders.LastBlockBuilder.SourcePage;
 
-public class GetLastBlock(string getUri) : GetSourcePage(getUri)
+public class GetLastBlock(string getUri) : GetSourcePage
 {
+    public override string GetUri { get; } = getUri;
+
     public GetLastBlock() : this($"{Environments.LastBlockDownloaderUrl.Get<string>()}{Environments.LastBlockKey.Get<string>()}") { }
 
     public override async Task<Dictionary<long, long>> FetchDataAsync()

src/DownloaderV2/Builders/LastBlockBuilder/SourcePage/GetSourcePage.cs

@@ -3,9 +3,9 @@
 
 namespace DownloaderV2.Builders.LastBlockBuilder.SourcePage;
 
-public abstract class GetSourcePage(string getUri)
+public abstract class GetSourcePage
 {
-    public readonly string GetUri = getUri;
+    public abstract string GetUri { get; }
 
     public abstract Task<Dictionary<long, long>> FetchDataAsync();
 

src/DownloaderV2/DownloadHandler.cs

@@ -20,7 +20,10 @@ public async Task<IEnumerable<ResultObject>> HandleAsync()
     {
         LogRouter.LogRouter.Initialize(context.GetType());
 
-        _lastBlockDictionary = await new LastBlockDownloader(new GetLastBlock()).LastBlockDictionary;
+        // TODO: From ServiceProvider in the next step
+        var lastBlockSource = LastBlockSource.GetInstance(new GetLastBlock());
+        _lastBlockDictionary = await lastBlockSource.LastBlockDictionary;
+
         var uniqueEvents = _settingDownloader.DownloaderSettings
             .GroupBy(x => new { x.ChainId, x.ContractAddress, x.EventHash })
             .Select(group => group.First())

test/DownloaderV2.Tests/Builders/LastBlockBuilder/LastBlockDownloaderTest.cs

@@ -1,8 +1,6 @@
-using DownloaderV2.Builders.LastBlockBuilder;
+using Moq;
+using DownloaderV2.Builders.LastBlockBuilder;
 using DownloaderV2.Builders.LastBlockBuilder.SourcePage;
-using DownloaderV2.Models.LastBlock;
-using Moq;
-using Newtonsoft.Json;
 
 namespace DownloaderV2.Tests.Builders.LastBlockBuilder
 {
@@ -27,12 +25,31 @@ public async Task LastBlockDictionary_ReturnsCorrectData()
             mockLastBlockService.Setup(service => service.FetchDataAsync())
                 .ReturnsAsync(expectedDictionary);
 
-            var downloader = new LastBlockDownloader(mockLastBlockService.Object);
+            ResetSingleton();
 
+            var downloader = LastBlockSource.GetInstance(mockLastBlockService.Object);
             var actualDictionary = await downloader.LastBlockDictionary;
 
             Assert.NotNull(actualDictionary);
             Assert.Equal(expectedDictionary, actualDictionary);
         }
+
+        [Fact]
+        public void GetInstance_ShouldReturnSameInstance()
+        {
+            var mockGetSourcePage = new Mock<GetLastBlock>("testUri");
+
+            var instance1 = LastBlockSource.GetInstance(mockGetSourcePage.Object);
+            var instance2 = LastBlockSource.GetInstance(mockGetSourcePage.Object);
+
+            Assert.Equal(instance1, instance2);
+        }
+
+        private static void ResetSingleton()
+        {
+            typeof(LastBlockSource)
+                .GetField("_instance", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic)
+                ?.SetValue(null, null);
+        }
     }
 }