added validation to blockchain client

Author: Alexandr Dolenko

block-chain/BlockChainCore/BlockChain.cs

@@ -28,6 +28,11 @@ public IBlock CreateBlock(string data)
         return block;
     }
 
+    /// <summary>
+    /// Adds an existing block to the blockchain.
+    /// </summary>
+    /// <param name="block">The block to be added.</param>
+    /// <exception cref="InvalidOperationException">Thrown when the block's previous hash does not match the hash of the last block in the blockchain.</exception>
     public void AddBlock(IBlock block)
     {
         var previousBlock = _blocks.Last();
@@ -81,5 +86,5 @@ public bool IsValid()
 
         return true;
     }
-
+    
 }

block-chain/bccli/Program.cs

@@ -69,17 +69,24 @@ await Task.Run(() =>
                 Console.WriteLine(lastJson);
                 continue;
             }
-            if (command.ToLower() == "clear")
+            if (command.Equals("clear", StringComparison.OrdinalIgnoreCase))
             {
                 Console.Clear();
                 continue;
             }
+            if (command.Equals("valid", StringComparison.OrdinalIgnoreCase))
+            {
+                var isValid = blockChain.IsValid();
+                Console.WriteLine($"Chain is valid: {isValid}");
+                continue;
+            }
             if (command.ToLower() == "help")
             {
                 Console.WriteLine("Commands: ");
                 Console.WriteLine("add 'item to add' - add a new block to the chain");
                 Console.WriteLine("showchain - to exit");
                 Console.WriteLine("showlast - to display the last block");
+                Console.WriteLine("valid -  to check if the chain is valid");
                 Console.WriteLine("clear - to clear the console");
                 Console.WriteLine("help - to display this message");
                 continue;