[Add] Get Accounts and Balances for GasToken (#3614)

* [Add] Get Accounts and Balances for GasToken

* Removed `BalanceOf` extension

* Added null check

* Changed `Seek` to `Find` for `DataCache`

---------

Co-authored-by: Jimmy <[email protected]>

src/Neo/Extensions/SmartContract/GasTokenExtensions.cs

@@ -0,0 +1,42 @@
+// Copyright (C) 2015-2024 The Neo Project.
+//
+// GasTokenExtensions.cs file belongs to the neo project and is free
+// software distributed under the MIT software license, see the
+// accompanying file LICENSE in the main directory of the
+// repository or http://www.opensource.org/licenses/mit-license.php
+// for more details.
+//
+// Redistribution and use in source and binary forms with or without
+// modifications are permitted.
+
+using Neo.Persistence;
+using Neo.SmartContract;
+using Neo.SmartContract.Native;
+using System;
+using System.Collections.Generic;
+using System.Numerics;
+
+namespace Neo.Extensions
+{
+    public static class GasTokenExtensions
+    {
+        public static IEnumerable<(UInt160 Address, BigInteger Balance)> GetAccounts(this GasToken gasToken, DataCache snapshot)
+        {
+            if (gasToken is null)
+                throw new ArgumentNullException(nameof(gasToken));
+
+            if (snapshot is null)
+                throw new ArgumentNullException(nameof(snapshot));
+
+            var kb = new KeyBuilder(gasToken.Id, GasToken.Prefix_Account);
+            var prefixKey = kb.ToArray();
+
+            foreach (var (key, value) in snapshot.Find(prefixKey, SeekDirection.Forward))
+            {
+                var keyBytes = key.ToArray();
+                var addressHash = new UInt160(keyBytes.AsSpan(prefixKey.Length));
+                yield return new(addressHash, value.GetInteroperable<AccountState>().Balance);
+            }
+        }
+    }
+}

src/Neo/SmartContract/Native/FungibleToken.cs

@@ -51,7 +51,7 @@ public abstract class FungibleToken<TState> : NativeContract
         /// <summary>
         /// The prefix for storing account states.
         /// </summary>
-        protected const byte Prefix_Account = 20;
+        protected internal const byte Prefix_Account = 20;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FungibleToken{TState}"/> class.

tests/Neo.UnitTests/Extensions/UT_GasTokenExtensions.cs

@@ -0,0 +1,53 @@
+// Copyright (C) 2015-2024 The Neo Project.
+//
+// UT_GasTokenExtensions.cs file belongs to the neo project and is free
+// software distributed under the MIT software license, see the
+// accompanying file LICENSE in the main directory of the
+// repository or http://www.opensource.org/licenses/mit-license.php
+// for more details.
+//
+// Redistribution and use in source and binary forms with or without
+// modifications are permitted.
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.Extensions;
+using Neo.SmartContract.Native;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Neo.UnitTests.Extensions
+{
+    [TestClass]
+    public class UT_GasTokenExtensions
+    {
+        private NeoSystem system;
+
+        [TestInitialize]
+        public void Initialize()
+        {
+            system = TestBlockchain.TheNeoSystem;
+        }
+
+        [TestCleanup]
+        public void Clean()
+        {
+            TestBlockchain.ResetStore();
+        }
+
+        [TestMethod]
+        public void TestGetAccounts()
+        {
+            UInt160 expected = "0x9f8f056a53e39585c7bb52886418c7bed83d126b";
+
+            var accounts = NativeContract.GAS.GetAccounts(system.StoreView);
+            var actual = accounts.FirstOrDefault();
+
+            Assert.AreEqual(expected, actual.Address);
+            Assert.AreEqual(5200000000000000, actual.Balance);
+        }
+    }
+}