change rep working

cw_nano/lib/nano_client.dart

@@ -72,6 +72,48 @@ class NanoClient {
     }
   }
 
+  Future<String> changeRep({
+    required String privateKey,
+    required String repAddress,
+    required String ourAddress,
+  }) async {
+    try {
+      final accountInfo = await getAccountInfo(ourAddress);
+
+      // construct the change block:
+      Map<String, String> changeBlock = {
+        "type": "state",
+        "account": ourAddress,
+        "previous": accountInfo["frontier"] as String,
+        "representative": repAddress,
+        "balance": accountInfo["balance"] as String,
+        "link": "0000000000000000000000000000000000000000000000000000000000000000",
+        "link_as_account": "nano_1111111111111111111111111111111111111111111111111111hifc8npp",
+      };
+
+      // sign the change block:
+      final String hash = NanoBlocks.computeStateHash(
+        NanoAccountType.NANO,
+        changeBlock["account"]!,
+        changeBlock["previous"]!,
+        changeBlock["representative"]!,
+        BigInt.parse(changeBlock["balance"]!),
+        changeBlock["link"]!,
+      );
+      final String signature = NanoSignatures.signBlock(hash, privateKey);
+
+      // get PoW for the send block:
+      final String work = await requestWork(accountInfo["frontier"] as String);
+
+      changeBlock["signature"] = signature;
+      changeBlock["work"] = work;
+
+      return await processBlock(changeBlock, "change");
+    } catch (e) {
+      throw Exception("error while changing representative");
+    }
+  }
+
   Future<String> requestWork(String hash) async {
     return http
         .post(

cw_nano/lib/nano_wallet.dart

@@ -270,6 +270,8 @@ abstract class NanoWalletBase
   @override
   String get seed => _mnemonic;
   
+  String get representative => _representativeAddress ?? "";
+
   @action
   @override
   Future<void> startSync() async {
@@ -350,6 +352,21 @@ abstract class NanoWalletBase
     }
   }
 
+  Future<void> changeRep(String address) async {
+    try {
+      final String hash = await _client.changeRep(
+        privateKey: _privateKey,
+        repAddress: address,
+        ourAddress: _publicAddress,
+      );
+      if (hash.isNotEmpty) {
+        _representativeAddress = address;
+      }
+    } catch (e) {
+      throw Exception("Failed to change representative address $e");
+    }
+  }
+
   Future<void>? updateBalance() async => await _updateBalance();
 
   void _onNewTransaction(FilterEvent event) {

lib/src/screens/nano/nano_change_rep_page.dart

@@ -1,8 +1,11 @@
 import 'package:cake_wallet/core/address_validator.dart';
+import 'package:cake_wallet/di.dart';
 import 'package:cake_wallet/src/widgets/alert_with_two_actions.dart';
 import 'package:cake_wallet/src/widgets/base_text_form_field.dart';
+import 'package:cake_wallet/store/app_store.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
 import 'package:cw_core/crypto_currency.dart';
+import 'package:cw_nano/nano_wallet.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
 import 'package:cake_wallet/generated/i18n.dart';
@@ -105,8 +108,17 @@ class NanoChangeRepPage extends BasePage {
                                 false;
 
                             if (confirmed) {
-                              // _wallet.
+                              try {
-                              Navigator.of(context).pop();
+                                final wallet = getIt.get<AppStore>().wallet!;
+                                if (wallet is NanoWallet) {
+                                  await wallet.changeRep(_addressController.text);
+                                }
+                                // TODO: show message saying success:
+
+                                Navigator.of(context).pop();
+                              } catch (e) {
+                                throw e;
+                              }
                             }
                           },
                           text: S.of(context).change,