Cw 268 contact address validation (#905)

* feat: Proper Bitcoin address validation in exchange screen

* fix: use custom validation in addition to RegEx to make sure all address cases are validated

- for cases like P2SH addresses starting with a 3, which are not validated by bitcoin_flutter functions

* feat: add bitcoin_flutter to root project

* refactor: improve conditional isValid return chain

* feat: enhance contact page address validation

- only shows address box when a currency is selected, to prevent the selected value from being null
- changes TextValidator() for the new AddressValidator()

* fix: use -1 for initial selectedAtIndex, since there is no currency yet selected

lib/src/screens/contact/contact_page.dart

@@ -1,13 +1,11 @@
-import 'package:cake_wallet/core/validator.dart';
+import 'package:cake_wallet/core/address_validator.dart';
 import 'package:cake_wallet/palette.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
 import 'package:cw_core/currency.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter/cupertino.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
 import 'package:mobx/mobx.dart';
 import 'package:cake_wallet/generated/i18n.dart';
-import 'package:cake_wallet/core/address_validator.dart';
 import 'package:cake_wallet/core/contact_name_validator.dart';
 import 'package:cake_wallet/core/execution_state.dart';
 import 'package:cake_wallet/view_model/contact_list/contact_view_model.dart';
@@ -33,8 +31,8 @@ class ContactPage extends BasePage {
     _addressController
         .addListener(() => contactViewModel.address = _addressController.text);
 
-    autorun((_) =>
-        _currencyTypeController.text = contactViewModel.currency?.toString()??'');
+    autorun((_) => _currencyTypeController.text =
+        contactViewModel.currency?.toString() ?? '');
   }
 
   @override
@@ -61,7 +59,8 @@ class ContactPage extends BasePage {
       }
     });
 
-    return ScrollableWithBottomSection(
+    return Observer(
+      builder: (_) => ScrollableWithBottomSection(
           contentPadding: EdgeInsets.all(24),
           content: Form(
             key: _formKey,
@@ -90,22 +89,25 @@ class ContactPage extends BasePage {
                     ),
                   ),
                 ),
+                if (contactViewModel.currency != null)
                   Padding(
                     padding: EdgeInsets.only(top: 20),
-                child: Observer(
-                    builder: (_) => AddressTextField(
+                    child: AddressTextField(
                       controller: _addressController,
                       options: [
                         AddressTextFieldOption.paste,
                         AddressTextFieldOption.qrCode,
                       ],
-                      buttonColor: Theme.of(context).accentTextTheme!.headline3!.color!,
+                      buttonColor:
+                          Theme.of(context).accentTextTheme!.headline3!.color!,
                       iconColor: PaletteDark.gray,
-                      borderColor: Theme.of(context).primaryTextTheme!.headline6!.backgroundColor!,
-                      validator: TextValidator()
-                      // AddressValidator(
-                      //     type: contactViewModel.currency),
-                    )),
+                      borderColor: Theme.of(context)
+                          .primaryTextTheme!
+                          .headline6!
+                          .backgroundColor!,
+                      validator:
+                          AddressValidator(type: contactViewModel.currency!),
+                    ),
                   )
               ],
             ),
@@ -130,27 +132,32 @@ class ContactPage extends BasePage {
                   child: Observer(
                       builder: (_) => PrimaryButton(
                           onPressed: () async {
-                          if (_formKey.currentState != null && !_formKey.currentState!.validate()) {
+                            if (_formKey.currentState != null &&
+                                !_formKey.currentState!.validate()) {
                               return;
                             }
 
                             await contactViewModel.save();
                           },
                           text: S.of(context).save,
-                        color: Theme.of(context).accentTextTheme!.bodyText1!.color!,
+                          color: Theme.of(context)
+                              .accentTextTheme!
+                              .bodyText1!
+                              .color!,
                           textColor: Colors.white,
                           isDisabled: !contactViewModel.isReady)))
             ],
-        ));
+          )),
+    );
   }
 
   void _presentCurrencyPicker(BuildContext context) {
     showPopUp<void>(
         builder: (_) => CurrencyPicker(
-            selectedAtIndex:
-              contactViewModel.currency != null
-                ? contactViewModel.currencies.indexOf(contactViewModel.currency!)
-                : 0,
+            selectedAtIndex: contactViewModel.currency != null
+                ? contactViewModel.currencies
+                    .indexOf(contactViewModel.currency!)
+                : -1,
             items: contactViewModel.currencies,
             title: S.of(context).please_select,
             hintText: S.of(context).search_currency,