Ability to cache currency selection (#5)

lib/data/prefs/CurrencyPair.dart

@@ -0,0 +1,6 @@
+class CurrencyPair {
+  String? currencyOne;
+  String? currencyTwo;
+
+  CurrencyPair(this.currencyOne, this.currencyTwo);
+}

lib/data/prefs/PreferenceProvider.dart

@@ -0,0 +1,27 @@
+import 'dart:ffi';
+
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'CurrencyPair.dart';
+
+const String CURRENCY_ONE = "conversion_one";
+const String CURRENCY_TWO = "conversion_two";
+class PreferenceProvider {
+  late final SharedPreferences _prefs;
+
+  Future<void> init() async {
+    _prefs = await SharedPreferences.getInstance();
+  }
+
+  Future<void> saveConversionPair(String s1, String s2) async {
+    await _prefs.setString(CURRENCY_ONE, s1);
+    await _prefs.setString(CURRENCY_TWO, s2);
+  }
+
+  CurrencyPair getConversionPair() {
+    String? s1 = _prefs.getString(CURRENCY_ONE);
+    String? s2 = _prefs.getString(CURRENCY_TWO);
+
+    return CurrencyPair(s1, s2);
+  }
+}

lib/data/repository/Repository.dart

@@ -0,0 +1,6 @@
+import '../prefs/CurrencyPair.dart';
+
+abstract class Repository {
+  CurrencyPair getConversionPair();
+  Future<void> setConversionPair(String fromCurrency, String toCurrency);
+}

lib/data/repository/RepositoryImpl.dart

@@ -0,0 +1,20 @@
+import 'package:easy_cc_flutter/data/prefs/CurrencyPair.dart';
+import 'package:easy_cc_flutter/data/prefs/PreferenceProvider.dart';
+
+import '../../locator.dart';
+import 'Repository.dart';
+
+class RepositoryImpl extends Repository {
+  final PreferenceProvider _prefs = locator<PreferenceProvider>();
+
+  @override
+  CurrencyPair getConversionPair() {
+    return _prefs.getConversionPair();
+  }
+
+  @override
+  Future<void> setConversionPair(String fromCurrency, String toCurrency) {
+    return _prefs.saveConversionPair(fromCurrency, toCurrency);
+  }
+
+}