add and use defaultFeeRate per ElectrumX coin

lib/electrumx_rpc/electrumx_client.dart

@@ -10,6 +10,7 @@
 
 import 'dart:async';
 import 'dart:io';
+import 'dart:math';
 
 import 'package:connectivity_plus/connectivity_plus.dart';
 import 'package:decimal/decimal.dart';
@@ -28,6 +29,7 @@ import '../services/tor_service.dart';
 import '../utilities/logger.dart';
 import '../utilities/prefs.dart';
 import '../wallets/crypto_currency/crypto_currency.dart';
+import '../wallets/crypto_currency/interfaces/electrumx_currency_interface.dart';
 import 'client_manager.dart';
 
 class WifiOnlyException implements Exception {}
@@ -1113,17 +1115,23 @@ class ElectrumXClient {
         ],
       );
       try {
-        // If the response is -1 or null, return a temporary hardcoded value for
-        // Dogecoin.  This is a temporary fix until the fee estimation is fixed.
-        if (cryptoCurrency is Dogecoin &&
-            (response == null ||
-                response == -1 ||
-                Decimal.parse(response.toString()) == Decimal.parse("-1"))) {
-          // Return 0.05 for slow, 0.2 for average, and 1 for fast txs.
-          // These numbers produce tx fees in line with txs in the wild on
-          // https://dogechain.info/
-          return Decimal.parse((1 / blocks).toString());
-          // TODO [prio=med]: Fix fee estimation.
+        // If the response is -1 or null, fall back to the defaultFeeRate.
+        if (response == null ||
+            response == -1 ||
+            Decimal.parse(response.toString()) == Decimal.parse("-1")) {
+          if (CryptoCurrency is! BitcoinFrost) {
+            // TODO [prio=low]: Take `blocks` into account.
+            return Decimal.parse(
+                ((cryptoCurrency as ElectrumXCurrencyInterface).defaultFeeRate /
+                        pow(10, cryptoCurrency.fractionDigits))
+                    .toString());
+          } else {
+            // Use Bitcoin's default fee rate for Bitcoin Frost.
+            return Decimal.parse(
+                ((Bitcoin(CryptoCurrencyNetwork.main).defaultFeeRate /
+                        pow(10, cryptoCurrency.fractionDigits))
+                    .toString()));
+          }
         }
         return Decimal.parse(response.toString());
       } catch (e, s) {

lib/wallets/crypto_currency/coins/bitcoin.dart

@@ -295,4 +295,8 @@ class Bitcoin extends Bip39HDCurrency
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 1000;
+  // https://github.com/bitcoin/bitcoin/blob/feab35189bc00bc4cf15e9dcb5cf6b34ff3a1e91/test/functional/mempool_limit.py#L259
 }

lib/wallets/crypto_currency/coins/bitcoin_frost.dart

@@ -201,4 +201,7 @@ class BitcoinFrost extends FrostCurrency {
         );
     }
   }
+
+  @override
+  int get defaultFeeRate => 1000;
 }

lib/wallets/crypto_currency/coins/bitcoincash.dart

@@ -367,4 +367,7 @@ class Bitcoincash extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 2;
+
+  @override
+  int get defaultFeeRate => 1000;
 }

lib/wallets/crypto_currency/coins/dogecoin.dart

@@ -252,4 +252,8 @@ class Dogecoin extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 1000000;
+  // https://github.com/dogecoin/dogecoin/blob/master/doc/fee-recommendation.md
 }

lib/wallets/crypto_currency/coins/ecash.dart

@@ -339,4 +339,7 @@ class Ecash extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 2;
+
+  @override
+  int get defaultFeeRate => 200;
 }

lib/wallets/crypto_currency/coins/firo.dart

@@ -270,4 +270,7 @@ class Firo extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 1000;
 }

lib/wallets/crypto_currency/coins/litecoin.dart

@@ -283,4 +283,7 @@ class Litecoin extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 1000;
 }

lib/wallets/crypto_currency/coins/namecoin.dart

@@ -255,4 +255,7 @@ class Namecoin extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 1000;
 }

lib/wallets/crypto_currency/coins/particl.dart

@@ -233,4 +233,7 @@ class Particl extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 1;
+
+  @override
+  int get defaultFeeRate => 20000;
 }

lib/wallets/crypto_currency/coins/peercoin.dart

@@ -257,4 +257,7 @@ class Peercoin extends Bip39HDCurrency with ElectrumXCurrencyInterface {
 
   @override
   int get transactionVersion => 3;
+
+  @override
+  int get defaultFeeRate => 5000;
 }

lib/wallets/crypto_currency/interfaces/electrumx_currency_interface.dart

@@ -2,4 +2,7 @@ import '../intermediate/bip39_hd_currency.dart';
 
 mixin ElectrumXCurrencyInterface on Bip39HDCurrency {
   int get transactionVersion;
+
+  /// The default fee rate in satoshis per kilobyte.
+  int get defaultFeeRate;
 }