cyphergoat: use Decimal for money values, error instead of default on missing fields

diff --git a/lib/services/exchange/cyphergoat/cyphergoat_api.dart b/lib/services/exchange/cyphergoat/cyphergoat_api.dart
index b421a6b..0c754f6 100644
--- a/lib/services/exchange/cyphergoat/cyphergoat_api.dart
+++ b/lib/services/exchange/cyphergoat/cyphergoat_api.dart
@@ -1,5 +1,7 @@
 import 'dart:convert';
 
+import 'package:decimal/decimal.dart';
+
 import '../../../app_config.dart';
 import '../../../exceptions/exchange/exchange_exception.dart';
 import '../../../external_api_keys.dart';
@@ -68,7 +70,7 @@ abstract class CypherGoatAPI {
 
   /// GET /estimate
   /// Returns all exchange provider estimates for the given pair and amount.
-  static Future<ExchangeResponse<({CgEstimatesResponse rates, double min})>>
+  static Future<ExchangeResponse<({CgEstimatesResponse rates, Decimal min})>>
   getEstimate({
     required String coin1,
     required String network1,
@@ -103,7 +105,9 @@ abstract class CypherGoatAPI {
       final rates = CgEstimatesResponse.fromMap(
         Map<String, dynamic>.from(ratesMap),
       );
-      final min = (map["min"] as num?)?.toDouble() ?? rates.min;
+      final min = map["min"] != null
+          ? Decimal.parse(map["min"].toString())
+          : rates.min;
 
       return ExchangeResponse(value: (rates: rates, min: min));
     } catch (e, s) {
diff --git a/lib/services/exchange/cyphergoat/cyphergoat_exchange.dart b/lib/services/exchange/cyphergoat/cyphergoat_exchange.dart
index 0764c2c..3b2e784 100644
--- a/lib/services/exchange/cyphergoat/cyphergoat_exchange.dart
+++ b/lib/services/exchange/cyphergoat/cyphergoat_exchange.dart
@@ -208,8 +208,8 @@ class CypherGoatExchange extends Exchange {
 
       if (response.value != null) {
         final liveMin = response.value!.min;
-        if (liveMin > 0) {
-          min = Decimal.parse(liveMin.toString());
+        if (liveMin > Decimal.zero) {
+          min = liveMin;
         }
       }
 
@@ -268,10 +268,10 @@ class CypherGoatExchange extends Exchange {
       final estimateIdStr = data.rates.estimateId.toString();
 
       final estimates = data.rates.results
-          .where((r) => r.amount > 0)
+          .where((r) => r.amount > Decimal.zero)
           .map(
             (r) => Estimate(
-              estimatedAmount: Decimal.parse(r.amount.toString()),
+              estimatedAmount: r.amount,
               fixedRate: false,
               reversed: false,
               exchangeProvider: r.exchange,
@@ -361,7 +361,7 @@ class CypherGoatExchange extends Exchange {
       return ExchangeResponse(
         value: Trade(
           uuid: const Uuid().v1(),
-          tradeId: tx.cgid.isNotEmpty ? tx.cgid : tx.id,
+          tradeId: tx.cgid ?? tx.id,
           rateType: "estimated",
           direction: "direct",
           timestamp: tx.createdAt,
@@ -370,7 +370,7 @@ class CypherGoatExchange extends Exchange {
           payInAmount: tx.sendAmount.toString(),
           payInAddress: tx.address,
           payInNetwork: tx.network1,
-          payInExtraId: tx.memo,
+          payInExtraId: tx.memo ?? "",
           payInTxid: "",
           payOutCurrency: tx.coin2.toUpperCase(),
           payOutAmount: tx.estimateAmount.toString(),
@@ -410,7 +410,7 @@ class CypherGoatExchange extends Exchange {
       return ExchangeResponse(
         value: Trade(
           uuid: const Uuid().v1(),
-          tradeId: tx.cgid.isNotEmpty ? tx.cgid : tradeId,
+          tradeId: tx.cgid ?? tradeId,
           rateType: "estimated",
           direction: "direct",
           timestamp: tx.createdAt,
@@ -419,7 +419,7 @@ class CypherGoatExchange extends Exchange {
           payInAmount: tx.sendAmount.toString(),
           payInAddress: tx.address,
           payInNetwork: tx.network1,
-          payInExtraId: tx.memo,
+          payInExtraId: tx.memo ?? "",
           payInTxid: "",
           payOutCurrency: tx.coin2.toUpperCase(),
           payOutAmount: tx.estimateAmount.toString(),
@@ -471,32 +471,21 @@ class CypherGoatExchange extends Exchange {
           direction: trade.direction,
           timestamp: trade.timestamp,
           updatedAt: DateTime.now(),
-          payInCurrency: tx.coin1.isNotEmpty
-              ? tx.coin1.toUpperCase()
-              : trade.payInCurrency,
-          payInAmount: tx.sendAmount > 0
-              ? tx.sendAmount.toString()
-              : trade.payInAmount,
-          payInAddress:
-              tx.address.isNotEmpty ? tx.address : trade.payInAddress,
+          payInCurrency: tx.coin1.toUpperCase(),
+          payInAmount: tx.sendAmount.toString(),
+          payInAddress: tx.address,
           payInNetwork: trade.payInNetwork,
-          payInExtraId: tx.memo.isNotEmpty ? tx.memo : trade.payInExtraId,
+          payInExtraId: tx.memo ?? trade.payInExtraId,
           payInTxid: trade.payInTxid,
-          payOutCurrency: tx.coin2.isNotEmpty
-              ? tx.coin2.toUpperCase()
-              : trade.payOutCurrency,
-          payOutAmount: tx.estimateAmount > 0
-              ? tx.estimateAmount.toString()
-              : trade.payOutAmount,
-          payOutAddress: tx.destinationAddress.isNotEmpty
-              ? tx.destinationAddress
-              : trade.payOutAddress,
+          payOutCurrency: tx.coin2.toUpperCase(),
+          payOutAmount: tx.estimateAmount.toString(),
+          payOutAddress: tx.destinationAddress,
           payOutNetwork: trade.payOutNetwork,
           payOutExtraId: trade.payOutExtraId,
           payOutTxid: trade.payOutTxid,
           refundAddress: trade.refundAddress,
           refundExtraId: trade.refundExtraId,
-          status: tx.status.isNotEmpty ? tx.status : trade.status,
+          status: tx.status,
           exchangeName: exchangeName,
         ),
       );
diff --git a/lib/services/exchange/cyphergoat/response_objects/cg_estimate.dart b/lib/services/exchange/cyphergoat/response_objects/cg_estimate.dart
index 6eedb6b..ea9fc16 100644
--- a/lib/services/exchange/cyphergoat/response_objects/cg_estimate.dart
+++ b/lib/services/exchange/cyphergoat/response_objects/cg_estimate.dart
@@ -1,9 +1,13 @@
+import 'package:decimal/decimal.dart';
+
+import 'cg_parse_utils.dart';
+
 class CgEstimateResult {
   final String exchange;
-  final double amount;
+  final Decimal amount;
   final int kycScore;
   final bool safeRouteOk;
-  final double safeRouteScore;
+  final Decimal safeRouteScore;
 
   CgEstimateResult({
     required this.exchange,
@@ -15,20 +19,20 @@ class CgEstimateResult {
 
   factory CgEstimateResult.fromMap(Map<String, dynamic> map) {
     return CgEstimateResult(
-      exchange: map["Exchange"] as String? ?? "",
-      amount: (map["Amount"] as num?)?.toDouble() ?? 0.0,
-      kycScore: (map["KYCScore"] as num?)?.toInt() ?? 0,
-      safeRouteOk: map["SafeRouteOK"] as bool? ?? false,
-      safeRouteScore: (map["SafeRouteScore"] as num?)?.toDouble() ?? 0.0,
+      exchange: requireCgString(map, "Exchange"),
+      amount: requireCgDecimal(map, "Amount"),
+      kycScore: requireCgInt(map, "KYCScore"),
+      safeRouteOk: requireCgBool(map, "SafeRouteOK"),
+      safeRouteScore: requireCgDecimal(map, "SafeRouteScore"),
     );
   }
 }
 
 class CgEstimatesResponse {
   final List<CgEstimateResult> results;
-  final double min;
-  final double tradeValueFiat;
-  final double tradeValueBtc;
+  final Decimal min;
+  final Decimal tradeValueFiat;
+  final Decimal tradeValueBtc;
   final int estimateId;
 
   CgEstimatesResponse({
@@ -40,15 +44,21 @@ class CgEstimatesResponse {
   });
 
   factory CgEstimatesResponse.fromMap(Map<String, dynamic> map) {
-    final resultsRaw = map["Results"] as List<dynamic>? ?? [];
+    final resultsRaw = map["Results"];
+    if (resultsRaw is! List) {
+      throw CgResponseFormatException("Missing required field 'Results'");
+    }
     return CgEstimatesResponse(
       results: resultsRaw
-          .map((e) => CgEstimateResult.fromMap(Map<String, dynamic>.from(e as Map)))
+          .map(
+            (e) =>
+                CgEstimateResult.fromMap(Map<String, dynamic>.from(e as Map)),
+          )
           .toList(),
-      min: (map["Min"] as num?)?.toDouble() ?? 0.0,
-      tradeValueFiat: (map["TradeValue_fiat"] as num?)?.toDouble() ?? 0.0,
-      tradeValueBtc: (map["TradeValue_btc"] as num?)?.toDouble() ?? 0.0,
-      estimateId: (map["EstimateId"] as num?)?.toInt() ?? 0,
+      min: requireCgDecimal(map, "Min"),
+      tradeValueFiat: requireCgDecimal(map, "TradeValue_fiat"),
+      tradeValueBtc: requireCgDecimal(map, "TradeValue_btc"),
+      estimateId: requireCgInt(map, "EstimateId"),
     );
   }
 }
diff --git a/lib/services/exchange/cyphergoat/response_objects/cg_parse_utils.dart b/lib/services/exchange/cyphergoat/response_objects/cg_parse_utils.dart
new file mode 100644
index 0000000..8df72ec
--- /dev/null
+++ b/lib/services/exchange/cyphergoat/response_objects/cg_parse_utils.dart
@@ -0,0 +1,57 @@
+import 'package:decimal/decimal.dart';
+
+/// Thrown when a CypherGoat API response is missing a field the client
+/// treats as mandatory, instead of silently substituting a default value.
+class CgResponseFormatException implements Exception {
+  final String message;
+  CgResponseFormatException(this.message);
+
+  @override
+  String toString() => "CgResponseFormatException: $message";
+}
+
+String requireCgString(Map<String, dynamic> map, String key) {
+  final v = map[key];
+  if (v is! String || v.isEmpty) {
+    throw CgResponseFormatException(
+      "Missing or empty required field '$key'",
+    );
+  }
+  return v;
+}
+
+String? optionalCgString(Map<String, dynamic> map, String key) {
+  final v = map[key];
+  if (v is String && v.isNotEmpty) return v;
+  return null;
+}
+
+Decimal requireCgDecimal(Map<String, dynamic> map, String key) {
+  final v = map[key];
+  if (v is! num && v is! String) {
+    throw CgResponseFormatException(
+      "Missing required numeric field '$key'",
+    );
+  }
+  return Decimal.parse(v.toString());
+}
+
+int requireCgInt(Map<String, dynamic> map, String key) {
+  final v = map[key];
+  if (v is! num) {
+    throw CgResponseFormatException(
+      "Missing required numeric field '$key'",
+    );
+  }
+  return v.toInt();
+}
+
+bool requireCgBool(Map<String, dynamic> map, String key) {
+  final v = map[key];
+  if (v is! bool) {
+    throw CgResponseFormatException(
+      "Missing required boolean field '$key'",
+    );
+  }
+  return v;
+}
diff --git a/lib/services/exchange/cyphergoat/response_objects/cg_transaction.dart b/lib/services/exchange/cyphergoat/response_objects/cg_transaction.dart
index e82817d..df38456 100644
--- a/lib/services/exchange/cyphergoat/response_objects/cg_transaction.dart
+++ b/lib/services/exchange/cyphergoat/response_objects/cg_transaction.dart
@@ -1,23 +1,27 @@
+import 'package:decimal/decimal.dart';
+
+import 'cg_parse_utils.dart';
+
 class CgTransaction {
   final String coin1;
   final String coin2;
   final String network1;
   final String network2;
   final String address;
-  final double estimateAmount;
+  final Decimal estimateAmount;
   final String provider;
   final String id;
-  final double sendAmount;
-  final String track;
+  final Decimal sendAmount;
+  final String? track;
   final String status;
-  final String kyc;
-  final String token;
+  final String? kyc;
+  final String? token;
   final bool done;
-  final String cgid;
+  final String? cgid;
   final DateTime createdAt;
-  final String affiliate;
-  final String memo;
-  final String source;
+  final String? affiliate;
+  final String? memo;
+  final String? source;
   final String destinationAddress;
   final bool payment;
   final DateTime? completedAt;
@@ -51,8 +55,7 @@ class CgTransaction {
 
   // Go's zero time ("0001-01-01T00:00:00Z") is returned when the field isn't
   // set yet; treat it as now rather than storing year 1.
-  static DateTime _parseDate(String? s) {
-    if (s == null) return DateTime.now();
+  static DateTime _parseDate(String s) {
     final dt = DateTime.tryParse(s);
     if (dt == null || dt.year <= 1) return DateTime.now();
     return dt;
@@ -60,31 +63,31 @@ class CgTransaction {
 
   factory CgTransaction.fromMap(Map<String, dynamic> map) {
     return CgTransaction(
-      coin1: map["Coin1"] as String? ?? "",
-      coin2: map["Coin2"] as String? ?? "",
-      network1: map["Network1"] as String? ?? "",
-      network2: map["Network2"] as String? ?? "",
-      address: map["Address"] as String? ?? "",
-      estimateAmount: (map["EstimateAmount"] as num?)?.toDouble() ?? 0.0,
-      provider: map["Provider"] as String? ?? "",
-      id: map["Id"] as String? ?? "",
-      sendAmount: (map["SendAmount"] as num?)?.toDouble() ?? 0.0,
-      track: map["Track"] as String? ?? "",
-      status: map["Status"] as String? ?? "waiting",
-      kyc: map["KYC"] as String? ?? "",
-      token: map["Token"] as String? ?? "",
-      done: map["Done"] as bool? ?? false,
-      cgid: map["CGID"] as String? ?? "",
-      createdAt: _parseDate(map["CreatedAt"] as String?),
-      affiliate: map["Affiliate"] as String? ?? "",
-      memo: map["Memo"] as String? ?? "",
-      source: map["Source"] as String? ?? "",
-      destinationAddress: map["DestinationAddress"] as String? ?? "",
-      payment: map["Payment"] as bool? ?? false,
+      coin1: requireCgString(map, "Coin1"),
+      coin2: requireCgString(map, "Coin2"),
+      network1: requireCgString(map, "Network1"),
+      network2: requireCgString(map, "Network2"),
+      address: requireCgString(map, "Address"),
+      estimateAmount: requireCgDecimal(map, "EstimateAmount"),
+      provider: requireCgString(map, "Provider"),
+      id: requireCgString(map, "Id"),
+      sendAmount: requireCgDecimal(map, "SendAmount"),
+      track: optionalCgString(map, "Track"),
+      status: requireCgString(map, "Status"),
+      kyc: optionalCgString(map, "KYC"),
+      token: optionalCgString(map, "Token"),
+      done: requireCgBool(map, "Done"),
+      cgid: optionalCgString(map, "CGID"),
+      createdAt: _parseDate(requireCgString(map, "CreatedAt")),
+      affiliate: optionalCgString(map, "Affiliate"),
+      memo: optionalCgString(map, "Memo"),
+      source: optionalCgString(map, "Source"),
+      destinationAddress: requireCgString(map, "DestinationAddress"),
+      payment: requireCgBool(map, "Payment"),
       completedAt: map["CompletedAt"] != null
           ? DateTime.tryParse(map["CompletedAt"] as String)
           : null,
-      estimateId: (map["EstimateId"] as num?)?.toInt() ?? 0,
+      estimateId: requireCgInt(map, "EstimateId"),
     );
   }
 }