add payment

lib/domain/entities/payment.dart

@@ -0,0 +1,50 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+
+class Payment {
+  String id;
+  String invoiceID;
+  DateTime paymentDate;
+  String paymentReceiptURL;
+  String status;
+  double amount;
+
+  Payment(
+      {this.id,
+      this.invoiceID,
+      this.paymentDate,
+      this.paymentReceiptURL,
+      this.status,
+      this.amount});
+
+  factory Payment.fromMap(Map<String, dynamic> map, String id) {
+    var _paymentDate = (map['payment_date'] as Timestamp);
+    return Payment(
+      id: id,
+      paymentDate: _paymentDate?.toDate(),
+      paymentReceiptURL: map['payment_receipt_url'],
+      status: map['status'],
+      amount: map['amount']?.toDouble() ?? 0,
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    return {
+      "id": id,
+      "invoice_id": invoiceID,
+      'payment_date': paymentDate?.toUtc()?.toIso8601String(),
+      'payment_receipt_url': paymentReceiptURL,
+      'status': status,
+      'amount': amount,
+    };
+  }
+
+  Payment clone() {
+    return Payment.fromMap(toMap(), this.id);
+  }
+
+  @override
+  bool operator ==(Object other) => other is Payment && other.id == id;
+
+  @override
+  int get hashCode => id.hashCode;
+}