Add fee type to estimate fee request

If fee type is "Included", fees is charged from receiver. If fee
type is "Extra", fee is charged from sender.

Sources/Stratis.Bitcoin.Features.Wallet/Controllers/DeStreamWalletController.cs

 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Net;
 using Microsoft.AspNetCore.Mvc;
@@ -12,7 +13,7 @@ using Stratis.Bitcoin.Utilities.JsonErrors;
 namespace Stratis.Bitcoin.Features.Wallet.Controllers
 {
     /// <summary>
-    /// Controller providing operations on a wallet.
+    ///     Controller providing operations on a wallet.
     /// </summary>
     [Route("api/[controller]")]
     public class DeStreamWalletController : Controller
@@ -30,7 +31,7 @@ namespace Stratis.Bitcoin.Features.Wallet.Controllers
         }
 
         /// <summary>
-        /// Builds a transaction.
+        ///     Builds a transaction.
         /// </summary>
         /// <param name="request">The transaction parameters.</param>
         /// <returns>All the details of the transaction, including the hex used to execute it.</returns>
@@ -58,16 +59,7 @@ namespace Stratis.Bitcoin.Features.Wallet.Controllers
                         true // We shuffle transaction outputs by default as it's better for anonymity.
                 };
 
-                if (Enum.TryParse(request.FeeType, out DeStreamFeeType feeType))
-                {
-                    if (feeType == DeStreamFeeType.Included)
-                    {
-                        foreach (Recipient recipient in context.Recipients)
-                            recipient.Amount = this._network.SubtractFee(recipient.Amount);
-                    }
-                }
-                else
-                    throw new FormatException($"FeeType {request.FeeType} is not a valid DeStreamFeeType");
+                this.ProcessFeeType(request.FeeType, context.Recipients);
 
                 Transaction transactionResult = this._walletTransactionHandler.BuildTransaction(context);
 
@@ -86,5 +78,63 @@ namespace Stratis.Bitcoin.Features.Wallet.Controllers
                 return ErrorHelpers.BuildErrorResponse(HttpStatusCode.BadRequest, e.Message, e.ToString());
             }
         }
+
+        /// <summary>
+        ///     Gets a transaction fee estimate.
+        ///     Fee can be estimated by creating a <see cref="TransactionBuildContext" /> with no password
+        ///     and then building the transaction and retrieving the fee from the context.
+        /// </summary>
+        /// <param name="request">The transaction parameters.</param>
+        /// <returns>The estimated fee for the transaction.</returns>
+        [Route("estimate-txfee")]
+        [HttpGet]
+        public IActionResult GetTransactionFeeEstimate([FromQuery] TxFeeEstimateRequest request)
+        {
+            Guard.NotNull(request, nameof(request));
+
+            // checks the request is valid
+            if (!this.ModelState.IsValid) return WalletController.BuildErrorResponse(this.ModelState);
+
+            try
+            {
+                Script destination = BitcoinAddress.Create(request.DestinationAddress, this._network).ScriptPubKey;
+                var context = new TransactionBuildContext(
+                    new WalletAccountReference(request.WalletName, request.AccountName),
+                    new[] {new Recipient {Amount = request.Amount, ScriptPubKey = destination}}.ToList())
+                {
+                    MinConfirmations = request.AllowUnconfirmed ? 0 : 1
+                };
+
+                this.ProcessFeeType(request.FeeType, context.Recipients);
+
+                return this.Json(this._walletTransactionHandler.EstimateFee(context));
+            }
+            catch (Exception e)
+            {
+                this._logger.LogError("Exception occurred: {0}", e.ToString());
+                return ErrorHelpers.BuildErrorResponse(HttpStatusCode.BadRequest, e.Message, e.ToString());
+            }
+        }
+
+        /// <summary>
+        ///     Modifies transfer funds amount according to fee type.
+        ///     For <see cref="DeStreamFeeType.Extra" /> fee type, fee is subtracted from transfer funds.
+        ///     For <see cref="DeStreamFeeType.Included" /> fee type, nothing changed.
+        /// </summary>
+        /// <param name="requestFeeType">Fee type in request</param>
+        /// <param name="recipients">Recipients</param>
+        /// <exception cref="FormatException">Fee type string is invalid</exception>
+        private void ProcessFeeType(string requestFeeType, IEnumerable<Recipient> recipients)
+        {
+            if (Enum.TryParse(requestFeeType, out DeStreamFeeType feeType))
+            {
+                if (feeType != DeStreamFeeType.Included) return;
+
+                foreach (Recipient recipient in recipients)
+                    recipient.Amount = this._network.SubtractFee(recipient.Amount);
+            }
+            else
+                throw new FormatException($"FeeType {requestFeeType} is not a valid DeStreamFeeType");
+        }
     }
 }
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