From 78dab343273e73b0c9581781bdd3d4199d29f57c Mon Sep 17 00:00:00 2001
From: Matt Mills <mmills@repay.com>
Date: Thu, 27 May 2021 11:24:42 -0500
Subject: [PATCH] Enable fixed length field truncation to keep the end instead
 of the beginning

---
 .../Tests/Common/OverflowModeTests.cs         | 28 ++++++++++++++++---
 FileHelpers/Fields/FixedLengthField.cs        |  4 ++-
 FileHelpers/Fields/OverflowMode.cs            |  4 +++
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/FileHelpers.Tests/Tests/Common/OverflowModeTests.cs b/FileHelpers.Tests/Tests/Common/OverflowModeTests.cs
index d91074c23..3711aa957 100644
--- a/FileHelpers.Tests/Tests/Common/OverflowModeTests.cs
+++ b/FileHelpers.Tests/Tests/Common/OverflowModeTests.cs
@@ -9,12 +9,19 @@ namespace FileHelpers.Tests.CommonTests
     public class OverflowModeTests
     {
         [FixedLengthRecord]
-        public class DiscardCustomer
+        public class DiscardEndCustomer
         {
             [FieldFixedLength(10, OverflowMode = OverflowMode.DiscardEnd)]
             public string mCustomerID;
         }
 
+        [FixedLengthRecord]
+        public class DiscardStartCustomer
+        {
+            [FieldFixedLength(10, OverflowMode = OverflowMode.DiscardStart)]
+            public string mCustomerID;
+        }
+
         [FixedLengthRecord]
         public class ErrorCustomer
         {
@@ -26,10 +33,23 @@ public class ErrorCustomer
         [TestCase("0123456789A", "0123456789")]
         [TestCase("0123456789", "0123456789")]
         [TestCase("012345678", "012345678 ")]
-        public void Discard(string originalValue, string expectedValue)
+        public void DiscardEnd(string originalValue, string expectedValue)
+        {
+            var engine = new FixedFileEngine<DiscardEndCustomer>();
+            var customer = new DiscardEndCustomer {mCustomerID = originalValue};
+            var res = engine.WriteString(new[] {customer});
+
+            Check.That(res).IsEqualTo($"{expectedValue}{Environment.NewLine}");
+        }
+
+        [TestCase("0123456789ABC", "3456789ABC")]
+        [TestCase("0123456789A", "123456789A")]
+        [TestCase("0123456789", "0123456789")]
+        [TestCase("012345678", "012345678 ")]
+        public void DiscardStart(string originalValue, string expectedValue)
         {
-            var engine = new FixedFileEngine<DiscardCustomer>();
-            var customer = new DiscardCustomer {mCustomerID = originalValue};
+            var engine = new FixedFileEngine<DiscardStartCustomer>();
+            var customer = new DiscardStartCustomer {mCustomerID = originalValue};
             var res = engine.WriteString(new[] {customer});
 
             Check.That(res).IsEqualTo($"{expectedValue}{Environment.NewLine}");
diff --git a/FileHelpers/Fields/FixedLengthField.cs b/FileHelpers/Fields/FixedLengthField.cs
index 5d4ddd218..4c181d9e7 100644
--- a/FileHelpers/Fields/FixedLengthField.cs
+++ b/FileHelpers/Fields/FixedLengthField.cs
@@ -158,6 +158,8 @@ private string GetActualValueBasedOnFieldConfiguration(string field)
                         throw new ConvertException(field,
                             FieldType,
                             $"Field value is too large for the field length ({FieldLength}) and field OverflowMode is set to {OverflowMode}.");
+                    case OverflowMode.DiscardStart:
+                        return field.Substring(field.Length - FieldLength);
                     case OverflowMode.DiscardEnd:
                     default:
                         return field.Substring(0, FieldLength);
@@ -186,4 +188,4 @@ protected override FieldBase CreateClone()
 
         #endregion
     }
-}
+}
diff --git a/FileHelpers/Fields/OverflowMode.cs b/FileHelpers/Fields/OverflowMode.cs
index 80f5cd9e9..1591fd57f 100644
--- a/FileHelpers/Fields/OverflowMode.cs
+++ b/FileHelpers/Fields/OverflowMode.cs
@@ -11,6 +11,10 @@ public enum OverflowMode
         /// </summary>
         DiscardEnd,
         /// <summary>
+        /// Discard overflowing characters at the start
+        /// </summary>
+        DiscardStart,
+        /// <summary>
         /// Throw an exception
         /// </summary>
         Error