Add flag enum support

Fixes #8

src/EnumDisplayName/EnumExtensions.cs

@@ -1,9 +1,13 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;
 
 #if NETSTANDARD1_3
+
 using System.Reflection;
+
 #endif
 
 namespace Enable.EnumDisplayName
@@ -35,26 +39,80 @@ public static string GetDisplayName(this Enum enumValue)
 
                 if (string.Compare(fieldName, field.Name, StringComparison.Ordinal) == 0)
                 {
-                    var customAttributes = field.GetCustomAttributes(false);
-                    var enumDisplayNameAttribute = customAttributes.OfType<EnumDisplayNameAttribute>().FirstOrDefault();
+                    var fieldAttributes = field.GetCustomAttributes(false).Cast<Attribute>();
+                    return GetNameFromEnumField(enumValue, fieldAttributes);
+                }
+            }
 
-                    if (enumDisplayNameAttribute != null)
-                    {
-                        return enumDisplayNameAttribute.GetDisplayName();
-                    }
+            return string.Empty;
+        }
+
+        /// <summary>
+        /// Returns the display names of a flag enum as a comma seperated string as specified by the
+        /// EnumDisplayNameAttribute declared on the enum field. If no EnumDisplayNameAttribute is
+        /// declared on the enum field then the name of the enum field is returned.
+        /// </summary>
+        public static string GetFlagsDisplayName(this Enum enumValue)
+        {
+            if (enumValue == null)
+            {
+                return string.Empty;
+            }
 
-                    var displayNameAttribute = customAttributes.OfType<DisplayAttribute>().FirstOrDefault();
+            var enumType = enumValue.GetType();
+            var fieldNames = Enum.GetNames(enumType);
+            var fields = enumType.GetFields()
+                .Where(o => fieldNames.Any(p => p == o.Name))
+                .ToArray();
 
-                    if (displayNameAttribute != null)
+            var fieldPosition = 0;
+            var result = string.Empty;
+            foreach (Enum currentValue in Enum.GetValues(enumType))
+            {
+                if (enumValue.HasFlag(currentValue))
+                {
+                    var currentField = fields[fieldPosition];
+                    if (currentField.IsSpecialName)
                     {
-                        return displayNameAttribute.GetName();
+                        fieldPosition += 1;
+                        continue;
                     }
 
-                    return fieldName;
+                    var fieldAttributes = currentField
+                        .GetCustomAttributes(false)
+                        .Cast<Attribute>();
+
+                    var fieldName = GetNameFromEnumField(enumValue, fieldAttributes);
+
+                    result = result == string.Empty ? fieldName
+                         : result + "," + fieldName;
                 }
+
+                fieldPosition += 1;
             }
 
-            return string.Empty;
+            return result;
+        }
+
+        private static string GetNameFromEnumField(Enum enumValue, IEnumerable<Attribute> fieldAttributes)
+        {
+            var enumType = enumValue.GetType();
+            var fieldName = Enum.GetName(enumType, enumValue);
+            var enumDisplayNameAttribute = fieldAttributes.OfType<EnumDisplayNameAttribute>().FirstOrDefault();
+
+            if (enumDisplayNameAttribute != null)
+            {
+                return enumDisplayNameAttribute.GetDisplayName();
+            }
+
+            var displayNameAttribute = fieldAttributes.OfType<DisplayAttribute>().FirstOrDefault();
+
+            if (displayNameAttribute != null)
+            {
+                return displayNameAttribute.GetName();
+            }
+
+            return fieldName;
         }
     }
 }

test/EnumDisplayName.Test/EnumExtensionsGetFlagsDisplayNameTests.cs

@@ -0,0 +1,99 @@
+using System;
+using Xunit;
+
+namespace Enable.EnumDisplayName
+{
+    public class EnumExtensionsGetFlagsDisplayNameTests
+    {
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsEmptyStringWhenSourceIsNull()
+        {
+            // Arrange
+            Enum source = null;
+
+            // Act
+            var result = source.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(string.Empty, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsEnumDisplayNameAttributeDisplayName()
+        {
+            // Act
+            var result = MockFlagEnum.EnumDisplayNameAttribute.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(MockEnumDisplayNames.EnumDisplayNameAttribute, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsEnumDisplayNameAttributeWithResourceDisplayName()
+        {
+            // Act
+            var result = MockFlagEnum.EnumDisplayNameAttributeWithResource.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(Resources.MockEnum.EnumDisplayNameAttributeWithResource, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsDisplayAttributeDisplayName()
+        {
+            // Act
+            var result = MockFlagEnum.DisplayAttribute.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(MockEnumDisplayNames.DisplayAttribute, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsFieldName()
+        {
+            // Act
+            var result = MockFlagEnum.NoAttribute.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(MockEnumDisplayNames.NoAttribute, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsEmptyStringWithSpecialNameAttribute()
+        {
+            // Act
+            var result = MockFlagEnum.SpecialName.GetFlagsDisplayName();
+
+            // Assert
+            Assert.Equal(string.Empty, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsCommaSeperatedStringForFlagValues()
+        {
+            // Arrange
+            var sut = MockFlagEnum.DisplayAttribute | MockFlagEnum.EnumDisplayNameAttribute;
+
+            // Act
+            var result = sut.GetFlagsDisplayName();
+
+            // Assert
+            var expected = $"{MockEnumDisplayNames.EnumDisplayNameAttribute},{MockEnumDisplayNames.DisplayAttribute}";
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void GetFlagsDisplayName_ReturnsCommaSeperatedStringForFlagValues_ExceptSpecialNameAttributes()
+        {
+            // Arrange
+            var sut = MockFlagEnum.DisplayAttribute | MockFlagEnum.SpecialName;
+
+            // Act
+            var result = sut.GetFlagsDisplayName();
+
+            // Assert
+            var expected = $"{MockEnumDisplayNames.DisplayAttribute}";
+            Assert.Equal(expected, result);
+        }
+    }
+}

test/EnumDisplayName.Test/Enums/MockFlagEnum.cs

@@ -0,0 +1,25 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Runtime.CompilerServices;
+
+namespace Enable.EnumDisplayName
+{
+    [Flags]
+    public enum MockFlagEnum
+    {
+        [EnumDisplayName(MockEnumDisplayNames.EnumDisplayNameAttribute)]
+        EnumDisplayNameAttribute = 1,
+
+        [EnumDisplayName(MockEnumDisplayNames.EnumDisplayNameAttributeWithResource, typeof(Resources.MockEnum))]
+        EnumDisplayNameAttributeWithResource = 2,
+
+        [Display(Name = MockEnumDisplayNames.DisplayAttribute)]
+        DisplayAttribute = 4,
+
+        NoAttribute = 8,
+
+        [SpecialName]
+        [EnumDisplayName(MockEnumDisplayNames.SpecialName)]
+        SpecialName = 16
+    }
+}