MultiTerm/Common/Helpers/EnumHelpers.cs

using System.ComponentModel;
using System.Reflection;

namespace Common.Helpers;

public static class EnumHelpers
{
    /// <summary>
    /// Parse enum from string to enum enumType.
    /// String must be exactly the same as generated by the default Enum.ToString() 
    /// method and cannot be a searchedDescription of the Enum value.
    /// </summary>
    /// <typeparam name="T">enumType of the enum</typeparam>
    /// <param name="value">value to parse to enum</param>
    /// <returns>returns enum object with value</returns>
    public static T ParseEnum<T>(string value)
    {
        return (T)Enum.Parse(typeof(T), value, true);
    }

    /// <summary>
    /// Creates an instance of the given <paramref name="enumType"/> if it is an enum type.
    /// Throws an exception if it is not an enum type.
    /// </summary>
    /// <param name="enumType">type of target enum</param>
    /// <returns>instance of enum tye with default value</returns>
    public static Enum CreateInstanceOfEnumType(Type enumType)
    {
        // generate instance of enum using target enumType
        if (Activator.CreateInstance(enumType) is not Enum enumObj)
        {
            throw new Exception($"'{nameof(CreateInstanceOfEnumType)}()' could not instanciate Enum of type {enumType}.");
        }

        return enumObj;
    }

    /// <summary>
    /// Gets the searchedDescription of an Enum value.
    /// If there is no Description set, the Enum Value will be converted to string.
    /// </summary>
    /// <param name="enumObject">Enum Object to get Description of.</param>
    /// <returns>String with Content of DescriptionAttribute of Enum object.</returns>
    public static string GetEnumDescription(Enum enumObject)
    {
        // guard argument null
        if (enumObject == null) { throw new ArgumentNullException(nameof(enumObject)); }

        // get field info from enum enumType
        FieldInfo? fieldInfo = enumObject.GetType().GetField(enumObject.ToString());
        // return string of enum value if there is no field info
        if (fieldInfo == null)
        {
            return enumObject.ToString();
        }

        // get searchedDescription attribute and return if it is present
        DescriptionAttribute? descAttrib = (DescriptionAttribute?)fieldInfo.GetCustomAttribute(typeof(DescriptionAttribute), true);
        if (descAttrib != null)
        {
            return descAttrib.Description;
        }

        // if no searchedDescription attribute was found => return string of enum value
        return enumObject.ToString();
    }

    /// <summary>
    /// Gets all Description Attributes of a Enum enumType.
    /// Descriptions must be unique!
    /// </summary>
    /// <param name="enumObject">An object of the Enum. Will be searched for other Descriptions</param>
    /// <returns>Key Value Pair of Description and respective Enum Value</returns>
    public static Dictionary<string, Enum> GetAllEnumDescriptions(Enum enumObject)
    {
        // guard argument null
        if (enumObject == null) { throw new ArgumentNullException(nameof(enumObject)); }

        Dictionary<string, Enum> descriptionsToEnumValues = new();

        // get members of enum enumType
        var members = enumObject.GetType().GetMembers();
        foreach (var member in members)
        {
            // get searchedDescription attributes of all members
            DescriptionAttribute? descAttrib = (DescriptionAttribute?)member.GetCustomAttribute(typeof(DescriptionAttribute), true);
            if (descAttrib != null)
            {
                // if a searchedDescription exists, add the searchedDescription and the enum value to the dictionary
                descriptionsToEnumValues.Add(descAttrib.Description, (Enum)Enum.Parse(enumObject.GetType(), member.Name));
            }
        }

        return descriptionsToEnumValues;
    }

    /// <summary>
    /// Searches and returns the Enum Value of which the <see cref="DescriptionAttribute"/> equals the <paramref name="searchedDescription"/>.
    /// Descriptions of enumType of <paramref name="enumObj"/> must be uniqe!
    /// </summary>
    /// <param name="enumObj">any instance of the enum enumType</param>
    /// <param name="searchedDescription">description that is compared to the <see cref="DescriptionAttribute"/></param>
    /// <returns>enum object of enumType of <paramref name="enumObj"/> or null if no enum with matching description found</returns>
    public static Enum? GetEnumValueByDescription(Enum enumObj, string searchedDescription)
    {
        // guard null
        if(enumObj == null) { return null; }

        // get all descriptions of the enum
        var descriptions = GetAllEnumDescriptions(enumObj);

        // return if equal
        foreach (var desc in descriptions) 
        {
            if (desc.Key.Equals(searchedDescription))
            {
                return desc.Value;
            }
        }

        // nothing found
        return null;
        //throw new Exception($"{nameof(GetEnumValueByDescription)} could not find an enum value in enumType {typeof(enumObj)} that has the Description {searchedDescription}.");
    }
}