GravatarHtmlHelper_NetCore.cs

using System;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using System.Security.Cryptography;
using System.Text;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;

/// <summary>
/// Globally Recognised Avatar - http://gravatar.com
/// </summary>
/// <remarks>
/// This implementation by Andrew Freemantle - http://www.fatlemon.co.uk/
/// <para>Source, Wiki and Issues: https://github.com/AndrewFreemantle/Gravatar-HtmlHelper </para>
/// </remarks>
public static class GravatarHtmlHelper {

    /// <summary>
    /// In addition to allowing you to use your own image, Gravatar has a number of built in options which you can also use as defaults. Most of these work by taking the requested email hash and using it to generate a themed image that is unique to that email address
    /// </summary>
    public enum DefaultImage {
        /// <summary>Default Gravatar logo</summary>
        [DescriptionAttribute("")]
        Default,
        /// <summary>404 - do not load any image if none is associated with the email hash, instead return an HTTP 404 (File Not Found) response</summary>
        [DescriptionAttribute("404")]
        Http404,
        /// <summary>Mystery-Man - a simple, cartoon-style silhouetted outline of a person (does not vary by email hash)</summary>
        [DescriptionAttribute("mm")]
        MysteryMan,
        /// <summary>Identicon - a geometric pattern based on an email hash</summary>
        [DescriptionAttribute("identicon")]
        Identicon,
        /// <summary>MonsterId - a generated 'monster' with different colors, faces, etc</summary>
        [DescriptionAttribute("monsterid")]
        MonsterId,
        /// <summary>Wavatar - generated faces with differing features and backgrounds</summary>
        [DescriptionAttribute("wavatar")]
        Wavatar,
        /// <summary>Retro - awesome generated, 8-bit arcade-style pixelated faces</summary>
        [DescriptionAttribute("retro")]
        Retro
    }


    /// <summary>
    /// Gravatar allows users to self-rate their images so that they can indicate if an image is appropriate for a certain audience. By default, only 'G' rated images are displayed unless you indicate that you would like to see higher ratings
    /// </summary>
    public enum Rating {
        /// <summary>Suitable for display on all websites with any audience type</summary>
        [DescriptionAttribute("g")]
        G,
        /// <summary>May contain rude gestures, provocatively dressed individuals, the lesser swear words, or mild violence</summary>
        [DescriptionAttribute("pg")]
        PG,
        /// <summary>May contain such things as harsh profanity, intense violence, nudity, or hard drug use</summary>
        [DescriptionAttribute("r")]
        R,
        /// <summary>May contain hardcore sexual imagery or extremely disturbing violence</summary>
        [DescriptionAttribute("x")]
        X
    }


    /// <summary>
    /// Returns a Globally Recognised Avatar as an &lt;img /&gt; - http://gravatar.com
    /// </summary>
    /// <param name="emailAddress">Email Address for the Gravatar</param>
    /// <param name="defaultImage">Default image if user hasn't created a Gravatar</param>
    /// <param name="size">Size in pixels (default: 80)</param>
    /// <param name="defaultImageUrl">URL to a custom default image (e.g: 'Url.Content("~/images/no-grvatar.png")' )</param>
    /// <param name="forceDefaultImage">Prefer the default image over the users own Gravatar</param>
    /// <param name="rating">Gravatar content rating (note that Gravatars are self-rated)</param>
    /// <param name="forceSecureRequest">Always do secure (https) requests</param>
    public static IHtmlContent GravatarImage(
      this IHtmlHelper htmlHelper,
      string emailAddress,
      int size = 80,
      DefaultImage defaultImage = DefaultImage.Default,
      string defaultImageUrl = "",
      bool forceDefaultImage = false,
      Rating rating = Rating.G,
      bool forceSecureRequest = false,
      string cssClass = "gravatar",
      string alt = "Gravatar image") {

        var imgTag = new TagBuilder("img");

        emailAddress = string.IsNullOrEmpty(emailAddress) ? string.Empty : emailAddress.Trim().ToLower();

        imgTag.Attributes.Add("src",
            string.Format("{0}://{1}.gravatar.com/avatar/{2}?s={3}{4}{5}{6}",
                htmlHelper.ViewContext.HttpContext.Request.IsHttps || forceSecureRequest ? "https" : "http",
                htmlHelper.ViewContext.HttpContext.Request.IsHttps || forceSecureRequest ? "secure" : "www",
                GetMd5Hash(emailAddress),
                size.ToString(),
                "&d=" + (!string.IsNullOrEmpty(defaultImageUrl) ? htmlHelper.UrlEncoder.Encode(defaultImageUrl) : defaultImage.GetDescription()),
                forceDefaultImage ? "&f=y" : "",
                "&r=" + rating.GetDescription()
                )
            );

        imgTag.Attributes.Add("class", cssClass);
        imgTag.Attributes.Add("alt", alt);
        imgTag.TagRenderMode = TagRenderMode.SelfClosing;

        return imgTag;
    }




    /// <summary>
    /// Generates an MD5 hash of the given string
    /// </summary>
    /// <remarks>Source: http://msdn.microsoft.com/en-us/library/system.security.cryptography.md5.aspx </remarks>
    private static string GetMd5Hash(string input) {

        // Convert the input string to a byte array and compute the hash.
        byte[] data = MD5.Create().ComputeHash(Encoding.UTF8.GetBytes(input));

        // Create a new Stringbuilder to collect the bytes
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();

        // Loop through each byte of the hashed data
        // and format each one as a hexadecimal string.
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }

        // Return the hexadecimal string.
        return sBuilder.ToString();
    }



    /// <summary>
    /// Returns the value of a DescriptionAttribute for a given Enum value
    /// </summary>
    /// <remarks>Source: http://blogs.msdn.com/b/abhinaba/archive/2005/10/21/483337.aspx </remarks>
    /// <param name="en"></param>
    /// <returns></returns>
    private static string GetDescription(this Enum en) {

        Type type = en.GetType();
        MemberInfo[] memInfo = type.GetMember(en.ToString());

        if (memInfo != null && memInfo.Length > 0)
        {
            var attrs = memInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), false);

            if (attrs != null && attrs.Count() > 0)
                return ((DescriptionAttribute)attrs.First()).Description;
        }

        return en.ToString();
    }

}