NoSpamEmailHyperlink: 1. Design

using System;
using System.Drawing;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.Design;
using System.ComponentModel;
using System.Text;
using System.Collections;
using CP.WebControls;

namespace CP.WebControls
{
	/// <summary>
	/// Control to create a mailto: link with an encoded email
	/// address which will pass any email validation routine
	/// </summary>
	[
	DefaultProperty("Email"), 
	ToolboxData("<{0}:NoSpamEmailHyperlink runat=server></{0}:NoSpamEmailHyperlink>"),
	ParseChildren(false),
	ControlBuilder(typeof(NoSpamEmailHyperlinkBuilder)),
	Designer(typeof(NoSpamEmailHyperlinkDesigner)),
	DataBindingHandler(typeof(NoSpamEmailHyperlinkDataBindingHandler))
	]
	public class NoSpamEmailHyperlink : System.Web.UI.WebControls.WebControl
	{
		/// <summary>
		/// Tag is A (hyperlink) rather than the default SPAN
		/// </summary>
		protected override HtmlTextWriterTag TagKey
		{
			get
			{
				return HtmlTextWriterTag.A;
			}
		}

		#region Text property (inner property)
		/// <summary>
		/// Text to display for link
		/// </summary>
		[
		Bindable(true), 
		Category("Data"), 
		DefaultValue(""),
		Description("Display text for hyperlink (may also be encoded)"),
		PersistenceMode(PersistenceMode.EncodedInnerDefaultProperty)
		]
		public virtual string Text 
		{
			get
			{
				return (ViewState["Text"] is string)
					? (string) ViewState["Text"]
					: String.Empty;
			}

			set
			{
				ViewState["Text"] = value;
			}
		}

		/// <summary>
		/// Handle the literal content of the control
		/// </summary>
		/// <param name="obj">Child control</param>
		protected override void AddParsedSubObject(object obj)
		{
			if (obj is LiteralControl)
			{
				// If inner text is a literal, we can
				// pick up the text at any point and
				// populate our Text property
				
				Text = ((LiteralControl)obj).Text;
			}
			else 
			{
				// If inner text is databound, we
				// need to pick up the text at render
				// time, so we'll add the control as
				// a child
				
				base.AddParsedSubObject(obj);
			}

			// NoSpamEmailHyperlinkBuilder.AppendSubBuilder
			// will throw out any other child controls at
			// parse-time, no other condition should exist
		}
		#endregion

		#region Attribute properties
		/// <summary>
		/// Email address to be encoded
		/// </summary>
		[
		Bindable(true), 
		Category("Data"), 
		DefaultValue(""),
		Description("Email address for hyperlink")
		]
		public virtual string Email
		{
			get
			{
				return (ViewState["Email"] is string)
					? (string) ViewState["Email"]
					: String.Empty;
			}

			set
			{
				ViewState["Email"] = value;
			}
		}

		/// <summary>
		/// Seed number for decoding script
		/// </summary>
		[
		Bindable(true), 
		Category("Data"), 
		DefaultValue(23),
		Description("Seed number for decoding script")
		]
		public virtual int ScrambleSeed
		{
			get
			{
				return (ViewState["ScrambleSeed"] is int)
					? (int) ViewState["ScrambleSeed"]
					: 23;
			}

			set
			{
				ViewState["ScrambleSeed"] = value;
			}
		}

		/// <summary>
		/// Set to false to avoid encoding where the email
		/// address is in the inner text
		/// </summary>
		[
		Bindable(true), 
		Category("Data"), 
		DefaultValue(true),
		Description("If the email address appears in the Text property, encode it")
		]
		public virtual bool EncodeInText
		{
			get
			{
				return (ViewState["EncodeInText"] is bool)
					? (bool) ViewState["EncodeInText"]
					: true;
			}

			set
			{
				ViewState["EncodeInText"] = value;
			}
		}

		/// <summary>
		/// Text to replace email address in the Text for Netscape pre-v6
		/// </summary>
		[
		Bindable(true), 
		Category("Data"), 
		DefaultValue("[Hidden]"),
		Description("Text to replace email address in the Text for Netscape pre-v6")
		]
		public virtual string HideText
		{
			get
			{
				return (ViewState["HideText"] is string)
					? (string) ViewState["HideText"]
					: "[Hidden]";
			}

			set
			{
				ViewState["HideText"] = value;
			}
		}
		#endregion

		#region Hidden properties for inheritors
		/// <summary>
		/// A base string for scrambling text
		/// </summary>
		/// <remarks>
		/// This should contain as many alpha-numeric characters
		/// as possible but each character should only appear once.
		/// Avoid using punctuation ('@', '.', '_', '-') which can
		/// make the address invalid.
		/// </remarks>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string CodeKey
		{
			get
			{
				return "yJzdeB4CcDnmEFbZtvuHlI1hA8SiLo9MwfN3O6Y5QaRqKTjUpxVk2WgXrP7Gs0";
			}
		}

		/// <summary>
		/// Unique name for registering Link Array
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string LinkArrayName
		{
			get
			{
				return GetType().Name + "_LinkNames";
			}
		}

		/// <summary>
		/// Unique name for registering Seed Array
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string SeedArrayName
		{
			get
			{
				return GetType().Name + "_Seeded";
			}
		}

		/// <summary>
		/// Unique name for registering function script
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string FuncScriptName
		{
			get
			{
				return GetType().Name + "_DecodeScript";
			}
		}

		/// <summary>
		/// Unique name for registering call script
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string CallScriptName
		{
			get
			{
				return GetType().Name + "_DecodeScriptCall";
			}
		}

		/// <summary>
		/// Variable name used for CodeKey string
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual string CodeKeyName
		{
			get
			{
				return "ky";
			}
		}

		/// <summary>
		/// If a broswer cannot set the innerHTML, this should identify it
		/// </summary>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected virtual bool BrowserNeedsHide
		{
			get
			{
				// If the Browser is Netscape (v4.x or less), we cannot change
				// the innerHTML at run time, so we'll just hide it

				HttpBrowserCapabilities bc = Page.Request.Browser;
				Version bv = new Version(bc.Version);

				return (bc.Browser.ToLower().IndexOf("netscape") > -1 
					&& bv.Major < 5);
			}
		}
		#endregion

		#region Script building methods
		/// <summary>
		/// Build the decoder function
		/// </summary>
		protected virtual string GetFuncScript()
		{
#if DEBUG
			// Formatted script text in debug version
			JavaScriptBuilder jsb = new JavaScriptBuilder(true);
#else
			// Compress script text in release version
			JavaScriptBuilder jsb = new JavaScriptBuilder();
#endif

			jsb.AddLine("function ", FuncScriptName, "(link, seed)");
			jsb.OpenBlock(); // function()
			jsb.AddCommentLine("This is the decoding key for all ", LinkArrayName, " objects");
			jsb.AddLine("var ", CodeKeyName, " = \"", CodeKey, "\";");
			jsb.AddLine();

			if (!BrowserNeedsHide)
			{
				jsb.AddCommentLine("Store the innerHTML so that it doesn't get");
				jsb.AddCommentLine("distorted when updating the href later");
				jsb.AddLine("var storeText = link.innerHTML;");
				jsb.AddLine();
			}

			jsb.AddCommentLine("Initialize variables");
			jsb.AddLine("var baseNum = parseInt(seed);");
			jsb.AddLine("var atSym = link.href.indexOf(\"@\");");
			jsb.AddLine("if (atSym == -1) atSym = 0;");
			jsb.AddLine("var dotidx = link.href.indexOf(\".\", atSym);");
			jsb.AddLine("if (dotidx == -1) dotidx = link.href.length;");
			jsb.AddLine("var scramble = link.href.substring(7, dotidx);");
			jsb.AddLine("var unscramble = \"\";");
			jsb.AddLine("var su = true;");
			jsb.AddLine();
			jsb.AddCommentLine("Go through the scrambled section of the address");
			jsb.AddLine("for (i=0; i < scramble.length; i++)");
			jsb.OpenBlock(); // for (i = 0; i < scramble.length; i++)
			jsb.AddCommentLine("Find each character in the scramble key string");
			jsb.AddLine("var ch = scramble.substring(i,i + 1);");
			jsb.AddLine("var idx = ", CodeKeyName, ".indexOf(ch);");
			jsb.AddLine();
			jsb.AddCommentLine("If it isn't there then add the character");
			jsb.AddCommentLine("directly to the unscrambled email address");
			jsb.AddLine("if (idx < 0)");
			jsb.OpenBlock(); // if (idx < 0)
			jsb.AddLine("unscramble = unscramble + ch;");
			jsb.AddLine("continue;");
			jsb.CloseBlock(); // if (idx < 0)
			jsb.AddLine();
			jsb.AddCommentLine("Decode the character");
			jsb.AddLine("idx -= (su ? -baseNum : baseNum);");
			jsb.AddLine("baseNum -= (su ? -i : i);");
			jsb.AddLine("while (idx < 0) idx += ", CodeKeyName, ".length;");
			jsb.AddLine("idx %= ", CodeKeyName, ".length;");
			jsb.AddLine();
			jsb.AddCommentLine("... and add it to the unscrambled email address");
			jsb.AddLine("unscramble = unscramble + ", CodeKeyName, ".substring(idx,idx + 1);");
			jsb.AddLine("su = !su;");
			jsb.CloseBlock(); // for (i = 0; i < scramble.length; i++)
			jsb.AddLine();
			jsb.AddCommentLine("Adjust the href property of the link");
			jsb.AddLine("var emAdd = unscramble + link.href.substring(dotidx, link.href.length + 1);");
			jsb.AddLine("link.href = \"mailto:\" + emAdd;");
			jsb.AddLine();

			if (!BrowserNeedsHide)
			{
				jsb.AddCommentLine("If the scrambled email address is also in the text");
				jsb.AddCommentLine("of the hyperlink, replace it");
				jsb.AddLine("var findEm = storeText.indexOf(scramble);");
				jsb.AddLine("while (findEm > -1)");
				jsb.OpenBlock(); // while (findEm > -1)
				jsb.AddLine("storeText = storeText.substring(0, findEm) + emAdd + storeText.substring(findEm + emAdd.length, storeText.length);");
				jsb.AddLine("findEm = storeText.indexOf(scramble);");
				jsb.CloseBlock(); // while (findEm > -1)
				jsb.AddLine();
				jsb.AddLine("link.innerHTML = storeText;");
			}

			jsb.CloseBlock(); // function()

			return jsb.ToString();
		}

		/// <summary>
		/// Build the call script text
		/// </summary>
		/// <remarks>
		/// Use the CallScriptName property to create variable names,
		/// so that we do not clash with similar (or even completely
		/// different) controls.
		/// </remarks>
		[
		DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
		]
		protected string GetCallScript()
		{
#if DEBUG
			// Formatted script text in debug version
			JavaScriptBuilder jsb = new JavaScriptBuilder(true);
#else
			// Compress script text in release version
			JavaScriptBuilder jsb = new JavaScriptBuilder();
#endif

			jsb.AddCommentLine("Run through all links in this page");

			if (Page.Request.Browser.Browser.IndexOf("ie") > -1)
			{
				jsb.AddLine("for (", CallScriptName, "_idx = 0; ", CallScriptName,	"_idx < ", LinkArrayName, ".length; ", CallScriptName,	"_idx++)");
				jsb.OpenBlock();
				jsb.AddLine(FuncScriptName, "(document.links.item(", LinkArrayName, "[", CallScriptName, "_idx]), ", SeedArrayName, "[", CallScriptName,"_idx]);");
				jsb.CloseBlock();
			}
			else
			{
				jsb.AddLine("for (", CallScriptName, "_idx = 0; ", CallScriptName, "_idx < document.links.length; ", CallScriptName, "_idx++)");
				jsb.OpenBlock();
				jsb.AddLine("for (", FuncScriptName, "_idx = 0; ", FuncScriptName, "_idx < ", LinkArrayName, ".length; ", FuncScriptName, "_idx++)");
				jsb.OpenBlock();
				jsb.AddLine("if (document.links[", CallScriptName, "_idx].id == ", LinkArrayName, "[", FuncScriptName, "_idx])");
				jsb.OpenBlock();
				jsb.AddLine(FuncScriptName, "(document.links[", CallScriptName, "_idx], ", SeedArrayName, "[", FuncScriptName,"_idx]);");
				jsb.CloseBlock();
				jsb.CloseBlock();
				jsb.CloseBlock();
			}

			return jsb.ToString();
		}
		#endregion

		#region Encoding Algorithm
		protected string Encode (string Unencoded, string ToEncode)
		{
			// Cannot String.Replace a zero-length string
			if (ToEncode.Length == 0) return Unencoded;

			// Encode all occurences of ToEncode in Unencoded
			return Unencoded.Replace(ToEncode, Encode(ToEncode));
		}

		protected virtual string Encode (string Unencoded)
		{
			// Convert string to char[]
			char[] scramble = Email.ToCharArray();

			// Initialize variables
			int baseNum = ScrambleSeed;
			bool subtract = true;

			// Find the @ symbol and the following .
			// if either don't exist then we don't have a
			// valid email address and should return it unencoded
			int atSymbol = Array.IndexOf(scramble, '@');
			if (atSymbol == -1) atSymbol = 0;
			int stopAt = Array.IndexOf(scramble, '.', atSymbol);
			if (stopAt == -1) stopAt = scramble.Length;

			// Go through the section of the address to be scrambled
			for (int i=0; i < stopAt; i++)
			{
				// Find each character in the scramble key string
				char ch = scramble[i];
				int idx = CodeKey.IndexOf(ch);

				// If it isn't there then ignore the character
				if (idx < 0) continue;

				// Encode the character
				idx += (subtract ? -baseNum : baseNum);
				baseNum -= (subtract ? -i : i);
				while (idx < 0) idx += CodeKey.Length;
				idx %= CodeKey.Length;
				scramble[i] = CodeKey[idx];
				subtract = !subtract;
			}

			// Return the encoded string
			return new string(scramble);
		}
		#endregion

		#region Rendering functionality
		/// <summary>
		/// Add the href atribute to the main tag
		/// </summary>
		/// <param name="writer">The HtmlTextWriter for the page</param>
		protected override void AddAttributesToRender(HtmlTextWriter writer)
		{
			if (Email.Length > 0)
			{
				writer.AddAttribute(HtmlTextWriterAttribute.Href, "mailto:" + Encode(Email));
			}

			base.AddAttributesToRender (writer);
		}

		/// <summary>
		/// Declare arrays and scripts before rendering
		/// </summary>
		/// <param name="e">EventArgs</param>
		protected override void OnPreRender(EventArgs e)
		{
			base.OnPreRender (e);

			if (Email.Length > 0)
			{
				// Register the Control's ID and Decode seed in scripted arrays
				Page.RegisterArrayDeclaration(
					LinkArrayName, String.Format("\"{0}\"", ClientID)
					);
				Page.RegisterArrayDeclaration(
					SeedArrayName, String.Format("\"{0}\"", ScrambleSeed)
					);

				// Register the decoder function script block
				if (!Page.IsClientScriptBlockRegistered(FuncScriptName))
					Page.RegisterClientScriptBlock(FuncScriptName, GetFuncScript());

				// Register the calling script block
				if (!Page.IsStartupScriptRegistered(CallScriptName))
					Page.RegisterStartupScript(CallScriptName, GetCallScript());
			}
		}

		/// <summary> 
		/// Render this control to the output parameter specified.
		/// </summary>
		/// <param name="output">The HtmlTextWriter for the page</param>
		protected override void Render(HtmlTextWriter output)
		{
			// If we don't have anything to display don't even render
			// the start and end blocks.  This assures that the page shows
			// nothing but the VS.NET designer has a selectable label
			if (Email.Length == 0 && Text.Length == 0 && Controls.Count == 0)
				return;

			base.Render(output);
		}

		protected override void RenderContents(HtmlTextWriter writer)
		{
			// The only controls that should be left at this
			// point should be DataBoundLiteralControls.  In theory,
			// if there are any then there should be exactly one 
			// and nothing else.  But we'll leave in a bit of
			// flexibility, in case the framework changes later.
			string displayText = null;

			if (Controls.Count > 0 && Controls[0] is DataBoundLiteralControl)
			{
				displayText = ((DataBoundLiteralControl)Controls[0]).Text;
			}
			else
			{
				// If there is some text, use it.  If not then display the
				// encoded email address or the hyperlink will not be
				// visible
				displayText = (Text.Length == 0)
					? Email
					: Text;
			}

			// If the EncodeInText flag is set and the email address
			// is somewhere in the Text, encode it.
			if (EncodeInText && Email.Length > 0)
			{
				int idx = displayText.IndexOf(Email);

				if (idx > -1) displayText = BrowserNeedsHide ? HideText : Encode(displayText, Email);
			}

			// Html encode any text that remains.
			writer.Write(HttpUtility.HtmlEncode(displayText));
		}
		#endregion
	}
}