using System;
using System.IO.Compression;
using System.Web;
using System.Web.Security;

/// <summary>
/// Implement two way HTTP compression for the SOAP API
/// Code taken from: http://netpl.blogspot.co.uk/2009/07/aspnet-webservices-two-way-response-and.html
/// Fix: Set Content-encoding: gzip header when an Exception occurs on the server.
/// Fix: Do not attempt to decrypt GZIP request stream when request was not GZIPed.
/// </summary>
public class HttpCompressionModule : IHttpModule
{
	private bool isDisposed = false;

	~HttpCompressionModule()
	{
		Dispose(false);
	}

	public void Init(HttpApplication context)
	{
		context.BeginRequest += new EventHandler(Context_BeginRequest);
		context.PreSendRequestHeaders += new EventHandler(context_PreSendRequestHeaders);
	}

	void context_PreSendRequestHeaders(object sender, EventArgs e)
	{
		// Fix headers having been lost if an exception occurred.
		HttpApplication app = sender as HttpApplication;
		HttpContext ctx = app.Context;
		if (app.Response.Filter is GZipStream) SetEncoding("gzip");
		else if (app.Response.Filter is DeflateStream) SetEncoding("deflate");

		// Fix double header
		if (ctx.Response.Headers["Content-encoding"] == "gzip,gzip") 
			ctx.Response.Headers.Set("Content-encoding", "gzip");
	}

	/// <summary>
	/// Fires at the start of each new web request
	/// </summary>
	/// <param name="sender">The Sender</param>
	/// <param name="e">Event Arguments</param>
	public void Context_BeginRequest(object sender, EventArgs e)
	{
		HttpApplication app = sender as HttpApplication;
		HttpContext ctx = app.Context;

		// Currently only enable for the Uploader API webservice
		//if (!ctx.Request.Url.PathAndQuery.ToLower().Contains("uploaderapi.asmx"))
		//{
		//	return;
		//}

		// Add request filter if request was GZIP encoded
		string requestEncoding = ctx.Request.Headers["Content-encoding"];
		if (requestEncoding != null && requestEncoding == "gzip")
		{
		   app.Request.Filter = 
			new System.IO.Compression.GZipStream(app.Request.Filter, CompressionMode.Decompress);
		}

		// Add response compression filter if the client accepts compressed responses
		if (IsEncodingAccepted("gzip"))
		{
			app.Response.Filter = new GZipStream(app.Response.Filter, CompressionMode.Compress);
			SetEncoding("gzip");
		}
		else if (IsEncodingAccepted("deflate"))
		{
			app.Response.Filter = new DeflateStream(app.Response.Filter, CompressionMode.Compress);
			SetEncoding("deflate");
		}
	}

	private bool IsEncodingAccepted(string encoding)
	{
		return HttpContext.Current.Request.Headers["Accept-encoding"] != null &&
			HttpContext.Current.Request.Headers["Accept-encoding"].Contains(encoding);
	}

	private void SetEncoding(string encoding)
	{
		HttpContext ctx = HttpContext.Current;
		string responseEncodings = ctx.Response.Headers.Get("Content-encoding");
		if (responseEncodings == null || !responseEncodings.Contains(encoding))
			HttpContext.Current.Response.AppendHeader("Content-encoding", encoding);
	}

	public void Dispose()
	{
		Dispose(true);
	}

	private void Dispose(bool dispose)
	{
		isDisposed = dispose;
	}
}