using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Web;
using ChadSoft.Web.ResponseFilters;

namespace ChadSoft.Web.Modules
{
    public class CdnRewriteModule : IHttpModule
    {
        public void Init(HttpApplication context)
        {
            context.PostReleaseRequestState += context_PostReleaseRequestState;
        }

        static void context_PostReleaseRequestState(object sender, EventArgs e)
        {
            var response = ((HttpApplication)sender).Response;
            response.Filter = new CdnPathRewriterFilter(response.Filter);
        }

        public void Dispose()
        {
            
        }

        
        public class CdnPathRewriterFilter : TextProcessingResponseFilter
        {
            const string TAG_EXPR = "(?<=<(?:script|img|link)[^>]*(?:src|href)=)['\"](?!http)/?(?<url>[^'\"]*)['\"]";
            const string TAG_REPLACE_EXPR = "'{0}/${{url}}'";

            static readonly Regex ResourceRegex = new Regex(TAG_EXPR, RegexOptions.IgnoreCase);

            private string _cdnBasePath = "http://static.jesschadwick.com";
            public string CdnBasePath
            {
                get { return _cdnBasePath; }
                set
                { 
                    _cdnBasePath = value;
                    // Invalidate the replacement text so it
                    // is rebuilt on the next request to it.
                    _replacementText = null;
                }
            }

            private string _replacementText;
            protected string ReplacementText
            {
                get 
                { 
                    if(string.IsNullOrEmpty(_replacementText))
                        _replacementText = string.Format(TAG_REPLACE_EXPR, CdnBasePath);
                    return _replacementText; 
                }
            }

            public CdnPathRewriterFilter(Stream stream) : base(stream)
            {
            }

            protected override string ProcessResponseText(string responseText)
            {
                return ResourceRegex.Replace(responseText, ReplacementText);
            }
        }
    }
}