Fetch og metadata with CsQuery

OgMetaFetcher.cs

// Fetch meta data from a web page
// Depends on CsQuery [https://github.com/jamietre/CsQuery]
// Nuget: install-package csquery

using CsQuery;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Meridium.OgMetaFetcher {

    public class OgMetaFetcher {
        public FetchResult Fetch(string url) {
            try {
                var dom = CQ.CreateFromUrl(url);

                var metadata = new OgMetaData {
                    Title = dom
                        .OgProperty("title")
                        .ElementText("title")
                        .Value,

                    Description = dom
                        .OgProperty("description")
                        .MetaValue("description")
                        .Value,

                    SiteName = dom
                        .OgProperty("site_name")
                        .Value(new Uri(url).Host),

                    Url = dom
                        .OgProperty("url")
                        .Value(url),

                    ImageUrl = dom
                        .OgProperty("image")
                        .Custom(d => FirstImageUrl(d, new Uri(url)))
                        .Value
                };

                return FetchResult.Success(url, metadata);
            } catch (Exception e) {
                return FetchResult.Failure(url, e);
            }
        }

        private string FirstImageUrl(CQ dom, Uri url) {
            var src = dom["img"].Attr("src") ?? "";
            if (src.StartsWith("/")) {
                return url.MakeAbsolute(src);
            }
            return src;
        }
    }

    static class Ext {
        public static string MakeAbsolute(this Uri self, string path) {
            return self.Scheme + "://" + self.Host + path;
        }

        public static ValueResult OgProperty(this CQ self, string property) {
            return new ValueResult {
                Value = self["meta[property='og:" + property + "']"].Attr("content"),
                Dom = self
            };
        }

        public static ValueResult MetaValue(this ValueResult self, string name) {
            if (self.HasValue) return self;
            return new ValueResult {
                Value = self.Dom["meta[name='" + name + "']"].Attr("content"),
                Dom = self.Dom
            };
        }

        public static ValueResult ElementText(this ValueResult self, string selector) {
            if (self.HasValue) return self;
            return new ValueResult {
                Value = self.Dom[selector].Text(),
                Dom = self.Dom
            };
        }

        public static ValueResult Custom(this ValueResult self, Func<CQ, string> selector) {
            if (self.HasValue) return self;

            return new ValueResult {
                Value = selector(self.Dom),
                Dom = self.Dom
            };
        }

        public static string Value(this ValueResult self, string value) {
            return self.HasValue ? self.Value : value;
        }
    }

    class ValueResult {
        public CQ Dom { get; set; }
        public string Value { get; set; }
        public bool HasValue { get { return !string.IsNullOrEmpty(Value); } }
    }

    public class FetchResult {
        public bool IsSuccess { get; private set; }
        public OgMetaData OgMetaData { get; private set; }
        public Exception Error { get; private set; }
        public string FetchUrl { get; private set; }

        public static FetchResult Failure(string fetchurl, Exception exception) {
            return new FetchResult {
                IsSuccess = false,
                Error = exception,
                OgMetaData = OgMetaData.Empty,
                FetchUrl = fetchurl
            };
        }

        public static FetchResult Success(string fetchurl, OgMetaData metadata ) {
            return new FetchResult {
                IsSuccess = true,
                OgMetaData = metadata,
                FetchUrl = fetchurl
            };
        }
    }

    public class OgMetaData {
        public string Title { get; set; }
        public string Description { get; set; }
        public string SiteName { get; set; }
        public string ImageUrl { get; set; }
        public string Url { get; set; }

        public static OgMetaData Empty {
            get {
                return new OgMetaData {
                    Title = "",
                    Description = "",
                    SiteName = "",
                    ImageUrl = "",
                    Url = ""
                };
            }
        }
    }
}