using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

using System.Linq;

public class Program

{

    private static readonly Dictionary<string, string> ShippingVendorTrackingUrls = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)

    {

        {"AMAZON", ""},

        {"AMAZONSHIPPING", "https://track.amazon.co.uk/tracking/##TRACKINGNUMBER##"},

        {"AUSPOSTCORP", "https://auspost.com.au/mypost/track/#/details/##TRACKINGNUMBER##"},

        {"DEUTSCHEPOST", "https://webtrack.dhlglobalmail.com/?trackingnumber=##TRACKINGNUMBER##"},

        {"DHL", "https://www.dhl.com/en/express/tracking.html?AWB=##TRACKINGNUMBER##&brand=DHL"},

        {"DHLUSDIRECT", "https://www.logistics.dhl/us-en/home/tracking/tracking-ecommerce.html?submit=1&tracking-id=##TRACKINGNUMBER##"},

        {"DHLEM", ""},

        {"DPD", "https://www.dpd.co.uk/apps/tracking/?reference=##TRACKINGNUMBER##"},

        {"ENDICIA", "https://www.endicia.com/status/?PIC=##TRACKINGNUMBER##"},

        {"FEDEX", "https://www.fedex.com/apps/fedextrack/?action=track&trackingnumber=##TRACKINGNUMBER##"},

        {"FIMS", ""},

        {"GFS", "https://seeker.justshoutgfs.com/ConsLinkv2.asp?ConsNumber=##TRACKINGNUMBER##&x=38&y=12&DSN_Tracking=1"},

        {"HERMESCORPORATE", ""},

        {"INTERLINK", "https://www.dpdlocal-online.co.uk/tracking/##TRACKINGNUMBER##"},

        {"MYHERMES", "https://new.myhermes.co.uk/track.html#/parcel/##TRACKINGNUMBER##/details"},

        {"MYPARCEL", ""},

        {"PARCELFORCE", "https://www.parcelforce.com/track-trace?trackNumber=##TRACKINGNUMBER##"},

        {"ROYALMAIL", "https://www.royalmail.com/track-your-item#/tracking-results/##TRACKINGNUMBER##"},

        {"ROYALMAILTRACKED", "https://www.royalmail.com/track-your-item#/tracking-results/##TRACKINGNUMBER##"},

        {"SHIPENGINE", ""},

        {"SPRING", "https://postnl.post/details/?barcode=##TRACKINGNUMBER##"},

        {"STAMPSCOM", "https://www.stamps.com/shipstatus/?confirmation=##TRACKINGNUMBER##"},

        {"UKMAIL", ""},

        {"UPS", "https://www.ups.com/track?tracknum=##TRACKINGNUMBER##"},

        {"YODEL", "https://www.yodel.co.uk/tracking/##TRACKINGNUMBER##"},

    };

    public static void Main()

    {

        Console.WriteLine("Match 1: " + BestMatchOrDefault("Deutsch Post", @"[A-Za-z0-9&]+", ShippingVendorTrackingUrls.Keys));

        Console.WriteLine("Match 2: " + BestMatchOrDefault("De_Post", @"[A-Za-z0-9&]+", ShippingVendorTrackingUrls.Keys));

        Console.WriteLine("Match 3: " + BestMatchOrDefault("ROYAL MAIL", @"[A-Za-z0-9&]+", ShippingVendorTrackingUrls.Keys));

    }

    private static string BestMatchOrDefault(string input, string pattern, IEnumerable<string> items)

    {

        var matches = new Dictionary<string, int>();

​

        foreach (string item in items)

        {

            foreach (Match match in Regex.Matches(input, pattern))

            {

                if (item.IndexOf(match.Value, StringComparison.InvariantCultureIgnoreCase) >= 0)

                {

                    if (!matches.ContainsKey(item))

                        matches.Add(item, 0);

​

                    matches[item]++;

                }

            }

        }

​

        if (matches.Any())

        {

            if (matches.Values.Where(v => v == matches.Values.Max()).Count() == 1)

                return matches.Aggregate((l, r) => l.Value > r.Value ? l : r).Key;

            else

                return null;

        }

        else

            return null;

    }

}