using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Runtime.InteropServices;

namespace GeoInfoService
{
    public static class GeoInfoService
    {
        private static readonly Dictionary<string, (string EnglishName, int GeoId, string ISO2Code, string ISO3Code)> _regionCodeMapping
            = CultureInfo.GetCultures(CultureTypes.SpecificCultures)
                .Select(ci => new RegionInfo(ci.LCID))
                .GroupBy(ri => ri.TwoLetterISORegionName)
                .ToDictionary(
                    g => g.Key,
                    g => g.First().Transform(x => (x.EnglishName, x.GeoId, x.TwoLetterISORegionName, x.ThreeLetterISORegionName))
                    );

        public static string GetFriendlyName(string code)
            => _regionCodeMapping[code].EnglishName;

        public enum SYSGEOTYPE
        {
            GEO_NATION = 0x0001,
            GEO_LATITUDE,
            GEO_LONGITUDE,
            GEO_ISO2,
            GEO_ISO3,
            GEO_RFC1766,
            GEO_LCID,
            GEO_FRIENDLYNAME,
            GEO_OFFICIALNAME,
            GEO_TIMEZONES,
            GEO_OFFICIALLANGUAGES,
            GEO_ISO_UN_NUMBER,
            GEO_PARENT,
            GEO_DIALINGCODE,
            GEO_CURRENCYCODE,
            GEO_CURRENCYSYMBOL,
            GEO_NAME,
            GEO_ID
        }

        public static string GetGeoInfoEx(string geoId, SYSGEOTYPE geoType)
        {
            switch (geoType)
            {
                case SYSGEOTYPE.GEO_NATION:
                case SYSGEOTYPE.GEO_RFC1766:
                case SYSGEOTYPE.GEO_LCID:
                case SYSGEOTYPE.GEO_ID:
                    throw new Exception("Not supported");
                case SYSGEOTYPE.GEO_TIMEZONES:
                case SYSGEOTYPE.GEO_OFFICIALLANGUAGES:
                    throw new Exception("Not implemented in the system");
                case SYSGEOTYPE.GEO_LATITUDE:
                case SYSGEOTYPE.GEO_LONGITUDE:
                case SYSGEOTYPE.GEO_ISO2:
                case SYSGEOTYPE.GEO_ISO3:
                case SYSGEOTYPE.GEO_FRIENDLYNAME:
                case SYSGEOTYPE.GEO_OFFICIALNAME:
                case SYSGEOTYPE.GEO_ISO_UN_NUMBER:
                case SYSGEOTYPE.GEO_PARENT:
                case SYSGEOTYPE.GEO_DIALINGCODE:
                case SYSGEOTYPE.GEO_CURRENCYCODE:
                case SYSGEOTYPE.GEO_CURRENCYSYMBOL:
                case SYSGEOTYPE.GEO_NAME:
                    break;
                default:
                    throw new Exception("Unexpected SYSGEOTYPE value");
            }

            string s = new string('\0', 256);
            int size = GetGeoInfoEx(geoId, geoType, s, 256);
            if (size <= 0) { return null; }

            return s.Substring(0, size - 1);
        }

        [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private extern static int GetGeoInfoEx(string location, SYSGEOTYPE geoType, string geoData, int geoDataCount);
    }
}