using System;
using System.Collections.Generic;
using System.Linq;
using Remotion.Linq.Clauses;

namespace CompatBot.Utils
{
    public static class TimeParser
    {
        private static readonly Dictionary<string, TimeZoneInfo> TimeZoneMap;

        static TimeParser()
        {
            var tzAcronyms = new Dictionary<string, string[]>
            {
                ["PT"] = new[] { "Pacific Standard Time" },
                ["PST"] = new[] { "Pacific Standard Time" },
                ["PDT"] = new[] { "Pacific Standard Time" },
                ["EST"] = new[] { "Eastern Standard Time" },
                ["EDT"] = new[] { "Eastern Standard Time" },
                ["CEST"] = new[] { "Central European Standard Time" },
                ["BST"] = new[] { "British Summer Time", "GMT Standard Time" },
                ["JST"] = new[] { "Japan Standard Time", "Tokyo Standard Time" },
            };
            var uniqueNames = new HashSet<string>(
                from tznl in tzAcronyms.Values
                from tzn in tznl
                select tzn
            );
            var tzList = TimeZoneInfo.GetSystemTimeZones();
            var result = new Dictionary<string, TimeZoneInfo>();
            foreach (var tzi in tzList)
            {
                if (uniqueNames.Contains(tzi.StandardName) || uniqueNames.Contains(tzi.StandardName))
                {
                    var acronyms = from tza in tzAcronyms
                        where tza.Value.Contains(tzi.StandardName) || tza.Value.Contains(tzi.DaylightName)
                        select tza.Key;
                    foreach (var tza in acronyms)
                        result[tza] = tzi;
                }
            }
            TimeZoneMap = result;
        }

        public static bool TryParse(string dateTime, out DateTime result)
        {
            result = default;
            if (string.IsNullOrEmpty(dateTime))
                return false;

            dateTime = dateTime.ToUpperInvariant();
            if (char.IsDigit(dateTime[dateTime.Length - 1]))
            {
                return DateTime.TryParse(dateTime, out result);
            }

            var cutIdx = dateTime.LastIndexOf(' ');
            if (cutIdx < 0)
                return false;

            var tza = dateTime.Substring(cutIdx + 1);
            dateTime = dateTime.Substring(0, cutIdx);
            if (TimeZoneMap.TryGetValue(tza, out var tzi))
            {
                if (!DateTime.TryParse(dateTime, out result))
                    return false;

                result = TimeZoneInfo.ConvertTimeToUtc(result, tzi);
                return true;
            }

            return false;
        }


        public static DateTime Normalize(this DateTime date)
        {
            if (date.Kind == DateTimeKind.Utc)
                return date;
            if (date.Kind == DateTimeKind.Local)
                return date.ToUniversalTime();
            return date.AsUtc();
        }

        public static List<string> GetSupportedTimeZoneAbbreviations() => TimeZoneMap.Keys.ToList();
    }
}