using System;
using System.Collections.Generic;
using System.Linq;

namespace LocalhostMES.Helpers
{
    /// <summary>
    /// 年/月/日与单字符编码互转（用于本地 SN 等场景）。
    /// </summary>
    public static class DateCodeConverter
    {
        private static readonly Dictionary<int, string> yearToCode = new Dictionary<int, string>
        {
            {2018, "1"}, {2019, "2"}, {2020, "3"}, {2021, "4"}, {2022, "5"},
            {2023, "6"}, {2024, "7"}, {2025, "8"}, {2026, "9"}, {2027, "A"},
            {2028, "B"}, {2029, "C"}, {2030, "D"}, {2031, "E"}, {2032, "F"},
            {2033, "G"}, {2034, "H"}, {2035, "J"}, {2036, "K"}, {2037, "L"},
            {2038, "M"}, {2039, "N"}, {2040, "P"}, {2041, "R"}, {2042, "S"},
            {2043, "T"}, {2044, "V"}, {2045, "W"}, {2046, "X"}, {2047, "Y"},
            {2048, "1"}, {2049, "2"}, {2050, "3"}, {2051, "4"}, {2052, "5"},
            {2053, "6"}, {2054, "7"}, {2055, "8"}, {2056, "9"}, {2057, "A"}
        };

        private static readonly Dictionary<int, string> monthToCode = new Dictionary<int, string>
        {
            {1, "1"}, {2, "2"}, {3, "3"}, {4, "4"}, {5, "5"}, {6, "6"},
            {7, "7"}, {8, "8"}, {9, "9"}, {10, "A"}, {11, "B"}, {12, "C"}
        };

        private static readonly Dictionary<int, string> dayToCode = new Dictionary<int, string>
        {
            {1, "1"}, {2, "2"}, {3, "3"}, {4, "4"}, {5, "5"}, {6, "6"}, {7, "7"}, {8, "8"}, {9, "9"},
            {10, "A"}, {11, "B"}, {12, "C"}, {13, "D"}, {14, "E"}, {15, "F"}, {16, "G"},
            {17, "H"}, {18, "J"}, {19, "K"}, {20, "L"}, {21, "M"}, {22, "N"}, {23, "P"}, {24, "R"},
            {25, "S"}, {26, "T"}, {27, "U"}, {28, "V"}, {29, "W"}, {30, "X"}, {31, "Y"}
        };

        private static readonly Dictionary<string, int> codeToYear;
        private static readonly Dictionary<string, int> codeToMonth;
        private static readonly Dictionary<string, int> codeToDay;

        static DateCodeConverter()
        {
            codeToYear = yearToCode
                .GroupBy(kv => kv.Value)
                .ToDictionary(g => g.Key, g => g.Last().Key);

            codeToMonth = monthToCode
                .ToDictionary(kv => kv.Value, kv => kv.Key);

            codeToDay = dayToCode
                .ToDictionary(kv => kv.Value, kv => kv.Key);
        }

        public static string GetYearCode(int year)
        {
            return yearToCode.TryGetValue(year, out string code) ? code : "未知年份";
        }

        public static int? GetYearByCode(string code)
        {
            return codeToYear.TryGetValue(code, out int year) ? year : (int?)null;
        }

        public static List<int> GetAllYearsByCode(string code)
        {
            return yearToCode
                .Where(kv => kv.Value == code)
                .Select(kv => kv.Key)
                .ToList();
        }

        public static string GetMonthCode(int month)
        {
            if (month < 1 || month > 12)
                return "无效月份";

            return monthToCode.TryGetValue(month, out string code) ? code : "未知月份";
        }

        public static int? GetMonthByCode(string code)
        {
            return codeToMonth.TryGetValue(code, out int month) ? month : (int?)null;
        }

        public static string GetDayCode(int day)
        {
            if (day < 1 || day > 31)
                return "无效日期";

            return dayToCode.TryGetValue(day, out string code) ? code : "未知日期";
        }

        public static int? GetDayByCode(string code)
        {
            return codeToDay.TryGetValue(code, out int day) ? day : (int?)null;
        }

        public static string ConvertToDateCode(DateTime date)
        {
            string yearCode = GetYearCode(date.Year);
            string monthCode = GetMonthCode(date.Month);
            string dayCode = GetDayCode(date.Day);

            if (yearCode == "未知年份" || monthCode == "无效月份" || dayCode == "无效日期" || dayCode == "未知日期")
            {
                return "无效日期";
            }

            return $"{yearCode}{monthCode}{dayCode}";
        }

        public static DateTime? ConvertFromDateCode(string dateCode)
        {
            if (string.IsNullOrEmpty(dateCode) || dateCode.Length != 3)
                return null;

            string yearCode = dateCode.Substring(0, 1);
            string monthCode = dateCode.Substring(1, 1);
            string dayCode = dateCode.Substring(2, 1);

            var year = GetYearByCode(yearCode);
            var month = GetMonthByCode(monthCode);
            var day = GetDayByCode(dayCode);

            if (!year.HasValue || !month.HasValue || !day.HasValue)
                return null;

            try
            {
                return new DateTime(year.Value, month.Value, day.Value);
            }
            catch (ArgumentOutOfRangeException)
            {
                return null;
            }
        }

        public static List<DateTime> ConvertAllFromDateCode(string dateCode)
        {
            var result = new List<DateTime>();

            if (string.IsNullOrEmpty(dateCode) || dateCode.Length != 3)
                return result;

            string yearCode = dateCode.Substring(0, 1);
            string monthCode = dateCode.Substring(1, 1);
            string dayCode = dateCode.Substring(2, 1);

            var allYears = GetAllYearsByCode(yearCode);
            var month = GetMonthByCode(monthCode);
            var day = GetDayByCode(dayCode);

            if (allYears.Count == 0 || !month.HasValue || !day.HasValue)
                return result;

            foreach (var year in allYears)
            {
                try
                {
                    result.Add(new DateTime(year, month.Value, day.Value));
                }
                catch (ArgumentOutOfRangeException)
                {
                }
            }

            return result;
        }
    }
}