namespace SeaHaven.Services.Helpers
{
    public static class UsStateCodes
    {
        private static readonly IReadOnlyDictionary<string, string> Names = new Dictionary<string, string>(StringComparer.Ordinal)
        {
            ["AL"] = "ALABAMA",
            ["AK"] = "ALASKA",
            ["AZ"] = "ARIZONA",
            ["AR"] = "ARKANSAS",
            ["CA"] = "CALIFORNIA",
            ["CO"] = "COLORADO",
            ["CT"] = "CONNECTICUT",
            ["DE"] = "DELAWARE",
            ["FL"] = "FLORIDA",
            ["GA"] = "GEORGIA",
            ["HI"] = "HAWAII",
            ["ID"] = "IDAHO",
            ["IL"] = "ILLINOIS",
            ["IN"] = "INDIANA",
            ["IA"] = "IOWA",
            ["KS"] = "KANSAS",
            ["KY"] = "KENTUCKY",
            ["LA"] = "LOUISIANA",
            ["ME"] = "MAINE",
            ["MD"] = "MARYLAND",
            ["MA"] = "MASSACHUSETTS",
            ["MI"] = "MICHIGAN",
            ["MN"] = "MINNESOTA",
            ["MS"] = "MISSISSIPPI",
            ["MO"] = "MISSOURI",
            ["MT"] = "MONTANA",
            ["NE"] = "NEBRASKA",
            ["NV"] = "NEVADA",
            ["NH"] = "NEW HAMPSHIRE",
            ["NJ"] = "NEW JERSEY",
            ["NM"] = "NEW MEXICO",
            ["NY"] = "NEW YORK",
            ["NC"] = "NORTH CAROLINA",
            ["ND"] = "NORTH DAKOTA",
            ["OH"] = "OHIO",
            ["OK"] = "OKLAHOMA",
            ["OR"] = "OREGON",
            ["PA"] = "PENNSYLVANIA",
            ["RI"] = "RHODE ISLAND",
            ["SC"] = "SOUTH CAROLINA",
            ["SD"] = "SOUTH DAKOTA",
            ["TN"] = "TENNESSEE",
            ["TX"] = "TEXAS",
            ["UT"] = "UTAH",
            ["VT"] = "VERMONT",
            ["VA"] = "VIRGINIA",
            ["WA"] = "WASHINGTON",
            ["WV"] = "WEST VIRGINIA",
            ["WI"] = "WISCONSIN",
            ["WY"] = "WYOMING"
        };

        private static readonly IReadOnlyDictionary<string, string> CodesByName =
            Names.ToDictionary(pair => pair.Value, pair => pair.Key, StringComparer.Ordinal);

        public static IReadOnlySet<string> All { get; } = new HashSet<string>(Names.Keys, StringComparer.Ordinal);

        /// <summary>
        /// Normalises a stored state value to its two-letter postal code. Accepts either a
        /// postal code ("IN") or a full state name ("Indiana"), case-insensitively, matching
        /// the storage forms produced by <see cref="ExpandStorageValues"/>. Returns null when
        /// the value is blank or is not a recognised US state.
        /// </summary>
        public static string? ToCode(string? value)
        {
            if (string.IsNullOrWhiteSpace(value))
                return null;

            var normalized = value.Trim().ToUpperInvariant();
            if (All.Contains(normalized))
                return normalized;

            return CodesByName.TryGetValue(normalized, out var code) ? code : null;
        }

        public static IReadOnlyCollection<string> ExpandStorageValues(IEnumerable<string> codes)
        {
            return codes
                .SelectMany(code => new[] { code, Names[code] })
                .ToArray();
        }
    }
}