using System;
using System.Collections.Generic;
using static PKHeX.Core.LegalityCheckStrings;
using static System.Buffers.Binary.BinaryPrimitives;

namespace PKHeX.Core;

public static class MysteryGiftVerifier
{
    private static readonly Dictionary<int, MysteryGiftRestriction>?[] RestrictionSet = Get();

    private static Dictionary<int, MysteryGiftRestriction>?[] Get()
    {
        var s = new Dictionary<int, MysteryGiftRestriction>?[PKX.Generation + 1];
        for (int i = 3; i < s.Length; i++)
            s[i] = GetRestriction(i);
        return s;
    }

    private static string RestrictionSetName(int generation) => $"mgrestrict{generation}.pkl";

    private static Dictionary<int, MysteryGiftRestriction> GetRestriction(int generation)
    {
        var resource = RestrictionSetName(generation);
        var data = Util.GetBinaryResource(resource).AsSpan();
        var dict = new Dictionary<int, MysteryGiftRestriction>();
        for (int i = 0; i < data.Length; i += 8)
        {
            var entry = data[i..];
            int hash = ReadInt32LittleEndian(entry);
            var restrict = ReadInt32LittleEndian(entry[4..]);
            dict.Add(hash, (MysteryGiftRestriction)restrict);
        }
        return dict;
    }

    public static CheckResult VerifyGift(PKM pk, MysteryGift g)
    {
        bool restricted = TryGetRestriction(g, out var value);
        if (!restricted)
            return new CheckResult(CheckIdentifier.GameOrigin);

        var ver = (int)value >> 16;
        if (ver != 0 && !CanVersionReceiveGift(g.Generation, ver, pk.Version))
            return new CheckResult(Severity.Invalid, LEncGiftVersionNotDistributed, CheckIdentifier.GameOrigin);

        var lang = value & MysteryGiftRestriction.LangRestrict;
        if (lang != 0 && !lang.HasFlagFast((MysteryGiftRestriction) (1 << pk.Language)))
            return new CheckResult(Severity.Invalid, string.Format(LOTLanguage, lang.GetSuggestedLanguage(), pk.Language), CheckIdentifier.GameOrigin);

        if (pk is IRegionOrigin tr)
        {
            var region = value & MysteryGiftRestriction.RegionRestrict;
            if (region != 0 && !region.HasFlagFast((MysteryGiftRestriction)((int)MysteryGiftRestriction.RegionBase << tr.ConsoleRegion)))
                return new CheckResult(Severity.Invalid, LGeoHardwareRange, CheckIdentifier.GameOrigin);
        }

        return new CheckResult(CheckIdentifier.GameOrigin);
    }

    private static bool TryGetRestriction(MysteryGift g, out MysteryGiftRestriction val)
    {
        var restrict = RestrictionSet[g.Generation];
        if (restrict != null)
            return restrict.TryGetValue(g.GetHashCode(), out val);
        val = MysteryGiftRestriction.None;
        return false;
    }

    public static bool IsValidChangedOTName(PKM pk, MysteryGift g)
    {
        bool restricted = TryGetRestriction(g, out var val);
        if (!restricted)
            return false; // no data
        if (!val.HasFlagFast(MysteryGiftRestriction.OTReplacedOnTrade))
            return false;
        return CurrentOTMatchesReplaced(g.Generation, pk.OT_Name);
    }

    private static bool CanVersionReceiveGift(int generation, int version4bit, int version)
    {
        return generation switch
        {
            _ => false,
        };
    }

    private static bool CurrentOTMatchesReplaced(int format, string pkOtName)
    {
        if (format <= 4 && IsMatchName(pkOtName, 4))
            return true;
        if (format <= 5 && IsMatchName(pkOtName, 5))
            return true;
        if (format <= 6 && IsMatchName(pkOtName, 6))
            return true;
        if (format <= 7 && IsMatchName(pkOtName, 7))
            return true;
        return false;
    }

    private static bool IsMatchName(string pkOtName, int generation)
    {
        return generation switch
        {
            _ => false,
        };
    }
}