using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;

namespace PKHeX.Core
{
    /// <summary>
    /// Common logic for <see cref="PKM"/> data providing and manipulation.
    /// </summary>
    public static class PKX
    {
        internal static readonly PersonalTable Personal = PersonalTable.GG;
        public const int Generation = 7;

        internal const int SIZE_1ULIST = 69;
        internal const int SIZE_1JLIST = 59;
        internal const int SIZE_1PARTY = 44;
        internal const int SIZE_1STORED = 33;

        internal const int SIZE_2ULIST = 73;
        internal const int SIZE_2JLIST = 63;
        internal const int SIZE_2PARTY = 48;
        internal const int SIZE_2STORED = 32;

        internal const int SIZE_3CSTORED = 312;
        internal const int SIZE_3XSTORED = 196;
        internal const int SIZE_3PARTY = 100;
        internal const int SIZE_3STORED = 80;
        internal const int SIZE_3BLOCK = 12;

        internal const int SIZE_4PARTY = 236;
        internal const int SIZE_4STORED = 136;
        internal const int SIZE_4BLOCK = 32;

        internal const int SIZE_5PARTY = 220;
        internal const int SIZE_5STORED = 136;
        internal const int SIZE_5BLOCK = 32;

        internal const int SIZE_6PARTY = 0x104;
        internal const int SIZE_6STORED = 0xE8;
        internal const int SIZE_6BLOCK = 56;

        private static readonly HashSet<int> Sizes = new HashSet<int>
        {
            SIZE_1JLIST, SIZE_1ULIST,
            SIZE_2ULIST, SIZE_2JLIST,
            SIZE_3STORED, SIZE_3PARTY,
            SIZE_3CSTORED, SIZE_3XSTORED,
            SIZE_4STORED, SIZE_4PARTY,
            SIZE_5PARTY,
            SIZE_6STORED, SIZE_6PARTY
        };

        /// <summary>
        /// Determines if the given length is valid for a <see cref="PKM"/>.
        /// </summary>
        /// <param name="len">Data length of the file/array.</param>
        /// <returns>A <see cref="bool"/> indicating whether or not the length is valid for a <see cref="PKM"/>.</returns>
        public static bool IsPKM(long len) => Sizes.Contains((int)len);

        public static uint LCRNG(uint seed) => RNG.LCRNG.Next(seed);
        public static uint LCRNG(ref uint seed) => seed = RNG.LCRNG.Next(seed);

        /// <summary>
        /// Species name lists indexed by the <see cref="PKM.Language"/> value.
        /// </summary>
        public static readonly string[][] SpeciesLang =
        {
            Util.GetSpeciesList("ja"), // 0 (unused, invalid)
            Util.GetSpeciesList("ja"), // 1
            Util.GetSpeciesList("en"), // 2
            Util.GetSpeciesList("fr"), // 3
            Util.GetSpeciesList("it"), // 4
            Util.GetSpeciesList("de"), // 5
            Util.GetSpeciesList("es"), // 6 (reserved for Gen3 KO?, unused)
            Util.GetSpeciesList("es"), // 7
            Util.GetSpeciesList("ko"), // 8
            Util.GetSpeciesList("zh"), // 9 Simplified
            Util.GetSpeciesList("zh2"), // 10 Traditional
        };

        public static readonly Dictionary<string, int>[] SpeciesDict = SpeciesLang.Select(z => z
            .Select((value, index) => new {value, index}).ToDictionary(pair => pair.value, pair => pair.index))
            .ToArray();

        /// <summary>
        /// Gets a Pokémon's default name for the desired language ID.
        /// </summary>
        /// <param name="species">National Dex number of the Pokémon. Should be 0 if an egg.</param>
        /// <param name="lang">Language ID of the Pokémon</param>
        /// <returns>The Species name if within expected range, else an empty string.</returns>
        /// <remarks>Should only be used externally for message displays; for accurate in-game names use <see cref="GetSpeciesNameGeneration"/>.</remarks>
        public static string GetSpeciesName(int species, int lang)
        {
            if (lang < 0 || SpeciesLang.Length <= lang)
                return string.Empty;
            if (species < 0 || SpeciesLang[0].Length <= species)
                return string.Empty;

            return SpeciesLang[lang][species];
        }

        /// <summary>
        /// Gets a Pokémon's default name for the desired language ID and generation.
        /// </summary>
        /// <param name="species">National Dex number of the Pokémon. Should be 0 if an egg.</param>
        /// <param name="lang">Language ID of the Pokémon</param>
        /// <param name="generation">Generation specific formatting option</param>
        /// <returns>Generation specific default species name</returns>
        public static string GetSpeciesNameGeneration(int species, int lang, int generation)
        {
            if (generation == 3 && species == 0)
                return "タマゴ";

            string nick = GetSpeciesName(species, lang);
            if (generation == 2 && lang == (int)LanguageID.Korean)
                return StringConverter.LocalizeKOR2(nick);

            if (generation < 5 && (generation != 4 || species != 0)) // All caps GenIV and previous, except GenIV eggs.
            {
                nick = nick.ToUpper();
                if (lang == (int)LanguageID.French)
                    nick = StringConverter.StripDiacriticsFR4(nick); // strips accents on E and I
            }
            if (generation < 3)
                nick = nick.Replace(" ", string.Empty);
            return nick;
        }

        /// <summary>
        /// Checks if a nickname matches the species name of any language.
        /// </summary>
        /// <param name="species">National Dex number of the Pokémon. Should be 0 if an egg.</param>
        /// <param name="nick">Current name</param>
        /// <param name="generation">Generation specific formatting option</param>
        /// <returns>True if it does not match any language name, False if not nicknamed</returns>
        public static bool IsNicknamedAnyLanguage(int species, string nick, int generation = Generation)
        {
            if (species == 083 && string.Equals(nick, "Farfetch'd", StringComparison.OrdinalIgnoreCase)) // stupid ’
                return false;
            var langs = GetAvailableGameLanguages(generation);
            return langs.All(lang => GetSpeciesNameGeneration(species, lang, generation) != nick);
        }

        private static ICollection<int> GetAvailableGameLanguages(int generation = Generation)
        {
            if (generation < 3)
                return Legal.Languages_GB;
            if (generation < 4)
                return Legal.Languages_3;
            if (generation < 7)
                return Legal.Languages_46;
            return Legal.Languages_7;
        }

        /// <summary>
        /// Gets the Species name Language ID for the current name and generation.
        /// </summary>
        /// <param name="species">National Dex number of the Pokémon. Should be 0 if an egg.</param>
        /// <param name="nick">Current name</param>
        /// <param name="generation">Generation specific formatting option</param>
        /// <param name="priorlang">Language ID with a higher priority</param>
        /// <returns>Language ID if it does not match any language name, -1 if no matches</returns>
        public static int GetSpeciesNameLanguage(int species, string nick, int generation = Generation, int priorlang = -1)
        {
            var langs = GetAvailableGameLanguages(generation);

            if (langs.Contains(priorlang) && GetSpeciesNameGeneration(species, priorlang, generation) == nick)
                return priorlang;

            foreach (var lang in langs)
            {
                if (GetSpeciesNameGeneration(species, lang, generation) == nick)
                    return lang;
            }

            return -1;
        }

        /// <summary>
        /// Gets randomized EVs for a given generation format
        /// </summary>
        /// <param name="generation">Generation specific formatting option</param>
        /// <returns>Array containing randomized EVs (H/A/B/S/C/D)</returns>
        public static int[] GetRandomEVs(int generation = Generation)
        {
            if (generation > 2)
            {
                var evs = new int[6];
                do
                {
                    int max = 510;
                    int randomEV() => (byte)Math.Min(Util.Rand.Next(Math.Min(300, max)), 252);
                    for (int i = 0; i < evs.Length - 1; i++)
                        max -= evs[i] = randomEV();
                    evs[5] = max;
                } while (evs[5] > 252);
                Util.Shuffle(evs);
                return evs;
            }
            else
            {
                var evs = new int[6];
                for (int i = 0; i < evs.Length; i++)
                    evs[i] = Util.Rand.Next(ushort.MaxValue + 1);
                return evs;
            }
        }

        /// <summary>
        /// Gets the current level of a species.
        /// </summary>
        /// <param name="exp">Experience points</param>
        /// <param name="species">National Dex number of the Pokémon.</param>
        /// <param name="forme">AltForm ID (starters in Let's Go)</param>
        /// <returns>Current level of the species.</returns>
        public static int GetLevel(uint exp, int species, int forme)
        {
            return Experience.GetLevel(exp, species, forme);
        }

        /// <summary>
        /// Gets the minimum Experience points for the specified level.
        /// </summary>
        /// <param name="level">Current level</param>
        /// <param name="species">National Dex number of the Pokémon.</param>
        /// <param name="forme">AltForm ID (starters in Let's Go)</param>
        /// <returns>Experience points needed to have specified level.</returns>
        public static uint GetEXP(int level, int species, int forme)
        {
            return Experience.GetEXP(level, species, forme);
        }

        /// <summary>
        /// Translates a Gender string to Gender integer.
        /// </summary>
        /// <param name="s">Gender string</param>
        /// <returns>Gender integer</returns>
        public static int GetGenderFromString(string s)
        {
            if (s == "♂" || s == "M")
                return 0;
            if (s == "♀" || s == "F")
                return 1;
            return 2;
        }

        /// <summary>
        /// Gets the nature modification values and checks if they are equal.
        /// </summary>
        /// <param name="nature">Nature</param>
        /// <param name="incr">Increased stat</param>
        /// <param name="decr">Decreased stat</param>
        /// <returns>True if nature modification values are equal or the Nature is out of range.</returns>
        public static bool GetNatureModification(int nature, out int incr, out int decr)
        {
            incr = (nature / 5) + 1;
            decr = (nature % 5) + 1;
            return incr == decr || nature >= 25; // invalid
        }

        /// <summary>
        /// Updates stats according to the specified nature.
        /// </summary>
        /// <param name="Stats">Current stats to amplify if appropriate</param>
        /// <param name="nature">Nature</param>
        public static void ModifyStatsForNature(ushort[] Stats, int nature)
        {
            if (GetNatureModification(nature, out int incr, out int decr))
                return;
            Stats[incr] *= 11; Stats[incr] /= 10;
            Stats[decr] *= 9; Stats[decr] /= 10;
        }

        /// <summary>
        /// Positions for shuffling.
        /// </summary>
        private static readonly byte[][] blockPosition =
        {
            new byte[] {0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3},
            new byte[] {1, 1, 2, 3, 2, 3, 0, 0, 0, 0, 0, 0, 2, 3, 1, 1, 3, 2, 2, 3, 1, 1, 3, 2},
            new byte[] {2, 3, 1, 1, 3, 2, 2, 3, 1, 1, 3, 2, 0, 0, 0, 0, 0, 0, 3, 2, 3, 2, 1, 1},
            new byte[] {3, 2, 3, 2, 1, 1, 3, 2, 3, 2, 1, 1, 3, 2, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0},
        };

        /// <summary>
        /// Positions for unshuffling.
        /// </summary>
        internal static readonly byte[] blockPositionInvert =
        {
            0, 1, 2, 4, 3, 5, 6, 7, 12, 18, 13, 19, 8, 10, 14, 20, 16, 22, 9, 11, 15, 21, 17, 23
        };

        /// <summary>
        /// Shuffles a 232 byte array containing <see cref="PKM"/> data.
        /// </summary>
        /// <param name="data">Data to shuffle</param>
        /// <param name="sv">Block Shuffle order</param>
        /// <param name="blockSize">Size of shuffling chunks</param>
        /// <returns>Shuffled byte array</returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static byte[] ShuffleArray(byte[] data, uint sv, int blockSize)
        {
            byte[] sdata = (byte[])data.Clone();
            for (int block = 0; block < 4; block++)
                Array.Copy(data, 8 + (blockSize * blockPosition[block][sv]), sdata, 8 + (blockSize * block), blockSize);
            return sdata;
        }

        /// <summary>
        /// Decrypts a 232 byte + party stat byte array.
        /// </summary>
        /// <param name="ekm">Encrypted <see cref="PKM"/> data.</param>
        /// <returns>Decrypted <see cref="PKM"/> data.</returns>
        /// <returns>Encrypted <see cref="PKM"/> data.</returns>
        public static byte[] DecryptArray(byte[] ekm)
        {
            uint pv = BitConverter.ToUInt32(ekm, 0);
            uint sv = (pv >> 0xD & 0x1F) % 24;

            CryptPKM(ekm, pv, SIZE_6BLOCK);
            return ShuffleArray(ekm, sv, SIZE_6BLOCK);
        }

        /// <summary>
        /// Encrypts a 232 byte + party stat byte array.
        /// </summary>
        /// <param name="pkm">Decrypted <see cref="PKM"/> data.</param>
        public static byte[] EncryptArray(byte[] pkm)
        {
            uint pv = BitConverter.ToUInt32(pkm, 0);
            uint sv = (pv >> 0xD & 0x1F) % 24;

            byte[] ekm = ShuffleArray(pkm, blockPositionInvert[sv], SIZE_6BLOCK);
            CryptPKM(ekm, pv, SIZE_6BLOCK);
            return ekm;
        }

        /// <summary>
        /// Decrypts a 136 byte + party stat byte array.
        /// </summary>
        /// <param name="ekm">Encrypted <see cref="PKM"/> data.</param>
        /// <returns>Decrypted <see cref="PKM"/> data.</returns>
        public static byte[] DecryptArray45(byte[] ekm)
        {
            uint pv = BitConverter.ToUInt32(ekm, 0);
            uint chk = BitConverter.ToUInt16(ekm, 6);
            uint sv = (pv >> 0xD & 0x1F) % 24;

            CryptPKM45(ekm, pv, chk, SIZE_4BLOCK);
            return ShuffleArray(ekm, sv, SIZE_4BLOCK);
        }

        /// <summary>
        /// Encrypts a 136 byte + party stat byte array.
        /// </summary>
        /// <param name="pkm">Decrypted <see cref="PKM"/> data.</param>
        /// <returns>Encrypted <see cref="PKM"/> data.</returns>
        public static byte[] EncryptArray45(byte[] pkm)
        {
            uint pv = BitConverter.ToUInt32(pkm, 0);
            uint chk = BitConverter.ToUInt16(pkm, 6);
            uint sv = (pv >> 0xD & 0x1F) % 24;

            byte[] ekm = ShuffleArray(pkm, blockPositionInvert[sv], SIZE_4BLOCK);
            CryptPKM45(ekm, pv, chk, SIZE_4BLOCK);
            return ekm;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void CryptPKM(byte[] data, uint pv, int blockSize)
        {
            const int start = 8;
            int end = (4 * blockSize) + start;
            CryptArray(data, pv, 8, end); // Blocks
            CryptArray(data, pv, end, data.Length); // Party Stats
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void CryptPKM45(byte[] data, uint pv, uint chk, int blockSize)
        {
            const int start = 8;
            int end = (4 * blockSize) + start;
            CryptArray(data, chk, start, end); // Blocks
            CryptArray(data, pv, end, data.Length); // Party Stats
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void CryptArray(byte[] data, uint seed, int start, int end)
        {
            for (int i = start; i < end; i += 2)
                Crypt(data, ref seed, i);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void Crypt(byte[] data, ref uint seed, int i)
        {
            seed = (0x41C64E6D * seed) + 0x00006073;
            data[i] ^= (byte)(seed >> 16);
            data[i + 1] ^= (byte)(seed >> 24);
        }

        /// <summary>
        /// Gets the checksum of a 232 byte array.
        /// </summary>
        /// <param name="data">Decrypted <see cref="PKM"/> data.</param>
        /// <returns></returns>
        public static ushort GetCHK(byte[] data)
        {
            ushort chk = 0;
            for (int i = 8; i < 232; i += 2) // Loop through the entire PKX
                chk += BitConverter.ToUInt16(data, i);

            return chk;
        }

        /// <summary>
        /// Gets the Wurmple Evolution Value for a given <see cref="PKM.EncryptionConstant"/>
        /// </summary>
        /// <param name="EC">Encryption Constant</param>
        /// <returns>Wurmple Evolution Value</returns>
        public static uint GetWurmpleEvoVal(uint EC)
        {
            var evoVal = EC >> 16;
            return evoVal % 10 / 5;
        }

        /// <summary>
        /// Gets the Wurmple <see cref="PKM.EncryptionConstant"/> for a given Evolution Value
        /// </summary>
        /// <param name="evoVal">Wurmple Evolution Value</param>
        /// <remarks>0 = Silcoon, 1 = Cascoon</remarks>
        /// <returns>Encryption Constant</returns>
        public static uint GetWurmpleEC(int evoVal)
        {
            uint EC;
            do EC = Util.Rand32();
            while (evoVal != GetWurmpleEvoVal(EC));
            return EC;
        }

        /// <summary>
        /// Gets a random PID according to specifications.
        /// </summary>
        /// <param name="species">National Dex ID</param>
        /// <param name="cg">Current Gender</param>
        /// <param name="origin">Origin Generation</param>
        /// <param name="nature">Nature</param>
        /// <param name="form">AltForm</param>
        /// <param name="OLDPID">Current PID</param>
        /// <remarks>Used to retain ability bits.</remarks>
        /// <returns>Rerolled PID.</returns>
        public static uint GetRandomPID(int species, int cg, int origin, int nature, int form, uint OLDPID)
        {
            uint bits = OLDPID & 0x00010001;
            int gt = Personal[species].Gender;
            if (origin >= 24)
                return Util.Rand32();

            bool g3unown = origin <= 5 && species == 201;
            while (true) // Loop until we find a suitable PID
            {
                uint pid = Util.Rand32();

                // Gen 3/4: Nature derived from PID
                if (origin <= 15 && pid%25 != nature)
                    continue;

                // Gen 3 Unown: Letter/form derived from PID
                if (g3unown)
                {
                    var pidLetter = GetUnownForm(pid);
                    if (pidLetter != form)
                        continue;
                }
                else if (bits != (pid & 0x00010001)) // keep ability bits
                {
                    continue;
                }

                if (gt == 255 || gt == 254 || gt == 0) // Set Gender(less)
                    return pid; // PID can be anything

                // Gen 3/4/5: Gender derived from PID
                if (cg == GetGenderFromPIDAndRatio(pid, gt))
                    return pid;
            }
        }

        // Data Requests
        public static string GetResourceStringBall(int ball) => $"_ball{ball}";
        private const string ResourceSeparator = "_";
        private const string ResourcePikachuCosplay = "c"; // osplay
        private const string ResourceShiny = "s"; // hiny
        private const string ResourceGGStarter = "p"; //artner
        public static bool AllowShinySprite { get; set; }

        public static string GetResourceStringSprite(int species, int form, int gender, int generation = Generation, bool shiny = false)
        {
            if (Legal.SpeciesDefaultFormSprite.Contains(species)) // Species who show their default sprite regardless of Form
                form = 0;

            var sb = new System.Text.StringBuilder();
            { sb.Append(ResourceSeparator); sb.Append(species); }
            if (form > 0)
            { sb.Append(ResourceSeparator); sb.Append(form); }
            else if (gender == 1 && Legal.SpeciesGenderedSprite.Contains(species)) // Frillish & Jellicent, Unfezant & Pyroar
            { sb.Append(ResourceSeparator); sb.Append(gender); }

            if (species == 25 && form > 0 && generation == 6) // Cosplay Pikachu
                sb.Append(ResourcePikachuCosplay);
            else if (GameVersion.GG.Contains(PKMConverter.Trainer.Game) && (species == 25 || species == 133) && form != 0)
                sb.Append(ResourceGGStarter);

            if (shiny && AllowShinySprite)
                sb.Append(ResourceShiny);
            return sb.ToString();
        }

        /// <summary>
        /// Gets a list of formes that the species can have.
        /// </summary>
        /// <param name="species">National Dex number of the Pokémon.</param>
        /// <param name="types">List of type names</param>
        /// <param name="forms">List of form names</param>
        /// <param name="genders">List of genders names</param>
        /// <param name="generation">Generation number for exclusive formes</param>
        /// <returns>A list of strings corresponding to the formes that a Pokémon can have.</returns>
        public static string[] GetFormList(int species, IReadOnlyList<string> types, IReadOnlyList<string> forms, IReadOnlyList<string> genders, int generation = Generation)
        {
            return FormConverter.GetFormList(species, types, forms, genders, generation);
        }

        /// <summary>Calculate the Hidden Power Type of the entered IVs.</summary>
        /// <param name="type">Hidden Power Type</param>
        /// <param name="ivs">Individual Values (H/A/B/S/C/D)</param>
        /// <param name="format">Generation specific format</param>
        /// <returns>Hidden Power Type</returns>
        public static int[] SetHPIVs(int type, int[] ivs, int format = Generation)
        {
            if (format <= 2)
            {
                ivs[1] = (ivs[1] & ~3) | (type >> 2);
                ivs[2] = (ivs[2] & ~3) | (type & 3);
                return ivs;
            }
            for (int i = 0; i < 6; i++)
                ivs[i] = (ivs[i] & 0x1E) + hpivs[type, i];
            return ivs;
        }

        /// <summary>
        /// Hidden Power IV values (even or odd) to achieve a specified Hidden Power Type
        /// </summary>
        /// <remarks>
        /// There are other IV combinations to achieve the same Hidden Power Type.
        /// These are just precomputed for fast modification.
        /// Individual Values (H/A/B/S/C/D)
        /// </remarks>
        public static readonly int[,] hpivs = {
            { 1, 1, 0, 0, 0, 0 }, // Fighting
            { 0, 0, 0, 1, 0, 0 }, // Flying
            { 1, 1, 0, 1, 0, 0 }, // Poison
            { 1, 1, 1, 1, 0, 0 }, // Ground
            { 1, 1, 0, 0, 1, 0 }, // Rock
            { 1, 0, 0, 1, 1, 0 }, // Bug
            { 1, 0, 1, 1, 1, 0 }, // Ghost
            { 1, 1, 1, 1, 1, 0 }, // Steel
            { 1, 0, 1, 0, 0, 1 }, // Fire
            { 1, 0, 0, 1, 0, 1 }, // Water
            { 1, 0, 1, 1, 0, 1 }, // Grass
            { 1, 1, 1, 1, 0, 1 }, // Electric
            { 1, 0, 1, 0, 1, 1 }, // Psychic
            { 1, 0, 0, 1, 1, 1 }, // Ice
            { 1, 0, 1, 1, 1, 1 }, // Dragon
            { 1, 1, 1, 1, 1, 1 }, // Dark
        };

        /// <summary>
        /// Gets the Unown Forme ID from PID.
        /// </summary>
        /// <param name="pid">Personality ID</param>
        /// <remarks>Should only be used for 3rd Generation origin specimens.</remarks>
        /// <returns></returns>
        public static int GetUnownForm(uint pid)
        {
            var val = (pid & 0x3000000) >> 18 | (pid & 0x30000) >> 12 | (pid & 0x300) >> 6 | (pid & 0x3);
            return (int)(val % 28);
        }

        /// <summary>
        /// Gets the gender ID of the species based on the Personality ID.
        /// </summary>
        /// <param name="species">National Dex ID.</param>
        /// <param name="PID">Personality ID.</param>
        /// <returns>Gender ID (0/1/2)</returns>
        /// <remarks>This method should only be used for Generations 3-5 origin.</remarks>
        public static int GetGenderFromPID(int species, uint PID)
        {
            int genderratio = Personal[species].Gender;
            return GetGenderFromPIDAndRatio(PID, genderratio);
        }

        public static int GetGenderFromPIDAndRatio(uint PID, int gr)
        {
            switch (gr)
            {
                case 255: return 2;
                case 254: return 1;
                case 0: return 0;
                default: return (PID & 0xFF) < gr ? 1 : 0;
            }
        }

        /// <summary>
        /// Decrypts an 80 byte format <see cref="PK3"/> byte array.
        /// </summary>
        /// <param name="ekm">Encrypted data.</param>
        /// <returns>Decrypted data.</returns>
        public static byte[] DecryptArray3(byte[] ekm)
        {
            if (ekm.Length != SIZE_3PARTY && ekm.Length != SIZE_3STORED)
                return null;

            uint PID = BitConverter.ToUInt32(ekm, 0);
            uint OID = BitConverter.ToUInt32(ekm, 4);
            uint seed = PID ^ OID;

            byte[] xorkey = BitConverter.GetBytes(seed);
            for (int i = 32; i < 80; i++)
                ekm[i] ^= xorkey[i & 3];
            return ShuffleArray3(ekm, PID%24);
        }

        /// <summary>
        /// Shuffles an 80 byte format <see cref="PK3"/> byte array.
        /// </summary>
        /// <param name="data">Unshuffled data.</param>
        /// <param name="sv">Block order shuffle value</param>
        /// <returns></returns>
        private static byte[] ShuffleArray3(byte[] data, uint sv)
        {
            byte[] sdata = new byte[data.Length];
            Array.Copy(data, sdata, 32); // Copy unshuffled bytes

            // Shuffle Away!
            for (int block = 0; block < 4; block++)
                Array.Copy(data, 32 + (12 * blockPosition[block][sv]), sdata, 32 + (12 * block), 12);

            // Fill the Battle Stats back
            if (data.Length > SIZE_3STORED)
                Array.Copy(data, SIZE_3STORED, sdata, SIZE_3STORED, data.Length - SIZE_3STORED);

            return sdata;
        }

        /// <summary>
        /// Encrypts an 80 byte format <see cref="PK3"/> byte array.
        /// </summary>
        /// <param name="pkm">Decrypted data.</param>
        /// <returns>Encrypted data.</returns>
        public static byte[] EncryptArray3(byte[] pkm)
        {
            if (pkm.Length != SIZE_3PARTY && pkm.Length != SIZE_3STORED)
                return null;

            uint PID = BitConverter.ToUInt32(pkm, 0);
            uint OID = BitConverter.ToUInt32(pkm, 4);
            uint seed = PID ^ OID;

            byte[] ekm = ShuffleArray3(pkm, blockPositionInvert[PID%24]);
            byte[] xorkey = BitConverter.GetBytes(seed);
            for (int i = 32; i < 80; i++)
                ekm[i] ^= xorkey[i & 3];
            return ekm;
        }

        /// <summary>
        /// Gets the Main Series language ID from a GameCube (C/XD) language ID.
        /// </summary>
        /// <param name="value">GameCube (C/XD) language ID.</param>
        /// <returns>Main Series language ID.</returns>
        public static byte GetMainLangIDfromGC(byte value)
        {
            if (value <= 2 || value > 7)
                return value;
            return (byte)GCtoMainSeries[(LanguageGC)value];
        }

        private static readonly Dictionary<LanguageGC, LanguageID> GCtoMainSeries = new Dictionary<LanguageGC, LanguageID>
        {
            {LanguageGC.German, LanguageID.German},
            {LanguageGC.French, LanguageID.French},
            {LanguageGC.Italian, LanguageID.Italian},
            {LanguageGC.Spanish, LanguageID.Spanish},
            {LanguageGC.UNUSED_6, LanguageID.UNUSED_6},
        };

        /// <summary>
        /// Gets the GameCube (C/XD) language ID from a Main Series language ID.
        /// </summary>
        /// <param name="value">Main Series language ID.</param>
        /// <returns>GameCube (C/XD) language ID.</returns>
        public static byte GetGCLangIDfromMain(byte value)
        {
            if (value <= 2 || value > 7)
                return value;
            return (byte)MainSeriesToGC[(LanguageID)value];
        }

        private static readonly Dictionary<LanguageID, LanguageGC> MainSeriesToGC = new Dictionary<LanguageID, LanguageGC>
        {
            {LanguageID.German, LanguageGC.German},
            {LanguageID.French, LanguageGC.French},
            {LanguageID.Italian, LanguageGC.Italian},
            {LanguageID.Spanish, LanguageGC.Spanish},
            {LanguageID.UNUSED_6, LanguageGC.UNUSED_6},
        };

        /// <summary>
        /// Gets an array of valid <see cref="PKM"/> file extensions.
        /// </summary>
        /// <param name="maxGeneration">Maximum Generation to permit</param>
        /// <returns>Valid <see cref="PKM"/> file extensions.</returns>
        public static string[] GetPKMExtensions(int maxGeneration = Generation)
        {
            var result = new List<string>();
            int min = maxGeneration <= 2 || maxGeneration >= 7 ? 1 : 3;
            for (int i = min; i <= maxGeneration; i++)
                result.Add($"pk{i}");

            if (maxGeneration >= 3)
            {
                result.Add("ck3");
                result.Add("xk3");
            }
            if (maxGeneration >= 4)
                result.Add("bk4");

            return result.ToArray();
        }

        /// <summary>
        /// Roughly detects the PKM format from the file's extension.
        /// </summary>
        /// <param name="ext">File extension.</param>
        /// <param name="prefer">Preference if not a valid extension, usually the highest acceptable format.</param>
        /// <returns>Format hint that the file is.</returns>
        public static int GetPKMFormatFromExtension(string ext, int prefer)
        {
            return ext?.Length > 1
                ? GetPKMFormatFromExtension(ext[ext.Length - 1], prefer)
                : prefer;
        }

        /// <summary>
        /// Roughly detects the PKM format from the file's extension.
        /// </summary>
        /// <param name="last">Last character of the file's extensio.n</param>
        /// <param name="prefer">Preference if not a valid extension, usually the highest acceptable format.</param>
        /// <returns>Format hint that the file is.</returns>
        public static int GetPKMFormatFromExtension(char last, int prefer)
        {
            if ('1' <= last && last <= '9')
                return last - '0';
            return last == 'x' ? 6 : prefer;
        }

        // Extensions
        /// <summary>
        /// Gets the Location Name for the <see cref="PKM"/>
        /// </summary>
        /// <param name="pk">PKM to fetch data for</param>
        /// <param name="eggmet">Location requested is the egg obtained location, not met location.</param>
        /// <returns>Location string</returns>
        public static string GetLocationString(this PKM pk, bool eggmet)
        {
            if (pk.Format < 2)
                return string.Empty;

            int locval = eggmet ? pk.Egg_Location : pk.Met_Location;
            return GameInfo.GetLocationName(eggmet, locval, pk.Format, pk.GenNumber, (GameVersion)pk.Version);
        }

        /// <summary>
        /// Copies a <see cref="PKM"/> list to the destination list, with an option to copy to a starting point.
        /// </summary>
        /// <param name="list">Source list to copy from</param>
        /// <param name="dest">Destination list/array</param>
        /// <param name="sav">Context for checking slot write protection</param>
        /// <param name="skip">Criteria for skipping a slot</param>
        /// <param name="start">Starting point to copy to</param>
        /// <returns>Count of <see cref="PKM"/> copied.</returns>
        public static int CopyTo(this IEnumerable<PKM> list, IList<PKM> dest, SaveFile sav, Func<int, int, bool> skip, int start = 0)
        {
            int ctr = start;
            foreach (var z in list)
            {
                if (dest.Count <= ctr)
                    break;
                var exist = dest[ctr];
                if (exist != null && skip(exist.Box, exist.Slot))
                    continue;
                dest[ctr++] = z;
            }
            return ctr - start;
        }

        /// <summary>
        /// Copies an <see cref="Enumerable"/> list to the destination list, with an option to copy to a starting point.
        /// </summary>
        /// <typeparam name="T">Typed object to copy</typeparam>
        /// <param name="list">Source list to copy from</param>
        /// <param name="dest">Destination list/array</param>
        /// <param name="start">Starting point to copy to</param>
        /// <returns>Count of <see cref="T"/> copied.</returns>
        public static int CopyTo<T>(this IEnumerable<T> list, IList<T> dest, int start = 0)
        {
            int ctr = start;
            foreach (var z in list)
            {
                if (dest.Count <= ctr)
                    break;
                dest[ctr++] = z;
            }
            return ctr - start;
        }

        /// <summary>
        /// Gets an <see cref="Enumerable"/> list of PKM data from a concatenated byte array binary.
        /// </summary>
        /// <param name="data"></param>
        /// <param name="len">Length of each PKM byte[]</param>
        /// <param name="start">Starting offset to rip from. If omitted, will iterate from the start of the <see cref="data"/>.</param>
        /// <param name="end">Ending offset to rip to. If omitted, will iterate to the end of the <see cref="data"/>.</param>
        /// <returns>Enumerable list of PKM byte arrays</returns>
        public static IEnumerable<byte[]> GetPKMDataFromConcatenatedBinary(byte[] data, int len, int start = 0, int end = -1)
        {
            if (end < 0)
                end = data.Length;
            // split up data to individual pkm
            for (int i = start; i < end; i += len)
            {
                var pk = new byte[len];
                Buffer.BlockCopy(data, i, pk, 0, len);
                yield return pk;
            }
        }

        /// <summary>
        /// Detects the language of a <see cref="PK1"/> or <see cref="PK2"/> by checking the current Species name against possible names.
        /// </summary>
        /// <param name="pk">PKM to fetch language for</param>
        /// <returns>Language ID best match (<see cref="LanguageID"/>)</returns>
        public static int GetVCLanguage(PKM pk)
        {
            if (pk.Japanese)
                return 1;
            if (pk.Korean)
                return 8;
            int lang = GetSpeciesNameLanguage(pk.Species, pk.Nickname, pk.Format);
            return lang > 0 ? lang : (int)LanguageID.English; // Default to ENG
        }

        internal static bool IsPKMPresentGB(byte[] data, int offset) => data[offset] != 0;
        internal static bool IsPKMPresentGC(byte[] data, int offset) => BitConverter.ToUInt16(data, offset) != 0;

        internal static bool IsPKMPresentGBA(byte[] data, int offset)
        {
            if (BitConverter.ToUInt32(data, offset) != 0) // PID
                return true;
            ushort species = BitConverter.ToUInt16(data, offset + 0x20);
            return species != 0;
        }

        internal static bool IsPKMPresent(byte[] data, int offset)
        {
            if (BitConverter.ToUInt32(data, offset) != 0) // PID
                return true;
            ushort species = BitConverter.ToUInt16(data, offset + 8);
            return species != 0;
        }

        public static Func<byte[], int, bool> GetFuncIsPKMPresent(PKM blank)
        {
            if (blank.Format >= 4)
                return IsPKMPresent;
            if (blank.Format <= 2)
                return IsPKMPresentGB;
            if (blank is PK3)
                return IsPKMPresentGBA;
            return IsPKMPresentGC;
        }

        /// <summary>
        /// Reorders (in place) the input array of stats to have the Speed value last rather than before the SpA/SpD stats.
        /// </summary>
        /// <param name="value">Input array to reorder</param>
        /// <returns>Same array, reordered.</returns>
        public static int[] ReorderSpeedLast(int[] value)
        {
            var spe = value[3];
            value[3] = value[4];
            value[4] = value[5];
            value[5] = spe;
            return value;
        }
    }
}