using System;
using System.Collections.Generic;
using static System.Buffers.Binary.BinaryPrimitives;

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.LA;
        public const int Generation = 8;

        private static readonly HashSet<int> Sizes = new()
        {
            PokeCrypto.SIZE_1JLIST,   PokeCrypto.SIZE_1ULIST,
            PokeCrypto.SIZE_2ULIST,   PokeCrypto.SIZE_2JLIST,   PokeCrypto.SIZE_2STADIUM,
            PokeCrypto.SIZE_3STORED,  PokeCrypto.SIZE_3PARTY,
            PokeCrypto.SIZE_3CSTORED, PokeCrypto.SIZE_3XSTORED,
            PokeCrypto.SIZE_4STORED,  PokeCrypto.SIZE_4PARTY,
            PokeCrypto.SIZE_5PARTY,
            PokeCrypto.SIZE_6STORED,  PokeCrypto.SIZE_6PARTY,
            PokeCrypto.SIZE_8STORED,  PokeCrypto.SIZE_8PARTY,
            PokeCrypto.SIZE_8ASTORED, PokeCrypto.SIZE_8APARTY,
        };

        /// <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);

        /// <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.Length != 1)
                return 2;
            return GetGenderFromChar(s[0]);
        }

        private static int GetGenderFromChar(char c) => c switch
        {
            '♂' or 'M' => 0,
            '♀' or 'F' => 1,
            _ => 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(Span<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>
        /// Gets a random PID according to specifications.
        /// </summary>
        /// <param name="rnd">RNG to use</param>
        /// <param name="species">National Dex ID</param>
        /// <param name="gender">Current Gender</param>
        /// <param name="origin">Origin Generation</param>
        /// <param name="nature">Nature</param>
        /// <param name="form">Form</param>
        /// <param name="oldPID">Current PID</param>
        /// <remarks>Used to retain ability bits.</remarks>
        /// <returns>Rerolled PID.</returns>
        public static uint GetRandomPID(Random rnd, int species, int gender, int origin, int nature, int form, uint oldPID)
        {
            // Gen6+ (and VC) PIDs do not tie PID to Nature/Gender/Ability
            if (origin >= 24)
                return rnd.Rand32();

            // Below logic handles Gen3-5.

            int gt = Personal[species].Gender;
            bool g34 = origin <= 15;
            uint abilBitVal = g34 ? oldPID & 0x0000_0001 : oldPID & 0x0001_0000;

            bool g3unown = origin <= 5 && species == (int)Species.Unown;
            bool singleGender = PersonalInfo.IsSingleGender(gt); // single gender, skip gender check
            while (true) // Loop until we find a suitable PID
            {
                uint pid = rnd.Rand32();

                // Gen 3/4: Nature derived from PID
                if (g34 && pid%25 != nature)
                    continue;

                // Gen 3 Unown: Letter/form derived from PID
                if (g3unown)
                {
                    var pidLetter = GetUnownForm(pid);
                    if (pidLetter != form)
                        continue;
                }
                else if (g34)
                {
                    if (abilBitVal != (pid & 0x0000_0001)) // keep ability bits
                        continue;
                }
                else
                {
                    if (abilBitVal != (pid & 0x0001_0000)) // keep ability bits
                        continue;
                }

                if (singleGender) // Set Gender(less)
                    return pid; // PID can be anything

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

        /// <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 value = (pid & 0x3000000) >> 18 | (pid & 0x30000) >> 12 | (pid & 0x300) >> 6 | (pid & 0x3);
            return (int)(value % 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 gt = Personal[species].Gender;
            return GetGenderFromPIDAndRatio(pid, gt);
        }

        public static int GetGenderFromPIDAndRatio(uint pid, int gr) => gr switch
        {
            PersonalInfo.RatioMagicGenderless => 2,
            PersonalInfo.RatioMagicFemale => 1,
            PersonalInfo.RatioMagicMale => 0,
            _ => (pid & 0xFF) < gr ? 1 : 0,
        };

        internal const string ExtensionPB7 = "pb7";
        internal const string ExtensionPB8 = "pb8";
        internal const string ExtensionPA8 = "pa8";

        /// <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 is <= 2 or >= 7 ? 1 : 3;
            for (int i = min; i <= maxGeneration; i++)
                result.Add($"pk{i}");

            if (maxGeneration >= 3)
            {
                result.Add("ck3"); // colosseum
                result.Add("xk3"); // xd
            }
            if (maxGeneration >= 4)
                result.Add("bk4"); // battle revolution
            if (maxGeneration >= 7)
                result.Add(ExtensionPB7); // let's go
            if (maxGeneration >= 8)
                result.Add(ExtensionPB8); // Brilliant Diamond & Shining Pearl
            if (maxGeneration >= 8)
                result.Add(ExtensionPA8); // Legends: Arceus

            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)
        {
            if (string.IsNullOrEmpty(ext))
                return prefer;
            return GetPKMFormatFromExtension(ext[^1], prefer);
        }

        /// <summary>
        /// Roughly detects the PKM format from the file's extension.
        /// </summary>
        /// <param name="last">Last character of the file's 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(char last, int prefer)
        {
            if (last is >= '1' and <= '9')
                return last - '0';
            return last == 'x' ? 6 : prefer;
        }

        internal static bool IsPKMPresentGB(ReadOnlySpan<byte> data) => data[0] != 0; // Species non-zero
        internal static bool IsPKMPresentGC(ReadOnlySpan<byte> data) => ReadUInt16BigEndian(data) != 0; // Species non-zero
        internal static bool IsPKMPresentGBA(ReadOnlySpan<byte> data) => (data[0x13] & 0xFB) == 2; // ignore egg flag, must be FlagHasSpecies.

        internal static bool IsPKMPresent(ReadOnlySpan<byte> data)
        {
            if (ReadUInt32LittleEndian(data) != 0) // PID
                return true;
            ushort species = ReadUInt16LittleEndian(data[8..]);
            return species != 0;
        }

        /// <summary>
        /// Gets a function that can check a byte array (at an offset) to see if a <see cref="PKM"/> is possibly present.
        /// </summary>
        /// <param name="blank"></param>
        /// <returns>Function that checks if a byte array (at an offset) has a <see cref="PKM"/> present</returns>
        public static Func<byte[], bool> GetFuncIsPKMPresent(PKM blank)
        {
            if (blank.Format >= 4)
                return x => IsPKMPresent(x);
            if (blank.Format <= 2)
                return x => IsPKMPresentGB(x);
            if (blank.Data.Length <= PokeCrypto.SIZE_3PARTY)
                return x => IsPKMPresentGBA(x);
            return x => IsPKMPresentGC(x);
        }

        /// <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 void ReorderSpeedLast(Span<int> value)
        {
            var spe = value[3];
            value[3] = value[4];
            value[4] = value[5];
            value[5] = spe;
        }
    }
}