using System;
using System.Collections.Generic;

namespace PKHeX.Core;

/// <summary>
/// Logic for converting Item IDs between the generation specific value sets.
/// </summary>
internal static class ItemConverter
{
    /// <summary>Unused item ID, placeholder for item/sprite finding in Generations 2-4.</summary>
    private const ushort NaN = 128;

    /// <summary>
    /// Checks if the item can be kept during 3->4 conversion.
    /// </summary>
    /// <param name="item">Generation 3 Item ID.</param>
    /// <returns>True if transferable, False if not transferable.</returns>
    internal static bool IsItemTransferable34(ushort item) => item != NaN && item > 0;

    /// <summary>
    /// Converts a Generation 3 Item ID to Generation 4+ Item ID.
    /// </summary>
    /// <param name="item">Generation 3 Item ID.</param>
    /// <returns>Generation 4+ Item ID.</returns>
    internal static ushort GetItemFuture3(ushort item) => item > arr3.Length ? NaN : arr3[item];

    /// <summary>
    /// Converts a Generation 2 Item ID to Generation 4+ Item ID.
    /// </summary>
    /// <param name="item">Generation 2 Item ID.</param>
    /// <returns>Generation 4+ Item ID.</returns>
    internal static ushort GetItemFuture2(byte item) => item > arr2.Length ? NaN : arr2[item];

    /// <summary>
    /// Converts a Generation 4+ Item ID to Generation 3 Item ID.
    /// </summary>
    /// <param name="item">Generation 4+ Item ID.</param>
    /// <returns>Generation 3 Item ID.</returns>
    private static ushort GetItemOld3(ushort item)
    {
        if (item == NaN)
            return 0;
        int index = Array.IndexOf(arr3, item);
        return (ushort)Math.Max(0, index);
    }

    /// <summary>
    /// Converts a Generation 4+ Item ID to Generation 2 Item ID.
    /// </summary>
    /// <param name="item">Generation 4+ Item ID.</param>
    /// <returns>Generation 2 Item ID.</returns>
    private static byte GetItemOld2(ushort item)
    {
        if (item == NaN)
            return 0;
        int index = Array.IndexOf(arr2, item);
        return (byte)Math.Max(0, index);
    }

    #region Item Mapping Tables
    /// <summary> Gen2 items (index) and their corresponding Gen4 item ID (value) </summary>
    private static readonly ushort[] arr2 =
    {
        000, 001, 002, 213, 003, 004, NaN, 450, 081, 018, // 0
        019, 020, 021, 022, 023, 024, 025, 026, 017, 078, // 1
        079, 041, 082, 083, 084, NaN, 045, 046, 047, 048, // 2
        256, 049, 050, 060, 085, 257, 092, 063, 027, 028, // 3
        029, 055, 076, 077, 056, NaN, 030, 031, 032, 057, // 4
        NaN, 058, 059, 061, 444, NaN, NaN, 216, 445, 446, // 5
        NaN, 447, 051, 038, 039, 040, 478, 464, 456, 484, // 6
        NaN, 482, 033, 217, 151, NaN, 237, 244, 149, 153, // 7
        152, 245, 221, 156, 150, 485, 086, 087, 222, 487, // 8
        NaN, 223, 486, 488, 224, 243, 248, 490, 241, 491, // 9
        NaN, 489, 240, 473, NaN, 259, 228, 246, 242, 157, // 10
        088, 089, 229, 247, 504, NaN, NaN, 239, 258, 230, // 11
        NaN, 034, 035, 036, 037, 238, 231, 475, 481, NaN, // 12
        NaN, 090, 091, 476, 480, NaN, NaN, NaN, 249, 043, // 13
        232, NaN, NaN, 233, 250, NaN, 234, NaN, NaN, NaN, // 14
        154, 235, NaN, NaN, NaN, NaN, 044, 495, NaN, 493, // 15
        NaN, 492, NaN, 236, 497, 498, 496, NaN, NaN, 080, // 16
        NaN, NaN, 252, 155, 158, 477, NaN, 500, 483, NaN, // 17
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, // 18
        NaN, 328, 329, 330, 331, 331, 332, 333, 334, 335, // 19
        336, 337, 338, 339, 340, 341, 342, 343, 344, 345, // 20
        346, 347, 348, 349, 350, 351, 352, 353, 354, 355, // 21
        355, 356, 357, 358, 359, 360, 361, 362, 363, 364, // 22
        365, 366, 367, 368, 369, 370, 371, 372, 373, 374, // 23
        375, 376, 377, 420, 421, 422, 423, 424, 425, 426, // 24
        427, NaN, NaN, NaN, NaN, NaN,
    };

    /// <summary> Gen3 items (index) and their corresponding Gen4 item ID (value) </summary>
    private static readonly ushort[] arr3 =
    {
        000, 001, 002, 003, 004, 005, 006, 007, 008, 009,
        010, 011, 012, 017, 018, 019, 020, 021, 022, 023,
        024, 025, 026, 027, 028, 029, 030, 031, 032, 033,
        034, 035, 036, 037, 038, 039, 040, 041, 042, 065,
        066, 067, 068, 069, 043, 044, 070, 071, 072, 073,
        074, 075, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, 045, 046, 047, 048, 049, 050, 051,
        052, 053, NaN, 055, 056, 057, 058, 059, 060, 061,
        063, 064, NaN, 076, 077, 078, 079, NaN, NaN, NaN,
        NaN, NaN, NaN, 080, 081, 082, 083, 084, 085, NaN,
        NaN, NaN, NaN, 086, 087, NaN, 088, 089, 090, 091,
        092, 093, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, 149, 150, 151, 152, 153, 154, 155,
        156, 157, 158, 159, 160, 161, 162, 163, 164, 165,
        166, 167, 168, 169, 170, 171, 172, 173, 174, 175,
        176, 177, 178, 179, 180, 181, 182, 183, 201, 202,
        203, 204, 205, 206, 207, 208, NaN, NaN, NaN, 213,
        214, 215, 216, 217, 218, 219, 220, 221, 222, 223,
        224, 225, 226, 227, 228, 229, 230, 231, 232, 233,
        234, 235, 236, 237, 238, 239, 240, 241, 242, 243,
        244, 245, 246, 247, 248, 249, 250, 251, 252, 253,
        254, 255, 256, 257, 258, 259, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, 260, 261, 262, 263, 264,

        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN,
        328, 329, 330, 331, 332, 333, 334, 335, 336, 337,
        338, 339, 340, 341, 342, 343, 344, 345, 346, 347,
        348, 349, 350, 351, 352, 353, 354, 355, 356, 357,
        358, 359, 360, 361, 362, 363, 364, 365, 366, 367,
        368, 369, 370, 371, 372, 373, 374, 375, 376, 377,
    };
    #endregion

    /// <summary>
    /// Converts a Generation 1 (Teru-sama) Item ID to Generation 2 Item ID.
    /// </summary>
    /// <param name="value">Gen1 Item ID</param>
    /// <returns>Gen2 Item ID</returns>
    /// <remarks>
    /// <br>https://github.com/pret/pokecrystal/blob/edb624c20ceb50eef9d73a5df0ac041cc156dd32/engine/link/link.asm#L1093-L1115</br>
    /// <br>https://github.com/pret/pokecrystal/blob/edb624c20ceb50eef9d73a5df0ac041cc156dd32/data/items/catch_rate_items.asm#L5-L17</br>
    /// </remarks>
    private static int GetTeruSamaItem(byte value) => value switch
    {
        0x19 => 0x92, // Leftovers
        0x2D => 0x53, // Bitter Berry
        0x32 => 0xAE, // Gold Berry
        0x5A or 0x64 or 0x78 or 0x87 or 0xBE or 0xC3 or 0xDC or 0xFA or 0xFF => 0xAD, // Berry
        _ => value,
    };

    /// <summary>
    /// Converts a Gen1 <see cref="PK1.Catch_Rate"/> value to Gen2 Item.
    /// </summary>
    /// <param name="value">Gen1 Item</param>
    /// <returns>Gen2 Item</returns>
    internal static int GetItemFuture1(byte value)
    {
        if (!IsItemTransferable12(value))
            return GetTeruSamaItem(value);
        return value;
    }

    private static bool IsItemTransferable12(ushort item) => ((IList<ushort>) Legal.HeldItems_GSC).Contains(item);

    /// <summary>
    /// Gets a format specific <see cref="PKM.HeldItem"/> value depending on the desired format and the provided item index &amp; origin format.
    /// </summary>
    /// <param name="srcItem">Held Item to apply</param>
    /// <param name="srcFormat">Format from importing</param>
    /// <param name="destFormat">Format required for holder</param>
    /// <returns>destItem</returns>
    internal static int GetItemForFormat(int srcItem, EntityContext srcFormat, EntityContext destFormat)
    {
        if (srcItem <= 0)
            return 0;

        if (destFormat == srcFormat)
            return srcItem;

        if (destFormat != srcFormat && srcFormat <= EntityContext.Gen3) // past gen items
        {
            if (destFormat > EntityContext.Gen3) // try remapping
                return srcFormat == EntityContext.Gen2 ? GetItemFuture2((byte)srcItem) : GetItemFuture3((ushort)srcItem);

            if (destFormat > srcFormat) // can't set past gen items
                return 0;

            // ShowdownSet checks gen3 then gen2. For gen2 collisions (if any?) remap 3->4->2.
            srcItem = GetItemFuture3((ushort)srcItem);
            srcItem = GetItemOld2((ushort)srcItem);
            if (srcItem <= 0)
                return 0;
        }

        return destFormat switch
        {
            EntityContext.Gen1 => 0,
            EntityContext.Gen2 => (byte) srcItem,
            EntityContext.Gen3 => GetItemOld3((ushort) srcItem),
            _ => srcItem,
        };
    }

    /// <summary>
    /// Checks if an item ID is an HM
    /// </summary>
    /// <param name="item">Item ID</param>
    /// <param name="generation">Generation the <see cref="item"/> exists in</param>
    /// <returns>True if is an HM</returns>
    internal static bool IsItemHM(ushort item, int generation) => generation switch
    {
        1 => item is (>= 196 and <= 200),
        2 => item is (>= 243 and <= 249),
        3 => item is (>= 339 and <= 346),
        _ => item is (>= 420 and <= 427) or 737,
    };
}