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

namespace PKHeX.Core;

/// <inheritdoc cref="EncounterArea" />
/// <summary>
/// <see cref="GameVersion.XY"/> encounter area
/// </summary>
public sealed record EncounterArea6XY : EncounterArea
{
    public readonly EncounterSlot6XY[] Slots;

    protected override IReadOnlyList<EncounterSlot> Raw => Slots;

    public static EncounterArea6XY[] GetAreas(BinLinkerAccessor input, GameVersion game, EncounterArea6XY safari)
    {
        int count = input.Length;
        var result = new EncounterArea6XY[count + 1];
        for (int i = 0; i < count; i++)
            result[i] = new EncounterArea6XY(input[i], game);
        result[^1] = safari;
        return result;
    }

    public EncounterArea6XY() : base(GameVersion.XY)
    {
        Location = 148; // Friend Safari
        Type = SlotType.FriendSafari;

        Slots = LoadSafariSlots();
    }

    private EncounterArea6XY(ReadOnlySpan<byte> data, GameVersion game) : base(game)
    {
        Location = ReadInt16LittleEndian(data);
        Type = (SlotType)data[2];

        Slots = ReadSlots(data);
    }

    private EncounterSlot6XY[] LoadSafariSlots()
    {
        const int SpeciesFormSlots = 4;

        // Single form species
        Span<ushort> species = stackalloc ushort[]
        {
            002, 005, 008, 012, 014, 016, 021, 025, 027, 035,
            038, 039, 043, 044, 046, 049, 049, 051, 056, 058,
            061, 063, 067, 077, 082, 083, 084, 087, 089, 091,
            095, 096, 098, 101, 105, 112, 113, 114, 125, 126,
            127, 130, 131, 132, 133, 148, 163, 165, 168, 175,
            178, 184, 190, 191, 194, 195, 202, 203, 205, 206,
            209, 213, 214, 215, 215, 216, 218, 219, 221, 222,
            224, 225, 227, 231, 235, 236, 247, 262, 267, 268,
            274, 281, 284, 286, 290, 294, 297, 299, 302, 303,
            303, 307, 310, 313, 314, 317, 323, 326, 328, 332,
            336, 342, 352, 353, 356, 357, 359, 361, 363, 372,
            375, 400, 404, 415, 417, 419, 423, 426, 437, 442,
            444, 447, 452, 454, 459, 506, 510, 511, 513, 515,
            517, 520, 523, 525, 527, 530, 531, 536, 538, 539,
            541, 544, 548, 551, 556, 557, 561, 569, 572, 575,
            578, 581, 586, 587, 596, 597, 600, 608, 611, 614,
            618, 619, 621, 623, 624, 627, 629, 636, 651, 654,
            657, 660, 662, 662, 668, 673, 674, 677, 682, 684,
            686, 689, 694, 701, 702, 702, 705, 707, 708, 710,
            712, 714,
        };

        var slots = new EncounterSlot6XY[species.Length + SpeciesFormSlots];
        int i = 0;
        for (; i < species.Length; i++)
            slots[i] = new EncounterSlot6XY(this, species[i], 0, 30, 30);

        // Floette has 3 separate forms (RBY)
        slots[i++] = new EncounterSlot6XY(this, (int)Species.Floette, 0, 30, 30);
        slots[i++] = new EncounterSlot6XY(this, (int)Species.Floette, 1, 30, 30);
        slots[i++] = new EncounterSlot6XY(this, (int)Species.Floette, 3, 30, 30);

        // Region Random Vivillon
        slots[i] = new EncounterSlot6XY(this, (int)Species.Vivillon, EncounterSlot.FormVivillon, 30, 30);
        return slots;
    }

    private EncounterSlot6XY[] ReadSlots(ReadOnlySpan<byte> data)
    {
        const int size = 4;
        int count = (data.Length - 4) / size;
        var slots = new EncounterSlot6XY[count];
        for (int i = 0; i < slots.Length; i++)
        {
            int offset = 4 + (size * i);
            var entry = data.Slice(offset, size);
            ushort species = ReadUInt16LittleEndian(entry);
            byte form = (byte)(species >> 11);
            species &= 0x3FF;
            byte min = entry[2];
            byte max = entry[3];
            slots[i] = new EncounterSlot6XY(this, species, form, min, max);
        }

        return slots;
    }

    public override IEnumerable<EncounterSlot> GetMatchingSlots(PKM pk, EvoCriteria[] chain)
    {
        foreach (var slot in Slots)
        {
            foreach (var evo in chain)
            {
                if (slot.Species != evo.Species)
                    continue;

                if (!slot.IsLevelWithinRange(pk.Met_Level))
                    break;

                if (slot.Form != evo.Form && !slot.IsRandomUnspecificForm && slot.Species is not ((int)Species.Burmy or (int)Species.Furfrou))
                {
                    // Only slot that can be form-mismatched via Pressure is Flabébé
                    if (slot.Species != (int)Species.Flabébé)
                        break;

                    var maxLevel = slot.LevelMax;
                    if (!ExistsPressureSlot(evo, ref maxLevel))
                        break;

                    if (maxLevel != pk.Met_Level)
                        break;

                    yield return slot.CreatePressureFormCopy(evo.Form);
                    break;
                }

                yield return slot;
                break;
            }
        }
    }

    private bool ExistsPressureSlot(EvoCriteria evo, ref byte level)
    {
        bool existsForm = false;
        foreach (var z in Slots)
        {
            if (z.Species != evo.Species)
                continue;
            if (z.Form == evo.Form)
                continue;
            if (z.LevelMax < level)
                continue;
            level = z.LevelMax;
            existsForm = true;
        }
        return existsForm;
    }
}