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

namespace PKHeX.Core;

/// <inheritdoc cref="EncounterArea" />
/// <summary>
/// <see cref="GameVersion.GG"/> encounter area
/// </summary>
public sealed record EncounterArea7b : EncounterArea
{
    public readonly EncounterSlot7b[] Slots;

    protected override IReadOnlyList<EncounterSlot> Raw => Slots;

    public static EncounterArea7b[] GetAreas(BinLinkerAccessor input, GameVersion game)
    {
        var result = new EncounterArea7b[input.Length];
        for (int i = 0; i < result.Length; i++)
            result[i] = new EncounterArea7b(input[i], game);
        return result;
    }

    private EncounterArea7b(ReadOnlySpan<byte> data, GameVersion game) : base(game)
    {
        Location = ReadInt16LittleEndian(data);
        Slots = ReadSlots(data);
    }

    private EncounterSlot7b[] ReadSlots(ReadOnlySpan<byte> data)
    {
        const int size = 4;
        int count = (data.Length - 2) / size;
        var slots = new EncounterSlot7b[count];
        for (int i = 0; i < slots.Length; i++)
        {
            int offset = 2 + (size * i);
            var entry = data.Slice(offset, size);
            slots[i] = ReadSlot(entry);
        }

        return slots;
    }

    private EncounterSlot7b ReadSlot(ReadOnlySpan<byte> entry)
    {
        ushort species = entry[0]; // always < 255; only original 151
        // form is always 0
        byte min = entry[2];
        byte max = entry[3];
        return new EncounterSlot7b(this, species, min, max);
    }

    private const int CatchComboBonus = 1;

    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;

                var met = pk.Met_Level;
                if (!slot.IsLevelWithinRange(met, 0, CatchComboBonus))
                    break;
                if (slot.Form != evo.Form)
                    break;

                yield return slot;
                break;
            }
        }
    }
}