using System;

namespace PKHeX.Core;

public static class EntityFileNamer
{
    /// <summary>
    /// Object that converts the <see cref="PKM"/> data into a <see cref="string"/> file name.
    /// </summary>
    public static IFileNamer<PKM> Namer { get; set; } = new DefaultEntityNamer();

    /// <summary>
    /// Gets the file name (without extension) for the input <see cref="pk"/> data.
    /// </summary>
    /// <param name="pk">Input entity to create a file name for.</param>
    /// <returns>File name for the <see cref="pk"/> data</returns>
    public static string GetName(PKM pk) => Namer.GetName(pk);
}

/// <summary>
/// PKHeX's default <see cref="PKM"/> file naming logic.
/// </summary>
public sealed class DefaultEntityNamer : IFileNamer<PKM>
{
    public string GetName(PKM obj)
    {
        if (obj is GBPKM gb)
            return GetGBPKM(gb);
        return GetRegular(obj);
    }

    private static string GetRegular(PKM pk)
    {
        var chk = pk is ISanityChecksum s ? s.Checksum : PokeCrypto.GetCHK(pk.Data.AsSpan()[8..pk.SIZE_STORED]);
        var form = pk.Form != 0 ? $"-{pk.Form:00}" : string.Empty;
        var star = pk.IsShiny ? " ★" : string.Empty;
        return $"{pk.Species:000}{form}{star} - {pk.Nickname} - {chk:X4}{pk.EncryptionConstant:X8}";
    }

    private static string GetGBPKM(GBPKM gb)
    {
        ReadOnlySpan<byte> raw = gb switch
        {
            PK1 pk1 => new PokeList1(pk1).Write(),
            PK2 pk2 => new PokeList2(pk2).Write(),
            _ => gb.Data,
        };
        var checksum = Checksums.CRC16_CCITT(raw);
        var form = gb.Form != 0 ? $"-{gb.Form:00}" : string.Empty;
        var star = gb.IsShiny ? " ★" : string.Empty;
        return $"{gb.Species:000}{form}{star} - {gb.Nickname} - {checksum:X4}";
    }
}

/// <summary>
/// Exposes a method to get a file name (no extension) for the type.
/// </summary>
/// <typeparam name="T">Type that the implementer can create a file name for.</typeparam>
public interface IFileNamer<in T>
{
    string GetName(T obj);
}