using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;
using GameGenreEntity = Domain.Entities.Store.GameGenre;

namespace Application.Features.Admin.Store.GameGenre.Save;

public sealed class Handler(IAppDbContext db) : ICommandHandler<Command, Result<Response>>
{
    public async Task<Result<Response>> Handle(Command request, CancellationToken ct)
    {
        var items = request.Items;

        var dbRows = await db.GameGenre.ToListAsync(ct);
        var dbByID = dbRows.ToDictionary(c => c.ID);

        var requestIDs = items.Where(c => c.ID.HasValue && c.ID.Value > 0).Select(c => c.ID!.Value).ToHashSet();

        var deleteTargets = dbRows.Where(x => !requestIDs.Contains(x.ID)).ToList();

        if (deleteTargets.Count > 0)
        {
            var deleteIDs = deleteTargets.Select(c => c.ID).ToList();
            var inUse = await db.GameGenreMap.AsNoTracking().AnyAsync(c => deleteIDs.Contains(c.GameGenreID), ct);

            if (inUse)
            {
                return Result.Failure<Response>(Error.Conflict("GameGenre.InUse", "게임에 연결된 장르는 삭제할 수 없습니다. 먼저 해당 게임에서 장르 선택을 해제하세요."));
            }

            db.GameGenre.RemoveRange(deleteTargets);
        }

        ushort inserted = 0;
        ushort updated = 0;

        foreach (var row in items)
        {
            if (string.IsNullOrWhiteSpace(row.KorName))
            {
                return Result.Failure<Response>(Error.Problem("GameGenre.KorNameRequired", "장르 한글명은 필수입니다."));
            }

            // 신규 추가
            if (!row.ID.HasValue || row.ID.Value <= 0)
            {
                if (await db.GameGenre.AnyAsync(c => c.KorName == row.KorName, ct))
                {
                    return Result.Failure<Response>(Error.Conflict("GameGenre.DuplicateKorName", $"`{row.KorName}`는 이미 등록된 장르입니다."));
                }

                db.GameGenre.Add(GameGenreEntity.Create(row.KorName, row.EngName, row.Order, row.IsActive));
                inserted++;
                continue;
            }

            // 수정
            if (!dbByID.TryGetValue(row.ID.Value, out var existing))
            {
                return Result.Failure<Response>(Error.NotFound("GameGenre.NotFound", $"존재하지 않는 ID: {row.ID.Value}"));
            }

            if (existing.KorName != row.KorName && await db.GameGenre.AnyAsync(c => c.KorName == row.KorName, ct))
            {
                return Result.Failure<Response>(Error.Conflict("GameGenre.DuplicateKorName", $"`{row.KorName}`는 이미 등록된 장르입니다."));
            }

            existing.Update(row.KorName, row.EngName, row.Order, row.IsActive);
            updated++;
        }

        var deleted = (ushort)deleteTargets.Count;

        await db.SaveChangesAsync(ct);

        return Result.Success(new Response(inserted, updated, deleted));
    }
}