using Application.Abstractions.Messaging;
using Application.Abstractions.Data;
using SharedKernel.Results;
using Microsoft.EntityFrameworkCore;

namespace Application.Features.Admin.Forum.BoardGroup.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.BoardGroup.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();

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

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

            if (hasBoards)
            {
                return Result.Failure<Response>(Error.Conflict("BoardGroup.HasBoards", "게시판이 등록된 분류는 삭제할 수 없습니다. 먼저 해당 게시판을 삭제하세요."));
            }

            db.BoardGroup.RemoveRange(deleteTargets);
        }

        ushort inserted = 0;
        ushort updated = 0;
        ushort deleted = 0;

        foreach (var row in items)
        {
            // 신규 추가
            if (!row.ID.HasValue || row.ID.Value <= 0)
            {
                if (await db.BoardGroup.AnyAsync(c => c.Code == row.Code, ct))
                {
                    return Result.Failure<Response>(Error.Conflict("BoardGroup.DuplicateCode", $"`{row.Code}`는 이미 등록되었습니다."));
                }

                db.BoardGroup.Add(new Domain.Entities.Forum.Boards.BoardGroup
                {
                    Code = row.Code,
                    Name = row.Name,
                    Order = row.Order
                });

                inserted++;
                continue;
            }

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

            if (existing.Code != row.Code && await db.BoardGroup.AnyAsync(c => c.Code == row.Code, ct))
            {
                return Result.Failure<Response>(Error.Conflict("BoardGroup.DuplicateCode", $"`{row.Code}`는 이미 등록되었습니다."));
            }

            existing.Code = row.Code;
            existing.Name = row.Name;
            existing.Order = row.Order;
            existing.UpdatedAt = DateTime.UtcNow;
            updated++;
        }

        deleted = (ushort)deleteTargets.Count;

        await db.SaveChangesAsync(ct);

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