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

namespace Application.Features.Admin.Forum.BoardManager.Save;

internal sealed class Handler(IAppDbContext db) : ICommandHandler<Command, Result>
{
    public async Task<Result> Handle(Command request, CancellationToken ct)
    {
        // 삭제
        if (request.DeleteIDs is { Length: > 0 })
        {
            var deleteTargets = await db.BoardManager
                .Where(c => c.BoardID == request.BoardID && request.DeleteIDs.Contains(c.ID))
                .ToListAsync(ct);

            if (deleteTargets.Count > 0)
            {
                db.BoardManager.RemoveRange(deleteTargets);
            }
        }

        // 수정
        if (request.Updates is { Count: > 0 })
        {
            var updateIDs = request.Updates.Select(c => c.ID).ToList();
            var updateTargets = await db.BoardManager
                .Where(c => c.BoardID == request.BoardID && updateIDs.Contains(c.ID))
                .ToListAsync(ct);

            var updateByID = updateTargets.ToDictionary(c => c.ID);

            foreach (var row in request.Updates)
            {
                if (!updateByID.TryGetValue(row.ID, out var existing))
                {
                    return Result.Failure(Error.NotFound("BoardManager.NotFound", $"존재하지 않는 ID: {row.ID}"));
                }

                existing.CanEdit = row.CanEdit;
                existing.CanDelete = row.CanDelete;
                existing.UpdatedAt = DateTime.UtcNow;
            }
        }

        // 신규 추가
        if (request.NewItem is not null)
        {
            // 회원 존재 확인 — FK 위반 사전 방지
            var memberExists = await db.Member
                .AsNoTracking()
                .AnyAsync(c => c.ID == request.NewItem.MemberID, ct);

            if (!memberExists)
            {
                return Result.Failure(Error.NotFound("BoardManager.MemberNotFound", $"존재하지 않는 회원 ID 입니다: {request.NewItem.MemberID}"));
            }

            var isDuplicate = await db.BoardManager
                .AsNoTracking()
                .AnyAsync(c => c.BoardID == request.BoardID && c.MemberID == request.NewItem.MemberID, ct);

            if (isDuplicate)
            {
                return Result.Failure(Error.Conflict("BoardManager.Duplicate", "이미 등록된 매니저입니다."));
            }

            db.BoardManager.Add(new Domain.Entities.Forum.Boards.BoardManager
            {
                BoardID = request.BoardID,
                MemberID = request.NewItem.MemberID,
                CanEdit = request.NewItem.CanEdit,
                CanDelete = request.NewItem.CanDelete
            });
        }

        await db.SaveChangesAsync(ct);

        return Result.Success();
    }
}