using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Abstractions.Notification;
using Domain.Entities.Feed;
using Domain.Entities.Notifications.ValueObject;
using Microsoft.EntityFrameworkCore;
using SharedKernel.Results;

namespace Application.Features.Api.Feed.CreateComment;

public sealed class Handler(IAppDbContext db, INotificationService notificationService) : ICommandHandler<Command, Result<Response>>
{
    private const int MaxContentLength = 2000;
    private const int MaxDepth = 10;

    public async Task<Result<Response>> Handle(Command request, CancellationToken ct)
    {
        if (request.MemberID <= 0)
        {
            return Result.Failure<Response>(Error.Problem("Feed.Comment.MemberRequired", "로그인이 필요합니다."));
        }

        if (string.IsNullOrWhiteSpace(request.Content))
        {
            return Result.Failure<Response>(Error.Problem("Feed.Comment.ContentRequired", "댓글 내용을 입력해주세요."));
        }

        var content = request.Content.Trim();
        if (content.Length > MaxContentLength)
        {
            return Result.Failure<Response>(Error.Problem("Feed.Comment.ContentTooLong", $"댓글은 최대 {MaxContentLength}자까지 입력 가능합니다."));
        }

        var post = await db.FeedPost.FirstOrDefaultAsync(p => p.ID == request.PostID && !p.IsDeleted, ct);
        if (post is null)
        {
            return Result.Failure<Response>(Error.NotFound("Feed.PostNotFound", "게시글을 찾을 수 없습니다."));
        }

        sbyte depth = 0;
        FeedComment? parent = null;

        if (request.ParentCommentID is int parentID && parentID > 0)
        {
            parent = await db.FeedComment.FirstOrDefaultAsync(c => c.ID == parentID && c.FeedPostID == request.PostID, ct);
            if (parent is null)
            {
                return Result.Failure<Response>(Error.NotFound("Feed.ParentCommentNotFound", "부모 댓글을 찾을 수 없습니다."));
            }
            depth = (sbyte)Math.Min(parent.Depth + 1, MaxDepth);
        }

        var comment = new FeedComment
        {
            FeedPostID = request.PostID,
            MemberID = request.MemberID,
            ParentID = parent?.ID,
            Depth = depth,
            Content = content
        };

        await db.FeedComment.AddAsync(comment, ct);

        post.Comments++;

        if (parent is not null)
        {
            parent.Replies++;
        }

        await db.SaveChangesAsync(ct);

        // ── 알림: 부모 댓글 작성자 + 포스트 작성자 (본인 제외, 중복 제외) ──
        var author = await db.Member.AsNoTracking().Where(m => m.ID == request.MemberID).Select(m => new { m.Name, m.SID }).FirstOrDefaultAsync(ct);
        var notifyTargets = new HashSet<int>();

        if (parent is not null && parent.MemberID != request.MemberID)
        {
            notifyTargets.Add(parent.MemberID);
        }
        if (post.MemberID != request.MemberID)
        {
            notifyTargets.Add(post.MemberID);
        }

        foreach (var targetID in notifyTargets)
        {
            await notificationService.SendAsync(
                memberID: targetID,
                type: NotificationType.NewFeedComment,
                title: parent is not null ? "새 답글" : "새 댓글",
                message: $"{author?.Name ?? author?.SID ?? "누군가"}님이 댓글을 남겼습니다.",
                actionUrl: $"/feed/post/{request.PostID}",
                relatedType: "FeedComment",
                relatedID: comment.ID,
                ct: ct
            );
        }

        return new Response(comment.ID);
    }
}