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

namespace Application.Features.Api.Feed.GetSuggestedFollows;

public sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var top = Math.Clamp(request.Top, 1, 20);
        var viewerID = request.ViewerMemberID ?? 0;

        var followingIDs = viewerID > 0
            ? await db.MemberFollow.AsNoTracking().Where(f => f.FollowerMemberID == viewerID).Select(f => f.FolloweeMemberID).ToListAsync(ct)
            : [];

        var query = db.Member.AsNoTracking()
            .Where(m => m.IsCreator && !m.IsWithdraw && !m.IsDenied && m.ID != viewerID && !followingIDs.Contains(m.ID))
            .Select(m => new
            {
                m.SID,
                m.Name,
                m.Thumb,
                m.Summary,
                m.IsCreator,
                FollowerCount = m.MemberStats != null ? m.MemberStats.FollowerCount : 0
            });

        var list = await query.OrderByDescending(x => x.FollowerCount).Take(top).ToListAsync(ct);

        if (list.Count < top)
        {
            var fallbackTake = top - list.Count;
            var existingSIDs = list.Select(x => x.SID).ToList();

            var fallback = await db.Member.AsNoTracking()
                .Where(m => !m.IsWithdraw && !m.IsDenied && m.ID != viewerID && !followingIDs.Contains(m.ID) && !existingSIDs.Contains(m.SID))
                .Select(m => new
                {
                    m.SID,
                    m.Name,
                    m.Thumb,
                    m.Summary,
                    m.IsCreator,
                    FollowerCount = m.MemberStats != null ? m.MemberStats.FollowerCount : 0
                })
                .OrderByDescending(x => x.FollowerCount)
                .Take(fallbackTake)
                .ToListAsync(ct);

            list.AddRange(fallback);
        }

        return new Response
        {
            List = [..list.Select(x => new Response.Row
            {
                SID = x.SID,
                Name = x.Name,
                Thumb = x.Thumb,
                Summary = x.Summary,
                IsCreator = x.IsCreator,
                FollowerCount = x.FollowerCount
            })]
        };
    }
}