using Application.Abstractions.Data;
using Application.Abstractions.Messaging;
using Application.Features.Api.Feed.Shared;
using Microsoft.EntityFrameworkCore;

namespace Application.Features.Api.Feed.GetForYou;

public sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var followingIDs = await db.MemberFollow.AsNoTracking()
            .Where(f => f.FollowerMemberID == request.MemberID && !f.IsMuted)
            .Select(f => f.FolloweeMemberID)
            .ToListAsync(ct);

        var since = DateTime.UtcNow.AddDays(-14);
        var take = Math.Max(20, request.PerPage * 3);

        var followingRows = followingIDs.Count > 0
            ? await QueryRowsAsync(since, take, p => followingIDs.Contains(p.MemberID), byRecency: true, ct)
            : [];

        var trendingRows = await QueryRowsAsync(since, take, p => !followingIDs.Contains(p.MemberID), byRecency: false, ct);

        var merged = new List<Row>();
        var seen = new HashSet<int>();

        var followTake = (int)Math.Round((followingRows.Count + trendingRows.Count) * 0.7);
        foreach (var r in followingRows.Take(followTake))
        {
            if (seen.Add(r.ID))
            {
                merged.Add(r);
            }
        }

        foreach (var r in trendingRows)
        {
            if (seen.Add(r.ID))
            {
                merged.Add(r);
            }
        }

        merged = [..merged.OrderByDescending(r => r.CreatedAt)];

        var total = merged.Count;
        var skip = (request.Page - 1) * request.PerPage;

        var list = merged.Skip(skip).Take(request.PerPage).Select(r => new FeedCardRow
        {
            PostID = r.ID,
            AuthorSID = r.AuthorSID,
            AuthorName = r.AuthorName,
            AuthorThumb = r.AuthorThumb,
            AuthorSummary = r.AuthorSummary,
            IsCreator = r.IsCreator,
            ChannelSID = r.ChannelSID,
            Subject = FeedContent.Excerpt(r.Content, 60),
            ContentExcerpt = FeedContent.Excerpt(r.Content, 200),
            Thumbnail = r.Thumbnail,
            Images = r.Images,
            Medias = r.Medias,
            Likes = r.Likes,
            Comments = r.Comments,
            Bookmarks = r.Bookmarks,
            Views = r.Views,
            Tags = [..r.Tags.Select(t => new FeedCardRow.TagRef { Name = t.Name, Slug = t.Slug })],
            CreatedAt = r.CreatedAt
        }).ToList();

        return new Response { Total = total, List = list };
    }

    private async Task<List<Row>> QueryRowsAsync(
        DateTime since,
        int take,
        System.Linq.Expressions.Expression<Func<Domain.Entities.Feed.FeedPost, bool>> additionalFilter,
        bool byRecency,
        CancellationToken ct
    ) {
        var query = db.FeedPost.AsNoTracking()
            .Where(p => !p.IsDeleted && p.CreatedAt >= since)
            .Where(additionalFilter);

        var ordered = byRecency
            ? query.OrderByDescending(p => p.CreatedAt)
            : query.OrderByDescending(p => p.Likes + p.Comments * 2 + p.Views * 0.1).ThenByDescending(p => p.CreatedAt);

        return await ordered.Take(take).Select(p => new Row
        {
            ID = p.ID,
            AuthorSID = p.Member.SID,
            AuthorName = p.Member.Name,
            AuthorThumb = p.Member.Thumb,
            AuthorSummary = p.Member.Summary,
            IsCreator = p.Member.IsCreator,
            ChannelSID = p.Member.Channel != null ? p.Member.Channel.SID : null,
            Content = p.Content,
            Thumbnail = p.Thumbnail,
            Images = p.Images,
            Medias = p.Medias,
            Likes = p.Likes,
            Comments = p.Comments,
            Bookmarks = p.Bookmarks,
            Views = p.Views,
            Tags = p.FeedPostTag.Select(pt => new TagRow { Name = pt.FeedTag.Name, Slug = pt.FeedTag.Slug }).ToList(),
            CreatedAt = p.CreatedAt
        }).ToListAsync(ct);
    }

    private sealed class Row
    {
        public int ID { get; set; }
        public string? AuthorSID { get; set; }
        public string? AuthorName { get; set; }
        public string? AuthorThumb { get; set; }
        public string? AuthorSummary { get; set; }
        public bool IsCreator { get; set; }
        public string? ChannelSID { get; set; }
        public string Content { get; set; } = default!;
        public string? Thumbnail { get; set; }
        public byte Images { get; set; }
        public byte Medias { get; set; }
        public int Likes { get; set; }
        public int Comments { get; set; }
        public int Bookmarks { get; set; }
        public int Views { get; set; }
        public DateTime CreatedAt { get; set; }
        public List<TagRow> Tags { get; set; } = [];
    }

    private sealed class TagRow
    {
        public string Name { get; set; } = default!;
        public string Slug { get; set; } = default!;
    }
}