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

namespace Application.Features.Api.Forum.StockBoard.ListPosts;

/// <summary>
/// 종목 가상보드 글 목록 (d2 §④ M2) — Post.StockCode 파티션 필터(최신순), StockBoardStats + 종목명 헤더 포함.
/// 삭제글 제외. 익명 열람.
/// </summary>
internal sealed class Handler(IAppDbContext db) : IQueryHandler<Query, Response>
{
    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var stockCode = request.StockCode?.Trim() ?? string.Empty;
        var page = request.Page < 1 ? 1 : request.Page;
        var perPage = request.PerPage == 0 ? (ushort)20 : request.PerPage;

        var stockName = await db.Stock.AsNoTracking().Where(c => c.Code == stockCode).Select(c => c.Name).FirstOrDefaultAsync(ct);

        var stats = await db.StockBoardStats.AsNoTracking().Where(c => c.StockCode == stockCode)
            .Select(c => new { c.Posts, c.Comments, c.LastPostAt })
            .FirstOrDefaultAsync(ct);

        var header = new Response.StatsHeader(
            stockCode,
            stockName,
            stats?.Posts ?? 0,
            stats?.Comments ?? 0,
            stats?.LastPostAt);

        var baseQuery = db.Post.AsNoTracking().Where(c => c.StockCode == stockCode && !c.IsDeleted);

        var total = await baseQuery.CountAsync(ct);

        var predictionPostIDs = await db.PostPrediction.AsNoTracking()
            .Where(c => c.StockCode == stockCode)
            .Select(c => c.PostID)
            .ToListAsync(ct);
        var predictionSet = predictionPostIDs.ToHashSet();

        var list = await baseQuery
            .OrderByDescending(c => c.ID)
            .Skip((page - 1) * perPage)
            .Take(perPage)
            .Select(c => new
            {
                c.ID,
                c.StockCode,
                c.Subject,
                c.Thumbnail,
                c.Name,
                c.SID,
                c.Views,
                c.Likes,
                c.Comments,
                c.Images,
                c.UpdatedAt,
                c.CreatedAt
            })
            .ToListAsync(ct);

        var startNum = total - ((page - 1) * perPage);

        return new Response(
            total,
            header,
            [..list.Select((c, i) => new Response.Row(
                Num: startNum - i,
                c.ID,
                c.StockCode ?? stockCode,
                c.Subject,
                c.Thumbnail,
                c.Name,
                c.SID,
                predictionSet.Contains(c.ID),
                c.Views,
                c.Likes,
                c.Comments,
                c.Images,
                c.UpdatedAt,
                c.CreatedAt
            ))]
        );
    }
}