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

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

/// <summary>
/// 종목 트렌딩 랭킹 (d2 §④·§⑥ M2) — Redis Sorted Set 캐시(TTL 10분)에서 상위 종목 코드/점수를 가져와
/// Stock(종목명·denorm 시세)·StockBoardStats(총 글 수)를 조인해 반환한다. 익명 열람.
/// </summary>
internal sealed class Handler(IAppDbContext db, IStockBoardTrendingCache cache) : IQueryHandler<Query, Response>
{
    private const int DefaultCount = 20;
    private const int MaxCount = 50;

    public async Task<Response> Handle(Query request, CancellationToken ct)
    {
        var count = request.Count <= 0 ? DefaultCount : Math.Min(request.Count, MaxCount);

        var ranked = await cache.GetTopAsync(count, db, ct);
        if (ranked.Count == 0)
        {
            return new Response([]);
        }

        var codes = ranked.Select(c => c.StockCode).ToList();

        var stocks = await db.Stock.AsNoTracking()
            .Where(c => codes.Contains(c.Code))
            .Select(c => new { c.Code, c.Name, c.LastClosePrice, c.LastChangeRate })
            .ToDictionaryAsync(c => c.Code, ct);

        var postCounts = await db.StockBoardStats.AsNoTracking()
            .Where(c => codes.Contains(c.StockCode))
            .Select(c => new { c.StockCode, c.Posts })
            .ToDictionaryAsync(c => c.StockCode, c => c.Posts, ct);

        var rows = new List<Response.Row>(ranked.Count);
        for (var i = 0; i < ranked.Count; i++)
        {
            var entry = ranked[i];
            stocks.TryGetValue(entry.StockCode, out var stock);
            postCounts.TryGetValue(entry.StockCode, out var posts);

            rows.Add(new Response.Row(
                Rank: i + 1,
                StockCode: entry.StockCode,
                StockName: stock?.Name,
                ClosePrice: stock?.LastClosePrice,
                ChangeRate: stock?.LastChangeRate,
                Posts: posts,
                Score: entry.Score));
        }

        return new Response(rows);
    }
}