function json(data, status = 200) {
  return new Response(JSON.stringify(data), {
    status,
    headers: { "content-type": "application/json; charset=UTF-8" },
  });
}

function toInt(v, d) {
  const n = Number(v);
  return Number.isFinite(n) && n > 0 ? Math.floor(n) : d;
}

function ratio(correct, total) {
  if (!total) return 0;
  return Math.round((correct / total) * 10000) / 100;
}

function item(total, correct) {
  const t = Number(total || 0);
  const c = Number(correct || 0);
  return {
    total: t,
    correct: c,
    incorrect: Math.max(0, t - c),
    accuracy: ratio(c, t),
  };
}

export async function onRequestGet(context) {
  const db = context.env.DB;
  if (!db) {
    return json({ success: false, error: "缺少 D1 绑定 DB" }, 500);
  }

  try {
    const url = new URL(context.request.url);
    const month = (url.searchParams.get("month") || new Date().toISOString().slice(0, 7)).trim();
    const page = toInt(url.searchParams.get("page"), 1);
    const limit = Math.min(100, toInt(url.searchParams.get("limit"), 10));
    const offset = (page - 1) * limit;

    const baseWhere = "date LIKE ?";
    const monthArg = `${month}%`;

    const dataSql = `
      SELECT
        date,
        SUM(CASE WHEN actual_result IS NOT NULL AND ensemble_prediction IS NOT NULL THEN 1 ELSE 0 END) AS ens_total,
        SUM(CASE WHEN ensemble_correct = 1 THEN 1 ELSE 0 END) AS ens_correct,

        SUM(CASE WHEN actual_result IS NOT NULL AND dlinear_prediction IS NOT NULL THEN 1 ELSE 0 END) AS dl_total,
        SUM(CASE WHEN dlinear_correct = 1 THEN 1 ELSE 0 END) AS dl_correct,

        SUM(CASE WHEN actual_result IS NOT NULL AND nbeats_prediction IS NOT NULL THEN 1 ELSE 0 END) AS nb_total,
        SUM(CASE WHEN nbeats_correct = 1 THEN 1 ELSE 0 END) AS nb_correct,

        SUM(CASE WHEN actual_result IS NOT NULL AND ttm_prediction IS NOT NULL THEN 1 ELSE 0 END) AS ttm_total,
        SUM(CASE WHEN ttm_correct = 1 THEN 1 ELSE 0 END) AS ttm_correct
      FROM backup_hourly_model_predictions
      WHERE ${baseWhere}
      GROUP BY date
      ORDER BY date DESC
      LIMIT ? OFFSET ?
    `;

    const countSql = `
      SELECT COUNT(*) AS cnt
      FROM (
        SELECT date
        FROM backup_hourly_model_predictions
        WHERE ${baseWhere}
        GROUP BY date
      ) x
    `;

    const dataResult = await db.prepare(dataSql).bind(monthArg, limit, offset).all();
    const countResult = await db.prepare(countSql).bind(monthArg).first();

    const rows = (dataResult.results || []).map((r) => ({
      date: r.date,
      Ensemble: item(r.ens_total, r.ens_correct),
      DLinear: item(r.dl_total, r.dl_correct),
      "N-BEATS": item(r.nb_total, r.nb_correct),
      "TTM-R2": item(r.ttm_total, r.ttm_correct),
    }));

    const total = Number(countResult?.cnt || 0);
    const totalPages = total > 0 ? Math.ceil(total / limit) : 1;

    return json({
      success: true,
      data: rows,
      page,
      limit,
      total,
      total_pages: totalPages,
    });
  } catch (error) {
    return json({ success: false, error: String(error) }, 500);
  }
}