const DEFAULT_CONFIG = {
  w_view: 0.1,
  w_like: 3.0,
  w_comment: 5.0,
  w_collect: 4.0,
  decay_base: 2.0,
  decay_exp: 1.5,
};

export function computeHotScore(stats, config = DEFAULT_CONFIG, nowMs = Date.now()) {
  const publishedAt = Number(stats.published_at ?? stats.publishedAt ?? nowMs);
  const ageHours = Math.max(0, (nowMs - publishedAt) / 3_600_000);
  const numerator =
    Number(stats.view_count ?? 0) * config.w_view +
    Number(stats.like_count ?? 0) * config.w_like +
    Number(stats.comment_count ?? 0) * config.w_comment +
    Number(stats.collect_count ?? 0) * config.w_collect;
  const denominator = Math.pow(ageHours + config.decay_base, config.decay_exp);
  if (denominator <= 0) return 0;
  return Math.max(0, numerator / denominator);
}

export async function loadAlgorithmConfig(pool) {
  const [rows] = await pool.query(`SELECT \`key\`, value FROM plaza_algorithm_config`);
  const config = { ...DEFAULT_CONFIG };
  for (const row of rows) {
    if (row.key in config) config[row.key] = Number(row.value);
  }
  return config;
}

export async function ensureAlgorithmConfig(pool) {
  const [rows] = await pool.query(`SELECT COUNT(*) AS count FROM plaza_algorithm_config`);
  if (Number(rows[0]?.count ?? 0) > 0) return;
  const now = Date.now();
  const seeds = [
    ['w_view', 0.1, '浏览量权重'],
    ['w_like', 3.0, '点赞权重'],
    ['w_comment', 5.0, '评论权重'],
    ['w_collect', 4.0, '收藏权重'],
    ['decay_base', 2.0, '时间衰减基数'],
    ['decay_exp', 1.5, '时间衰减指数'],
  ];
  for (const [key, value, description] of seeds) {
    await pool.query(
      `INSERT INTO plaza_algorithm_config (\`key\`, value, description, updated_at)
       VALUES (?, ?, ?, ?)`,
      [key, value, description, now],
    );
  }
}

export async function recalculateHotScores(pool, { windowHours = 48 } = {}) {
  await ensureAlgorithmConfig(pool);
  const config = await loadAlgorithmConfig(pool);
  const now = Date.now();
  const windowStart = now - windowHours * 3_600_000;
  const [rows] = await pool.query(
    `SELECT id, view_count, like_count, comment_count, collect_count, published_at
     FROM plaza_posts
     WHERE status = 'published' AND published_at >= ?`,
    [windowStart],
  );
  if (rows.length === 0) return { updated: 0 };

  const conn = await pool.getConnection();
  try {
    await conn.beginTransaction();
    for (const row of rows) {
      const hotScore = computeHotScore(row, config, now);
      await conn.query(
        `UPDATE plaza_posts SET hot_score = ?, hot_updated_at = ?, updated_at = ? WHERE id = ?`,
        [hotScore, now, now, row.id],
      );
    }
    await conn.commit();
  } catch (error) {
    await conn.rollback();
    throw error;
  } finally {
    conn.release();
  }
  return { updated: rows.length };
}

export const algorithmInternals = {
  DEFAULT_CONFIG,
  computeHotScore,
};