export function parsePageQuery(query, defaultPageSize = 20) {
  const page = Math.max(1, Number(query.page) || 1);
  const pageSize = Math.min(Math.max(Number(query.pageSize) || defaultPageSize, 1), 200);
  const offset = (page - 1) * pageSize;
  return { page, pageSize, offset };
}

export function paginateArray(items, query, defaultPageSize = 20) {
  const { page, pageSize, offset } = parsePageQuery(query, defaultPageSize);
  const total = items.length;
  return {
    items: items.slice(offset, offset + pageSize),
    total,
    page,
    pageSize,
    totalPages: Math.max(1, Math.ceil(total / pageSize)),
  };
}

export async function listUsagePaged(pool, query) {
  const { page, pageSize, offset } = parsePageQuery(query, 20);
  const userId = typeof query.userId === 'string' && query.userId ? query.userId : null;
  const params = [];
  let where = '';
  if (userId) {
    where = 'WHERE r.user_id = ?';
    params.push(userId);
  }
  const [[{ total }]] = await pool.query(
    `SELECT COUNT(*) AS total FROM h5_usage_records r ${where}`,
    params,
  );
  const [rows] = await pool.query(
    `SELECT r.id, r.user_id, u.username, r.agent_session_id, r.request_id,
            r.input_tokens, r.output_tokens, r.cost_cents, r.balance_after_cents, r.created_at
     FROM h5_usage_records r
     JOIN h5_users u ON u.id = r.user_id
     ${where}
     ORDER BY r.created_at DESC
     LIMIT ? OFFSET ?`,
    [...params, pageSize, offset],
  );
  return {
    records: rows.map((row) => ({
      id: Number(row.id),
      userId: row.user_id,
      username: row.username,
      agentSessionId: row.agent_session_id,
      requestId: row.request_id,
      inputTokens: Number(row.input_tokens),
      outputTokens: Number(row.output_tokens),
      costCents: Number(row.cost_cents),
      balanceAfterCents: Number(row.balance_after_cents),
      createdAt: Number(row.created_at),
    })),
    total: Number(total),
    page,
    pageSize,
    totalPages: Math.max(1, Math.ceil(Number(total) / pageSize)),
  };
}

export async function listLedgerPaged(pool, query) {
  const { page, pageSize, offset } = parsePageQuery(query, 20);
  const userId = typeof query.userId === 'string' && query.userId ? query.userId : null;
  const params = [];
  const clauses = [];
  if (userId) {
    clauses.push('l.user_id = ?');
    params.push(userId);
  }
  const where = clauses.length ? `WHERE ${clauses.join(' AND ')}` : '';
  const [[{ total }]] = await pool.query(
    `SELECT COUNT(*) AS total FROM h5_billing_ledger l ${where}`,
    params,
  );
  const [rows] = await pool.query(
    `SELECT l.id, l.user_id, u.username, l.type, l.amount_cents, l.tokens,
            l.session_id, l.note, l.created_at
     FROM h5_billing_ledger l
     JOIN h5_users u ON u.id = l.user_id
     ${where}
     ORDER BY l.created_at DESC
     LIMIT ? OFFSET ?`,
    [...params, pageSize, offset],
  );
  return {
    entries: rows.map((row) => ({
      id: Number(row.id),
      userId: row.user_id,
      username: row.username,
      type: row.type,
      amountCents: Number(row.amount_cents),
      tokens: Number(row.tokens),
      sessionId: row.session_id,
      note: row.note,
      createdAt: Number(row.created_at),
    })),
    total: Number(total),
    page,
    pageSize,
    totalPages: Math.max(1, Math.ceil(Number(total) / pageSize)),
  };
}