src/search/executors/limit_executor.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 *
 */

#pragma once

#include "search/plan_executor.h"

namespace kqir {

struct LimitExecutor : ExecutorNode {
  Limit *limit;
  size_t step = 0;

  LimitExecutor(ExecutorContext *ctx, Limit *limit) : ExecutorNode(ctx), limit(limit) {}

  StatusOr<Result> Next() override {
    auto offset = limit->limit->offset;
    auto count = limit->limit->count;

    if (step == count) {
      return end;
    }

    if (step == 0) {
      while (offset--) {
        auto res = GET_OR_RET(ctx->Get(limit->op)->Next());

        if (std::holds_alternative<End>(res)) {
          return end;
        }
      }
    }

    auto res = GET_OR_RET(ctx->Get(limit->op)->Next());
    step++;
    return res;
  }
};

}  // namespace kqir