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// 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.

package org.apache.impala.analysis;

import org.apache.impala.common.AnalysisException;

import com.google.common.base.Preconditions;

import static org.apache.impala.analysis.ToSqlOptions.DEFAULT;

/**
 * Combination of limit and offset expressions.
 */
class LimitElement {
  /////////////////////////////////////////
  // BEGIN: Members that need to be reset()

  private final Expr limitExpr_;
  private final Expr offsetExpr_;
  private long limit_;
  private long offset_;
  private boolean isAnalyzed_;

  // END: Members that need to be reset()
  /////////////////////////////////////////

  /**
   * Constructs the LimitElement.
   * @param limitExpr The limit expression. May be null if there is no LIMIT clause.
   * @param offsetExpr The offset expression. May be null if there is no OFFSET clause.
   */
  public LimitElement(Expr limitExpr, Expr offsetExpr) {
    this.limitExpr_ = limitExpr;
    this.offsetExpr_ = offsetExpr;
    isAnalyzed_ = false;
    limit_ = -1;
    offset_ = 0;
  }

  /**
   * Copy c'tor used in clone().
   */
  protected LimitElement(LimitElement other) {
    limitExpr_ = (other.limitExpr_ != null) ? other.limitExpr_.clone() : null;
    offsetExpr_ = (other.offsetExpr_ != null) ? other.offsetExpr_.clone() : null;
    limit_ = other.limit_;
    offset_ = other.offset_;
    isAnalyzed_ = other.isAnalyzed_;
  }

  public Expr getLimitExpr() { return limitExpr_; }
  public Expr getOffsetExpr() { return offsetExpr_; }

  /**
   * Returns the integer limit, evaluated from the limit expression. Must call analyze()
   * first. If no limit was set, then -1 is returned.
   */
  public long getLimit() {
    Preconditions.checkState(isAnalyzed_);
    return limit_;
  }

  /**
   * Returns the integer offset, evaluated from the offset expression. Must call
   * analyze() first. If no offsetExpr exists, then 0 (the default offset) is returned.
   */
  public long getOffset() {
    Preconditions.checkState(isAnalyzed_);
    return offset_;
  }

  public final String toSql() { return toSql(DEFAULT); }

  public String toSql(ToSqlOptions options) {
    StringBuilder sb = new StringBuilder();
    if (limitExpr_ != null) {
      sb.append(" LIMIT ");
      sb.append(limitExpr_.toSql(options));
    }
    // Don't add the offset if it is the default value. However, we do print it if it
    // hasn't been analyzed yet because we need to output the expression used in errors.
    if (offsetExpr_ != null && (offset_ != 0 || !isAnalyzed_)) {
      sb.append(" OFFSET ");
      sb.append(offsetExpr_.toSql(options));
    }
    return sb.toString();
  }

  public void analyze(Analyzer analyzer) throws AnalysisException {
    isAnalyzed_ = true;
    if (limitExpr_ != null) {
      limit_ = limitExpr_.evalToNonNegativeInteger(analyzer, "LIMIT");
    }
    if (limit_ == 0) analyzer.setHasEmptyResultSet();
    if (offsetExpr_ != null) {
      offset_ = offsetExpr_.evalToNonNegativeInteger(analyzer, "OFFSET");
    }
  }

  @Override
  public LimitElement clone() { return new LimitElement(this); }

  public void reset() {
    isAnalyzed_ = false;
    limit_ = -1;
    offset_ = 0;
    if (limitExpr_ != null) limitExpr_.reset();
    if (offsetExpr_ != null) offsetExpr_.reset();
  }
}