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core module for querydsl
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/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * Licensed 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 com.querydsl.core;

import java.io.Serializable;
import java.util.List;
import java.util.Objects;
import org.jetbrains.annotations.Nullable;
import org.jetbrains.annotations.Range;

/**
 * {@code QueryModifiers} combines limit and offset info into a single immutable value type.
 *
 * @author tiwe
 */
public final class QueryModifiers implements Serializable {

  private static final long serialVersionUID = 2934344588433680339L;

  /** No limit and not offset restriction */
  public static final QueryModifiers EMPTY = new QueryModifiers();

  private static int toInt(Long l) {
    if (l <= Integer.MAX_VALUE) {
      return l.intValue();
    } else {
      return Integer.MAX_VALUE;
    }
  }

  public static QueryModifiers limit(@Range(from = 0, to = Integer.MAX_VALUE) long limit) {
    return new QueryModifiers(limit, null);
  }

  public static QueryModifiers offset(@Range(from = 0, to = Integer.MAX_VALUE) long offset) {
    return new QueryModifiers(null, offset);
  }

  @Nullable private final Long limit, offset;

  private QueryModifiers() {
    limit = null;
    offset = null;
  }

  public QueryModifiers(@Nullable Long limit, @Nullable Long offset) {
    this.limit = limit;
    if (limit != null && limit <= 0) {
      throw new IllegalArgumentException("Limit must be greater than 0.");
    }
    this.offset = offset;
    if (offset != null && offset < 0) {
      throw new IllegalArgumentException("Offset must not be negative.");
    }
  }

  public QueryModifiers(QueryModifiers modifiers) {
    this.limit = modifiers.getLimit();
    this.offset = modifiers.getOffset();
  }

  @Nullable
  public Long getLimit() {
    return limit;
  }

  @Nullable
  public Integer getLimitAsInteger() {
    return limit != null ? toInt(limit) : null;
  }

  @Nullable
  public Long getOffset() {
    return offset;
  }

  @Nullable
  public Integer getOffsetAsInteger() {
    return offset != null ? toInt(offset) : null;
  }

  /**
   * Checks if is restricting.
   *
   * @return true, if is restricting
   */
  public boolean isRestricting() {
    return limit != null || offset != null;
  }

  /**
   * Get a sublist based on the restriction of limit and offset
   *
   * @param 
   * @param list list to be handled
   * @return sublist with limit and offset applied
   */
  public  List subList(List list) {
    if (!list.isEmpty()) {
      int from = offset != null ? toInt(offset) : 0;
      int to = limit != null ? (from + toInt(limit)) : list.size();
      return list.subList(from, Math.min(to, list.size()));
    } else {
      return list;
    }
  }

  @Override
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    } else if (o instanceof QueryModifiers) {
      QueryModifiers qm = (QueryModifiers) o;
      return Objects.equals(qm.getLimit(), limit) && Objects.equals(qm.getOffset(), offset);
    } else {
      return false;
    }
  }

  @Override
  public int hashCode() {
    return Objects.hash(limit, offset);
  }
}