content: /*
   * 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.
   */
  package org.apache.calcite.rel.type;
  
  import org.apache.calcite.avatica.util.TimeUnit;
  
  import org.apache.commons.math3.fraction.BigFraction;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** Time frame.
   *
   * <p>Belongs to a {@link TimeFrameSet}.
   * The default set is {@link TimeFrames#CORE};
   * to create custom time frame sets, call {@link TimeFrameSet#builder()}. */
  public interface TimeFrame {
    /** Returns the time frame set that this frame belongs to. */
    TimeFrameSet frameSet();
  
    /** Name of this time frame.
     *
     * <p>A time frame based on a built-in Avatica
     * {@link org.apache.calcite.avatica.util.TimeUnit} will have the same
     * name.
     *
     * @see TimeFrameSet#get(TimeUnit) */
    String name();
  
    /** If this time frame has units in common with another time frame, returns
     * the number of this time frame in one of that time frame.
     *
     * <p>For example, {@code MONTH.per(YEAR)} returns 12;
     * {@code YEAR.per(MONTH)} returns 1 / 12.
     */
    @Nullable BigFraction per(TimeFrame timeFrame);
  
    /** Returns a date where this time frame is at the start of a cycle.
     *
     * <p>For example, the {@code WEEK} time frame starts on a Monday,
     * and {@code 1970-01-05} was a Monday,
     * and the date {@code 1970-01-05} is represented as integer 5,
     * so for the {@code WEEK} time frame this method returns 5.
     * But it would also be valid to return the date value of {@code 1900/01/01},
     * which was also a Monday.  Because we know that a week is 7 days, we can
     * compute every other point at which a week advances. */
    default int dateEpoch() {
      return 0;
    }
  
    /** Returns a timestamp where this time frame is at the start of a cycle.
     *
     * @see #dateEpoch() */
    default long timestampEpoch() {
      return 0L;
    }
  
    /** Returns a month number where this time frame is at the start of a cycle.
     *
     * @see #dateEpoch()
     */
    default int monthEpoch() {
      return 0;
    }
  
    /** Whether this frame can roll up to {@code toFrame}.
     *
     * <p>Examples:
     * <ul>
     *   <li>{@code SECOND} can roll up to {@code MINUTE}, {@code HOUR},
     *   {@code DAY}, {@code WEEK}, {@code MONTH}, {@code MILLENNIUM};
     *   <li>{@code SECOND} cannot roll up to {@code MILLISECOND} (because it is
     *   finer grained);
     *   <li>{@code WEEK} cannot roll up to {@code MONTH}, {@code YEAR},
     *   {@code MILLENNIUM} (because weeks cross month boundaries).
     * </ul>
     *
     * <p>If two time frames have the same core, and one is an integer simple
     * multiple of another, and they have the same offset, then they can roll up.
     * For example, suppose that {@code MINUTE15} and {@code HOUR3} are both based
     * on {@code SECOND};
     * {@code MINUTE15} is 15 * 60 seconds and
     * {@code HOUR3} is 3 * 60 * 60 seconds;
     * therefore one {@code HOUR3} interval equals twelve {@code MINUTE15}
     * intervals.
     * They have the same offset (both start at {@code 1970-01-01 00:00:00}) and
     * therefore {@code MINUTE15} can roll up to {@code HOUR3}.
     *
     * <p>Even if two frames are not multiples, if they are aligned then they can
     * roll up. {@code MONTH} and {@code DAY} are an example. For more about
     * alignment, see {@link TimeFrameSet.Builder#addRollup(String, String)}.
     */
    boolean canRollUpTo(TimeFrame toFrame);
  
    /** Returns the built-in unit of this frame, or null if it does not correspond
     * to a built-in unit. */
    default @Nullable TimeUnit unit() {
      return frameSet().getUnit(this);
    }
  }
  