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.core;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelInput;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.RelWriter;
  import org.apache.calcite.rel.SingleRel;
  import org.apache.calcite.rel.hint.Hintable;
  import org.apache.calcite.rel.hint.RelHint;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.rex.RexShuttle;
  import org.apache.calcite.sql.type.SqlTypeUtil;
  import org.apache.calcite.util.Litmus;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Relational expression that returns the contents of a relation expression as
   * it was at a given time in the past.
   *
   * <p>For example, if {@code Products} is a temporal table, and
   * {@link TableScan}(Products) is a relational operator that returns all
   * versions of the contents of the table, then
   * {@link Snapshot}(TableScan(Products)) is a relational operator that only
   * returns the contents whose versions that overlap with the given specific
   * period (i.e. those that started before given period and ended after it).
   */
  public abstract class Snapshot extends SingleRel implements Hintable {
    //~ Instance fields --------------------------------------------------------
  
    private final RexNode period;
  
    protected final ImmutableList<RelHint> hints;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a Snapshot by parsing serialized output.
     */
    public Snapshot(RelInput input) {
      this(input.getCluster(),
          input.getTraitSet(),
          ImmutableList.of(),
          input.getInput(),
          requireNonNull(input.getExpression("period"), "period"));
    }
  
    /**
     * Creates a Snapshot.
     *
     * @param cluster   Cluster that this relational expression belongs to
     * @param traitSet  The traits of this relational expression
     * @param hints     Hints for this node
     * @param input     Input relational expression
     * @param period    Timestamp expression which as the table was at the given
     *                  time in the past
     */
    @SuppressWarnings("method.invocation.invalid")
    protected Snapshot(RelOptCluster cluster, RelTraitSet traitSet, List<RelHint> hints,
        RelNode input, RexNode period) {
      super(cluster, traitSet, input);
      this.period = requireNonNull(period, "period");
      this.hints = ImmutableList.copyOf(hints);
      assert isValid(Litmus.THROW, null);
    }
  
    /**
     * Creates a Snapshot.
     *
     * @param cluster   Cluster that this relational expression belongs to
     * @param traitSet  The traits of this relational expression
     * @param input     Input relational expression
     * @param period    Timestamp expression which as the table was at the given
     *                  time in the past
     */
    @SuppressWarnings("method.invocation.invalid")
    protected Snapshot(
        RelOptCluster cluster, RelTraitSet traitSet, RelNode input, RexNode period) {
      this(cluster, traitSet, ImmutableList.of(), input, period);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public final RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
      return copy(traitSet, sole(inputs), getPeriod());
    }
  
    public abstract Snapshot copy(RelTraitSet traitSet, RelNode input, RexNode period);
  
    @Override public RelNode accept(RexShuttle shuttle) {
      RexNode condition = shuttle.apply(this.period);
      if (this.period == condition) {
        return this;
      }
      return copy(traitSet, getInput(), condition);
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .item("period", period);
    }
  
    public RexNode getPeriod() {
      return period;
    }
  
    @Override public boolean isValid(Litmus litmus, @Nullable Context context) {
      RelDataType dataType = period.getType();
      if (!SqlTypeUtil.isTimestamp(dataType)) {
        return litmus.fail("The system time period specification expects Timestamp type but is '"
            + dataType.getSqlTypeName() + "'");
      }
      return litmus.succeed();
    }
  
    @Override public ImmutableList<RelHint> getHints() {
      return hints;
    }
  }
  