org.immutables.criteria.expression.Expressions Maven / Gradle / Ivy

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/*
 * Copyright 2019 Immutables Authors and Contributors
 *
 * 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 org.immutables.criteria.expression;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;

import javax.annotation.Nullable;
import java.lang.reflect.Type;
import java.util.Arrays;

/**
 * A set of predefined utilities and factories for expressions like {@link Constant} or {@link Call}
 */
public final class Expressions {

  private Expressions() {}

  public static Constant constant(final Object value) {
    return Constant.of(value);
  }

  public static Expression and(Expression first, Expression second) {
    return and(Arrays.asList(first, second));
  }

  public static  Expression and(Iterable expressions) {
    return reduce(Operators.AND, expressions);
  }

  public static Expression or(Expression first, Expression second) {
    return or(Arrays.asList(first ,second));
  }

  public static Expression or(Iterable expressions) {
    return reduce(Operators.OR, expressions);
  }

  public static Expression aggregation(AggregationOperators operator, Type returnType, Expression expression) {
    return new AggregationCall(ImmutableList.of(expression), operator, returnType);
  }

  public static Query root(Class entityClass) {
    return Query.of(entityClass);
  }

  private static  Expression reduce(Operator operator, Iterable expressions) {
    final int size = Iterables.size(expressions);

    if (size == 0) {
      throw new IllegalArgumentException("Empty iterator");
    } else if (size == 1) {
      return expressions.iterator().next();
    }

    return call(operator, expressions);
  }

  /**
   * Converts a {@link ExpressionVisitor} into a {@link ExpressionBiVisitor} (with ignored payload).
   */
  static  ExpressionBiVisitor toBiVisitor(ExpressionVisitor visitor) {
    return new ExpressionBiVisitor() {
      @Override
      public V visit(Call call, @Nullable Void context) {
        return visitor.visit(call);
      }

      @Override
      public V visit(Constant constant, @Nullable Void context) {
        return visitor.visit(constant);
      }

      @Override
      public V visit(Path path, @Nullable Void context) {
        return visitor.visit(path);
      }

    };
  }

  public static Call not(Expression call) {
    return Expressions.call(Operators.NOT, call);
  }

  public static Call call(final Operator operator, Expression ... operands) {
    return call(operator, ImmutableList.copyOf(operands));
  }

  public static Call call(final Operator operator, final Iterable operands) {
    return new SimpleCall(ImmutableList.copyOf(operands), operator);
  }

}