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.linq4j.tree;
  
  import org.apache.calcite.linq4j.function.Function1;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Entry point for optimizers that factor out deterministic expressions to
   * final static fields.
   * Instances of this class should not be reused, so new visitor should be
   * created for optimizing a new expression tree.
   */
  public class ClassDeclarationFinder extends Shuttle {
    protected final @Nullable ClassDeclarationFinder parent;
  
    /**
     * The list of new final static fields to be added to the current class.
     */
    protected final List<MemberDeclaration> addedDeclarations = new ArrayList<>();
  
    private final Function1<ClassDeclarationFinder, ClassDeclarationFinder> childFactory;
  
    private static final Function1<ClassDeclarationFinder,
        ClassDeclarationFinder> DEFAULT_CHILD_FACTORY =
        DeterministicCodeOptimizer::new;
  
    /**
     * Creates visitor that uses default optimizer.
     *
     * @return optimizing visitor
     */
    public static ClassDeclarationFinder create() {
      return create(DEFAULT_CHILD_FACTORY);
    }
  
    /**
     * Creates visitor that uses given class as optimizer.
     * The implementation should support ({@code ClassDeclarationFinder})
     * constructor.
     *
     * @param optimizingClass class that implements optimizations
     * @return optimizing visitor
     */
    public static ClassDeclarationFinder create(
        final Class<? extends ClassDeclarationFinder> optimizingClass) {
      return create(newChildCreator(optimizingClass));
    }
  
    /**
     * Creates visitor that uses given factory to create optimizers.
     *
     * @param childFactory factory that creates optimizers
     * @return optimizing visitor
     */
    public static ClassDeclarationFinder create(
        Function1<ClassDeclarationFinder, ClassDeclarationFinder> childFactory) {
      return new ClassDeclarationFinder(childFactory);
    }
  
    /**
     * Creates factory that creates instances of optimizing visitors.
     * The implementation should support ({@code ClassDeclarationFinder})
     * constructor.
     *
     * @param optimizingClass class that implements optimizations
     * @return factory that creates instances of given classes
     */
    private static Function1<ClassDeclarationFinder, ClassDeclarationFinder> newChildCreator(
        Class<? extends ClassDeclarationFinder> optimizingClass) {
      try {
        final Constructor<? extends ClassDeclarationFinder> constructor =
            optimizingClass.getConstructor(ClassDeclarationFinder.class);
        return a0 -> {
          try {
            return constructor.newInstance(a0);
          } catch (InstantiationException | InvocationTargetException | IllegalAccessException e) {
            throw new IllegalStateException(
                "Unable to create optimizer via " + constructor, e);
          }
        };
      } catch (NoSuchMethodException e) {
        throw new IllegalArgumentException("Given class " + optimizingClass
            + "does not support (ClassDeclarationFinder) constructor", e);
      }
    }
  
    /**
     * Creates optimizer with no parent.
     */
    private ClassDeclarationFinder(
        Function1<ClassDeclarationFinder, ClassDeclarationFinder> childFactory) {
      this.parent = null;
      this.childFactory = childFactory;
    }
  
    /**
     * Creates a child optimizer.
     * Typically a child is created for each class declaration,
     * so each optimizer collects fields for exactly one class.
     *
     * @param parent parent optimizer
     */
    protected ClassDeclarationFinder(ClassDeclarationFinder parent) {
      this.parent = parent;
      this.childFactory = parent.childFactory;
    }
  
    /**
     * Creates optimizer local to the newly generated anonymous class.
     *
     * @param newExpression expression to optimize
     * @return nested visitor if anonymous class is given
     */
    @Override public Shuttle preVisit(NewExpression newExpression) {
      if (newExpression.memberDeclarations == null) {
        return this;
      }
      ClassDeclarationFinder visitor = goDeeper();
      visitor.learnFinalStaticDeclarations(newExpression.memberDeclarations);
      return visitor;
    }
  
    /**
     * Creates optimizer local to the newly generated class.
     *
     * @param classDeclaration expression to optimize
     * @return nested visitor
     */
    @Override public Shuttle preVisit(ClassDeclaration classDeclaration) {
      ClassDeclarationFinder visitor = goDeeper();
      visitor.learnFinalStaticDeclarations(classDeclaration.memberDeclarations);
      return visitor;
    }
  
    @Override public Expression visit(NewExpression newExpression,
        List<Expression> arguments, @Nullable List<MemberDeclaration> memberDeclarations) {
      if (parent == null) {
        // Unable to optimize since no wrapper class exists to put fields to.
        arguments = newExpression.arguments;
      } else if (memberDeclarations != null) {
        // Arguments to new Test(1+2) { ... } should be optimized via parent
        // optimizer.
        arguments = Expressions.acceptExpressions(newExpression.arguments, parent);
      }
  
      Expression result =
          super.visit(newExpression, arguments, memberDeclarations);
  
      if (memberDeclarations == null) {
        return tryOptimizeNewInstance((NewExpression) result);
      }
  
      memberDeclarations = optimizeDeclarations(memberDeclarations);
      return super.visit((NewExpression) result, arguments,
          memberDeclarations);
    }
  
    /**
     * Processes the list of declarations when class expression detected.
     * Sub-classes might figure out the existing fields for reuse.
     *
     * @param memberDeclarations list of declarations to process.
     */
    protected void learnFinalStaticDeclarations(
        List<MemberDeclaration> memberDeclarations) {
    }
  
    /**
     * Optimizes {@code new Type()} constructs.
     *
     * @param newExpression expression to optimize
     * @return always returns un-optimized expression
     */
    protected Expression tryOptimizeNewInstance(NewExpression newExpression) {
      return newExpression;
    }
  
    @Override public ClassDeclaration visit(ClassDeclaration classDeclaration,
        List<MemberDeclaration> memberDeclarations) {
      memberDeclarations = optimizeDeclarations(memberDeclarations);
      return super.visit(classDeclaration, memberDeclarations);
    }
  
    /**
     * Adds new declarations (e.g. final static fields) to the list of existing
     * ones.
     *
     * @param memberDeclarations existing list of declarations
     * @return new list of declarations or the same if no modifications required
     */
    protected List<MemberDeclaration> optimizeDeclarations(
        List<MemberDeclaration> memberDeclarations) {
      if (addedDeclarations.isEmpty()) {
        return memberDeclarations;
      }
      List<MemberDeclaration> newDecls =
          new ArrayList<>(memberDeclarations.size()
              + addedDeclarations.size());
      newDecls.addAll(memberDeclarations);
      newDecls.addAll(addedDeclarations);
      return newDecls;
    }
  
    /**
     * Verifies if the expression is effectively constant.
     * This method should be overridden in sub-classes.
     *
     * @param expression expression to test
     * @return always returns false
     */
    protected boolean isConstant(Expression expression) {
      return false;
    }
  
    /**
     * Verifies if all the expressions in given list are  effectively constant.
     *
     * @param list list of expressions to test
     * @return true when all the expressions are known to be constant
     */
    protected boolean isConstant(Iterable<? extends Expression> list) {
      for (Expression expression : list) {
        if (!isConstant(expression)) {
          return false;
        }
      }
      return true;
    }
  
    /**
     * Finds if there exists ready for reuse declaration for given expression.
     * This method should be overridden in sub-classes.
     *
     * @param expression input expression
     * @return always returns null
     */
    protected @Nullable ParameterExpression findDeclaredExpression(Expression expression) {
      return null;
    }
  
    /**
     * Verifies if the variable name is already in use.
     * This method should be overridden in sub-classes.
     *
     * @param name name of the variable to test
     * @return always returns false
     */
    protected boolean hasField(String name) {
      return false;
    }
  
    /**
     * Creates child visitor. It is used to traverse nested class declarations.
     *
     * @return new {@code Visitor} that is used to optimize class declarations
     */
    protected ClassDeclarationFinder goDeeper() {
      return childFactory.apply(this);
    }
  }
  