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.schema.impl;
  
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rel.type.RelDataTypeFactory;
  import org.apache.calcite.schema.Function;
  import org.apache.calcite.schema.FunctionContext;
  import org.apache.calcite.schema.FunctionParameter;
  import org.apache.calcite.util.ReflectUtil;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.Constructor;
  import java.lang.reflect.Method;
  import java.util.ArrayList;
  import java.util.List;
  
  import static org.apache.calcite.util.ReflectUtil.isPublic;
  
  /**
   * Implementation of a function that is based on a method.
   * This class mainly solves conversion of method parameter types to {@code
   * List<FunctionParameter>} form.
   */
  public abstract class ReflectiveFunctionBase implements Function {
    /** Method that implements the function. */
    public final Method method;
    /** Types of parameter for the function call. */
    public final List<FunctionParameter> parameters;
  
    /**
     * Creates a ReflectiveFunctionBase.
     *
     * @param method Method that is used to get type information from
     */
    protected ReflectiveFunctionBase(Method method) {
      this.method = method;
      this.parameters = builder().addMethodParameters(method).build();
    }
  
    /**
     * Returns the parameters of this function.
     *
     * @return Parameters; never null
     */
    @Override public List<FunctionParameter> getParameters() {
      return parameters;
    }
  
    /**
     * Returns whether a class has a public constructor with zero arguments.
     *
     * @param clazz Class to verify
     * @return whether class has a public constructor with zero arguments
     */
    static boolean classHasPublicZeroArgsConstructor(Class<?> clazz) {
      for (Constructor<?> constructor : clazz.getConstructors()) {
        if (constructor.getParameterCount() == 0 && isPublic(constructor)) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * Returns whether a class has a public constructor with one argument
     * of type {@link FunctionContext}.
     *
     * @param clazz Class to verify
     * @return whether class has a public constructor with one FunctionContext
     * argument
     */
    static boolean classHasPublicFunctionContextConstructor(Class<?> clazz) {
      for (Constructor<?> constructor : clazz.getConstructors()) {
        if (constructor.getParameterCount() == 1
            && constructor.getParameterTypes()[0] == FunctionContext.class
            && isPublic(constructor)) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * Finds a method in a given class by name.
     *
     * @param clazz class to search method in
     * @param name name of the method to find
     * @return the first method with matching name or null when no method found
     */
    static @Nullable Method findMethod(Class<?> clazz, String name) {
      for (Method method : clazz.getMethods()) {
        if (method.getName().equals(name) && !method.isBridge()) {
          return method;
        }
      }
      return null;
    }
  
    /** Creates a ParameterListBuilder. */
    public static ParameterListBuilder builder() {
      return new ParameterListBuilder();
    }
  
    /** Helps build lists of
     * {@link org.apache.calcite.schema.FunctionParameter}. */
    public static class ParameterListBuilder {
      final List<FunctionParameter> builder = new ArrayList<>();
  
      public ImmutableList<FunctionParameter> build() {
        return ImmutableList.copyOf(builder);
      }
  
      public ParameterListBuilder add(final Class<?> type, final String name) {
        return add(type, name, false);
      }
  
      public ParameterListBuilder add(final Class<?> type, final String name,
          final boolean optional) {
        final int ordinal = builder.size();
        builder.add(
            new FunctionParameter() {
              @Override public String toString() {
                return ordinal + ": " + name + " " + type.getSimpleName()
                    + (optional ? "?" : "");
              }
  
              @Override public int getOrdinal() {
                return ordinal;
              }
  
              @Override public String getName() {
                return name;
              }
  
              @Override public RelDataType getType(RelDataTypeFactory typeFactory) {
                return typeFactory.createJavaType(type);
              }
  
              @Override public boolean isOptional() {
                return optional;
              }
            });
        return this;
      }
  
      public ParameterListBuilder addMethodParameters(Method method) {
        final Class<?>[] types = method.getParameterTypes();
        for (int i = 0; i < types.length; i++) {
          add(types[i], ReflectUtil.getParameterName(method, i),
              ReflectUtil.isParameterOptional(method, i));
        }
        return this;
      }
    }
  }
  