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.adapter.enumerable.CallImplementor;
  import org.apache.calcite.adapter.enumerable.NullPolicy;
  import org.apache.calcite.adapter.enumerable.ReflectiveCallNotNullImplementor;
  import org.apache.calcite.adapter.enumerable.RexImpTable;
  import org.apache.calcite.linq4j.function.SemiStrict;
  import org.apache.calcite.linq4j.function.Strict;
  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.ImplementableFunction;
  import org.apache.calcite.schema.ScalarFunction;
  import org.apache.calcite.schema.TableFunction;
  import org.apache.calcite.sql.SqlOperatorBinding;
  
  import com.google.common.collect.ImmutableMultimap;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.lang.reflect.Method;
  
  import static org.apache.calcite.util.ReflectUtil.isStatic;
  import static org.apache.calcite.util.Static.RESOURCE;
  
  /**
  * Implementation of {@link org.apache.calcite.schema.ScalarFunction}.
  */
  public class ScalarFunctionImpl extends ReflectiveFunctionBase
      implements ScalarFunction, ImplementableFunction {
    private final CallImplementor implementor;
  
    /** Private constructor. */
    private ScalarFunctionImpl(Method method, CallImplementor implementor) {
      super(method);
      this.implementor = implementor;
    }
  
    /**
     * Creates {@link org.apache.calcite.schema.ScalarFunction} for each method in
     * a given class.
     */
    @Deprecated // to be removed before 2.0
    public static ImmutableMultimap<String, ScalarFunction> createAll(
        Class<?> clazz) {
      final ImmutableMultimap.Builder<String, ScalarFunction> builder =
          ImmutableMultimap.builder();
      for (Method method : clazz.getMethods()) {
        if (method.getDeclaringClass() == Object.class) {
          continue;
        }
        if (!isStatic(method)
            && !classHasPublicZeroArgsConstructor(clazz)) {
          continue;
        }
        final ScalarFunction function = create(method);
        builder.put(method.getName(), function);
      }
      return builder.build();
    }
  
    /**
     * Returns a map of all functions based on the methods in a given class.
     * It is keyed by method names and maps to both
     * {@link org.apache.calcite.schema.ScalarFunction}
     * and {@link org.apache.calcite.schema.TableFunction}.
     */
    public static ImmutableMultimap<String, Function> functions(Class<?> clazz) {
      final ImmutableMultimap.Builder<String, Function> builder =
          ImmutableMultimap.builder();
      for (Method method : clazz.getMethods()) {
        if (method.getDeclaringClass() == Object.class) {
          continue;
        }
        if (!isStatic(method)
            && !classHasPublicZeroArgsConstructor(clazz)) {
          continue;
        }
        final TableFunction tableFunction = TableFunctionImpl.create(method);
        if (tableFunction != null) {
          builder.put(method.getName(), tableFunction);
        } else {
          final ScalarFunction function = create(method);
          builder.put(method.getName(), function);
        }
      }
      return builder.build();
    }
  
    /**
     * Creates {@link org.apache.calcite.schema.ScalarFunction} from given class.
     *
     * <p>If a method of the given name is not found, or it does not suit,
     * returns {@code null}.
     *
     * @param clazz class that is used to implement the function
     * @param methodName Method name (typically "eval")
     * @return created {@link ScalarFunction} or null
     */
    public static @Nullable ScalarFunction create(Class<?> clazz, String methodName) {
      final Method method = findMethod(clazz, methodName);
      if (method == null) {
        return null;
      }
      return create(method);
    }
  
    /**
     * Creates {@link org.apache.calcite.schema.ScalarFunction} from given method.
     * When {@code eval} method does not suit, {@code null} is returned.
     *
     * @param method method that is used to implement the function
     * @return created {@link ScalarFunction} or null
     */
    public static ScalarFunction create(Method method) {
      if (!isStatic(method)) {
        Class<?> clazz = method.getDeclaringClass();
        if (!classHasPublicZeroArgsConstructor(clazz)
            && !classHasPublicFunctionContextConstructor(clazz)) {
          throw RESOURCE.requireDefaultConstructor(clazz.getName()).ex();
        }
      }
      CallImplementor implementor = createImplementor(method);
      return new ScalarFunctionImpl(method, implementor);
    }
  
  
    /**
     * Creates unsafe version of {@link ScalarFunction} from any method. The method
     * does not need to be static or belong to a class with default constructor. It is
     * the responsibility of the underlying engine to initialize the UDF object that
     * contain the method.
     *
     * @param method method that is used to implement the function
     */
    public static ScalarFunction createUnsafe(Method method) {
      CallImplementor implementor = createImplementor(method);
      return new ScalarFunctionImpl(method, implementor);
    }
  
    @Override public RelDataType getReturnType(RelDataTypeFactory typeFactory) {
      return typeFactory.createJavaType(method.getReturnType());
    }
  
    @Override public CallImplementor getImplementor() {
      return implementor;
    }
  
    private static CallImplementor createImplementor(final Method method) {
      final NullPolicy nullPolicy = getNullPolicy(method);
      return RexImpTable.createImplementor(
          new ReflectiveCallNotNullImplementor(method), nullPolicy, false);
    }
  
    private static NullPolicy getNullPolicy(Method m) {
      if (m.getAnnotation(Strict.class) != null) {
        return NullPolicy.STRICT;
      } else if (m.getAnnotation(SemiStrict.class) != null) {
        return NullPolicy.SEMI_STRICT;
      } else if (m.getDeclaringClass().getAnnotation(Strict.class) != null) {
        return NullPolicy.STRICT;
      } else if (m.getDeclaringClass().getAnnotation(SemiStrict.class) != null) {
        return NullPolicy.SEMI_STRICT;
      } else {
        return NullPolicy.NONE;
      }
    }
  
    public RelDataType getReturnType(RelDataTypeFactory typeFactory,
        SqlOperatorBinding opBinding) {
      // Strict and semi-strict functions can return null even if their Java
      // functions return a primitive type. Because when one of their arguments
      // is null, they won't even be called.
      final RelDataType returnType = getReturnType(typeFactory);
      switch (getNullPolicy(method)) {
      case STRICT:
        for (RelDataType type : opBinding.collectOperandTypes()) {
          if (type.isNullable()) {
            return typeFactory.createTypeWithNullability(returnType, true);
          }
        }
        break;
      case SEMI_STRICT:
        return typeFactory.createTypeWithNullability(returnType, true);
      default:
        break;
      }
      return returnType;
    }
  }
  