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.beam.sdk.extensions.sql.impl;
  
  import java.lang.reflect.Method;
  import java.lang.reflect.Modifier;
  import java.util.Arrays;
  import java.util.Collection;
  import org.apache.beam.sdk.extensions.sql.udf.ScalarFn;
  import org.apache.beam.sdk.util.common.ReflectHelpers;
  
  /** Reflection-based implementation logic for {@link ScalarFn}. */
  public class ScalarFnReflector {
    /**
     * Gets the method annotated with {@link
     * org.apache.beam.sdk.extensions.sql.udf.ScalarFn.ApplyMethod} from {@code scalarFn}.
     *
     * <p>There must be exactly one method annotated with {@link
     * org.apache.beam.sdk.extensions.sql.udf.ScalarFn.ApplyMethod}, and it must be public.
     */
    public static Method getApplyMethod(ScalarFn scalarFn) {
      Class<? extends ScalarFn> clazz = scalarFn.getClass();
      Collection<Method> matches =
          ReflectHelpers.declaredMethodsWithAnnotation(
              ScalarFn.ApplyMethod.class, clazz, ScalarFn.class);
  
      if (matches.isEmpty()) {
        throw new IllegalArgumentException(
            String.format(
                "No method annotated with @%s found in class %s.",
                ScalarFn.ApplyMethod.class.getSimpleName(), clazz.getName()));
      }
  
      // If we have at least one match, then either it should be the only match
      // or it should be an extension of the other matches (which came from parent
      // classes).
      Method first = matches.iterator().next();
      for (Method other : matches) {
        if (!first.getName().equals(other.getName())
            || !Arrays.equals(first.getParameterTypes(), other.getParameterTypes())) {
          throw new IllegalArgumentException(
              String.format(
                  "Found multiple methods annotated with @%s. [%s] and [%s]",
                  ScalarFn.ApplyMethod.class.getSimpleName(),
                  ReflectHelpers.formatMethod(first),
                  ReflectHelpers.formatMethod(other)));
        }
      }
  
      // Method must be public.
      if ((first.getModifiers() & Modifier.PUBLIC) == 0) {
        throw new IllegalArgumentException(
            String.format("Method %s is not public.", ReflectHelpers.formatMethod(first)));
      }
  
      return first;
    }
  }
  